Add NewAccountFromMnemonic common utility

ocp/common/account.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"crypto/ed25519"
 	"fmt"
+	"strings"
 
 	"filippo.io/edwards25519"
 	slip10 "github.com/anyproto/go-slip10"
@@ -164,7 +165,29 @@ func NewAccountFromEntropy(entropy []byte) (*Account, error) {
 		return nil, errors.Wrap(err, "error deriving mnemonic from entropy")
 	}
 
-	seed := bip39.NewSeed(mnemonic, "")
+	return NewAccountFromMnemonic(mnemonic)
+}
+
+// NewAccountFromMnemonic deterministically derives an account from a 12 word
+// BIP-39 mnemonic phrase following the standard Solana key derivation used by
+// Code and other wallets:
+//
+//	mnemonic -> BIP-39 seed (PBKDF2) -> SLIP-0010 ed25519 key at m/44'/501'/0'/0'
+//
+// Words are expected to be space delimited and the checksum must be valid. An
+// empty passphrase is assumed.
+func NewAccountFromMnemonic(mnemonic string) (*Account, error) {
+	words := strings.Fields(mnemonic)
+	if len(words) != 12 {
+		return nil, errors.New("mnemonic must be 12 words")
+	}
+	normalized := strings.Join(words, " ")
+
+	if !bip39.IsMnemonicValid(normalized) {
+		return nil, errors.New("mnemonic is invalid")
+	}
+
+	seed := bip39.NewSeed(normalized, "")
 
 	node, err := slip10.DeriveForPath(solanaDerivationPath, seed)
 	if err != nil {
@@ -174,7 +197,7 @@ func NewAccountFromEntropy(entropy []byte) (*Account, error) {
 
 	derivedKey, err := NewKeyFromBytes(privateKey)
 	if err != nil {
-		return nil, errors.Wrap(err, "error creating private key from entropy")
+		return nil, errors.Wrap(err, "error creating private key from mnemonic")
 	}
 
 	return NewAccountFromPrivateKey(derivedKey)

ocp/common/account_test.go

@@ -112,6 +112,46 @@ func TestNewAccountFromEntropy(t *testing.T) {
 	}
 }
 
+func TestNewAccountFromMnemonic(t *testing.T) {
+	// The canonical "abandon ... about" mnemonic, whose Solana account at
+	// m/44'/501'/0'/0' (empty passphrase) is a well-known address shared with
+	// standard wallets (Phantom, Solana CLI).
+	mnemonic := "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about"
+
+	account, err := NewAccountFromMnemonic(mnemonic)
+	require.NoError(t, err)
+	require.NotNil(t, account.PrivateKey())
+	assert.Equal(t, "HAgk14JpMQLgt6rVgv7cBQFJWFto5Dqxi472uT3DKpqk", account.PublicKey().ToBase58())
+
+	// The mnemonic derivation is equivalent to the entropy it encodes.
+	fromEntropy, err := NewAccountFromEntropy(make([]byte, 16))
+	require.NoError(t, err)
+	assert.Equal(t, fromEntropy.PublicKey().ToBase58(), account.PublicKey().ToBase58())
+	assert.Equal(t, fromEntropy.PrivateKey().ToBase58(), account.PrivateKey().ToBase58())
+
+	// Surrounding and repeated whitespace is tolerated.
+	untidy, err := NewAccountFromMnemonic("  abandon\tabandon  abandon abandon abandon abandon abandon abandon abandon abandon abandon about\n")
+	require.NoError(t, err)
+	assert.Equal(t, account.PublicKey().ToBase58(), untidy.PublicKey().ToBase58())
+
+	// A different mnemonic is unrelated.
+	other, err := NewAccountFromMnemonic("legal winner thank year wave sausage worth useful legal winner thank yellow")
+	require.NoError(t, err)
+	assert.NotEqual(t, account.PublicKey().ToBase58(), other.PublicKey().ToBase58())
+
+	for _, invalid := range []string{
+		"",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon",                          // 11 words
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",            // 13 words
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon",                  // Bad checksum
+		"notaword abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",                   // Word outside the wordlist
+		"legal winner thank year wave sausage worth useful legal winner thank yellow legal winner thank year wave sausage", // 18 words
+	} {
+		_, err := NewAccountFromMnemonic(invalid)
+		assert.Error(t, err)
+	}
+}
+
 // TestNewAccountFromEntropy_SpecVectors anchors each stage of the derivation
 // pipeline to its canonical specification test vector, guarding against a
 // dependency behaving non-standardly.