From 73489fbd339f7b62a93b3fafd41843ac8bdaef91 Mon Sep 17 00:00:00 2001
From: Pavol Rusnak <stick@gk2.sk>
Date: Sun, 2 Feb 2014 20:36:03 +0100
Subject: [PATCH] split signing into ecdsa_sign_digest and
 ecdsa_sign/ecdsa_sign_double

---
 ecdsa.c | 33 +++++++++++++++++++++++----------
 ecdsa.h |  2 ++
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/ecdsa.c b/ecdsa.c
index 6954ac59d..3fbfe27ab 100644
--- a/ecdsa.c
+++ b/ecdsa.c
@@ -195,28 +195,41 @@ int generate_k_rfc6979(bignum256 *secret, const uint8_t *priv_key, const uint8_t
 	return 1;
 }
 
-// uses secp256k1 curve
-// priv_key is a 32 byte big endian stored number
 // msg is a data to be signed
 // msg_len is the message length
-// sig is 64 bytes long array for the signature
 int ecdsa_sign(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig)
 {
-	uint32_t i;
 	uint8_t hash[32];
+	SHA256_Raw(msg, msg_len, hash);
+	return ecdsa_sign_digest(priv_key, hash, sig);
+}
+
+// msg is a data to be signed
+// msg_len is the message length
+int ecdsa_sign_double(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig)
+{
+	uint8_t hash[32];
+	SHA256_Raw(msg, msg_len, hash);
+	SHA256_Raw(hash, 32, hash);
+	return ecdsa_sign_digest(priv_key, hash, sig);
+}
+
+// uses secp256k1 curve
+// priv_key is a 32 byte big endian stored number
+// sig is 64 bytes long array for the signature
+// digest is 32 bytes of digest
+int ecdsa_sign_digest(const uint8_t *priv_key, const uint8_t *digest, uint8_t *sig)
+{
+	uint32_t i;
 	curve_point R;
 	bignum256 k, z;
 	bignum256 *da = &R.y;
-	// compute hash function of message
-	SHA256_Raw(msg, msg_len, hash);
-	// if double hash is required uncomment the following line:
-	// SHA256_Raw(hash, 32, hash);
 
-	bn_read_be(hash, &z);
+	bn_read_be(digest, &z);
 
 #if USE_RFC6979
 	// generate K deterministically
-	if (generate_k_rfc6979(&k, priv_key, hash) != 0) {
+	if (generate_k_rfc6979(&k, priv_key, digest) != 0) {
 		return 1;
 	}
 #else
diff --git a/ecdsa.h b/ecdsa.h
index e1e9d3ffb..4c0bdd9ce 100644
--- a/ecdsa.h
+++ b/ecdsa.h
@@ -37,6 +37,8 @@ void point_double(curve_point *cp);
 void scalar_multiply(bignum256 *k, curve_point *res);
 
 int ecdsa_sign(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig);
+int ecdsa_sign_double(const uint8_t *priv_key, const uint8_t *msg, uint32_t msg_len, uint8_t *sig);
+int ecdsa_sign_digest(const uint8_t *priv_key, const uint8_t *digest, uint8_t *sig);
 void ecdsa_get_public_key33(const uint8_t *priv_key, uint8_t *pub_key);
 void ecdsa_get_public_key65(const uint8_t *priv_key, uint8_t *pub_key);
 void ecdsa_get_address(const uint8_t *pub_key, uint8_t version, char *addr);