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200 lines
4.9 KiB
200 lines
4.9 KiB
package words
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import (
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"math/big"
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"strings"
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"github.com/pkg/errors"
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"github.com/tendermint/go-crypto/keys/words/wordlist"
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)
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const BankSize = 2048
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// TODO: add error-checking codecs for invalid phrases
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type Codec interface {
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BytesToWords([]byte) ([]string, error)
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WordsToBytes([]string) ([]byte, error)
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}
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type WordCodec struct {
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words []string
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bytes map[string]int
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check ECC
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}
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var _ Codec = &WordCodec{}
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func NewCodec(words []string) (codec *WordCodec, err error) {
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if len(words) != BankSize {
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return codec, errors.Errorf("Bank must have %d words, found %d", BankSize, len(words))
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}
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res := &WordCodec{
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words: words,
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// TODO: configure this outside???
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check: NewIEEECRC32(),
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// check: NewIBMCRC16(),
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}
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return res, nil
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}
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// LoadCodec loads a pre-compiled language file
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func LoadCodec(bank string) (codec *WordCodec, err error) {
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words, err := loadBank(bank)
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if err != nil {
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return codec, err
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}
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return NewCodec(words)
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}
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// MustLoadCodec panics if word bank is missing, only for tests
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func MustLoadCodec(bank string) *WordCodec {
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codec, err := LoadCodec(bank)
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if err != nil {
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panic(err)
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}
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return codec
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}
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// loadBank opens a wordlist file and returns all words inside
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func loadBank(bank string) ([]string, error) {
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filename := "keys/words/wordlist/" + bank + ".txt"
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words, err := wordlist.Asset(filename)
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if err != nil {
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return nil, err
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}
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wordsAll := strings.Split(strings.TrimSpace(string(words)), "\n")
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return wordsAll, nil
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}
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// // TODO: read from go-bind assets
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// func getData(filename string) (string, error) {
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// f, err := os.Open(filename)
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// if err != nil {
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// return "", errors.WithStack(err)
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// }
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// defer f.Close()
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// data, err := ioutil.ReadAll(f)
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// if err != nil {
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// return "", errors.WithStack(err)
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// }
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// return string(data), nil
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// }
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// given this many bytes, we will produce this many words
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func wordlenFromBytes(numBytes int) int {
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// 2048 words per bank, which is 2^11.
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// 8 bits per byte, and we add +10 so it rounds up
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return (8*numBytes + 10) / 11
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}
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// given this many words, we will produce this many bytes.
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// sometimes there are two possibilities.
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// if maybeShorter is true, then represents len OR len-1 bytes
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func bytelenFromWords(numWords int) (length int, maybeShorter bool) {
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// calculate the max number of complete bytes we could store in this word
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length = 11 * numWords / 8
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// if one less byte would also generate this length, set maybeShorter
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if wordlenFromBytes(length-1) == numWords {
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maybeShorter = true
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}
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return
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}
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// TODO: add checksum
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func (c *WordCodec) BytesToWords(raw []byte) (words []string, err error) {
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// always add a checksum to the data
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data := c.check.AddECC(raw)
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numWords := wordlenFromBytes(len(data))
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n2048 := big.NewInt(2048)
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nData := big.NewInt(0).SetBytes(data)
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nRem := big.NewInt(0)
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// Alternative, use condition "nData.BitLen() > 0"
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// to allow for shorter words when data has leading 0's
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for i := 0; i < numWords; i++ {
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nData.DivMod(nData, n2048, nRem)
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rem := nRem.Int64()
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w := c.words[rem]
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// double-check bank on generation...
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_, err := c.GetIndex(w)
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if err != nil {
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return nil, err
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}
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words = append(words, w)
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}
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return words, nil
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}
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func (c *WordCodec) WordsToBytes(words []string) ([]byte, error) {
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l := len(words)
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if l == 0 {
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return nil, errors.New("Didn't provide any words")
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}
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n2048 := big.NewInt(2048)
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nData := big.NewInt(0)
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// since we output words based on the remainder, the first word has the lowest
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// value... we must load them in reverse order
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for i := 1; i <= l; i++ {
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rem, err := c.GetIndex(words[l-i])
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if err != nil {
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return nil, err
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}
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nRem := big.NewInt(int64(rem))
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nData.Mul(nData, n2048)
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nData.Add(nData, nRem)
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}
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// we copy into a slice of the expected size, so it is not shorter if there
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// are lots of leading 0s
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dataBytes := nData.Bytes()
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// copy into the container we have with the expected size
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outLen, flex := bytelenFromWords(len(words))
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toCheck := make([]byte, outLen)
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if len(dataBytes) > outLen {
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return nil, errors.New("Invalid data, could not have been generated by this codec")
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}
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copy(toCheck[outLen-len(dataBytes):], dataBytes)
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// validate the checksum...
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output, err := c.check.CheckECC(toCheck)
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if flex && err != nil {
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// if flex, try again one shorter....
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toCheck = toCheck[1:]
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output, err = c.check.CheckECC(toCheck)
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}
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return output, err
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}
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// GetIndex finds the index of the words to create bytes
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// Generates a map the first time it is loaded, to avoid needless
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// computation when list is not used.
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func (c *WordCodec) GetIndex(word string) (int, error) {
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// generate the first time
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if c.bytes == nil {
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b := map[string]int{}
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for i, w := range c.words {
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if _, ok := b[w]; ok {
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return -1, errors.Errorf("Duplicate word in list: %s", w)
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}
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b[w] = i
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}
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c.bytes = b
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}
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// get the index, or an error
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rem, ok := c.bytes[word]
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if !ok {
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return -1, errors.Errorf("Unrecognized word: %s", word)
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}
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return rem, nil
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}
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