lnd.xprv/invoice/bech32.go

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package invoice
import (
"fmt"
"strings"
)
const charset = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
var gen = []int{0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3}
// NOTE: This method it a slight modification of the method bech32.Decode found
// btcutil, allowing strings to be more than 90 characters.
// decodeBech32 decodes a bech32 encoded string, returning the human-readable
// part and the data part excluding the checksum.
// Note: the data will be base32 encoded, that is each element of the returned
// byte array will encode 5 bits of data. Use the ConvertBits method to convert
// this to 8-bit representation.
func decodeBech32(bech string) (string, []byte, error) {
// The maximum allowed length for a bech32 string is 90. It must also
// be at least 8 characters, since it needs a non-empty HRP, a
// separator, and a 6 character checksum.
// NB: The 90 character check specified in BIP173 is skipped here, to
// allow strings longer than 90 characters.
if len(bech) < 8 {
return "", nil, fmt.Errorf("invalid bech32 string length %d",
len(bech))
}
// Only ASCII characters between 33 and 126 are allowed.
for i := 0; i < len(bech); i++ {
if bech[i] < 33 || bech[i] > 126 {
return "", nil, fmt.Errorf("invalid character in "+
"string: '%c'", bech[i])
}
}
// The characters must be either all lowercase or all uppercase.
lower := strings.ToLower(bech)
upper := strings.ToUpper(bech)
if bech != lower && bech != upper {
return "", nil, fmt.Errorf("string not all lowercase or all " +
"uppercase")
}
// We'll work with the lowercase string from now on.
bech = lower
// The string is invalid if the last '1' is non-existent, it is the
// first character of the string (no human-readable part) or one of the
// last 6 characters of the string (since checksum cannot contain '1'),
// or if the string is more than 90 characters in total.
one := strings.LastIndexByte(bech, '1')
if one < 1 || one+7 > len(bech) {
return "", nil, fmt.Errorf("invalid index of 1")
}
// The human-readable part is everything before the last '1'.
hrp := bech[:one]
data := bech[one+1:]
// Each character corresponds to the byte with value of the index in
// 'charset'.
decoded, err := toBytes(data)
if err != nil {
return "", nil, fmt.Errorf("failed converting data to bytes: "+
"%v", err)
}
if !bech32VerifyChecksum(hrp, decoded) {
moreInfo := ""
checksum := bech[len(bech)-6:]
expected, err := toChars(bech32Checksum(hrp,
decoded[:len(decoded)-6]))
if err == nil {
moreInfo = fmt.Sprintf("Expected %v, got %v.",
expected, checksum)
}
return "", nil, fmt.Errorf("checksum failed. " + moreInfo)
}
// We exclude the last 6 bytes, which is the checksum.
return hrp, decoded[:len(decoded)-6], nil
}
// toBytes converts each character in the string 'chars' to the value of the
// index of the correspoding character in 'charset'.
func toBytes(chars string) ([]byte, error) {
decoded := make([]byte, 0, len(chars))
for i := 0; i < len(chars); i++ {
index := strings.IndexByte(charset, chars[i])
if index < 0 {
return nil, fmt.Errorf("invalid character not part of "+
"charset: %v", chars[i])
}
decoded = append(decoded, byte(index))
}
return decoded, nil
}
// toChars converts the byte slice 'data' to a string where each byte in 'data'
// encodes the index of a character in 'charset'.
func toChars(data []byte) (string, error) {
result := make([]byte, 0, len(data))
for _, b := range data {
if int(b) >= len(charset) {
return "", fmt.Errorf("invalid data byte: %v", b)
}
result = append(result, charset[b])
}
return string(result), nil
}
// For more details on the checksum calculation, please refer to BIP 173.
func bech32Checksum(hrp string, data []byte) []byte {
// Convert the bytes to list of integers, as this is needed for the
// checksum calculation.
integers := make([]int, len(data))
for i, b := range data {
integers[i] = int(b)
}
values := append(bech32HrpExpand(hrp), integers...)
values = append(values, []int{0, 0, 0, 0, 0, 0}...)
polymod := bech32Polymod(values) ^ 1
var res []byte
for i := 0; i < 6; i++ {
res = append(res, byte((polymod>>uint(5*(5-i)))&31))
}
return res
}
// For more details on the polymod calculation, please refer to BIP 173.
func bech32Polymod(values []int) int {
chk := 1
for _, v := range values {
b := chk >> 25
chk = (chk&0x1ffffff)<<5 ^ v
for i := 0; i < 5; i++ {
if (b>>uint(i))&1 == 1 {
chk ^= gen[i]
}
}
}
return chk
}
// For more details on HRP expansion, please refer to BIP 173.
func bech32HrpExpand(hrp string) []int {
v := make([]int, 0, len(hrp)*2+1)
for i := 0; i < len(hrp); i++ {
v = append(v, int(hrp[i]>>5))
}
v = append(v, 0)
for i := 0; i < len(hrp); i++ {
v = append(v, int(hrp[i]&31))
}
return v
}
// For more details on the checksum verification, please refer to BIP 173.
func bech32VerifyChecksum(hrp string, data []byte) bool {
integers := make([]int, len(data))
for i, b := range data {
integers[i] = int(b)
}
concat := append(bech32HrpExpand(hrp), integers...)
return bech32Polymod(concat) == 1
}