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