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package verify
import (
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/sha256"
"encoding/base64"
"encoding/binary"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"math/big"
"strings"
"github.com/Fuwn/plutia/internal/config"
"github.com/Fuwn/plutia/internal/types"
"github.com/decred/dcrd/dcrec/secp256k1/v4"
secpECDSA "github.com/decred/dcrd/dcrec/secp256k1/v4/ecdsa"
"github.com/fxamacker/cbor/v2"
"github.com/mr-tron/base58"
)
type Verifier struct {
Policy string
}
func New(policy string) *Verifier {
return &Verifier{Policy: policy}
}
func (v *Verifier) ShouldVerify(existing *types.StateV1, seq uint64) bool {
switch v.Policy {
case config.VerifyLazy:
return false
case config.VerifyStateOnly:
if existing == nil {
return true
}
return seq >= existing.LatestOpSeq
default:
return true
}
}
func (v *Verifier) VerifyOperation(op types.ParsedOperation, existing *types.StateV1) error {
if !v.ShouldVerify(existing, op.Sequence) {
return nil
}
if existing != nil && existing.ChainTipHash != "" {
if op.Prev == "" {
return errors.New("missing prev on non-genesis operation")
}
if op.Prev != existing.ChainTipHash {
return fmt.Errorf("prev linkage mismatch: got %s want %s", op.Prev, existing.ChainTipHash)
}
}
sig, ok := findString(op.Payload, "sig", "signature")
if !ok || strings.TrimSpace(sig) == "" {
return errors.New("missing signature")
}
pubKeys := make([]string, 0, 8)
if existing != nil && len(existing.RotationKeys) > 0 {
pubKeys = append(pubKeys, existing.RotationKeys...)
}
pubKeys = append(pubKeys, extractPublicKeys(op.Payload)...)
if len(pubKeys) == 0 {
return errors.New("missing verification public key")
}
sigBytes, err := decodeFlexible(sig)
if err != nil {
return fmt.Errorf("decode signature: %w", err)
}
payload, err := signaturePayload(op.Payload)
if err != nil {
return err
}
for _, key := range pubKeys {
vk, err := decodePublicKey(key)
if err != nil {
continue
}
switch vk.Algo {
case "ed25519":
if ed25519.Verify(vk.Ed25519, payload, sigBytes) {
return nil
}
case "secp256k1":
if verifySecp256k1(vk.Secp256k1, payload, sigBytes) {
return nil
}
case "p256":
if verifyP256(vk.P256, payload, sigBytes) {
return nil
}
}
}
return errors.New("signature verification failed")
}
func signaturePayload(m map[string]any) ([]byte, error) {
if raw, ok := findString(m, "sigPayload", "signaturePayload"); ok && raw != "" {
decoded, err := decodeFlexible(raw)
if err == nil && json.Valid(decoded) {
return types.CanonicalizeJSON(decoded)
}
}
clone := make(map[string]any, len(m))
for k, v := range m {
switch k {
case "sig", "signature", "sigPayload", "signaturePayload":
continue
default:
clone[k] = v
}
}
encMode, err := cbor.CanonicalEncOptions().EncMode()
if err != nil {
return nil, fmt.Errorf("init canonical cbor encoder: %w", err)
}
b, err := encMode.Marshal(clone)
if err != nil {
return nil, fmt.Errorf("marshal signature payload cbor: %w", err)
}
return b, nil
}
func findString(m map[string]any, keys ...string) (string, bool) {
for _, k := range keys {
if v, ok := m[k].(string); ok {
return v, true
}
}
return "", false
}
func extractPublicKeys(payload map[string]any) []string {
out := make([]string, 0, 6)
seen := map[string]struct{}{}
add := func(v string) {
v = strings.TrimSpace(v)
if v == "" {
return
}
if _, ok := seen[v]; ok {
return
}
seen[v] = struct{}{}
out = append(out, v)
}
if arr, ok := payload["rotationKeys"].([]any); ok {
for _, v := range arr {
if s, ok := v.(string); ok {
add(s)
}
}
}
if v, ok := findString(payload, "publicKey", "verificationMethod", "signingKey", "recoveryKey"); ok {
add(v)
}
if vm, ok := payload["verificationMethods"].(map[string]any); ok {
if v, ok := vm["atproto"].(string); ok {
add(v)
}
for _, anyV := range vm {
if s, ok := anyV.(string); ok {
add(s)
}
}
}
return out
}
type verificationKey struct {
Algo string
Ed25519 ed25519.PublicKey
Secp256k1 *secp256k1.PublicKey
P256 *ecdsa.PublicKey
}
func decodePublicKey(value string) (verificationKey, error) {
if strings.HasPrefix(value, "did:key:") {
mb := strings.TrimPrefix(value, "did:key:")
if mb == "" || mb[0] != 'z' {
return verificationKey{}, errors.New("did:key must be multibase base58btc")
}
decoded, err := base58.Decode(mb[1:])
if err != nil {
return verificationKey{}, fmt.Errorf("decode did:key base58: %w", err)
}
if len(decoded) < 3 {
return verificationKey{}, errors.New("invalid did:key length")
}
code, n := binary.Uvarint(decoded)
if n <= 0 || n >= len(decoded) {
return verificationKey{}, errors.New("invalid did:key multicodec prefix")
}
keyBytes := decoded[n:]
switch code {
case 0xED:
if len(keyBytes) != ed25519.PublicKeySize {
return verificationKey{}, errors.New("invalid did:key ed25519 length")
}
return verificationKey{
Algo: "ed25519",
Ed25519: ed25519.PublicKey(keyBytes),
}, nil
case 0xE7:
pub, err := secp256k1.ParsePubKey(keyBytes)
if err != nil {
return verificationKey{}, fmt.Errorf("parse secp256k1 did:key: %w", err)
}
return verificationKey{Algo: "secp256k1", Secp256k1: pub}, nil
case 0x1200:
x, y := elliptic.UnmarshalCompressed(elliptic.P256(), keyBytes)
if x == nil || y == nil {
return verificationKey{}, errors.New("parse p256 did:key: invalid compressed key")
}
return verificationKey{
Algo: "p256",
P256: &ecdsa.PublicKey{Curve: elliptic.P256(), X: x, Y: y},
}, nil
default:
return verificationKey{}, errors.New("unsupported did:key multicodec")
}
}
b, err := decodeFlexible(value)
if err != nil {
return verificationKey{}, fmt.Errorf("decode public key: %w", err)
}
if len(b) == ed25519.PublicKeySize {
return verificationKey{Algo: "ed25519", Ed25519: ed25519.PublicKey(b)}, nil
}
pub, err := secp256k1.ParsePubKey(b)
if err == nil {
return verificationKey{Algo: "secp256k1", Secp256k1: pub}, nil
}
if x, y := elliptic.UnmarshalCompressed(elliptic.P256(), b); x != nil && y != nil {
return verificationKey{
Algo: "p256",
P256: &ecdsa.PublicKey{Curve: elliptic.P256(), X: x, Y: y},
}, nil
}
return verificationKey{}, fmt.Errorf("invalid public key length/type: %d", len(b))
}
func verifySecp256k1(pub *secp256k1.PublicKey, payload, sig []byte) bool {
if pub == nil {
return false
}
var parsed *secpECDSA.Signature
if len(sig) == 64 {
var r, s secp256k1.ModNScalar
r.SetByteSlice(sig[:32])
s.SetByteSlice(sig[32:])
parsed = secpECDSA.NewSignature(&r, &s)
} else {
der, err := secpECDSA.ParseDERSignature(sig)
if err != nil {
return false
}
parsed = der
}
sum := sha256.Sum256(payload)
return parsed.Verify(sum[:], pub)
}
func verifyP256(pub *ecdsa.PublicKey, payload, sig []byte) bool {
if pub == nil {
return false
}
sum := sha256.Sum256(payload)
if len(sig) == 64 {
r := new(big.Int).SetBytes(sig[:32])
s := new(big.Int).SetBytes(sig[32:])
return ecdsa.Verify(pub, sum[:], r, s)
}
return ecdsa.VerifyASN1(pub, sum[:], sig)
}
func decodeFlexible(v string) ([]byte, error) {
if b, err := base64.RawURLEncoding.DecodeString(v); err == nil {
return b, nil
}
if b, err := base64.StdEncoding.DecodeString(v); err == nil {
return b, nil
}
if b, err := hex.DecodeString(v); err == nil {
return b, nil
}
return nil, errors.New("unsupported encoding")
}
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