// Copyright 2015 Jeffrey Wilcke, Felix Lange, Gustav Simonsson. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be found in
// the LICENSE file.
// secp256k1_context_create_sign_verify creates a context for signing and signature verification.
static secp256k1_context* secp256k1_context_create_sign_verify() {
return secp256k1_context_create(SECP256K1_CONTEXT_SIGN | SECP256K1_CONTEXT_VERIFY);
}
// secp256k1_ext_ecdsa_recover recovers the public key of an encoded compact signature.
//
// Returns: 1: recovery was successful
// 0: recovery was not successful
// Args: ctx: pointer to a context object (cannot be NULL)
// Out: pubkey_out: the serialized 65-byte public key of the signer (cannot be NULL)
// In: sigdata: pointer to a 65-byte signature with the recovery id at the end (cannot be NULL)
// msgdata: pointer to a 32-byte message (cannot be NULL)
static int secp256k1_ext_ecdsa_recover(
const secp256k1_context* ctx,
unsigned char *pubkey_out,
const unsigned char *sigdata,
const unsigned char *msgdata
) {
secp256k1_ecdsa_recoverable_signature sig;
secp256k1_pubkey pubkey;
if (!secp256k1_ecdsa_recoverable_signature_parse_compact(ctx, &sig, sigdata, (int)sigdata[64])) {
return 0;
}
if (!secp256k1_ecdsa_recover(ctx, &pubkey, &sig, msgdata)) {
return 0;
}
size_t outputlen = 65;
return secp256k1_ec_pubkey_serialize(ctx, pubkey_out, &outputlen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
}
// secp256k1_ext_ecdsa_verify verifies an encoded compact signature.
//
// Returns: 1: signature is valid
// 0: signature is invalid
// Args: ctx: pointer to a context object (cannot be NULL)
// In: sigdata: pointer to a 64-byte signature (cannot be NULL)
// msgdata: pointer to a 32-byte message (cannot be NULL)
// pubkeydata: pointer to public key data (cannot be NULL)
// pubkeylen: length of pubkeydata
static int secp256k1_ext_ecdsa_verify(
const secp256k1_context* ctx,
const unsigned char *sigdata,
const unsigned char *msgdata,
const unsigned char *pubkeydata,
size_t pubkeylen
) {
secp256k1_ecdsa_signature sig;
secp256k1_pubkey pubkey;
if (!secp256k1_ecdsa_signature_parse_compact(ctx, &sig, sigdata)) {
return 0;
}
if (!secp256k1_ec_pubkey_parse(ctx, &pubkey, pubkeydata, pubkeylen)) {
return 0;
}
return secp256k1_ecdsa_verify(ctx, &sig, msgdata, &pubkey);
}
// 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: conversion successful
// 0: conversion unsuccessful
// Args: ctx: pointer to a context object (cannot be NULL)
// 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 *out,
size_t outlen,
const unsigned char *pubkeydata,
size_t pubkeylen
) {
secp256k1_pubkey pubkey;
if (!secp256k1_ec_pubkey_parse(ctx, &pubkey, pubkeydata, pubkeylen)) {
return 0;
}
unsigned int flag = (outlen == 33) ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED;
return secp256k1_ec_pubkey_serialize(ctx, out, &outlen, &pubkey, flag);
}
// secp256k1_ext_scalar_mul multiplies a point by a scalar in constant time.
//
// Returns: 1: multiplication was successful
// 0: scalar was invalid (zero or overflow)
// Args: ctx: pointer to a context object (cannot be NULL)
// Out: point: the multiplied point (usually secret)
// In: point: pointer to a 64-byte public point,
// encoded as two 256bit big-endian numbers.
// scalar: a 32-byte scalar with which to multiply the point
int secp256k1_ext_scalar_mul(const secp256k1_context* ctx, unsigned char *point, const unsigned char *scalar) {
int ret = 0;
int overflow = 0;
secp256k1_fe feX, feY;
secp256k1_gej res;
secp256k1_ge ge;
secp256k1_scalar s;
ARG_CHECK(point != NULL);
ARG_CHECK(scalar != NULL);
(void)ctx;
secp256k1_fe_set_b32(&feX, point);
secp256k1_fe_set_b32(&feY, point+32);
secp256k1_ge_set_xy(&ge, &feX, &feY);
secp256k1_scalar_set_b32(&s, scalar, &overflow);
if (overflow || secp256k1_scalar_is_zero(&s)) {
ret = 0;
} else {
secp256k1_ecmult_const(&res, &ge, &s);
secp256k1_ge_set_gej(&ge, &res);
/* Note: can't use secp256k1_pubkey_save here because it is not constant time. */
secp256k1_fe_normalize(&ge.x);
secp256k1_fe_normalize(&ge.y);
secp256k1_fe_get_b32(point, &ge.x);
secp256k1_fe_get_b32(point+32, &ge.y);
ret = 1;
}
secp256k1_scalar_clear(&s);
return ret;
}
