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The module, the script entrypoints and Makefile, Docker-only linting, the mnemonic sources in the specified order with their refusals, the BIP-85 derivation, and keyfunc ssh pub and priv with the README test vectors as tests. Two review rounds; the second passed with no findings. Model: opus-5 (implementation and review); fable-5-1 (landing)
118 lines
2.7 KiB
Go
118 lines
2.7 KiB
Go
// Package mnemonic finds the mnemonic the keys are derived from.
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package mnemonic
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import (
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"bytes"
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"context"
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"errors"
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"fmt"
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"os"
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"os/exec"
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"strings"
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bip39 "github.com/tyler-smith/go-bip39"
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"golang.org/x/term"
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)
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const (
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// CommandVariable holds a shell command whose output is the
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// mnemonic.
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CommandVariable = "KEYFUNC_MNEMONIC_COMMAND"
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// Variable holds the mnemonic itself.
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Variable = "KEYFUNC_MNEMONIC"
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)
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// ErrMissing is returned when there is nowhere left to look and
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// standard input is not a terminal, so there is nobody to ask.
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var ErrMissing = errors.New(
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"no mnemonic given and standard input is not a terminal",
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)
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// ErrChecksum is returned for a mnemonic that fails the BIP-39
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// checksum.
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var ErrChecksum = errors.New("the mnemonic fails its BIP-39 checksum")
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// Read returns the mnemonic. The command given on the command line is
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// used first; then the command in KEYFUNC_MNEMONIC_COMMAND; then the
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// mnemonic in KEYFUNC_MNEMONIC; then a prompt on the terminal with
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// echo turned off. The first source that has one wins.
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func Read(ctx context.Context, command string) (string, error) {
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if command == "" {
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command = os.Getenv(CommandVariable)
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}
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if command != "" {
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words, err := run(ctx, command)
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if err != nil {
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return "", err
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}
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return checked(words)
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}
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if words := os.Getenv(Variable); words != "" {
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return checked(words)
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}
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return ask()
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}
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// run executes the command with sh and returns its standard output.
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// If the command fails, its standard error becomes part of the error.
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func run(ctx context.Context, command string) (string, error) {
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//nolint:gosec // running the user's own command is the point
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shell := exec.CommandContext(ctx, "sh", "-c", command)
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var complaint bytes.Buffer
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shell.Stderr = &complaint
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out, err := shell.Output()
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if err != nil {
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said := strings.TrimSpace(complaint.String())
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if said == "" {
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return "", fmt.Errorf("the mnemonic command failed: %w", err)
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}
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return "", fmt.Errorf(
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"the mnemonic command failed: %w: %s", err, said,
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)
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}
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return string(out), nil
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}
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// ask prompts on the terminal with echo turned off.
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func ask() (string, error) {
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fd := int(os.Stdin.Fd())
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if !term.IsTerminal(fd) {
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return "", ErrMissing
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}
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fmt.Fprint(os.Stderr, "mnemonic: ")
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typed, err := term.ReadPassword(fd)
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fmt.Fprintln(os.Stderr)
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if err != nil {
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return "", fmt.Errorf("reading the mnemonic: %w", err)
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}
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return checked(string(typed))
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}
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// checked drops the surrounding whitespace and refuses a mnemonic that
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// does not pass the BIP-39 checksum.
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func checked(words string) (string, error) {
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words = strings.TrimSpace(words)
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if !bip39.IsMnemonicValid(words) {
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return "", ErrChecksum
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}
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return words, nil
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}
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