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| 1 | +package secp256k1 |
| 2 | + |
| 3 | +import ( |
| 4 | + "crypto" |
| 5 | + "crypto/sha256" |
| 6 | + "fmt" |
| 7 | + |
| 8 | + "github.com/alanshaw/ucantone/did" |
| 9 | + "github.com/alanshaw/ucantone/principal" |
| 10 | + "github.com/alanshaw/ucantone/principal/secp256k1/verifier" |
| 11 | + "github.com/alanshaw/ucantone/varsig" |
| 12 | + "github.com/multiformats/go-multibase" |
| 13 | + "github.com/multiformats/go-varint" |
| 14 | + "gitlab.com/yawning/secp256k1-voi/secec" |
| 15 | +) |
| 16 | + |
| 17 | +const Code = 0x1301 |
| 18 | + |
| 19 | +var SignatureAlgorithm = verifier.SignatureAlgorithm |
| 20 | + |
| 21 | +var tagSize = varint.UvarintSize(Code) |
| 22 | + |
| 23 | +const keySize = 32 |
| 24 | + |
| 25 | +var size = tagSize + keySize |
| 26 | + |
| 27 | +func Generate() (Signer, error) { |
| 28 | + sk, err := secec.GenerateKey() |
| 29 | + if err != nil { |
| 30 | + return nil, fmt.Errorf("generating secp256k1 key: %w", err) |
| 31 | + } |
| 32 | + s := make(Signer, size) |
| 33 | + varint.PutUvarint(s, Code) |
| 34 | + copy(s[tagSize:], sk.Bytes()) |
| 35 | + return s, nil |
| 36 | +} |
| 37 | + |
| 38 | +// Parse parses a multibase encoded string containing a secp256k1 signer |
| 39 | +// multiformat varint (0x1301) + byte secp256k1 raw scalar value. |
| 40 | +func Parse(str string) (Signer, error) { |
| 41 | + _, bytes, err := multibase.Decode(str) |
| 42 | + if err != nil { |
| 43 | + return nil, fmt.Errorf("decoding multibase string: %w", err) |
| 44 | + } |
| 45 | + return Decode(bytes) |
| 46 | +} |
| 47 | + |
| 48 | +// Decode decodes a buffer of a secp256k1 signer multiformat varint (0x1301) + |
| 49 | +// 32 byte secp256k1 raw scalar value. |
| 50 | +func Decode(b []byte) (Signer, error) { |
| 51 | + if len(b) != size { |
| 52 | + return nil, fmt.Errorf("invalid length: %d wanted: %d", len(b), size) |
| 53 | + } |
| 54 | + skc, _, err := varint.FromUvarint(b) |
| 55 | + if err != nil { |
| 56 | + return nil, fmt.Errorf("reading private key uvarint: %w", err) |
| 57 | + } |
| 58 | + if skc != Code { |
| 59 | + return nil, fmt.Errorf("invalid private key codec: 0x%02x, expected: 0x%02x", skc, Code) |
| 60 | + } |
| 61 | + _, err = secec.NewPrivateKey(b[tagSize:]) |
| 62 | + if err != nil { |
| 63 | + return nil, fmt.Errorf("creating private key: %w", err) |
| 64 | + } |
| 65 | + s := make(Signer, size) |
| 66 | + copy(s, b) |
| 67 | + return s, nil |
| 68 | +} |
| 69 | + |
| 70 | +// FromRaw takes raw 32 byte scalar value and tags with the secp256k1 |
| 71 | +// signer multiformat code, returning a secp256k1 signer. |
| 72 | +func FromRaw(b []byte) (Signer, error) { |
| 73 | + if len(b) != keySize { |
| 74 | + return nil, fmt.Errorf("invalid length: %d wanted: %d", len(b), keySize) |
| 75 | + } |
| 76 | + s := make(Signer, size) |
| 77 | + varint.PutUvarint(s, Code) |
| 78 | + copy(s[tagSize:], b) |
| 79 | + return s, nil |
| 80 | +} |
| 81 | + |
| 82 | +type Signer []byte |
| 83 | + |
| 84 | +var _ principal.Signer = (Signer)(nil) |
| 85 | + |
| 86 | +func (s Signer) Code() uint64 { |
| 87 | + return Code |
| 88 | +} |
| 89 | + |
| 90 | +func (s Signer) SignatureAlgorithm() varsig.SignatureAlgorithm { |
| 91 | + return SignatureAlgorithm |
| 92 | +} |
| 93 | + |
| 94 | +func (s Signer) Verifier() principal.Verifier { |
| 95 | + sk, _ := secec.NewPrivateKey(s[tagSize:]) |
| 96 | + v, _ := verifier.FromRaw(sk.PublicKey().CompressedBytes()) |
| 97 | + return v |
| 98 | +} |
| 99 | + |
| 100 | +func (s Signer) DID() did.DID { |
| 101 | + return s.Verifier().DID() |
| 102 | +} |
| 103 | + |
| 104 | +// Bytes returns the private key bytes with multiformat prefix varint. |
| 105 | +func (s Signer) Bytes() []byte { |
| 106 | + return s |
| 107 | +} |
| 108 | + |
| 109 | +// Raw encodes the bytes of the private key without multiformats tags. |
| 110 | +func (s Signer) Raw() []byte { |
| 111 | + pk := make([]byte, keySize) |
| 112 | + copy(pk, s[tagSize:size]) |
| 113 | + return pk |
| 114 | +} |
| 115 | + |
| 116 | +func (s Signer) Sign(msg []byte) []byte { |
| 117 | + sk, _ := secec.NewPrivateKey(s[tagSize:]) |
| 118 | + hash := sha256.New() |
| 119 | + hash.Write(msg) |
| 120 | + sig, _ := sk.Sign( |
| 121 | + secec.RFC6979SHA256(), // for deterministic signatures, per RFC6979 |
| 122 | + hash.Sum(nil), |
| 123 | + &secec.ECDSAOptions{ |
| 124 | + Encoding: secec.EncodingCompact, |
| 125 | + Hash: crypto.SHA256, |
| 126 | + SelfVerify: false, |
| 127 | + }, |
| 128 | + ) |
| 129 | + return sig |
| 130 | +} |
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