267 lines
8.1 KiB
Go
267 lines
8.1 KiB
Go
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package bip39
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import (
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"crypto/rand"
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"crypto/sha256"
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"crypto/sha512"
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"encoding/binary"
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"errors"
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"math/big"
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"strings"
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"github.com/tyler-smith/go-bip39/wordlists"
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"golang.org/x/crypto/pbkdf2"
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)
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var (
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// Some bitwise operands for working with big.Ints
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last11BitsMask = big.NewInt(2047)
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rightShift11BitsDivider = big.NewInt(2048)
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bigOne = big.NewInt(1)
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bigTwo = big.NewInt(2)
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// wordList is the set of words to use
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wordList []string
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// wordMap is a reverse lookup map for wordList
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wordMap map[string]int
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)
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var (
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// ErrInvalidMnemonic is returned when trying to use a malformed mnemonic.
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ErrInvalidMnemonic = errors.New("Invalid menomic")
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// ErrEntropyLengthInvalid is returned when trying to use an entropy set with
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// an invalid size.
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ErrEntropyLengthInvalid = errors.New("Entropy length must be [128, 256] and a multiple of 32")
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// ErrValidatedSeedLengthMismatch is returned when a validated seed is not the
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// same size as the given seed. This should never happen is present only as a
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// sanity assertion.
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ErrValidatedSeedLengthMismatch = errors.New("Seed length does not match validated seed length")
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// ErrChecksumIncorrect is returned when entropy has the incorrect checksum.
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ErrChecksumIncorrect = errors.New("Checksum incorrect")
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)
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func init() {
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SetWordList(wordlists.English)
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}
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// SetWordList sets the list of words to use for mnemonics. Currently the list
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// that is set is used package-wide.
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func SetWordList(list []string) {
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wordList = list
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wordMap = map[string]int{}
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for i, v := range wordList {
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wordMap[v] = i
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}
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}
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// NewEntropy will create random entropy bytes
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// so long as the requested size bitSize is an appropriate size.
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func NewEntropy(bitSize int) ([]byte, error) {
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err := validateEntropyBitSize(bitSize)
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if err != nil {
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return nil, err
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}
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entropy := make([]byte, bitSize/8)
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_, err = rand.Read(entropy)
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return entropy, err
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}
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// NewMnemonic will return a string consisting of the mnemonic words for
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// the given entropy.
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// If the provide entropy is invalid, an error will be returned.
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func NewMnemonic(entropy []byte) (string, error) {
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// Compute some lengths for convenience
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entropyBitLength := len(entropy) * 8
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checksumBitLength := entropyBitLength / 32
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sentenceLength := (entropyBitLength + checksumBitLength) / 11
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err := validateEntropyBitSize(entropyBitLength)
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if err != nil {
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return "", err
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}
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// Add checksum to entropy
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entropy = addChecksum(entropy)
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// Break entropy up into sentenceLength chunks of 11 bits
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// For each word AND mask the rightmost 11 bits and find the word at that index
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// Then bitshift entropy 11 bits right and repeat
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// Add to the last empty slot so we can work with LSBs instead of MSB
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// Entropy as an int so we can bitmask without worrying about bytes slices
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entropyInt := new(big.Int).SetBytes(entropy)
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// Slice to hold words in
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words := make([]string, sentenceLength)
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// Throw away big int for AND masking
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word := big.NewInt(0)
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for i := sentenceLength - 1; i >= 0; i-- {
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// Get 11 right most bits and bitshift 11 to the right for next time
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word.And(entropyInt, last11BitsMask)
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entropyInt.Div(entropyInt, rightShift11BitsDivider)
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// Get the bytes representing the 11 bits as a 2 byte slice
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wordBytes := padByteSlice(word.Bytes(), 2)
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// Convert bytes to an index and add that word to the list
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words[i] = wordList[binary.BigEndian.Uint16(wordBytes)]
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}
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return strings.Join(words, " "), nil
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}
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// MnemonicToByteArray takes a mnemonic string and turns it into a byte array
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// suitable for creating another mnemonic.
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// An error is returned if the mnemonic is invalid.
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func MnemonicToByteArray(mnemonic string) ([]byte, error) {
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var (
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mnemonicSlice = strings.Split(mnemonic, " ")
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entropyBitSize = len(mnemonicSlice) * 11
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checksumBitSize = entropyBitSize % 32
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fullByteSize = (entropyBitSize-checksumBitSize)/8 + 1
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checksumByteSize = fullByteSize - (fullByteSize % 4)
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)
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// Pre validate that the mnemonic is well formed and only contains words that
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// are present in the word list
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if !IsMnemonicValid(mnemonic) {
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return nil, ErrInvalidMnemonic
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}
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// Convert word indices to a `big.Int` representing the entropy
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checksummedEntropy := big.NewInt(0)
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modulo := big.NewInt(2048)
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for _, v := range mnemonicSlice {
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index := big.NewInt(int64(wordMap[v]))
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checksummedEntropy.Mul(checksummedEntropy, modulo)
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checksummedEntropy.Add(checksummedEntropy, index)
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}
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// Calculate the unchecksummed entropy so we can validate that the checksum is
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// correct
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checksumModulo := big.NewInt(0).Exp(bigTwo, big.NewInt(int64(checksumBitSize)), nil)
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rawEntropy := big.NewInt(0).Div(checksummedEntropy, checksumModulo)
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// Convert `big.Int`s to byte padded byte slices
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rawEntropyBytes := padByteSlice(rawEntropy.Bytes(), checksumByteSize)
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checksummedEntropyBytes := padByteSlice(checksummedEntropy.Bytes(), fullByteSize)
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// Validate that the checksum is correct
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newChecksummedEntropyBytes := padByteSlice(addChecksum(rawEntropyBytes), fullByteSize)
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if !compareByteSlices(checksummedEntropyBytes, newChecksummedEntropyBytes) {
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return nil, ErrChecksumIncorrect
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}
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return checksummedEntropyBytes, nil
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}
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// NewSeedWithErrorChecking creates a hashed seed output given the mnemonic string and a password.
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// An error is returned if the mnemonic is not convertible to a byte array.
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func NewSeedWithErrorChecking(mnemonic string, password string) ([]byte, error) {
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_, err := MnemonicToByteArray(mnemonic)
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if err != nil {
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return nil, err
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}
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return NewSeed(mnemonic, password), nil
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}
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// NewSeed creates a hashed seed output given a provided string and password.
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// No checking is performed to validate that the string provided is a valid mnemonic.
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func NewSeed(mnemonic string, password string) []byte {
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return pbkdf2.Key([]byte(mnemonic), []byte("mnemonic"+password), 2048, 64, sha512.New)
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}
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// IsMnemonicValid attempts to verify that the provided mnemonic is valid.
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// Validity is determined by both the number of words being appropriate,
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// and that all the words in the mnemonic are present in the word list.
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func IsMnemonicValid(mnemonic string) bool {
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// Create a list of all the words in the mnemonic sentence
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words := strings.Fields(mnemonic)
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// Get word count
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wordCount := len(words)
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// The number of words should be 12, 15, 18, 21 or 24
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if wordCount%3 != 0 || wordCount < 12 || wordCount > 24 {
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return false
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}
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// Check if all words belong in the wordlist
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for _, word := range words {
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if _, ok := wordMap[word]; !ok {
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return false
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}
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}
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return true
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}
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// Appends to data the first (len(data) / 32)bits of the result of sha256(data)
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// Currently only supports data up to 32 bytes
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func addChecksum(data []byte) []byte {
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// Get first byte of sha256
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hasher := sha256.New()
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hasher.Write(data)
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hash := hasher.Sum(nil)
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firstChecksumByte := hash[0]
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// len() is in bytes so we divide by 4
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checksumBitLength := uint(len(data) / 4)
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// For each bit of check sum we want we shift the data one the left
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// and then set the (new) right most bit equal to checksum bit at that index
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// staring from the left
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dataBigInt := new(big.Int).SetBytes(data)
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for i := uint(0); i < checksumBitLength; i++ {
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// Bitshift 1 left
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dataBigInt.Mul(dataBigInt, bigTwo)
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// Set rightmost bit if leftmost checksum bit is set
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if uint8(firstChecksumByte&(1<<(7-i))) > 0 {
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dataBigInt.Or(dataBigInt, bigOne)
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}
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}
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return dataBigInt.Bytes()
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}
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// validateEntropyBitSize ensures that entropy is the correct size for being a
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// mnemonic.
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func validateEntropyBitSize(bitSize int) error {
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if (bitSize%32) != 0 || bitSize < 128 || bitSize > 256 {
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return ErrEntropyLengthInvalid
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}
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return nil
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}
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// padByteSlice returns a byte slice of the given size with contents of the
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// given slice left padded and any empty spaces filled with 0's.
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func padByteSlice(slice []byte, length int) []byte {
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if len(slice) >= length {
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return slice
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}
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newSlice := make([]byte, length-len(slice))
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return append(newSlice, slice...)
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}
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// compareByteSlices returns true of the byte slices have equal contents and
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// returns false otherwise.
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func compareByteSlices(a, b []byte) bool {
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if len(a) != len(b) {
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return false
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}
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for i := range a {
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if a[i] != b[i] {
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return false
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}
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}
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return true
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}
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