derive_seed.go

package bip39

import (
	"crypto/sha512"
	"strings"

	"golang.org/x/crypto/pbkdf2"
)

const (
	// SeedSaltPrefix is the salt used for BIP39 seed generation via the PBKDF2 function.
	SeedSaltPrefix = "mnemonic"
	// SeedIterationCount is the PBKDF2 iteration count used to generate seeds.
	SeedKDFIterationCount = 2048
	// SeedLength is the output size of BIP39 seeds generated by the PBKDF2 function.
	SeedLength = 64
)

// DeriveSeed determinstically converts a BIP39 mnemonic and passphrase
// into 64-bytes suitable for use as a cryptographic key.
//
// NOTE: the validity of the mnemonic is not checked in this function.
// Use DecodeWords to confirm the words and checksum are valid before
// deriving key material from a user-given mnemonic.
func DeriveSeed(words []string, passphrase string) []byte {
	mnemonic := []byte(strings.Join(words, " "))
	salt := []byte(SeedSaltPrefix + passphrase)
	return pbkdf2.Key(
		mnemonic,
		salt,
		SeedKDFIterationCount,
		SeedLength,
		sha512.New,
	)
}