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Drop the BIP39 passphrase from cbk

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The seed is always computed with an empty passphrase; Params is just
the mnemonic and the BIP85 index.
This commit is contained in:
sneak
2026-10-31 11:41:11 -07:00
parent fe6dbba428
commit ad1d51a9f9
3 changed files with 30 additions and 77 deletions
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pkg/cbk/cbk.go
+14 -17
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@@ -3,13 +3,14 @@
// resulting keys are plain 32-byte crypto_box keys for use with
// golang.org/x/crypto/nacl/box.
//
// The same mnemonic, passphrase, and index always produce the same keypair:
// The same mnemonic and index always produce the same keypair:
//
// 1. The mnemonic is validated and canonicalized with
// bip39wordlist.NormalizeWordlist (lowercase, single spaces).
// 2. The standard 64-byte BIP39 seed is computed from the canonical
// mnemonic and the optional passphrase with PBKDF2-HMAC-SHA512 (2048
// rounds, salt "mnemonic" + passphrase), exactly as a wallet would.
// mnemonic with PBKDF2-HMAC-SHA512 (2048 rounds, salt "mnemonic"),
// exactly as a wallet would with an empty passphrase. BIP39
// passphrases are deliberately not supported.
// 3. The seed becomes a BIP32 master key.
// 4. BIP85 (sneak.berlin/go/secret/pkg/bip85) derives 32 bytes of
// application entropy from the master key with the HEX application,
@@ -70,11 +71,6 @@ type Params struct {
// whitespace between words is accepted; it is normalized before use.
Mnemonic string
// Passphrase is the optional BIP39 passphrase (sometimes called the
// "25th word"). It is used verbatim: it is case sensitive and is not
// trimmed. An empty passphrase is the common case.
Passphrase string
// Index selects which of the keypairs derivable from the mnemonic to
// return. It is the final component of the BIP85 derivation path, so
// each index yields an independent keypair. Zero is the first.
@@ -87,9 +83,9 @@ type CryptoBoxKeypair struct {
PrivateKey CryptoBoxKey
}
// New derives the keypair for the mnemonic, passphrase, and index in p. If
// the mnemonic is not valid it returns an error wrapping one of the
// bip39wordlist sentinel errors.
// New derives the keypair for the mnemonic and index in p. If the mnemonic
// is not valid it returns an error wrapping one of the bip39wordlist
// sentinel errors.
func New(p Params) (CryptoBoxKeypair, error) {
if p.Index > MaxIndex {
return CryptoBoxKeypair{}, fmt.Errorf("%w: %d", ErrIndexTooLarge, p.Index)
@@ -100,10 +96,11 @@ func New(p Params) (CryptoBoxKeypair, error) {
return CryptoBoxKeypair{}, err
}
// The network parameters only choose the version bytes used when a
// key is serialized; they do not affect derivation.
// The seed is always computed with an empty BIP39 passphrase. The
// network parameters only choose the version bytes used when a key is
// serialized; they do not affect derivation.
masterKey, err := hdkeychain.NewMaster(
bip39.NewSeed(mnemonic, p.Passphrase), &chaincfg.MainNetParams,
bip39.NewSeed(mnemonic, ""), &chaincfg.MainNetParams,
)
if err != nil {
return CryptoBoxKeypair{}, fmt.Errorf("cbk: deriving BIP32 master key: %w", err)
@@ -130,10 +127,10 @@ func New(p Params) (CryptoBoxKeypair, error) {
}, nil
}
// FromMnemonic derives the keypair for mnemonic with an empty passphrase
// at index zero. It is shorthand for New(Params{Mnemonic: mnemonic}).
// FromMnemonic derives the keypair for mnemonic at index zero. It is
// shorthand for New(Params{Mnemonic: mnemonic}).
func FromMnemonic(mnemonic string) (CryptoBoxKeypair, error) {
return New(Params{Mnemonic: mnemonic, Passphrase: "", Index: 0})
return New(Params{Mnemonic: mnemonic, Index: 0})
}
// PublicKeyBytes returns a copy of the public key as a byte slice.