From f0199b83dfb56af9edf2c121449b639dc0402145 Mon Sep 17 00:00:00 2001 From: Felix Lange Date: Thu, 7 Dec 2017 13:26:59 +0100 Subject: [PATCH] crypto, crypto/secp256k1: add CompressPubkey --- crypto/secp256k1/ext.h | 30 ++++++++++++++++++------------ crypto/secp256k1/secp256.go | 28 ++++++++++++++++++++++++---- crypto/signature_cgo.go | 5 +++++ crypto/signature_nocgo.go | 5 +++++ crypto/signature_test.go | 14 ++++++++++++++ 5 files changed, 66 insertions(+), 16 deletions(-) diff --git a/crypto/secp256k1/ext.h b/crypto/secp256k1/ext.h index 134b205968..c166837b3e 100644 --- a/crypto/secp256k1/ext.h +++ b/crypto/secp256k1/ext.h @@ -74,26 +74,32 @@ static int secp256k1_ext_ecdsa_verify( return secp256k1_ecdsa_verify(ctx, &sig, msgdata, &pubkey); } -// secp256k1_ext_decompress_pubkey decompresses a public key. +// secp256k1_ext_reencode_pubkey decodes then encodes a public key. It can be used to +// convert between public key formats. The input/output formats are chosen depending on the +// length of the input/output buffers. // -// Returns: 1: public key is valid -// 0: public key is invalid +// Returns: 1: conversion successful +// 0: conversion unsuccessful // Args: ctx: pointer to a context object (cannot be NULL) -// Out: pubkey_out: the serialized 65-byte public key (cannot be NULL) -// In: pubkeydata: pointer to 33 bytes of compressed public key data (cannot be NULL) -static int secp256k1_ext_decompress_pubkey( +// Out: out: output buffer that will contain the reencoded key (cannot be NULL) +// In: outlen: length of out (33 for compressed keys, 65 for uncompressed keys) +// pubkeydata: the input public key (cannot be NULL) +// pubkeylen: length of pubkeydata +static int secp256k1_ext_reencode_pubkey( const secp256k1_context* ctx, - unsigned char *pubkey_out, - const unsigned char *pubkeydata + unsigned char *out, + size_t outlen, + const unsigned char *pubkeydata, + size_t pubkeylen ) { secp256k1_pubkey pubkey; - if (!secp256k1_ec_pubkey_parse(ctx, &pubkey, pubkeydata, 33)) { + if (!secp256k1_ec_pubkey_parse(ctx, &pubkey, pubkeydata, pubkeylen)) { return 0; } - size_t outputlen = 65; - return secp256k1_ec_pubkey_serialize(ctx, pubkey_out, &outputlen, &pubkey, SECP256K1_EC_UNCOMPRESSED); -} + unsigned int flag = (outlen == 33) ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED; + return secp256k1_ec_pubkey_serialize(ctx, out, &outlen, &pubkey, flag); +}i // secp256k1_ext_scalar_mul multiplies a point by a scalar in constant time. // diff --git a/crypto/secp256k1/secp256.go b/crypto/secp256k1/secp256.go index 1650601149..eefbb99ee4 100644 --- a/crypto/secp256k1/secp256.go +++ b/crypto/secp256k1/secp256.go @@ -139,15 +139,35 @@ func DecompressPubkey(pubkey []byte) (x, y *big.Int) { if len(pubkey) != 33 { return nil, nil } - out := make([]byte, 65) - outdata := (*C.uchar)(unsafe.Pointer(&out[0])) - pubkeydata := (*C.uchar)(unsafe.Pointer(&pubkey[0])) - if C.secp256k1_ext_decompress_pubkey(context, outdata, pubkeydata) == 0 { + var ( + pubkeydata = (*C.uchar)(unsafe.Pointer(&pubkey[0])) + pubkeylen = C.size_t(len(pubkey)) + out = make([]byte, 65) + outdata = (*C.uchar)(unsafe.Pointer(&out[0])) + outlen = C.size_t(len(out)) + ) + if C.secp256k1_ext_reencode_pubkey(context, outdata, outlen, pubkeydata, pubkeylen) == 0 { return nil, nil } return new(big.Int).SetBytes(out[1:33]), new(big.Int).SetBytes(out[33:]) } +// CompressPubkey encodes a public key to 33-byte compressed format. +func CompressPubkey(x, y *big.Int) []byte { + var ( + pubkey = S256().Marshal(x, y) + pubkeydata = (*C.uchar)(unsafe.Pointer(&pubkey[0])) + pubkeylen = C.size_t(len(pubkey)) + out = make([]byte, 33) + outdata = (*C.uchar)(unsafe.Pointer(&out[0])) + outlen = C.size_t(len(out)) + ) + if C.secp256k1_ext_reencode_pubkey(context, outdata, outlen, pubkeydata, pubkeylen) == 0 { + panic("libsecp256k1 error") + } + return out +} + func checkSignature(sig []byte) error { if len(sig) != 65 { return ErrInvalidSignatureLen diff --git a/crypto/signature_cgo.go b/crypto/signature_cgo.go index 381d8a1bbc..340bfc221e 100644 --- a/crypto/signature_cgo.go +++ b/crypto/signature_cgo.go @@ -76,6 +76,11 @@ func DecompressPubkey(pubkey []byte) (*ecdsa.PublicKey, error) { return &ecdsa.PublicKey{X: x, Y: y, Curve: S256()}, nil } +// CompressPubkey encodes a public key to the 33-byte compressed format. +func CompressPubkey(pubkey *ecdsa.PublicKey) []byte { + return secp256k1.CompressPubkey(pubkey.X, pubkey.Y) +} + // S256 returns an instance of the secp256k1 curve. func S256() elliptic.Curve { return secp256k1.S256() diff --git a/crypto/signature_nocgo.go b/crypto/signature_nocgo.go index 17fd613b21..78b99c02b0 100644 --- a/crypto/signature_nocgo.go +++ b/crypto/signature_nocgo.go @@ -102,6 +102,11 @@ func DecompressPubkey(pubkey []byte) (*ecdsa.PublicKey, error) { return key.ToECDSA(), nil } +// CompressPubkey encodes a public key to the 33-byte compressed format. +func CompressPubkey(pubkey *ecdsa.PublicKey) []byte { + return (*btcec.PublicKey)(pubkey).SerializeCompressed() +} + // S256 returns an instance of the secp256k1 curve. func S256() elliptic.Curve { return btcec.S256() diff --git a/crypto/signature_test.go b/crypto/signature_test.go index abcab425b5..e7e2b67db3 100644 --- a/crypto/signature_test.go +++ b/crypto/signature_test.go @@ -18,10 +18,12 @@ package crypto import ( "bytes" + "crypto/ecdsa" "testing" "github.com/ethereum/go-ethereum/common" "github.com/ethereum/go-ethereum/common/hexutil" + "github.com/ethereum/go-ethereum/common/math" ) var ( @@ -86,6 +88,18 @@ func TestDecompressPubkey(t *testing.T) { } } +func TestCompressPubkey(t *testing.T) { + key := &ecdsa.PublicKey{ + Curve: S256(), + X: math.MustParseBig256("0xe32df42865e97135acfb65f3bae71bdc86f4d49150ad6a440b6f15878109880a"), + Y: math.MustParseBig256("0x0a2b2667f7e725ceea70c673093bf67663e0312623c8e091b13cf2c0f11ef652"), + } + compressed := CompressPubkey(key) + if !bytes.Equal(compressed, testpubkeyc) { + t.Errorf("wrong public key result: got %x, want %x", compressed, testpubkeyc) + } +} + func BenchmarkEcrecoverSignature(b *testing.B) { for i := 0; i < b.N; i++ { if _, err := Ecrecover(testmsg, testsig); err != nil {