1 files changed, 130 insertions, 0 deletions
diff --git a/crypto/secp256k1/ext.h b/crypto/secp256k1/ext.h
new file mode 100644
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+++ b/crypto/secp256k1/ext.h
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+// 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;
+}