package bip39
import (
"crypto/rand"
"crypto/sha256"
"crypto/sha512"
"encoding/binary"
"errors"
"fmt"
"math/big"
"strings"
"golang.org/x/crypto/pbkdf2"
)
// Some bitwise operands for working with big.Ints
var (
Last11BitsMask = big.NewInt(2047)
RightShift11BitsDivider = big.NewInt(2048)
BigOne = big.NewInt(1)
BigTwo = big.NewInt(2)
)
// NewEntropy will create random entropy bytes
// so long as the requested size bitSize is an appropriate size.
func NewEntropy(bitSize int) ([]byte, error) {
err := validateEntropyBitSize(bitSize)
if err != nil {
return nil, err
}
entropy := make([]byte, bitSize/8)
_, err = rand.Read(entropy)
return entropy, err
}
// NewMnemonic will return a string consisting of the mnemonic words for
// the given entropy.
// If the provide entropy is invalid, an error will be returned.
func NewMnemonic(entropy []byte) (string, error) {
// Compute some lengths for convenience
entropyBitLength := len(entropy) * 8
checksumBitLength := entropyBitLength / 32
sentenceLength := (entropyBitLength + checksumBitLength) / 11
err := validateEntropyBitSize(entropyBitLength)
if err != nil {
return "", err
}
// Add checksum to entropy
entropy = addChecksum(entropy)
// Break entropy up into sentenceLength chunks of 11 bits
// For each word AND mask the rightmost 11 bits and find the word at that index
// Then bitshift entropy 11 bits right and repeat
// Add to the last empty slot so we can work with LSBs instead of MSB
// Entropy as an int so we can bitmask without worrying about bytes slices
entropyInt := new(big.Int).SetBytes(entropy)
// Slice to hold words in
words := make([]string, sentenceLength)
// Throw away big int for AND masking
word := big.NewInt(0)
for i := sentenceLength - 1; i >= 0; i-- {
// Get 11 right most bits and bitshift 11 to the right for next time
word.And(entropyInt, Last11BitsMask)
entropyInt.Div(entropyInt, RightShift11BitsDivider)
// Get the bytes representing the 11 bits as a 2 byte slice
wordBytes := padByteSlice(word.Bytes(), 2)
// Convert bytes to an index and add that word to the list
words[i] = WordList[binary.BigEndian.Uint16(wordBytes)]
}
return strings.Join(words, " "), nil
}
// MnemonicToByteArray takes a mnemonic string and turns it into a byte array
// suitable for creating another mnemonic.
// An error is returned if the mnemonic is invalid.
// FIXME
// This does not work for all values in
// the test vectors. Namely
// Vectors 0, 4, and 8.
// This is not really important because BIP39 doesnt really define a conversion
// from string to bytes.
func MnemonicToByteArray(mnemonic string) ([]byte, error) {
if IsMnemonicValid(mnemonic) == false {
return nil, fmt.Errorf("Invalid mnemonic")
}
mnemonicSlice := strings.Split(mnemonic, " ")
bitSize := len(mnemonicSlice) * 11
err := validateEntropyWithChecksumBitSize(bitSize)
if err != nil {
return nil, err
}
checksumSize := bitSize % 32
b := big.NewInt(0)
modulo := big.NewInt(2048)
for _, v := range mnemonicSlice {
index, found := ReverseWordMap[v]
if found == false {
return nil, fmt.Errorf("Word `%v` not found in reverse map", v)
}
add := big.NewInt(int64(index))
b = b.Mul(b, modulo)
b = b.Add(b, add)
}
hex := b.Bytes()
checksumModulo := big.NewInt(0).Exp(big.NewInt(2), big.NewInt(int64(checksumSize)), nil)
entropy, _ := big.NewInt(0).DivMod(b, checksumModulo, big.NewInt(0))
entropyHex := entropy.Bytes()
byteSize := bitSize/8 + 1
if len(hex) != byteSize {
tmp := make([]byte, byteSize)
diff := byteSize - len(hex)
for i := 0; i < len(hex); i++ {
tmp[i+diff] = hex[i]
}
hex = tmp
}
validationHex := addChecksum(entropyHex)
if len(validationHex) != byteSize {
tmp2 := make([]byte, byteSize)
diff2 := byteSize - len(validationHex)
for i := 0; i < len(validationHex); i++ {
tmp2[i+diff2] = validationHex[i]
}
validationHex = tmp2
}
if len(hex) != len(validationHex) {
panic("[]byte len mismatch - it shouldn't happen")
}
for i := range validationHex {
if hex[i] != validationHex[i] {
return nil, fmt.Errorf("Invalid byte at position %v", i)
}
}
return hex, nil
}
// NewSeedWithErrorChecking creates a hashed seed output given the mnemonic string and a password.
// An error is returned if the mnemonic is not convertible to a byte array.
func NewSeedWithErrorChecking(mnemonic string, password string) ([]byte, error) {
_, err := MnemonicToByteArray(mnemonic)
if err != nil {
return nil, err
}
return NewSeed(mnemonic, password), nil
}
// NewSeed creates a hashed seed output given a provided string and password.
// No checking is performed to validate that the string provided is a valid mnemonic.
func NewSeed(mnemonic string, password string) []byte {
return pbkdf2.Key([]byte(mnemonic), []byte("mnemonic"+password), 2048, 64, sha512.New)
}
// Appends to data the first (len(data) / 32)bits of the result of sha256(data)
// Currently only supports data up to 32 bytes
func addChecksum(data []byte) []byte {
// Get first byte of sha256
hasher := sha256.New()
hasher.Write(data)
hash := hasher.Sum(nil)
firstChecksumByte := hash[0]
// len() is in bytes so we divide by 4
checksumBitLength := uint(len(data) / 4)
// For each bit of check sum we want we shift the data one the left
// and then set the (new) right most bit equal to checksum bit at that index
// staring from the left
dataBigInt := new(big.Int).SetBytes(data)
for i := uint(0); i < checksumBitLength; i++ {
// Bitshift 1 left
dataBigInt.Mul(dataBigInt, BigTwo)
// Set rightmost bit if leftmost checksum bit is set
if uint8(firstChecksumByte&(1<<(7-i))) > 0 {
dataBigInt.Or(dataBigInt, BigOne)
}
}
return dataBigInt.Bytes()
}
func padByteSlice(slice []byte, length int) []byte {
newSlice := make([]byte, length-len(slice))
return append(newSlice, slice...)
}
func validateEntropyBitSize(bitSize int) error {
if (bitSize%32) != 0 || bitSize < 128 || bitSize > 256 {
return errors.New("Entropy length must be [128, 256] and a multiple of 32")
}
return nil
}
func validateEntropyWithChecksumBitSize(bitSize int) error {
if (bitSize != 128+4) && (bitSize != 160+5) && (bitSize != 192+6) && (bitSize != 224+7) && (bitSize != 256+8) {
return fmt.Errorf("Wrong entropy + checksum size - expected %v, got %v", int((bitSize-bitSize%32)+(bitSize-bitSize%32)/32), bitSize)
}
return nil
}
// IsMnemonicValid attempts to verify that the provided mnemonic is valid.
// Validity is determined by both the number of words being appropriate,
// and that all the words in the mnemonic are present in the word list.
func IsMnemonicValid(mnemonic string) bool {
// Create a list of all the words in the mnemonic sentence
words := strings.Fields(mnemonic)
//Get num of words
numOfWords := len(words)
// The number of words should be 12, 15, 18, 21 or 24
if numOfWords%3 != 0 || numOfWords < 12 || numOfWords > 24 {
return false
}
// Check if all words belong in the wordlist
for i := 0; i < numOfWords; i++ {
if !contains(WordList, words[i]) {
return false
}
}
return true
}
func contains(s []string, e string) bool {
for _, a := range s {
if a == e {
return true
}
}
return false
}
