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|
package secp256k1
import (
"fmt"
"math/big"
"strings"
)
// Bech32 alphabet (no 1, b, i, o to avoid confusion)
const bech32Alphabet = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
// bech32Polymod computes the Bech32 checksum
func bech32Polymod(values []int) int {
gen := []int{0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3}
chk := 1
for _, v := range values {
top := chk >> 25
chk = (chk&0x1ffffff)<<5 ^ v
for i := 0; i < 5; i++ {
if (top>>i)&1 == 1 {
chk ^= gen[i]
}
}
}
return chk
}
// bech32HRPExpand expands the human-readable part for checksum
func bech32HRPExpand(hrp string) []int {
result := make([]int, len(hrp)*2+1)
for i, c := range hrp {
result[i] = int(c) >> 5
}
result[len(hrp)] = 0
for i, c := range hrp {
result[len(hrp)+1+i] = int(c) & 31
}
return result
}
// bech32CreateChecksum creates a 6-character checksum
func bech32CreateChecksum(hrp string, data []int) []int {
values := append(bech32HRPExpand(hrp), data...)
values = append(values, []int{0, 0, 0, 0, 0, 0}...)
polymod := bech32Polymod(values) ^ 1
checksum := make([]int, 6)
for i := 0; i < 6; i++ {
checksum[i] = (polymod >> (5 * (5 - i))) & 31
}
return checksum
}
// bech32VerifyChecksum verifies a bech32 checksum
func bech32VerifyChecksum(hrp string, data []int) bool {
return bech32Polymod(append(bech32HRPExpand(hrp), data...)) == 1
}
// convertBits converts between bit groups
func convertBits(data []byte, fromBits, toBits int, pad bool) ([]int, error) {
acc := 0
bits := 0
result := []int{}
maxv := (1 << toBits) - 1
for _, value := range data {
acc = (acc << fromBits) | int(value)
bits += fromBits
for bits >= toBits {
bits -= toBits
result = append(result, (acc>>bits)&maxv)
}
}
if pad {
if bits > 0 {
result = append(result, (acc<<(toBits-bits))&maxv)
}
} else if bits >= fromBits || ((acc<<(toBits-bits))&maxv) != 0 {
return nil, fmt.Errorf("invalid padding")
}
return result, nil
}
// Bech32Encode encodes data with a human-readable prefix
func Bech32Encode(hrp string, data []byte) (string, error) {
// Convert 8-bit bytes to 5-bit groups
values, err := convertBits(data, 8, 5, true)
if err != nil {
return "", err
}
// Add checksum
checksum := bech32CreateChecksum(hrp, values)
combined := append(values, checksum...)
// Build result string
var result strings.Builder
result.WriteString(hrp)
result.WriteByte('1')
for _, v := range combined {
result.WriteByte(bech32Alphabet[v])
}
return result.String(), nil
}
// Bech32Decode decodes a bech32 string
func Bech32Decode(s string) (string, []byte, error) {
// Find separator
pos := strings.LastIndex(s, "1")
if pos < 1 || pos+7 > len(s) {
return "", nil, fmt.Errorf("invalid bech32: separator position")
}
// Split HRP and data
hrp := strings.ToLower(s[:pos])
dataStr := strings.ToLower(s[pos+1:])
// Decode data characters
data := make([]int, len(dataStr))
for i, c := range dataStr {
idx := strings.IndexRune(bech32Alphabet, c)
if idx < 0 {
return "", nil, fmt.Errorf("invalid bech32: character %c", c)
}
data[i] = idx
}
// Verify checksum
if !bech32VerifyChecksum(hrp, data) {
return "", nil, fmt.Errorf("invalid bech32: checksum")
}
// Remove checksum and convert back to 8-bit
values := data[:len(data)-6]
bytes, err := convertBitsToBytes(values)
if err != nil {
return "", nil, err
}
return hrp, bytes, nil
}
// convertBitsToBytes converts 5-bit groups back to bytes
func convertBitsToBytes(data []int) ([]byte, error) {
acc := 0
bits := 0
result := []byte{}
for _, value := range data {
acc = (acc << 5) | value
bits += 5
for bits >= 8 {
bits -= 8
result = append(result, byte((acc>>bits)&0xff))
}
}
return result, nil
}
// === Nostr-specific helpers ===
// Nsec returns the private key as a Nostr nsec string
func (priv *PrivateKey) Nsec() string {
encoded, _ := Bech32Encode("nsec", priv.Bytes())
return encoded
}
// Npub returns the public key as a Nostr npub string (x-only)
func (pub *PublicKey) Npub() string {
encoded, _ := Bech32Encode("npub", pub.XOnlyBytes())
return encoded
}
// PrivateKeyFromNsec parses an nsec string
func PrivateKeyFromNsec(nsec string) (*PrivateKey, error) {
hrp, data, err := Bech32Decode(nsec)
if err != nil {
return nil, fmt.Errorf("invalid nsec: %w", err)
}
if hrp != "nsec" {
return nil, fmt.Errorf("invalid nsec: wrong prefix %q", hrp)
}
if len(data) != 32 {
return nil, fmt.Errorf("invalid nsec: wrong length %d", len(data))
}
return NewPrivateKeyFromBytes(data)
}
// PublicKeyFromNpub parses an npub string
func PublicKeyFromNpub(npub string) (*PublicKey, error) {
hrp, data, err := Bech32Decode(npub)
if err != nil {
return nil, fmt.Errorf("invalid npub: %w", err)
}
if hrp != "npub" {
return nil, fmt.Errorf("invalid npub: wrong prefix %q", hrp)
}
if len(data) != 32 {
return nil, fmt.Errorf("invalid npub: wrong length %d", len(data))
}
// Lift x-coordinate to full point
point, err := liftX(new(big.Int).SetBytes(data))
if err != nil {
return nil, fmt.Errorf("invalid npub: %w", err)
}
return &PublicKey{Point: point}, nil
}
|
