Deterministic signing

Author: sipa

src/key.cpp

@@ -5,6 +5,7 @@
 #include "key.h"
 
 #include "crypto/hmac_sha512.h"
+#include "crypto/rfc6979_hmac_sha256.h"
 #include "eccryptoverify.h"
 #include "pubkey.h"
 #include "random.h"
@@ -71,30 +72,36 @@ CPubKey CKey::GetPubKey() const {
     return result;
 }
 
-bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
+bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, uint32_t test_case) const {
     if (!fValid)
         return false;
     vchSig.resize(72);
-    int nSigLen = 72;
-    CKey nonce;
+    RFC6979_HMAC_SHA256 prng(begin(), 32, (unsigned char*)&hash, 32);
     do {
-        nonce.MakeNewKey(true);
-        if (secp256k1_ecdsa_sign((const unsigned char*)&hash, 32, (unsigned char*)&vchSig[0], &nSigLen, begin(), nonce.begin()))
-            break;
+        uint256 nonce;
+        prng.Generate((unsigned char*)&nonce, 32);
+        nonce += test_case;
+        int nSigLen = 72;
+        int ret = secp256k1_ecdsa_sign((const unsigned char*)&hash, 32, (unsigned char*)&vchSig[0], &nSigLen, begin(), (unsigned char*)&nonce);
+        vchSig.resize(nSigLen);
+        nonce = 0;
+        if (ret)
+            return true;
     } while(true);
-    vchSig.resize(nSigLen);
-    return true;
 }
 
 bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
     if (!fValid)
         return false;
     vchSig.resize(65);
     int rec = -1;
-    CKey nonce;
+    RFC6979_HMAC_SHA256 prng(begin(), 32, (unsigned char*)&hash, 32);
     do {
-        nonce.MakeNewKey(true);
-        if (secp256k1_ecdsa_sign_compact((const unsigned char*)&hash, 32, &vchSig[1], begin(), nonce.begin(), &rec))
+        uint256 nonce;
+        prng.Generate((unsigned char*)&nonce, 32);
+        int ret = secp256k1_ecdsa_sign_compact((const unsigned char*)&hash, 32, &vchSig[1], begin(), (unsigned char*)&nonce, &rec);
+        nonce = 0;
+        if (ret)
             break;
     } while(true);
     assert(rec != -1);

src/key.h

@@ -121,8 +121,12 @@ class CKey
      */
     CPubKey GetPubKey() const;
 
-    //! Create a DER-serialized signature.
-    bool Sign(const uint256& hash, std::vector<unsigned char>& vchSig) const;
+    /**
+     * Create a DER-serialized signature.
+     * The test_case parameter tweaks the deterministic nonce, and is only for
+     * testing. It should be zero for normal use.
+     */
+    bool Sign(const uint256& hash, std::vector<unsigned char>& vchSig, uint32_t test_case = 0) const;
 
     /**
      * Create a compact signature (65 bytes), which allows reconstructing the used public key.

src/test/key_tests.cpp

@@ -8,6 +8,7 @@
 #include "script/script.h"
 #include "uint256.h"
 #include "util.h"
+#include "utilstrencodings.h"
 
 #include <string>
 #include <vector>
@@ -142,6 +143,28 @@ BOOST_AUTO_TEST_CASE(key_test1)
         BOOST_CHECK(rkey1C == pubkey1C);
         BOOST_CHECK(rkey2C == pubkey2C);
     }
+
+    // test deterministic signing
+
+    std::vector<unsigned char> detsig, detsigc;
+    string strMsg = "Very deterministic message";
+    uint256 hashMsg = Hash(strMsg.begin(), strMsg.end());
+    BOOST_CHECK(key1.Sign(hashMsg, detsig));
+    BOOST_CHECK(key1C.Sign(hashMsg, detsigc));
+    BOOST_CHECK(detsig == detsigc);
+    BOOST_CHECK(detsig == ParseHex("304402205dbbddda71772d95ce91cd2d14b592cfbc1dd0aabd6a394b6c2d377bbe59d31d022014ddda21494a4e221f0824f0b8b924c43fa43c0ad57dccdaa11f81a6bd4582f6"));
+    BOOST_CHECK(key2.Sign(hashMsg, detsig));
+    BOOST_CHECK(key2C.Sign(hashMsg, detsigc));
+    BOOST_CHECK(detsig == detsigc);
+    BOOST_CHECK(detsig == ParseHex("3044022052d8a32079c11e79db95af63bb9600c5b04f21a9ca33dc129c2bfa8ac9dc1cd5022061d8ae5e0f6c1a16bde3719c64c2fd70e404b6428ab9a69566962e8771b5944d"));
+    BOOST_CHECK(key1.SignCompact(hashMsg, detsig));
+    BOOST_CHECK(key1C.SignCompact(hashMsg, detsigc));
+    BOOST_CHECK(detsig == ParseHex("1c5dbbddda71772d95ce91cd2d14b592cfbc1dd0aabd6a394b6c2d377bbe59d31d14ddda21494a4e221f0824f0b8b924c43fa43c0ad57dccdaa11f81a6bd4582f6"));
+    BOOST_CHECK(detsigc == ParseHex("205dbbddda71772d95ce91cd2d14b592cfbc1dd0aabd6a394b6c2d377bbe59d31d14ddda21494a4e221f0824f0b8b924c43fa43c0ad57dccdaa11f81a6bd4582f6"));
+    BOOST_CHECK(key2.SignCompact(hashMsg, detsig));
+    BOOST_CHECK(key2C.SignCompact(hashMsg, detsigc));
+    BOOST_CHECK(detsig == ParseHex("1c52d8a32079c11e79db95af63bb9600c5b04f21a9ca33dc129c2bfa8ac9dc1cd561d8ae5e0f6c1a16bde3719c64c2fd70e404b6428ab9a69566962e8771b5944d"));
+    BOOST_CHECK(detsigc == ParseHex("2052d8a32079c11e79db95af63bb9600c5b04f21a9ca33dc129c2bfa8ac9dc1cd561d8ae5e0f6c1a16bde3719c64c2fd70e404b6428ab9a69566962e8771b5944d"));
 }
 
 BOOST_AUTO_TEST_SUITE_END()

src/test/script_tests.cpp

@@ -248,8 +248,9 @@ class TestBuilder
     {
         uint256 hash = SignatureHash(scriptPubKey, spendTx, 0, nHashType);
         std::vector<unsigned char> vchSig, r, s;
+        uint32_t iter = 0;
         do {
-            key.Sign(hash, vchSig);
+            key.Sign(hash, vchSig, iter++);
             if ((lenS == 33) != (vchSig[5 + vchSig[3]] == 33)) {
                 NegateSignatureS(vchSig);
             }