TODO.md

@@ -18,6 +18,13 @@ https://git.eeqj.de/sneak/secret/milestone/12
 
 # Completed Steps
 
+- 2026-10-12: A mnemonic typed with extra spaces, tabs or line breaks gives the
+  same long-term key as its words separated by single spaces
+  (https://git.eeqj.de/sneak/secret/issues/135). The key was derived from the
+  text exactly as typed, so a vault made with a double or trailing space did not
+  open with the same words typed normally. `agehd.DeriveEntropy`, which every
+  use of the mnemonic goes through, now joins the words with single spaces and
+  puts them in Unicode NFKD, as BIP39 defines, before making the seed.
 - 2026-10-12: The keychain and Secure Enclave unlockers are gone from the code
   and the documents (https://git.eeqj.de/sneak/secret/issues/132). They were
   research: neither works without macOS code signing and entitlements, which

go.mod

@@ -19,6 +19,7 @@ require (
 	golang.org/x/crypto v0.38.0
 	golang.org/x/sys v0.33.0
 	golang.org/x/term v0.32.0
+	golang.org/x/text v0.25.0
 )
 
 require (
@@ -31,6 +32,5 @@ require (
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/spf13/pflag v1.0.6 // indirect
-	golang.org/x/text v0.25.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

pkg/agehd/agehd.go

@@ -17,6 +17,7 @@ import (
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcutil/bech32"
+	"golang.org/x/text/unicode/norm"
 	"sneak.berlin/go/secret/internal/bip39"
 	"sneak.berlin/go/secret/pkg/bip85"
 )
@@ -73,8 +74,12 @@ func IdentityFromEntropy(ent []byte) (*age.X25519Identity, error) {
 // DeriveEntropy derives 32 bytes of application-scoped entropy from the
 // supplied BIP-39 mnemonic and index n using BIP85.
 func DeriveEntropy(mnemonic string, n uint32) ([]byte, error) {
-	// Convert mnemonic to seed
-	seed := bip39.NewSeed(mnemonic, "")
+	// BIP-39 makes the seed from the words joined by single spaces, in
+	// Unicode NFKD. NewSeed hashes its input as given, so the mnemonic is
+	// brought to that form first: the same words, however they were
+	// typed, then give the same seed.
+	sentence := norm.NFKD.String(strings.Join(strings.Fields(mnemonic), " "))
+	seed := bip39.NewSeed(sentence, "")
 
 	// Create master key from seed
 	masterKey, err := hdkeychain.NewMaster(seed, &chaincfg.MainNetParams)

pkg/agehd/agehd_test.go

@@ -175,6 +175,34 @@ func TestDeterministicDerivation(t *testing.T) {
 	t.Logf("Index 1: %s", id3.String())
 }
 
+// TestDeriveIdentityIgnoresExtraWhitespace checks that the same words give
+// the same identity however they are spaced, as when a mnemonic is typed or
+// pasted with a double space or a trailing newline.
+func TestDeriveIdentityIgnoresExtraWhitespace(t *testing.T) {
+	t.Parallel()
+
+	want, err := DeriveIdentity(mnemonic, 0)
+	if err != nil {
+		t.Fatalf("derive: %v", err)
+	}
+
+	typedMnemonics := []string{
+		strings.Replace(mnemonic, " ", "  ", 1) + " ",
+		"\t" + strings.ReplaceAll(mnemonic, " ", "\n") + "\n",
+	}
+
+	for _, typed := range typedMnemonics {
+		got, err := DeriveIdentity(typed, 0)
+		if err != nil {
+			t.Fatalf("derive from %q: %v", typed, err)
+		}
+
+		if got.String() != want.String() {
+			t.Errorf("%q derives a different identity from %q", typed, mnemonic)
+		}
+	}
+}
+
 func TestDeterministicXPRVDerivation(t *testing.T) {
 	t.Parallel()