Merge pull request '1.0: ssh install that never replaces what it did not read, current dependencies, a real --version' (#28) from next into main

Reviewed-on: #28

.dockerignore

@@ -18,9 +18,16 @@
 # does not need .git/config; that file can hold a credential, such as a
 # password in a remote URL or the token the CI checkout step stores there.
 # Each submodule keeps a config with the same exposure in its git directory
-# under .git/modules/, nested again for a submodule's own submodules.
-.git/config
-.git/modules/**/config
+# under .git/modules/, nested again for a submodule's own submodules, or in
+# its own .git directory when it keeps one.
+# KNOWN GAP: a submodule whose name has a `config` segment (`config`,
+# `deploy/config`, `config/lib`) loses its whole git directory, because
+# `**/.git/modules/**/config` also matches that segment's directory
+# under .git/modules/. Go's version stamping then fails the build;
+# nothing leaks. Name such a submodule without that segment:
+# `git submodule add --name`.
+**/.git/config
+**/.git/modules/**/config
 
 # Agent scratch: one full checkout of the repo per in-flight agent.
 # Anchored because it occurs once where agents run at the repo root.
@@ -44,7 +51,9 @@
 **/[iI][dD]_[rR][sS][aA]
 **/[iI][dD]_[dD][sS][aA]
 **/[iI][dD]_[eE][cC][dD][sS][aA]
+**/[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
 **/[iI][dD]_[eE][dD]25519
+**/[iI][dD]_[eE][dD]25519_[sS][kK]
 
 # Dependencies: restored inside the image, never copied in.
 **/node_modules
@@ -62,7 +71,5 @@
 **/.vscode
 **/*.sublime-*
 
-# The binary `make build` writes, and the CI workflow, which is not a
-# build input.
+# The binary `make build` writes.
 /keyfunc
-.gitea

.gitignore

@@ -42,7 +42,9 @@ node_modules/
 [iI][dD]_[rR][sS][aA]
 [iI][dD]_[dD][sS][aA]
 [iI][dD]_[eE][cC][dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
 [iI][dD]_[eE][dD]25519
+[iI][dD]_[eE][dD]25519_[sS][kK]
 
 # The binary `make build` writes.
 /keyfunc

README.md

@@ -66,8 +66,11 @@ calls into `internal/`. The packages there are:
 - `internal/childmnemonic` derives a child mnemonic from the main one using
   BIP-85's own mnemonic application.
 - `internal/cli` builds the cobra command tree and runs it. Under it,
-  `cli/options` holds the flags every command shares, and `cli/ssh`, `cli/age`
-  and `cli/mnemonic` are the command groups.
+  `cli/options` holds the flags every command shares, `cli/signals` catches
+  SIGINT, SIGTERM and SIGHUP for the commands that clean up before they end, and
+  `cli/ssh`, `cli/age` and `cli/mnemonic` are the command groups.
+- `internal/bip39` is a copy of `github.com/tyler-smith/go-bip39` v1.1.0,
+  trimmed to what keyfunc uses.
 
 ### Adding a key type
 
@@ -176,10 +179,13 @@ same way: one that cannot be read fails the first listing, and one that can be
 read but not entered fails the second, after which the tool says that `~/.ssh`
 cannot be entered. The wording of a missing file elsewhere does not count
 either, since `ssh` writes `No such file or directory` about an `-i` it cannot
-find on a session that then authenticates through the agent. If an identical
-line is already in the file, the tool prints `already present` and connects no
-further. Otherwise the line is added (after a newline, if the file did not end
-with one) and a second connection:
+find on a session that then authenticates through the agent. An
+`authorized_keys` that the first listing shows to be a symlink is refused and
+left as it is, since the rename below would replace the link itself and the file
+it points at would never get the key. If an identical line is already in the
+file, the tool prints `already present` and connects no further. Otherwise the
+line is added (after a newline, if the file did not end with one) and a second
+connection:
 
 - makes `~/.ssh` and sets it to mode `0700`, but only when the first connection
   found none; a `~/.ssh` that was already there keeps the mode it had;
@@ -249,11 +255,21 @@ identity's own recipient, plus any given with `--to`, so the same mnemonic can
 always decrypt what it encrypted. Output goes to `-o` or standard output;
 `--armor` writes the text form. Nothing is written except the output.
 
+A `-o` path that is the same file as the tool's own standard output or standard
+error, under any name such as `/dev/stdout` or `/dev/fd/2`, is written to that
+stream, as leaving out `-o` writes to standard output; the file the stream is
+redirected to is written as the redirect says and never replaced, so with `>>`
+the output follows what the file already held. Otherwise, a regular file already
+at the `-o` path is replaced, and the new file has mode `0600`. A symlink there
+is followed, and what it points at is treated the same way, so the link keeps
+pointing where it did; a symlink that points at nothing is refused. A named pipe
+or a device, such as `/dev/null`, is written to directly.
+
 ### `keyfunc age decrypt [-n N] [-o <file>] [<file>]`
 
 Decrypts the file (or standard input) with the derived identity. Output goes to
-`-o` or standard output. If the identity is not one of the recipients, the tool
-says so and exits with status 1.
+`-o`, which is treated as for `encrypt`, or standard output. If the identity is
+not one of the recipients, the tool says so and exits with status 1.
 
 ## Derived mnemonics: `keyfunc mnemonic`
 
@@ -288,6 +304,21 @@ girl mad pet galaxy egg matter matrix prison refuse sense ordinary nose
 Errors go to standard error and the exit status is 1, except for `ssh to`, which
 passes through `ssh`'s own exit status.
 
+SIGINT, SIGTERM and SIGHUP end any command at once, at the mnemonic prompt too,
+with the status a shell gives a program killed by that signal (130 for SIGINT).
+While `age encrypt -o` or `age decrypt -o` is writing a new file or replacing a
+regular one, the signal makes it remove the unfinished file, leave a file
+already at the named path as it was, and exit with status 1. That holds for a
+signal that has reached `keyfunc` when its input ends; a later one leaves the
+whole file in place. Ctrl-C on a pipeline ends the input at the same moment, and
+on Linux `keyfunc` sees the signal first, though no system promises that. A
+named pipe or a device at the `-o` path, or a path that is the same file as
+standard output or standard error, is written to directly, and the signal ends
+the tool there as it ends any other command. While `ssh to` or `ssh install` has
+`ssh` or `sftp` running, the signal ends that program instead, the tool removes
+its agent socket or working files, and it exits with status 1, or for `ssh to`
+with `ssh`'s own status if `ssh` reported one.
+
 ## Entrypoints
 
 The repo adheres to the
@@ -344,9 +375,7 @@ standard: most Makefile targets are thin shims over an executable in `script/`
 
 ## TODO
 
-The open issues that stand between the tree and a 1.0 release:
-
-- [#42 go-bip39 no longer exists upstream: keep it, or copy it into the repo?](https://git.eeqj.de/sneak/keyfunc/issues/42)
+No issues are open.
 
 ## License
 

REPO_POLICIES.md

@@ -104,10 +104,14 @@ style conventions are in separate documents:
   `lint` phase and a `test` phase, with the final stage depending on both so the
   image cannot be built unless they pass. For non-server repos the final stage
   brings up a development environment; for server repos it is the runtime image.
-  Dockerfiles install development prerequisites by running `script/bootstrap`
-  rather than duplicating installs inline; COPY `script/` and the dependency
-  manifests (`package.json` + `yarn.lock`, `go.mod` + `go.sum`, etc.) before
-  running it.
+  The gate phases and the build stage start from their pinned base images and
+  install what those images lack either inline, as the canonical Go `Dockerfile`
+  below does for `git`, or by running `script/bootstrap`, as the `prompts`
+  repo's own `Dockerfile` does for its yarn packages. The development
+  environment stage installs development prerequisites by running
+  `script/bootstrap` rather than duplicating its installs inline. A stage that
+  runs `script/bootstrap` COPYs `script/` and the dependency manifests
+  (`package.json` + `yarn.lock`, `go.mod` + `go.sum`, etc.) before running it.
 
 - **Linting and testing run in Docker, as phases of the `Dockerfile`.** There is
   no separate lint file. `script/lint` and `script/test` each build one phase
@@ -156,6 +160,9 @@ style conventions are in separate documents:
   not evidence that anything ran: a sub-second build reporting success is a
   cache hit, not a result. Never invalidate by pruning — `docker builder prune`
   and friends destroy a build cache shared with every other build on the host.
+  When a check is added or changed, prove it works by planting a defect it must
+  catch and watching the run fail on it, then revert the defect. A green run
+  alone shows neither that the check ran nor that it covers what it should.
 
 - **The gate phases are separate stages, and the build stage depends on both.**
   The lint phase is based on the `golangci/golangci-lint` image (pinned by
@@ -236,13 +243,28 @@ style conventions are in separate documents:
       (e.g. a web frontend compiled in a separate stage), the lint phase must
       create placeholder files so the embed directives resolve. Example:
       `RUN mkdir -p web/dist && touch web/dist/index.html web/dist/style.css`.
-    - If the project requires CGO or system libraries for linting (e.g.
-      `vips-dev`), install them in the lint phase with `apk add`.
-    - `.dockerignore` lets `.git` into the build context. It keeps out
-      `.git/config` and each submodule's `config` under `.git/modules/` at any
-      depth (`.git/modules/**/config`), which `git describe` does not need and
-      which can hold a credential: a password in a remote URL, or the token the
-      CI checkout step stores there. The stage that compiles has `git` (the
+    - If the project requires CGO or system libraries for linting, install them
+      in the lint phase. The `golangci/golangci-lint` image is Debian-based and
+      has no `apk`, so install with `apt-get` under the Debian package name
+      (`libvips-dev`, where alpine says `vips-dev`), and delete the package
+      lists in the same `RUN`, so the layer does not keep them:
+
+        ```dockerfile
+        RUN apt-get update \
+            && apt-get install -y --no-install-recommends libvips-dev \
+            && rm -rf /var/lib/apt/lists/*
+        ```
+
+    - `.dockerignore` lets `.git` into the build context. It keeps out every git
+      `config` at any depth (`**/.git/config`, `**/.git/modules/**/config`): the
+      repository's own, each submodule's under `.git/modules/`, and that of a
+      submodule keeping its own `.git` directory. `git describe` does not need
+      them, and each can hold a credential: a password in a remote URL, or the
+      token the CI checkout step stores there. A submodule whose name has a
+      `config` segment (`config`, `deploy/config`, `config/lib`) loses its whole
+      git directory to `**/.git/modules/**/config`, and Go's version stamping
+      then fails the build: give it a name without that segment
+      (`git submodule add --name`). The stage that compiles has `git` (the
       Debian Go image has it; an alpine one needs `apk add --no-cache git`) and
       takes the version from the `VERSION` build argument when one is given,
       otherwise from `git describe --tags --always`. That gives the tag on a
@@ -264,7 +286,12 @@ style conventions are in separate documents:
   carry the same guarantee, because its gate phases may come from the cache. The
   image build is uncached and so runs the gate phases a second time. That is the
   price of the rule above, and it is worth paying: the image that ships is built
-  from a run of its own gates rather than from a cache entry.
+  from a run of its own gates rather than from a cache entry. A separate
+  workflow limited to `main` by a `branches` list under `on: push` cannot be
+  checked by review: to try a change to it, add the feature branch to that list
+  and push, then remove the branch from the list again before merging. Keep any
+  job in it that publishes behind `if: github.ref_name == 'main'`, so the run
+  from the feature branch publishes nothing.
 
 - Use platform-standard formatters: `black` for Python, `prettier` for
   JS/CSS/Markdown/HTML, `go fmt` for Go. Always use default configuration with
@@ -495,6 +522,11 @@ style conventions are in separate documents:
 
     Keep it POSIX sh: no arrays, no `[[`, no `grep -P`.
 
+    A Go tool a repo needs on the host is installed with `go install` pinned to
+    a commit hash (`go install <package>@<commit hash>`). It is never tracked as
+    a `go.mod` tool dependency or through a `tools.go` file, either of which
+    pulls the tool's own dependencies into the repo's `go.mod` and `go.sum`.
+
 - When pinning images or packages by hash, add a comment above the reference
   with the version and date (YYYY-MM-DD).
 
@@ -607,10 +639,10 @@ style conventions are in separate documents:
   settings.
 
 - Avoid putting files in the repo root unless necessary. Root should contain
-  only project-level config files (`README.md`, `Makefile`, `Dockerfile`,
-  `LICENSE`, `.gitignore`, `.editorconfig`, `REPO_POLICIES.md`, and
-  language-specific config). Everything else goes in a subdirectory. Canonical
-  subdirectory names:
+  only project-level config files (`README.md`, `AGENTS.md`, `Makefile`,
+  `Dockerfile`, `LICENSE`, `.gitignore`, `.editorconfig`, `REPO_POLICIES.md`,
+  and language-specific config). Everything else goes in a subdirectory.
+  Canonical subdirectory names:
     - `bin/` — executable scripts and tools
     - `cmd/` — Go command entrypoints; thin only: one `main.go` per binary whose
       body is a single call into `internal/` or `pkg/`, no project logic in
@@ -641,3 +673,7 @@ style conventions are in separate documents:
     - Go: `go.mod`, `go.sum`, `.golangci.yml`
     - JS: `package.json`, `yarn.lock`, `.prettierrc`, `.prettierignore`
     - Python: `pyproject.toml`
+
+- Guidance for coding agents lives in one `AGENTS.md` at the repository root. It
+  is never committed under a file or directory named after one agent tool, such
+  as `CLAUDE.md` or `.claude/`, and never split into separate memory files.

go.mod

@@ -9,7 +9,6 @@ require (
 	github.com/btcsuite/btcd/btcutil v1.2.0
 	github.com/spf13/cobra v1.10.2
 	github.com/stretchr/testify v1.12.1
-	github.com/tyler-smith/go-bip39 v1.1.0
 	golang.org/x/crypto v0.57.0
 	golang.org/x/term v0.46.0
 )

go.sum

@@ -35,16 +35,10 @@ github.com/tyler-smith/go-bip39 v1.1.0/go.mod h1:gUYDtqQw1JS3ZJ8UWVcGTGqqr6YIN3C
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
 go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
 golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
-golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
 golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
 golang.org/x/term v0.46.0 h1:3+OXuTbaKDgwk8jTi3aSLHRlmWqHEUDUtxnbFigO4YE=
 golang.org/x/term v0.46.0/go.mod h1:+K02xbkittuwc0Am4abfA3Fc+XRGXkvBXNO88NCXPoc=
-golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/bip39/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2014-2018 Tyler Smith and contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

internal/bip39/bip39.go

@@ -0,0 +1,268 @@
+// Package bip39 is the Golang implementation of the BIP39 spec.
+//
+// The official BIP39 spec can be found at
+// https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
+//
+// It is a copy of github.com/tyler-smith/go-bip39 v1.1.0, trimmed to what
+// keyfunc uses.
+//
+//nolint:mnd // the numbers are BIP-39's own, written as upstream writes them
+package bip39
+
+import (
+	"crypto/sha256"
+	"crypto/sha512"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math/big"
+	"strings"
+
+	"golang.org/x/crypto/pbkdf2"
+)
+
+var (
+	// ErrInvalidMnemonic is returned when trying to use a malformed mnemonic.
+	ErrInvalidMnemonic = errors.New("invalid mnenomic")
+
+	// ErrEntropyLengthInvalid is returned when trying to use an entropy set with
+	// an invalid size.
+	ErrEntropyLengthInvalid = errors.New(
+		"entropy length must be [128, 256] and a multiple of 32",
+	)
+
+	// ErrChecksumIncorrect is returned when entropy has the incorrect checksum.
+	ErrChecksumIncorrect = errors.New("checksum incorrect")
+)
+
+// EntropyFromMnemonic takes a mnemonic generated by this library,
+// and returns the input entropy used to generate the given mnemonic.
+// An error is returned if the given mnemonic is invalid.
+func EntropyFromMnemonic(mnemonic string) ([]byte, error) {
+	mnemonicSlice, isValid := splitMnemonicWords(mnemonic)
+	if !isValid {
+		return nil, ErrInvalidMnemonic
+	}
+
+	// Some bitwise operands for working with big.Ints
+	shift11BitsMask := big.NewInt(2048)
+	bigOne := big.NewInt(1)
+
+	// used to isolate the checksum bits from the entropy+checksum byte array
+	wordLengthChecksumMasksMapping := map[int]*big.Int{
+		12: big.NewInt(15),
+		15: big.NewInt(31),
+		18: big.NewInt(63),
+		21: big.NewInt(127),
+		24: big.NewInt(255),
+	}
+	// used to use only the desired x of 8 available checksum bits.
+	// 256 bit (word length 24) requires all 8 bits of the checksum,
+	// and thus no shifting is needed for it (we would get a divByZero crash if we did)
+	wordLengthChecksumShiftMapping := map[int]*big.Int{
+		12: big.NewInt(16),
+		15: big.NewInt(8),
+		18: big.NewInt(4),
+		21: big.NewInt(2),
+	}
+
+	// wordMap is a reverse lookup map for the word list
+	wordMap := map[string]int{}
+	for i, v := range English() {
+		wordMap[v] = i
+	}
+
+	// Decode the words into a big.Int.
+	b := big.NewInt(0)
+
+	for _, v := range mnemonicSlice {
+		index, found := wordMap[v]
+		if !found {
+			return nil, fmt.Errorf(
+				"%w: word `%v` not found in reverse map", ErrInvalidMnemonic, v,
+			)
+		}
+
+		var wordBytes [2]byte
+
+		//nolint:gosec // the index of a word in the list is below 2048
+		binary.BigEndian.PutUint16(wordBytes[:], uint16(index))
+
+		b = b.Mul(b, shift11BitsMask)
+		b = b.Or(b, big.NewInt(0).SetBytes(wordBytes[:]))
+	}
+
+	// Build and add the checksum to the big.Int.
+	checksum := big.NewInt(0)
+	checksumMask := wordLengthChecksumMasksMapping[len(mnemonicSlice)]
+	checksum = checksum.And(b, checksumMask)
+
+	b.Div(b, big.NewInt(0).Add(checksumMask, bigOne))
+
+	// The entropy is the underlying bytes of the big.Int. Any upper bytes of
+	// all 0's are not returned so we pad the beginning of the slice with empty
+	// bytes if necessary.
+	entropy := b.Bytes()
+	entropy = padByteSlice(entropy, len(mnemonicSlice)/3*4)
+
+	// Generate the checksum and compare with the one we got from the mneomnic.
+	entropyChecksumBytes := computeChecksum(entropy)
+	entropyChecksum := big.NewInt(int64(entropyChecksumBytes[0]))
+
+	if l := len(mnemonicSlice); l != 24 {
+		checksumShift := wordLengthChecksumShiftMapping[l]
+		entropyChecksum.Div(entropyChecksum, checksumShift)
+	}
+
+	if checksum.Cmp(entropyChecksum) != 0 {
+		return nil, ErrChecksumIncorrect
+	}
+
+	return entropy, nil
+}
+
+// NewMnemonic will return a string consisting of the mnemonic words for
+// the given entropy.
+// If the provide entropy is invalid, an error will be returned.
+func NewMnemonic(entropy []byte) (string, error) {
+	// Compute some lengths for convenience.
+	entropyBitLength := len(entropy) * 8
+	checksumBitLength := entropyBitLength / 32
+	sentenceLength := (entropyBitLength + checksumBitLength) / 11
+
+	// Validate that the requested size is supported.
+	err := validateEntropyBitSize(entropyBitLength)
+	if err != nil {
+		return "", err
+	}
+
+	// Some bitwise operands for working with big.Ints
+	last11BitsMask := big.NewInt(2047)
+	shift11BitsMask := big.NewInt(2048)
+
+	// wordList is the set of words to use
+	wordList := English()
+
+	// Add checksum to entropy.
+	entropy = addChecksum(entropy)
+
+	// Break entropy up into sentenceLength chunks of 11 bits.
+	// For each word AND mask the rightmost 11 bits and find the word at that index.
+	// Then bitshift entropy 11 bits right and repeat.
+	// Add to the last empty slot so we can work with LSBs instead of MSB.
+
+	// Entropy as an int so we can bitmask without worrying about bytes slices.
+	entropyInt := new(big.Int).SetBytes(entropy)
+
+	// Slice to hold words in.
+	words := make([]string, sentenceLength)
+
+	// Throw away big.Int for AND masking.
+	word := big.NewInt(0)
+
+	for i := sentenceLength - 1; i >= 0; i-- {
+		// Get 11 right most bits and bitshift 11 to the right for next time.
+		word.And(entropyInt, last11BitsMask)
+		entropyInt.Div(entropyInt, shift11BitsMask)
+
+		// Get the bytes representing the 11 bits as a 2 byte slice.
+		wordBytes := padByteSlice(word.Bytes(), 2)
+
+		// Convert bytes to an index and add that word to the list.
+		words[i] = wordList[binary.BigEndian.Uint16(wordBytes)]
+	}
+
+	return strings.Join(words, " "), nil
+}
+
+// NewSeed creates a hashed seed output given a provided string and password.
+// No checking is performed to validate that the string provided is a valid mnemonic.
+func NewSeed(mnemonic string, password string) []byte {
+	return pbkdf2.Key([]byte(mnemonic), []byte("mnemonic"+password), 2048, 64, sha512.New)
+}
+
+// IsMnemonicValid attempts to verify that the provided mnemonic is valid.
+// Validity is determined by both the number of words being appropriate,
+// and that all the words in the mnemonic are present in the word list.
+func IsMnemonicValid(mnemonic string) bool {
+	_, err := EntropyFromMnemonic(mnemonic)
+
+	return err == nil
+}
+
+// Appends to data the first (len(data) / 32)bits of the result of sha256(data)
+// Currently only supports data up to 32 bytes
+func addChecksum(data []byte) []byte {
+	// Some bitwise operands for working with big.Ints
+	bigOne := big.NewInt(1)
+	bigTwo := big.NewInt(2)
+
+	// Get first byte of sha256
+	hash := computeChecksum(data)
+	firstChecksumByte := hash[0]
+
+	// len() is in bytes so we divide by 4
+	checksumBitLength := uint(len(data) / 4)
+
+	// For each bit of check sum we want we shift the data one the left
+	// and then set the (new) right most bit equal to checksum bit at that index
+	// staring from the left
+	dataBigInt := new(big.Int).SetBytes(data)
+	for i := range checksumBitLength {
+		// Bitshift 1 left
+		dataBigInt.Mul(dataBigInt, bigTwo)
+
+		// Set rightmost bit if leftmost checksum bit is set
+		if firstChecksumByte&(1<<(7-i)) > 0 {
+			dataBigInt.Or(dataBigInt, bigOne)
+		}
+	}
+
+	return dataBigInt.Bytes()
+}
+
+func computeChecksum(data []byte) []byte {
+	hasher := sha256.New()
+	hasher.Write(data)
+
+	return hasher.Sum(nil)
+}
+
+// validateEntropyBitSize ensures that entropy is the correct size for being a
+// mnemonic.
+func validateEntropyBitSize(bitSize int) error {
+	if (bitSize%32) != 0 || bitSize < 128 || bitSize > 256 {
+		return ErrEntropyLengthInvalid
+	}
+
+	return nil
+}
+
+// padByteSlice returns a byte slice of the given size with contents of the
+// given slice left padded and any empty spaces filled with 0's.
+func padByteSlice(slice []byte, length int) []byte {
+	offset := length - len(slice)
+	if offset <= 0 {
+		return slice
+	}
+
+	newSlice := make([]byte, length)
+	copy(newSlice[offset:], slice)
+
+	return newSlice
+}
+
+func splitMnemonicWords(mnemonic string) ([]string, bool) {
+	// Create a list of all the words in the mnemonic sentence
+	words := strings.Fields(mnemonic)
+
+	// Get num of words
+	numOfWords := len(words)
+
+	// The number of words should be 12, 15, 18, 21 or 24
+	if numOfWords%3 != 0 || numOfWords < 12 || numOfWords > 24 {
+		return nil, false
+	}
+
+	return words, true
+}

internal/bip39/bip39_internal_test.go

@@ -0,0 +1,442 @@
+package bip39
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"testing"
+)
+
+type vector struct {
+	entropy  string
+	mnemonic string
+	seed     string
+}
+
+func TestNewMnemonic(t *testing.T) {
+	t.Parallel()
+
+	for _, vector := range testVectors() {
+		entropy, err := hex.DecodeString(vector.entropy)
+		assertNil(t, err)
+
+		mnemonic, err := NewMnemonic(entropy)
+		assertNil(t, err)
+		assertEqualString(t, vector.mnemonic, mnemonic)
+
+		seed := NewSeed(mnemonic, "TREZOR")
+		assertEqualString(t, vector.seed, hex.EncodeToString(seed))
+	}
+}
+
+func TestNewMnemonicInvalidEntropy(t *testing.T) {
+	t.Parallel()
+
+	_, err := NewMnemonic([]byte{})
+	assertNotNil(t, err)
+}
+
+func TestIsMnemonicValid(t *testing.T) {
+	t.Parallel()
+
+	for _, vector := range badMnemonicSentences() {
+		assertFalse(t, IsMnemonicValid(vector.mnemonic))
+	}
+
+	for _, vector := range testVectors() {
+		assertTrue(t, IsMnemonicValid(vector.mnemonic))
+	}
+}
+
+func TestPadByteSlice(t *testing.T) {
+	t.Parallel()
+
+	assertEqualByteSlices(t, []byte{0}, padByteSlice([]byte{}, 1))
+	assertEqualByteSlices(t, []byte{0, 1}, padByteSlice([]byte{1}, 2))
+	assertEqualByteSlices(t, []byte{1, 1}, padByteSlice([]byte{1, 1}, 2))
+	assertEqualByteSlices(t, []byte{1, 1, 1}, padByteSlice([]byte{1, 1, 1}, 2))
+}
+
+//nolint:funlen // the test vectors, kept as upstream wrote them
+func TestMnemonicToByteArrayForZeroLeadingSeeds(t *testing.T) {
+	t.Parallel()
+
+	ms := []string{
+		"00000000000000000000000000000000",
+		"00a84c51041d49acca66e6160c1fa999",
+		"00ca45df1673c76537a2020bfed1dafd",
+		"0019d5871c7b81fd83d474ef1c1e1dae",
+		"00dcb021afb35ffcdd1d032d2056fc86",
+		"0062be7bd09a27288b6cf0eb565ec739",
+		"00dc705b5efa0adf25b9734226ba60d4",
+		"0017747418d54c6003fa64fade83374b",
+		"000d44d3ee7c3dfa45e608c65384431b",
+		"008241c1ef976b0323061affe5bf24b9",
+		"00a6aec77e4d16bea80b50a34991aaba",
+		"0011527b8c6ddecb9d0c20beccdeb58d",
+		"001c938c503c8f5a2bba2248ff621546",
+		"0002f90aaf7a8327698f0031b6317c36",
+		"00bff43071ed7e07f77b14f615993bac",
+		"00da143e00ef17fc63b6fb22dcc2c326",
+		"00ffc6764fb32a354cab1a3ddefb015d",
+		"0062ef47e0985e8953f24760b7598cdd",
+		"003bf9765064f71d304908d906c065f5",
+		"00993851503471439d154b3613947474",
+		"007ad0ffe9eae753a483a76af06dfa67",
+		"00091824db9ec19e663bee51d64c83cc",
+		"00f48ac621f7e3cb39b2012ac3121543",
+		"0072917415cdca24dfa66c4a92c885b4",
+		"0027ced2b279ea8a91d29364487cdbf4",
+		"00b9c0d37fb10ba272e55842ad812583",
+		"004b3d0d2b9285946c687a5350479c8c",
+		"00c7c12a37d3a7f8c1532b17c89b724c",
+		"00f400c5545f06ae17ad00f3041e4e26",
+		"001e290be10df4d209f247ac5878662b",
+		"00bf0f74568e582a7dd1ee64f792ec8b",
+		"00d2e43ecde6b72b847db1539ed89e23",
+		"00cecba6678505bb7bfec8ed307251f6",
+		"000aeed1a9edcbb4bc88f610d3ce84eb",
+		"00d06206aadfc25c2b21805d283f15ae",
+		"00a31789a2ab2d54f8fadd5331010287",
+		"003493c5f520e8d5c0483e895a121dc9",
+		"004706112800b76001ece2e268bc830e",
+		"00ab31e28bb5305be56e38337dbfa486",
+		"006872fe85df6b0fa945248e6f9379d1",
+		"00717e5e375da6934e3cfdf57edaf3bd",
+		"007f1b46e7b9c4c76e77c434b9bccd6b",
+		"00dc93735aa35def3b9a2ff676560205",
+		"002cd5dcd881a49c7b87714c6a570a76",
+		"0013b5af9e13fac87e0c505686cfb6bf",
+		"007ab1ec9526b0bc04b64ae65fd42631",
+		"00abb4e11d8385c1cca905a6a65e9144",
+		"00574fc62a0501ad8afada2e246708c3",
+		"005207e0a815bb2da6b4c35ec1f2bf52",
+		"00f3460f136fb9700080099cbd62bc18",
+		"007a591f204c03ca7b93981237112526",
+		"00cfe0befd428f8e5f83a5bfc801472e",
+		"00987551ac7a879bf0c09b8bc474d9af",
+		"00cadd3ce3d78e49fbc933a85682df3f",
+		"00bfbf2e346c855ccc360d03281455a1",
+		"004cdf55d429d028f715544ce22d4f31",
+		"0075c84a7d15e0ac85e1e41025eed23b",
+		"00807dddd61f71725d336cab844d2cb5",
+		"00422f21b77fe20e367467ed98c18410",
+		"00b44d0ac622907119c626c850a462fd",
+		"00363f5e7f22fc49f3cd662a28956563",
+		"000fe5837e68397bbf58db9f221bdc4e",
+		"0056af33835c888ef0c22599686445d3",
+		"00790a8647fd3dfb38b7e2b6f578f2c6",
+		"00da8d9009675cb7beec930e263014fb",
+		"00d4b384540a5bb54aa760edaa4fb2fe",
+		"00be9b1479ed680fdd5d91a41eb926d0",
+		"009182347502af97077c40a6e74b4b5c",
+		"00f5c90ee1c67fa77fd821f8e9fab4f1",
+		"005568f9a2dd6b0c0cc2f5ba3d9cac38",
+		"008b481f8678577d9cf6aa3f6cd6056b",
+		"00c4323ece5e4fe3b6cd4c5c932931af",
+		"009791f7550c3798c5a214cb2d0ea773",
+		"008a7baab22481f0ad8167dd9f90d55c",
+		"00f0e601519aafdc8ff94975e64c946d",
+		"0083b61e0daa9219df59d697c270cd31",
+	}
+
+	for _, m := range ms {
+		seed, _ := hex.DecodeString(m)
+
+		mnemonic, err := NewMnemonic(seed)
+		if err != nil {
+			t.Errorf("%v", err)
+		}
+
+		_, err = EntropyFromMnemonic(mnemonic)
+		if err != nil {
+			t.Errorf("Failed for %x - %v", seed, mnemonic)
+		}
+	}
+}
+
+func TestEntropyFromMnemonic128(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 128)
+}
+
+func TestEntropyFromMnemonic160(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 160)
+}
+
+func TestEntropyFromMnemonic192(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 192)
+}
+
+func TestEntropyFromMnemonic224(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 224)
+}
+
+func TestEntropyFromMnemonic256(t *testing.T) {
+	t.Parallel()
+
+	testEntropyFromMnemonic(t, 256)
+}
+
+//nolint:dupword,lll // the test vector, kept as upstream wrote it
+func TestEntropyFromMnemonicInvalidChecksum(t *testing.T) {
+	t.Parallel()
+
+	_, err := EntropyFromMnemonic("abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon yellow")
+	assertEqual(t, ErrChecksumIncorrect, err)
+}
+
+//nolint:dupword // the test vectors, kept as upstream wrote them
+func TestEntropyFromMnemonicInvalidMnemonicSize(t *testing.T) {
+	t.Parallel()
+
+	for _, mnemonic := range []string{
+		"a a a a a a a a a a a a a a a a a a a a a a a a a", // Too many words
+		"a",                           // Too few
+		"a a a a a a a a a a a a a a", // Not multiple of 3
+	} {
+		_, err := EntropyFromMnemonic(mnemonic)
+		assertEqual(t, ErrInvalidMnemonic, err)
+	}
+}
+
+func testEntropyFromMnemonic(t *testing.T, bitSize int) {
+	t.Helper()
+
+	for range 512 {
+		expectedEntropy := make([]byte, bitSize/8)
+		_, err := rand.Read(expectedEntropy)
+		assertNil(t, err)
+		assertTrue(t, len(expectedEntropy) != 0)
+
+		mnemonic, err := NewMnemonic(expectedEntropy)
+		assertNil(t, err)
+		assertTrue(t, len(mnemonic) != 0)
+
+		actualEntropy, err := EntropyFromMnemonic(mnemonic)
+		assertNil(t, err)
+		assertEqualByteSlices(t, expectedEntropy, actualEntropy)
+	}
+}
+
+//nolint:dupword,funlen,lll // the BIP-39 test vectors, kept as upstream wrote them
+func testVectors() []vector {
+	return []vector{
+		{
+			entropy:  "00000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+			seed:     "c55257c360c07c72029aebc1b53c05ed0362ada38ead3e3e9efa3708e53495531f09a6987599d18264c1e1c92f2cf141630c7a3c4ab7c81b2f001698e7463b04",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank yellow",
+			seed:     "2e8905819b8723fe2c1d161860e5ee1830318dbf49a83bd451cfb8440c28bd6fa457fe1296106559a3c80937a1c1069be3a3a5bd381ee6260e8d9739fce1f607",
+		},
+		{
+			entropy:  "80808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage above",
+			seed:     "d71de856f81a8acc65e6fc851a38d4d7ec216fd0796d0a6827a3ad6ed5511a30fa280f12eb2e47ed2ac03b5c462a0358d18d69fe4f985ec81778c1b370b652a8",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong",
+			seed:     "ac27495480225222079d7be181583751e86f571027b0497b5b5d11218e0a8a13332572917f0f8e5a589620c6f15b11c61dee327651a14c34e18231052e48c069",
+		},
+		{
+			entropy:  "000000000000000000000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent",
+			seed:     "035895f2f481b1b0f01fcf8c289c794660b289981a78f8106447707fdd9666ca06da5a9a565181599b79f53b844d8a71dd9f439c52a3d7b3e8a79c906ac845fa",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will",
+			seed:     "f2b94508732bcbacbcc020faefecfc89feafa6649a5491b8c952cede496c214a0c7b3c392d168748f2d4a612bada0753b52a1c7ac53c1e93abd5c6320b9e95dd",
+		},
+		{
+			entropy:  "808080808080808080808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always",
+			seed:     "107d7c02a5aa6f38c58083ff74f04c607c2d2c0ecc55501dadd72d025b751bc27fe913ffb796f841c49b1d33b610cf0e91d3aa239027f5e99fe4ce9e5088cd65",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when",
+			seed:     "0cd6e5d827bb62eb8fc1e262254223817fd068a74b5b449cc2f667c3f1f985a76379b43348d952e2265b4cd129090758b3e3c2c49103b5051aac2eaeb890a528",
+		},
+		{
+			entropy:  "0000000000000000000000000000000000000000000000000000000000000000",
+			mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art",
+			seed:     "bda85446c68413707090a52022edd26a1c9462295029f2e60cd7c4f2bbd3097170af7a4d73245cafa9c3cca8d561a7c3de6f5d4a10be8ed2a5e608d68f92fcc8",
+		},
+		{
+			entropy:  "7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f",
+			mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title",
+			seed:     "bc09fca1804f7e69da93c2f2028eb238c227f2e9dda30cd63699232578480a4021b146ad717fbb7e451ce9eb835f43620bf5c514db0f8add49f5d121449d3e87",
+		},
+		{
+			entropy:  "8080808080808080808080808080808080808080808080808080808080808080",
+			mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless",
+			seed:     "c0c519bd0e91a2ed54357d9d1ebef6f5af218a153624cf4f2da911a0ed8f7a09e2ef61af0aca007096df430022f7a2b6fb91661a9589097069720d015e4e982f",
+		},
+		{
+			entropy:  "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+			mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote",
+			seed:     "dd48c104698c30cfe2b6142103248622fb7bb0ff692eebb00089b32d22484e1613912f0a5b694407be899ffd31ed3992c456cdf60f5d4564b8ba3f05a69890ad",
+		},
+		{
+			entropy:  "77c2b00716cec7213839159e404db50d",
+			mnemonic: "jelly better achieve collect unaware mountain thought cargo oxygen act hood bridge",
+			seed:     "b5b6d0127db1a9d2226af0c3346031d77af31e918dba64287a1b44b8ebf63cdd52676f672a290aae502472cf2d602c051f3e6f18055e84e4c43897fc4e51a6ff",
+		},
+		{
+			entropy:  "b63a9c59a6e641f288ebc103017f1da9f8290b3da6bdef7b",
+			mnemonic: "renew stay biology evidence goat welcome casual join adapt armor shuffle fault little machine walk stumble urge swap",
+			seed:     "9248d83e06f4cd98debf5b6f010542760df925ce46cf38a1bdb4e4de7d21f5c39366941c69e1bdbf2966e0f6e6dbece898a0e2f0a4c2b3e640953dfe8b7bbdc5",
+		},
+		{
+			entropy:  "3e141609b97933b66a060dcddc71fad1d91677db872031e85f4c015c5e7e8982",
+			mnemonic: "dignity pass list indicate nasty swamp pool script soccer toe leaf photo multiply desk host tomato cradle drill spread actor shine dismiss champion exotic",
+			seed:     "ff7f3184df8696d8bef94b6c03114dbee0ef89ff938712301d27ed8336ca89ef9635da20af07d4175f2bf5f3de130f39c9d9e8dd0472489c19b1a020a940da67",
+		},
+		{
+			entropy:  "0460ef47585604c5660618db2e6a7e7f",
+			mnemonic: "afford alter spike radar gate glance object seek swamp infant panel yellow",
+			seed:     "65f93a9f36b6c85cbe634ffc1f99f2b82cbb10b31edc7f087b4f6cb9e976e9faf76ff41f8f27c99afdf38f7a303ba1136ee48a4c1e7fcd3dba7aa876113a36e4",
+		},
+		{
+			entropy:  "72f60ebac5dd8add8d2a25a797102c3ce21bc029c200076f",
+			mnemonic: "indicate race push merry suffer human cruise dwarf pole review arch keep canvas theme poem divorce alter left",
+			seed:     "3bbf9daa0dfad8229786ace5ddb4e00fa98a044ae4c4975ffd5e094dba9e0bb289349dbe2091761f30f382d4e35c4a670ee8ab50758d2c55881be69e327117ba",
+		},
+		{
+			entropy:  "2c85efc7f24ee4573d2b81a6ec66cee209b2dcbd09d8eddc51e0215b0b68e416",
+			mnemonic: "clutch control vehicle tonight unusual clog visa ice plunge glimpse recipe series open hour vintage deposit universe tip job dress radar refuse motion taste",
+			seed:     "fe908f96f46668b2d5b37d82f558c77ed0d69dd0e7e043a5b0511c48c2f1064694a956f86360c93dd04052a8899497ce9e985ebe0c8c52b955e6ae86d4ff4449",
+		},
+		{
+			entropy:  "eaebabb2383351fd31d703840b32e9e2",
+			mnemonic: "turtle front uncle idea crush write shrug there lottery flower risk shell",
+			seed:     "bdfb76a0759f301b0b899a1e3985227e53b3f51e67e3f2a65363caedf3e32fde42a66c404f18d7b05818c95ef3ca1e5146646856c461c073169467511680876c",
+		},
+		{
+			entropy:  "7ac45cfe7722ee6c7ba84fbc2d5bd61b45cb2fe5eb65aa78",
+			mnemonic: "kiss carry display unusual confirm curtain upgrade antique rotate hello void custom frequent obey nut hole price segment",
+			seed:     "ed56ff6c833c07982eb7119a8f48fd363c4a9b1601cd2de736b01045c5eb8ab4f57b079403485d1c4924f0790dc10a971763337cb9f9c62226f64fff26397c79",
+		},
+		{
+			entropy:  "4fa1a8bc3e6d80ee1316050e862c1812031493212b7ec3f3bb1b08f168cabeef",
+			mnemonic: "exile ask congress lamp submit jacket era scheme attend cousin alcohol catch course end lucky hurt sentence oven short ball bird grab wing top",
+			seed:     "095ee6f817b4c2cb30a5a797360a81a40ab0f9a4e25ecd672a3f58a0b5ba0687c096a6b14d2c0deb3bdefce4f61d01ae07417d502429352e27695163f7447a8c",
+		},
+		{
+			entropy:  "18ab19a9f54a9274f03e5209a2ac8a91",
+			mnemonic: "board flee heavy tunnel powder denial science ski answer betray cargo cat",
+			seed:     "6eff1bb21562918509c73cb990260db07c0ce34ff0e3cc4a8cb3276129fbcb300bddfe005831350efd633909f476c45c88253276d9fd0df6ef48609e8bb7dca8",
+		},
+		{
+			entropy:  "18a2e1d81b8ecfb2a333adcb0c17a5b9eb76cc5d05db91a4",
+			mnemonic: "board blade invite damage undo sun mimic interest slam gaze truly inherit resist great inject rocket museum chief",
+			seed:     "f84521c777a13b61564234bf8f8b62b3afce27fc4062b51bb5e62bdfecb23864ee6ecf07c1d5a97c0834307c5c852d8ceb88e7c97923c0a3b496bedd4e5f88a9",
+		},
+		{
+			entropy:  "15da872c95a13dd738fbf50e427583ad61f18fd99f628c417a61cf8343c90419",
+			mnemonic: "beyond stage sleep clip because twist token leaf atom beauty genius food business side grid unable middle armed observe pair crouch tonight away coconut",
+			seed:     "b15509eaa2d09d3efd3e006ef42151b30367dc6e3aa5e44caba3fe4d3e352e65101fbdb86a96776b91946ff06f8eac594dc6ee1d3e82a42dfe1b40fef6bcc3fd",
+		},
+	}
+}
+
+//nolint:dupword,lll // the test vectors, kept as upstream wrote them
+func badMnemonicSentences() []vector {
+	return []vector{
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thank yellow yellow"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice caged above"},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo, wrong"},
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will will will"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always."},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo why"},
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art art"},
+		{mnemonic: "legal winner thank year wave sausage worth useful legal winner thanks year wave worth useful legal winner thank year wave sausage worth title"},
+		{mnemonic: "letter advice cage absurd amount doctor acoustic avoid letters advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless"},
+		{mnemonic: "zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo voted"},
+		{mnemonic: "jello better achieve collect unaware mountain thought cargo oxygen act hood bridge"},
+		{mnemonic: "renew, stay, biology, evidence, goat, welcome, casual, join, adapt, armor, shuffle, fault, little, machine, walk, stumble, urge, swap"},
+		{mnemonic: "dignity pass list indicate nasty"},
+
+		// From issue 32
+		{mnemonic: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon letter"},
+	}
+}
+
+func assertNil(t *testing.T, object any) {
+	t.Helper()
+
+	if object != nil {
+		t.Errorf("Expected nil, got %v", object)
+	}
+}
+
+func assertNotNil(t *testing.T, object any) {
+	t.Helper()
+
+	if object == nil {
+		t.Error("Expected not nil")
+	}
+}
+
+func assertTrue(t *testing.T, a bool) {
+	t.Helper()
+
+	if !a {
+		t.Error("Expected true, got false")
+	}
+}
+
+func assertFalse(t *testing.T, a bool) {
+	t.Helper()
+
+	if a {
+		t.Error("Expected false, got true")
+	}
+}
+
+func assertEqual(t *testing.T, a, b any) {
+	t.Helper()
+
+	if a != b {
+		t.Errorf("Objects not equal, expected `%s` and got `%s`", a, b)
+	}
+}
+
+func assertEqualString(t *testing.T, a, b string) {
+	t.Helper()
+
+	if a != b {
+		t.Errorf("Strings not equal, expected `%s` and got `%s`", a, b)
+	}
+}
+
+func assertEqualByteSlices(t *testing.T, a, b []byte) {
+	t.Helper()
+
+	if len(a) != len(b) {
+		t.Errorf("Byte slices not equal, expected %v and got %v", a, b)
+
+		return
+	}
+
+	for i := range a {
+		if a[i] != b[i] {
+			t.Errorf("Byte slices not equal, expected %v and got %v", a, b)
+
+			return
+		}
+	}
+}

internal/bip39/english_internal_test.go

@@ -0,0 +1,19 @@
+package bip39
+
+import (
+	"hash/crc32"
+	"testing"
+)
+
+func TestEnglishChecksum(t *testing.T) {
+	t.Parallel()
+
+	// Ensure word list is correct
+	// $ wget https://raw.githubusercontent.com/bitcoin/bips/master/bip-0039/english.txt
+	// $ crc32 english.txt
+	// c1dbd296
+	checksum := crc32.ChecksumIEEE([]byte(english))
+	if checksum != 0xc1dbd296 {
+		t.Error("english checksum invalid")
+	}
+}

internal/bip39/example_test.go

@@ -0,0 +1,30 @@
+package bip39_test
+
+import (
+	"encoding/hex"
+	"fmt"
+
+	"sneak.berlin/go/keyfunc/internal/bip39"
+)
+
+//nolint:lll // the test vector and its output, kept as upstream wrote them
+func ExampleNewMnemonic() {
+	// the entropy can be any byte slice, generated how pleased,
+	// as long its bit size is a multiple of 32 and is within
+	// the inclusive range of {128,256}
+	entropy, _ := hex.DecodeString("066dca1a2bb7e8a1db2832148ce9933eea0f3ac9548d793112d9a95c9407efad")
+
+	// generate a mnemomic
+	mnemomic, _ := bip39.NewMnemonic(entropy)
+	fmt.Println(mnemomic)
+	// output:
+	// all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform
+}
+
+//nolint:lll // the test vector and its output, kept as upstream wrote them
+func ExampleNewSeed() {
+	seed := bip39.NewSeed("all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform", "TREZOR")
+	fmt.Println(hex.EncodeToString(seed))
+	// output:
+	// 26e975ec644423f4a4c4f4215ef09b4bd7ef924e85d1d17c4cf3f136c2863cf6df0a475045652c57eb5fb41513ca2a2d67722b77e954b4b3fc11f7590449191d
+}

internal/childmnemonic/childmnemonic.go

@@ -7,7 +7,7 @@ import (
 
 	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 	"sneak.berlin/go/keyfunc/internal/derive"
 )
 

internal/childmnemonic/childmnemonic_test.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/stretchr/testify/require"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 	"sneak.berlin/go/keyfunc/internal/childmnemonic"
 	"sneak.berlin/go/keyfunc/internal/derive"
 )

internal/cli/age/age.go

@@ -3,17 +3,28 @@
 package age
 
 import (
+	"context"
+	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
+	"os/signal"
 	"path/filepath"
 
 	"github.com/spf13/cobra"
 	"sneak.berlin/go/keyfunc/internal/agekey"
 	"sneak.berlin/go/keyfunc/internal/cli/options"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 	"sneak.berlin/go/keyfunc/internal/derive"
 )
 
+// ErrInterrupted is returned when SIGINT, SIGTERM or SIGHUP has been
+// received by the time the work writing the file --output names ends.
+var ErrInterrupted = errors.New(
+	"interrupted by a signal; the output file was left as it was",
+)
+
 // Command returns the age command and everything under it.
 func Command() *cobra.Command {
 	group := &cobra.Command{
@@ -128,8 +139,12 @@ func runDecrypt(cmd *cobra.Command, args []string) error {
 	return through(cmd, args, key.Decrypt)
 }
 
-// through opens the input and the output the arguments ask for, hands
-// them to the work, and finishes the output afterwards either way.
+// through opens the input the arguments ask for and hands it to the
+// work, with the file --output names to write to, or the command's own
+// output when it names none or names the same file as that output, and
+// the command's own error output when it names the same file as that.
+// Those two are the streams the tool already has, so whatever they are
+// redirected to is written as the redirect says, never replaced.
 func through(
 	cmd *cobra.Command, args []string,
 	work func(io.Writer, io.Reader) error,
@@ -141,14 +156,41 @@ func through(
 
 	defer closeSrc()
 
-	dst, done, err := output(cmd)
+	name, err := cmd.Flags().GetString("output")
 	if err != nil {
-		return err
+		return fmt.Errorf("reading the output file: %w", err)
 	}
 
-	err = work(dst, src)
+	switch {
+	case name == "", same(name, cmd.OutOrStdout()):
+		return work(cmd.OutOrStdout(), src)
+	case same(name, cmd.ErrOrStderr()):
+		return work(cmd.ErrOrStderr(), src)
+	default:
+		return output(name, src, work)
+	}
+}
 
-	return done(err)
+// same reports whether the named path, followed to the end, is the
+// file the stream writes to, whatever name it is reached by, such as
+// /dev/stdout or /dev/fd/1 for standard output.
+func same(name string, stream io.Writer) bool {
+	file, ok := stream.(*os.File)
+	if !ok {
+		return false
+	}
+
+	streamInfo, err := file.Stat()
+	if err != nil {
+		return false
+	}
+
+	info, err := os.Stat(name)
+	if err != nil {
+		return false
+	}
+
+	return os.SameFile(info, streamInfo)
 }
 
 // input returns what to read from: the named file, or the command's
@@ -167,35 +209,127 @@ func input(cmd *cobra.Command, args []string) (io.Reader, func(), error) {
 	return file, func() { _ = file.Close() }, nil
 }
 
-// output returns what to write to: a new file beside the one --output
-// names, or the command's own output when it names none. The second
-// result finishes the write, and is given whatever the work returned:
-// the new file takes the named file's place only when the work
-// succeeded, so a file that is already there survives a run that
-// failed.
-func output(cmd *cobra.Command) (io.Writer, func(error) error, error) {
-	name, err := cmd.Flags().GetString("output")
+// output has the work write to the named path, going by what is there
+// without following a final symlink:
+//
+//   - nothing, or a regular file: replace writes a new file beside it
+//     and renames that over it;
+//   - a symlink: the same for what it points at, so that the link keeps
+//     pointing where it did; one that points at nothing is refused;
+//   - anything else, such as a named pipe or a device like /dev/null:
+//     direct writes to it, since a rename would put a regular file in
+//     its place.
+func output(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	info, err := os.Lstat(name)
+
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		return replace(name, src, work)
+	case err != nil:
+		return fmt.Errorf("looking at %s: %w", name, err)
+	case info.Mode().IsRegular():
+		return replace(name, src, work)
+	case info.Mode().Type() == fs.ModeSymlink:
+		// os.Stat follows the link as opening it would. /dev/fd/3
+		// needs that: it reaches a pipe or a terminal through a link
+		// that names no path.
+		info, err = os.Stat(name)
 		if err != nil {
-		return nil, nil, fmt.Errorf("reading the output file: %w", err)
+			return fmt.Errorf("following %s: %w", name, err)
 		}
 
-	if name == "" {
-		return cmd.OutOrStdout(), func(failed error) error {
-			return failed
-		}, nil
+		if !info.Mode().IsRegular() {
+			return direct(name, src, work)
 		}
 
+		target, err := filepath.EvalSymlinks(name)
+		if err != nil {
+			return fmt.Errorf("following %s: %w", name, err)
+		}
+
+		return replace(target, src, work)
+	default:
+		return direct(name, src, work)
+	}
+}
+
+// direct has the work write straight to the named path, which is there
+// and is not a regular file. No signal is caught, so one ends the tool
+// as it ends any other command.
+func direct(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	file, err := os.OpenFile(name, os.O_WRONLY, 0) //nolint:gosec // the -o path
+	if err != nil {
+		return fmt.Errorf("opening %s: %w", name, err)
+	}
+
+	failed := work(file, src)
+	closeErr := file.Close()
+
+	if failed != nil {
+		return failed
+	}
+
+	if closeErr != nil {
+		return fmt.Errorf("finishing %s: %w", name, closeErr)
+	}
+
+	return nil
+}
+
+// replace has the work write a new file beside the named one, and puts
+// the new file in the named file's place only when the work succeeded,
+// so a file that is already there survives a run that failed.
+//
+// Meanwhile SIGINT, SIGTERM and SIGHUP are caught, as signals.Context
+// does. One the tool has received by the time the work ends wins: the
+// new file is removed and ErrInterrupted returned, at once if the work
+// is still running, without waiting for it, since it may be blocked
+// reading its input.
+func replace(
+	name string, src io.Reader, work func(io.Writer, io.Reader) error,
+) error {
+	// received is registered before the context, so it gets every
+	// signal the context gets.
+	received := make(chan os.Signal, 1)
+	signals.Notify(received)
+
+	defer signal.Stop(received)
+
+	// The context goes on catching the signals until the file is in
+	// place or removed, so that a later one cannot end the tool with
+	// the new file left beside the named one.
+	interrupted, stop := signals.Context(context.Background())
+	defer stop()
+
 	// The file is made in the same directory so that putting it in
 	// place is a rename and never a copy, and it is readable only by
 	// its owner, which is the mode it keeps once renamed.
 	file, err := os.CreateTemp(filepath.Dir(name), filepath.Base(name)+".")
 	if err != nil {
-		return nil, nil, fmt.Errorf("creating a file beside %s: %w", name, err)
+		return fmt.Errorf("creating a file beside %s: %w", name, err)
 	}
 
-	return file, func(failed error) error {
+	worked := make(chan error, 1)
+
+	go func() { worked <- work(file, src) }()
+
+	select {
+	case failed := <-worked:
+		// Stop returns only once every signal the tool has received
+		// has been handed over, so an empty received means none came.
+		signal.Stop(received)
+
+		if len(received) == 0 {
 			return finish(file, name, failed)
-	}, nil
+		}
+	case <-interrupted.Done():
+	}
+
+	return finish(file, name, ErrInterrupted)
 }
 
 // finish closes the new file and puts it in the named file's place, or

internal/cli/age_test.go

@@ -1,13 +1,22 @@
 package cli_test
 
 import (
+	"errors"
+	"io"
+	"io/fs"
 	"os"
+	"os/exec"
+	"os/signal"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 	"sneak.berlin/go/keyfunc/internal/agekey"
+	"sneak.berlin/go/keyfunc/internal/cli"
+	"sneak.berlin/go/keyfunc/internal/cli/age"
 	"sneak.berlin/go/keyfunc/internal/mnemonic"
 )
 
@@ -90,6 +99,360 @@ func TestARefusedDecryptionLeavesTheOutputFileAlone(t *testing.T) {
 	require.Equal(t, "what was already there\n", string(kept))
 }
 
+func TestASymlinkAtTheOutputPathStaysAndItsTargetGetsTheOutput(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	target := written(t, "notes.age", "what was already there\n")
+	link := filepath.Join(t.TempDir(), "notes.age")
+	require.NoError(t, os.Symlink(target, link))
+
+	run(t, "age", "encrypt", "-o", link, plain)
+
+	pointsAt, err := os.Readlink(link)
+	require.NoError(t, err)
+	require.Equal(t, target, pointsAt)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", target))
+}
+
+func TestANamedPipeAtTheOutputPathIsWrittenToAndStaysAPipe(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	plain := written(t, "notes.txt", "the secret\n")
+	pipe := filepath.Join(t.TempDir(), "notes.age")
+	require.NoError(t, syscall.Mkfifo(pipe, fileMode))
+
+	// Opening the pipe to read waits until the tool opens it to write.
+	var sealed []byte
+
+	finished := make(chan error, 1)
+
+	go func() {
+		var err error
+
+		sealed, err = os.ReadFile(pipe) //nolint:gosec // the test's own path
+		finished <- err
+	}()
+
+	run(t, "age", "encrypt", "-o", pipe, plain)
+
+	select {
+	case err := <-finished:
+		require.NoError(t, err)
+	case <-time.After(5 * time.Second):
+		t.Fatal("nothing was written to the pipe")
+	}
+
+	info, err := os.Lstat(pipe)
+	require.NoError(t, err)
+	require.Equal(t, fs.ModeNamedPipe, info.Mode().Type())
+
+	sealedFile := written(t, "notes.age", string(sealed))
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", sealedFile))
+}
+
+func TestANameForStandardOutputAddsToTheFileItIsAppendedTo(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := filepath.Join(t.TempDir(), "notes.age")
+	run(t, "age", "encrypt", "-o", sealed, written(t, "notes.txt", "the secret\n"))
+
+	for _, name := range []string{"/dev/stdout", "/dev/fd/1"} {
+		appendedThrough(t, name, sealed)
+	}
+}
+
+// appendedThrough decrypts sealed with -o name while the tool's standard
+// output is appended to a file that already has contents, as the shell's
+// ">> notes.out" does, and checks that the file is the same one, with
+// the same mode, and holds its earlier contents and then the output.
+func appendedThrough(t *testing.T, name, sealed string) {
+	t.Helper()
+
+	// A mode of its own, so that a replaced file would show.
+	const ownMode = 0o644
+
+	existing := written(t, "notes.out", "what was already there\n")
+	require.NoError(t, os.Chmod(existing, ownMode))
+
+	before, err := os.Stat(existing)
+	require.NoError(t, err)
+
+	//nolint:gosec // the test made this path itself
+	appended, err := os.OpenFile(existing, os.O_WRONLY|os.O_APPEND, 0)
+	require.NoError(t, err)
+
+	defer func() { _ = appended.Close() }()
+
+	//nolint:gosec // this test's own binary as the tool
+	command := exec.CommandContext(
+		t.Context(), os.Args[0], "age", "decrypt", "-o", name, sealed,
+	)
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+	command.Stdout = appended
+
+	require.NoError(t, command.Run(), name)
+	require.Equal(t,
+		"what was already there\nthe secret\n", read(t, existing), name,
+	)
+
+	after, err := os.Stat(existing)
+	require.NoError(t, err)
+	require.True(t, os.SameFile(before, after), name)
+	require.Equal(t, os.FileMode(ownMode), after.Mode().Perm(), name)
+}
+
+func TestASignalStopsAnEncryptionAndLeavesNoFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		interrupted(t, ending, "encrypt", "the start of the secret\n")
+	}
+}
+
+func TestASignalStopsADecryptionAndLeavesNoFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	// All of an encryption but its last byte, so the tool reads the
+	// header and then waits for the rest.
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+	cut := sealed[:len(sealed)-1]
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		interrupted(t, ending, "decrypt", cut)
+	}
+}
+
+func TestASignalReceivedAsTheInputEndsLeavesTheFileAsItWas(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+
+	for _, ending := range []syscall.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		receivedAtTheEnd(t, ending, "encrypt", "the secret\n")
+		receivedAtTheEnd(t, ending, "decrypt", sealed)
+	}
+}
+
+func TestASignalAsTheInputEndsLeavesNoUnfinishedFile(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	sealed := run(t, "age", "encrypt", written(t, "notes.txt", "the secret\n"))
+
+	// Ctrl-C on "producer | keyfunc age encrypt -o file" ends the
+	// producer too, so the input ends just as the signal comes, with
+	// enough of it in hand for a whole encryption or decryption. Which
+	// of the two the tool has first varies, so it is tried often, and
+	// a whole file in place is accepted as well as none.
+	for range 25 {
+		named := signalledAsTheInputEnds(t, "encrypt", "the start of the secret\n")
+		if named != "" {
+			require.Equal(t,
+				"the start of the secret\n", run(t, "age", "decrypt", named),
+			)
+		}
+
+		named = signalledAsTheInputEnds(t, "decrypt", sealed)
+		if named != "" {
+			require.Equal(t, "the secret\n", read(t, named))
+		}
+	}
+}
+
+func TestAnEncryptionStartedUnderNohupSurvivesAHangup(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	directory := t.TempDir()
+	named := filepath.Join(directory, "notes")
+
+	// nohup starts the tool with SIGHUP ignored. A tool that caught it
+	// anyway would turn it back on and be ended by it.
+	command, producer := writing(
+		t, directory, "the secret\n",
+		"nohup", os.Args[0], "age", "encrypt", "-o", named,
+	)
+
+	require.NoError(t, command.Process.Signal(syscall.SIGHUP))
+	require.NoError(t, producer.Close())
+	waitForTool(t, "SIGHUP under nohup", command)
+
+	require.Equal(t, 0, command.ProcessState.ExitCode())
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Len(t, left, 1)
+	require.Equal(t, "the secret\n", run(t, "age", "decrypt", named))
+}
+
+// interrupted runs "age encrypt -o" or "age decrypt -o", as the
+// operation says, writing into a directory of its own, and once it has
+// begun writing sends it the signal and leaves the input open. The tool
+// has to end with status 1 and leave the directory empty. A tool that
+// went on reading would not end until the input did; one that did not
+// remove the file it was writing would leave it there, with what it had
+// written so far.
+func interrupted(t *testing.T, ending os.Signal, operation, input string) {
+	t.Helper()
+
+	name := operation + " " + ending.String()
+	directory := t.TempDir()
+
+	command, _ := writing(
+		t, directory, input,
+		os.Args[0], "age", operation, "-o", filepath.Join(directory, "notes"),
+	)
+
+	require.NoError(t, command.Process.Signal(ending))
+	waitForTool(t, name, command)
+
+	require.Equal(t, 1, command.ProcessState.ExitCode(), name)
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+	require.Empty(t, left, name)
+}
+
+// signalledAsTheInputEnds runs "age encrypt -o" or "age decrypt -o", as
+// the operation says, writing into a directory of its own, and once it
+// has begun writing sends it SIGINT and at once ends its input. Either
+// the tool ends with status 1 and leaves the directory empty, and ""
+// is returned, or it ends otherwise and leaves only the named file,
+// whose path is returned for the caller to check that it is whole.
+func signalledAsTheInputEnds(t *testing.T, operation, input string) string {
+	t.Helper()
+
+	directory := t.TempDir()
+	named := filepath.Join(directory, "notes")
+
+	command, producer := writing(
+		t, directory, input, os.Args[0], "age", operation, "-o", named,
+	)
+
+	require.NoError(t, command.Process.Signal(syscall.SIGINT))
+	require.NoError(t, producer.Close())
+	waitForTool(t, operation, command)
+
+	left, err := os.ReadDir(directory)
+	require.NoError(t, err)
+
+	if command.ProcessState.ExitCode() == failedStatus {
+		require.Empty(t, left, operation)
+
+		return ""
+	}
+
+	require.Len(t, left, 1, operation)
+
+	return named
+}
+
+// receivedAtTheEnd runs "age encrypt -o" or "age decrypt -o", as the
+// operation says, in this process, over a file that is already there,
+// with an input that at its end sends this process the signal and waits
+// until it has been received. The tool has to return ErrInterrupted and
+// leave that file as it was, with nothing beside it. A tool that went
+// by the end of the input alone would put its new file in place.
+func receivedAtTheEnd(
+	t *testing.T, ending syscall.Signal, operation, input string,
+) {
+	t.Helper()
+
+	name := operation + " " + ending.String()
+	existing := written(t, "notes", "what was already there\n")
+
+	// The test catches the signal as well, so that it does not end the
+	// test binary and so that the input can wait for it.
+	received := make(chan os.Signal, 1)
+	signal.Notify(received, ending)
+
+	defer signal.Stop(received)
+
+	root := cli.Root()
+	root.SetIn(&endingInASignal{
+		rest: strings.NewReader(input), ending: ending, received: received,
+	})
+	root.SetOut(io.Discard)
+	root.SetErr(io.Discard)
+	root.SetArgs([]string{"age", operation, "-o", existing})
+
+	err := root.ExecuteContext(t.Context())
+	require.ErrorIs(t, err, age.ErrInterrupted, name)
+
+	require.Equal(t, "what was already there\n", read(t, existing), name)
+
+	left, err := os.ReadDir(filepath.Dir(existing))
+	require.NoError(t, err)
+	require.Len(t, left, 1, name)
+}
+
+// endingInASignal is an input that, when it runs out, sends this
+// process its signal and waits for it on received before it reports its
+// end. It sends the signal only once: once nothing catches it, another
+// would end the test binary.
+type endingInASignal struct {
+	rest     io.Reader
+	ending   syscall.Signal
+	received chan os.Signal
+	sent     bool
+}
+
+func (input *endingInASignal) Read(buffer []byte) (int, error) {
+	n, err := input.rest.Read(buffer)
+	if !errors.Is(err, io.EOF) || input.sent {
+		return n, err
+	}
+
+	input.sent = true
+
+	err = syscall.Kill(os.Getpid(), input.ending)
+	if err != nil {
+		return n, err
+	}
+
+	<-input.received
+
+	return n, io.EOF
+}
+
+// writing starts argv, the tool told to write into directory, as a
+// subprocess reading the input from a pipe, and returns once the tool
+// has begun writing the file beside the one it was named. The pipe is
+// left open for the caller to end.
+func writing(
+	t *testing.T, directory, input string, argv ...string,
+) (*exec.Cmd, io.WriteCloser) {
+	t.Helper()
+
+	//nolint:gosec // this test's own binary as the tool, or nohup running it
+	command := exec.CommandContext(t.Context(), argv[0], argv[1:]...)
+
+	command.Env = append(os.Environ(), runAsTool+"=1")
+
+	producer, err := command.StdinPipe()
+	require.NoError(t, err)
+	require.NoError(t, command.Start())
+
+	_, err = io.WriteString(producer, input)
+	require.NoError(t, err)
+
+	// The file beside the named one is made once the mnemonic has been
+	// read, before any input is.
+	require.Eventually(t, func() bool {
+		entries, err := os.ReadDir(directory)
+
+		return err == nil && len(entries) > 0
+	}, 5*time.Second, 5*time.Millisecond)
+
+	return command, producer
+}
+
 // written puts the contents in a file of that name in a directory of
 // this test's own and returns the path to it.
 func written(t *testing.T, name, contents string) string {

internal/cli/cli.go

@@ -2,13 +2,11 @@
 package cli
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"os"
-	"os/signal"
+	"runtime"
 	"runtime/debug"
-	"syscall"
 
 	"github.com/spf13/cobra"
 	"sneak.berlin/go/keyfunc/internal/cli/age"
@@ -64,24 +62,33 @@ func Root() *cobra.Command {
 	return root
 }
 
+// init keeps the command on the main thread. Linux hands a signal sent
+// to the tool to that thread first, and a thread runs a pending signal
+// handler before its own code, so when "age encrypt -o" or "age
+// decrypt -o" checks for a signal as its input ends, one sent before
+// then, as by Ctrl-C on a pipeline, has been received.
+//
+//nolint:gochecknoinits // only an init can keep main on the main thread
+func init() {
+	runtime.LockOSThread()
+}
+
 // Main runs the tool and returns the status the process should exit
 // with. An error ends the tool with status 1, except when it carries a
 // status of its own, which "ssh to" uses to hand on the status ssh
 // ended with. ssh has already said whatever it had to say in that
 // case, so nothing more is printed.
 //
-// SIGINT, SIGTERM and SIGHUP cancel the command's context instead of
-// killing the process outright, so the child ssh or sftp ends and the
-// deferred cleanup that removes the agent socket and the install
-// working directory still runs.
+// SIGINT, SIGTERM and SIGHUP end the tool at once, as they end any Go
+// program, so a command waiting at the mnemonic prompt or reading what
+// it encrypts or decrypts goes no further. The exceptions catch the
+// signals to clean up first: "ssh to" and "ssh install" while they
+// have ssh or sftp running, so the child ends and their own cleanup
+// still runs, and "age encrypt -o" and "age decrypt -o" while they
+// write a new file to rename over the named one, so the unfinished file
+// is removed.
 func Main() int {
-	ctx, stop := signal.NotifyContext(
-		context.Background(),
-		syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP,
-	)
-	defer stop()
-
-	err := Root().ExecuteContext(ctx)
+	err := Root().Execute()
 	if err == nil {
 		return 0
 	}

internal/cli/cli_test.go

@@ -6,8 +6,8 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
-	bip39 "github.com/tyler-smith/go-bip39"
 	"golang.org/x/crypto/ssh"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 	"sneak.berlin/go/keyfunc/internal/childmnemonic"
 	"sneak.berlin/go/keyfunc/internal/cli"
 	"sneak.berlin/go/keyfunc/internal/derive"

internal/cli/signals/signals.go

@@ -0,0 +1,53 @@
+// Package signals catches the signals that end the tool, for the
+// commands that clean up before they end.
+package signals
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+// Context is signal.NotifyContext for SIGINT, SIGTERM and SIGHUP: the
+// context it returns is cancelled when one of them arrives, and stop
+// stops catching them. It leaves out any of the three the tool was
+// started with set to be ignored, as nohup does with SIGHUP, because
+// catching a signal turns an ignored one back on and would end a run
+// that was meant to survive it.
+func Context(parent context.Context) (context.Context, context.CancelFunc) {
+	endings := caught()
+
+	// Given no signals at all, NotifyContext would catch every one.
+	if len(endings) == 0 {
+		return context.WithCancel(parent)
+	}
+
+	return signal.NotifyContext(parent, endings...)
+}
+
+// Notify is signal.Notify for the signals Context catches: each one
+// that arrives is sent to c, until signal.Stop(c).
+func Notify(c chan<- os.Signal) {
+	endings := caught()
+
+	// Given no signals at all, Notify would catch every one.
+	if len(endings) > 0 {
+		signal.Notify(c, endings...)
+	}
+}
+
+// caught returns those of SIGINT, SIGTERM and SIGHUP that the tool was
+// not started with set to be ignored.
+func caught() []os.Signal {
+	endings := []os.Signal{syscall.SIGINT, syscall.SIGTERM, syscall.SIGHUP}
+	kept := make([]os.Signal, 0, len(endings))
+
+	for _, ending := range endings {
+		if !signal.Ignored(ending) {
+			kept = append(kept, ending)
+		}
+	}
+
+	return kept
+}

internal/cli/ssh/install.go

@@ -11,8 +11,11 @@ import (
 	"path/filepath"
 	"slices"
 	"strings"
+	"syscall"
+	"time"
 
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 )
 
 // Where the key goes on the host and what the file it arrives in is
@@ -33,12 +36,33 @@ const (
 	localMode     = 0o600
 )
 
+// waitDelay is the WaitDelay sftp runs with: from a signal, or from sftp
+// ending, how long the tool waits for sftp to end and its output to
+// close before it kills sftp and stops reading. That is ample for sftp
+// to stop the ssh it started, and short enough that a signal still ends
+// the tool within a second.
+const waitDelay = 250 * time.Millisecond
+
 // ErrCannotEnter is the refusal of a host whose .ssh is there but
 // cannot be entered, so that nothing in it can be read or written.
 var ErrCannotEnter = errors.New(
 	"~/.ssh is there on the host but cannot be entered",
 )
 
+// ErrSymlink is the refusal of a host whose authorized_keys is a
+// symlink: the rename that puts the new file in place would replace the
+// link itself, and the file it points at would never get the key.
+var ErrSymlink = errors.New(
+	"~/.ssh/authorized_keys on the host is a symlink, which the tool " +
+		"leaves alone",
+)
+
+// ErrStrayArgument is the refusal of anything but the host before --,
+// which would otherwise be handed to sftp in front of the host.
+var ErrStrayArgument = errors.New(
+	"only the host goes before --; options for sftp go after --",
+)
+
 // install returns the command that adds the public key to a host.
 func install() *cobra.Command {
 	cmd := &cobra.Command{
@@ -50,7 +74,22 @@ func install() *cobra.Command {
 			"beside it which is then renamed over it. Nothing is run " +
 			"on the host. Anything after -- is given to sftp " +
 			"unchanged, which is where the port goes (-P).",
-		Args: cobra.MinimumNArgs(1),
+		Args: cobra.MatchAll(
+			cobra.MinimumNArgs(1),
+			func(cmd *cobra.Command, args []string) error {
+				// ArgsLenAtDash is -1 when there is no --.
+				before := cmd.ArgsLenAtDash()
+				if before == -1 {
+					before = len(args)
+				}
+
+				if before != 1 {
+					return ErrStrayArgument
+				}
+
+				return nil
+			},
+		),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			key, comment, err := derived(cmd)
 			if err != nil {
@@ -62,6 +101,14 @@ func install() *cobra.Command {
 				return err
 			}
 
+			// From here on a signal cancels the context, which
+			// sftp runs under, instead of ending the tool, so sftp
+			// ends and the working directory is still removed.
+			ctx, stop := signals.Context(cmd.Context())
+			defer stop()
+
+			cmd.SetContext(ctx)
+
 			return add(cmd, args[0], args[1:], line)
 		},
 	}
@@ -178,8 +225,24 @@ func session(
 	command.Stdout = &said
 	command.Stderr = &said
 
+	// A cancelled context means a signal arrived. Send sftp a SIGTERM
+	// rather than the default kill, so it stops the ssh it started
+	// before it goes. Anything sftp started that still holds its output
+	// keeps the tool waiting no longer than waitDelay.
+	command.Cancel = func() error {
+		return command.Process.Signal(syscall.SIGTERM)
+	}
+	command.WaitDelay = waitDelay
+
 	err := command.Run()
 
+	// sftp ended well and only something it started, such as the
+	// master ssh leaves running for ControlPersist under -v, still held
+	// its output: the session worked.
+	if errors.Is(err, exec.ErrWaitDelay) {
+		err = nil
+	}
+
 	_, _ = cmd.ErrOrStderr().Write(said.Bytes())
 
 	if err != nil {
@@ -222,14 +285,23 @@ func merge(content, line string) (string, bool) {
 // it can be looked up, not even ".". The first listing of such a
 // directory comes up empty, as the server leaves out every name it
 // cannot look up.
+//
+// The first listing is a long one, which shows an authorized_keys that
+// is a symlink as one. That is refused before anything else sftp said
+// is read, so a link the get could not follow is refused in the same
+// words.
 func fetch(
 	cmd *cobra.Command, host string, options []string, into string,
 ) (string, bool, error) {
 	said, err := session(cmd, host, options, []string{
-		"ls -1 " + directory,
+		"ls -n " + directory,
 		"ls -1 " + directory + "/.",
 		"get " + authorized + " " + quoted(into),
 	})
+	if symlinked(said) {
+		return "", false, ErrSymlink
+	}
+
 	if err != nil {
 		if listingNotFound(said, directory) {
 			return "", false, nil
@@ -292,6 +364,22 @@ func reportedCannotList(line string) (string, bool) {
 	return strings.TrimSuffix(strings.TrimPrefix(line, before), after), true
 }
 
+// symlinked says whether the long listing of .ssh shows authorized_keys
+// as a symlink. With -n the client writes each line itself, as ls -l
+// does, whatever the server: the type comes first, "l" for a symlink,
+// and the path as the listing named it comes last.
+func symlinked(said string) bool {
+	for line := range strings.Lines(said) {
+		fields := strings.Fields(line)
+		if len(fields) > 0 && strings.HasPrefix(fields[0], "l") &&
+			fields[len(fields)-1] == authorized {
+			return true
+		}
+	}
+
+	return false
+}
+
 // absent says whether sftp reported the file that was asked for as
 // not being there, which is the one failure of the fetch that is read
 // as an empty authorized_keys. The reading is taken only from the

internal/cli/ssh/install_test.go

@@ -10,7 +10,7 @@ import "testing"
 const (
 	echoed = `sftp> get .ssh/authorized_keys "/tmp/keyfunc/authorized_keys"
 `
-	listed  = "sftp> ls -1 .ssh\n"
+	listed  = "sftp> ls -n .ssh\n"
 	warning = `Warning: Identity file /gone not accessible: ` +
 		"No such file or directory.\n"
 )

internal/cli/ssh/to.go

@@ -10,6 +10,7 @@ import (
 	"syscall"
 
 	"github.com/spf13/cobra"
+	"sneak.berlin/go/keyfunc/internal/cli/signals"
 )
 
 // StatusError says the tool should end with the status ssh ended with.
@@ -42,7 +43,14 @@ func to() *cobra.Command {
 				return err
 			}
 
-			served, err := key.Serve(cmd.Context(), comment)
+			// From here until the agent is taken down, a signal
+			// cancels the context instead of ending the tool, so
+			// ssh ends and the socket and its directory are still
+			// removed.
+			ctx, stop := signals.Context(cmd.Context())
+			defer stop()
+
+			served, err := key.Serve(ctx, comment)
 			if err != nil {
 				return err
 			}
@@ -53,7 +61,7 @@ func to() *cobra.Command {
 				"-o", "IdentityAgent=" + served.Socket(),
 			}, args)
 
-			return connect(cmd.Context(), argv)
+			return connect(ctx, argv)
 		},
 	}
 
@@ -76,7 +84,7 @@ func connect(ctx context.Context, argv []string) error {
 	command.Stdout = os.Stdout
 	command.Stderr = os.Stderr
 
-	// A cancelled context means a signal ended the tool. Send ssh a
+	// A cancelled context means a signal arrived. Send ssh a
 	// SIGTERM rather than the default kill, so it puts the terminal
 	// back the way it found it before it goes.
 	command.Cancel = func() error {

internal/cli/ssh_test.go

@@ -20,13 +20,13 @@ import (
 
 // runAsTool, set in the environment of a re-executed test binary, tells
 // TestMain to run the tool through Main rather than the suite, so the
-// signal test can drive the real signal path in a process it can send a
-// signal to.
+// signal tests can drive the real signal path in a process they can
+// send a signal to.
 const runAsTool = "KEYFUNC_TEST_RUN_AS_TOOL"
 
 // TestMain re-executes the test binary as the tool when runAsTool is
-// set, and otherwise runs the suite. The signal test starts the tool
-// this way, as a subprocess it can signal and watch clean up.
+// set, and otherwise runs the suite. The signal tests start the tool
+// this way, as a subprocess they can signal and watch end.
 func TestMain(m *testing.M) {
 	if os.Getenv(runAsTool) == "1" {
 		os.Exit(cli.Main())
@@ -99,6 +99,8 @@ const marker = "KEYFUNC_TEST_MARKER"
 //
 // The listing and the two ways a get can fail are worded as the
 // OpenSSH client words them, each naming the path the server expanded.
+// A long listing (-n) writes each entry as the client does, its type
+// first, so that a symlink shows as one.
 // A listing fails one way when .ssh is not there and another when it is
 // there but shut to the user; the first is the only failure read as a
 // host with no file. A get fails one way for a file that is not there,
@@ -137,8 +139,7 @@ while IFS= read -r line; do
 	worked=yes
 	case "$1" in
 	ls)
-		dir=$2
-		[ "$dir" = -1 ] && dir=$3
+		dir=$3
 		if [ ! -e "$home/$dir" ]; then
 			worked=no
 			printf 'Can'\''t ls: "%s" not found\n' "$home/$dir" >&2
@@ -149,7 +150,13 @@ while IFS= read -r line; do
 		else
 			for entry in "$home/$dir"/*; do
 				[ -e "$entry" ] || continue
-				printf '%s/%s\n' "$dir" "$(basename "$entry")"
+				name="$dir/$(basename "$entry")"
+				if [ "$2" = -n ]; then
+					printf '%s    ? someone  users  0 Oct  4 15:44 %s\n' \
+						"$(stat -c '%A' "$entry")" "$name"
+				else
+					printf '%s\n' "$name"
+				fi
 			done
 		fi
 		;;
@@ -209,6 +216,18 @@ fi
 sleep 5
 `
 
+// stalled is a stand-in for the system sftp that starts a child, notes
+// it has started, and then blocks, so a test can signal the tool while
+// sftp is running. The child holds the output the tool reads sftp
+// through, as the ssh that sftp starts does, and is started before the
+// note so that it is there when the signal ends the shell and still
+// holds that output afterwards.
+const stalled = `
+sleep 5 &
+touch "$KEYFUNC_TEST_STARTED"
+wait
+`
+
 // pretended is where a stand-in writes down what it was asked to do.
 type pretended struct {
 	// home stands in for the home directory on the host.
@@ -294,7 +313,7 @@ func TestTheFileIsUploadedBesideTheOldOneAndThenRenamedOverIt(t *testing.T) {
 
 	// The listing fails on a host with no .ssh, so the get never runs;
 	// the write session then makes the directory and puts the file.
-	require.Equal(t, "ls -1 .ssh", sent[0])
+	require.Equal(t, "ls -n .ssh", sent[0])
 	require.Equal(t, "-mkdir .ssh", sent[1])
 	require.Equal(t, "chmod 700 .ssh", sent[2])
 	require.Equal(t, "put", strings.Fields(sent[3])[0])
@@ -360,6 +379,59 @@ func TestADirectoryThatCannotBeEnteredIsRefusedBeforeAnyUpload(t *testing.T) {
 	require.Equal(t, notADirectory, read(t, inTheWay))
 }
 
+func TestASymlinkedFileIsRefusedBeforeAnyUpload(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// The file the link points at, which the key would never reach.
+	target := filepath.Join(pretend.home, "keys")
+	require.NoError(t,
+		os.WriteFile(target, []byte("somebody else\n"), fileMode),
+	)
+
+	directory := filepath.Join(pretend.home, keptUnder)
+	require.NoError(t, os.Mkdir(directory, directoryMode))
+
+	link := filepath.Join(directory, keptIn)
+	require.NoError(t, os.Symlink(target, link))
+
+	printed, _, err := attempt(t, host)
+	require.ErrorIs(t, err, ssh.ErrSymlink)
+	require.Empty(t, printed)
+
+	// The read and nothing after it: no upload was tried, the link
+	// still points where it did, and what it points at is unchanged.
+	require.Equal(t, 1, connections(t, pretend))
+
+	pointsAt, err := os.Readlink(link)
+	require.NoError(t, err)
+	require.Equal(t, target, pointsAt)
+	require.Equal(t, "somebody else\n", read(t, target))
+}
+
+func TestAnArgumentBesideTheHostIsRefusedBeforeAnyConnection(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	runs := [][]string{
+		{host, "frank@example.com"},
+		{host, "2222"},
+		{host, "frank@example.com", "--", "-P", "2222"},
+		{"--", host},
+	}
+
+	for _, args := range runs {
+		printed, _, err := attempt(t, args...)
+		require.ErrorIs(t, err, ssh.ErrStrayArgument)
+		require.Empty(t, printed)
+	}
+
+	// sftp was never started, so nothing was uploaded.
+	require.NoFileExists(t, pretend.arguments)
+}
+
 func TestAnExistingDirectoryKeepsItsModeAndIsNotRemade(t *testing.T) {
 	t.Setenv(mnemonic.Variable, example())
 
@@ -485,6 +557,22 @@ func TestWhatComesAfterTheDashesIsGivenToSFTP(t *testing.T) {
 	)
 }
 
+func TestAProcessSFTPLeavesBehindDoesNotFailTheRun(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	pretend := pretendHost(t)
+
+	// A session that works ends by leaving a child behind that holds
+	// sftp's output, as the master ssh leaves running for ControlPersist
+	// does under -v.
+	standIn(t, "sftp", installer+"sleep 5 &\n")
+
+	require.Equal(t, "added\n", install(t, host))
+	require.Equal(t, keyLine,
+		read(t, filepath.Join(pretend.home, keptUnder, keptIn)),
+	)
+}
+
 func TestSSHIsPointedAtTheAgentAndItsStatusIsHandedOn(t *testing.T) {
 	t.Setenv(mnemonic.Variable, example())
 
@@ -544,7 +632,7 @@ func TestASignalTakesTheAgentDirectoryDown(t *testing.T) {
 // ssh that blocks, waits until the agent is up and ssh is running
 // against it, sends the tool the signal, and requires the agent socket
 // and its directory to be gone once the tool has ended. The subprocess
-// goes through Main and its signal handling, so with that handling
+// goes through Main and the command's signal handling, so with that handling
 // removed the signal kills the tool outright, no deferred cleanup runs,
 // the directory is left behind, and the check fails.
 func signalEndsTheTool(t *testing.T, name string, signal os.Signal) {
@@ -611,6 +699,62 @@ func waitForSocket(t *testing.T, noted string) string {
 	return socket
 }
 
+func TestASignalTakesTheInstallWorkingDirectoryDown(t *testing.T) {
+	t.Setenv(mnemonic.Variable, example())
+
+	for _, ending := range []os.Signal{
+		syscall.SIGTERM, syscall.SIGINT, syscall.SIGHUP,
+	} {
+		signalEndsTheInstall(t, ending.String(), ending)
+	}
+}
+
+// signalEndsTheInstall runs "ssh install" as a subprocess against a
+// stand-in sftp that blocks, with a temporary directory of the test's
+// own, waits until sftp is running, sends the tool the signal, and
+// requires the tool to end within a second with status 1 and the
+// working directory it made there to be gone.
+func signalEndsTheInstall(t *testing.T, name string, signal os.Signal) {
+	t.Helper()
+
+	temporary := t.TempDir()
+	started := filepath.Join(t.TempDir(), "started")
+	t.Setenv("KEYFUNC_TEST_STARTED", started)
+	standIn(t, "sftp", stalled)
+
+	//nolint:gosec // the binary is this test's own, re-run as the tool
+	command := exec.CommandContext(
+		t.Context(), os.Args[0], subcommand, installing, host,
+	)
+
+	command.Env = append(os.Environ(), runAsTool+"=1", "TMPDIR="+temporary)
+	require.NoError(t, command.Start())
+
+	// sftp is started only once the working directory has been made.
+	require.Eventually(t, func() bool {
+		_, err := os.Stat(started)
+
+		return err == nil
+	}, 5*time.Second, 5*time.Millisecond)
+
+	working, err := os.ReadDir(temporary)
+	require.NoError(t, err)
+	require.Len(t, working, 1, name)
+
+	sent := time.Now()
+
+	require.NoError(t, command.Process.Signal(signal))
+	waitForTool(t, name, command)
+
+	// The child sftp started would hold sftp's output for seconds yet.
+	require.Less(t, time.Since(sent), time.Second, name)
+	require.Equal(t, failedStatus, command.ProcessState.ExitCode(), name)
+
+	left, err := os.ReadDir(temporary)
+	require.NoError(t, err)
+	require.Empty(t, left, name)
+}
+
 func TestTheMnemonicIsNotHandedToSFTP(t *testing.T) {
 	t.Setenv(mnemonic.CommandVariable, "echo "+example())
 	t.Setenv(mnemonic.Variable, example())

internal/derive/derive.go

@@ -8,7 +8,7 @@ import (
 	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/btcsuite/btcd/chaincfg"
-	bip39 "github.com/tyler-smith/go-bip39"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 )
 
 const (

internal/mnemonic/mnemonic.go

@@ -10,8 +10,8 @@ import (
 	"os/exec"
 	"strings"
 
-	bip39 "github.com/tyler-smith/go-bip39"
 	"golang.org/x/term"
+	"sneak.berlin/go/keyfunc/internal/bip39"
 )
 
 const (

package.json

@@ -1,4 +1,5 @@
 {
+  "license": "MIT",
   "devDependencies": {
     "prettier": "3.8.1"
   }