4 files changed, 121 insertions, 0 deletions
diff --git a/src/Makefile.am b/src/Makefile.am
index 1a5c57a3fa..2863a7961e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -206,12 +206,14 @@ crypto_libbitcoin_crypto_a_SOURCES = \
   crypto/sha256.cpp \
   crypto/sha512.cpp \
   crypto/hmac_sha256.cpp \
+  crypto/rfc6979_hmac_sha256.cpp \
   crypto/hmac_sha512.cpp \
   crypto/ripemd160.cpp \
   crypto/common.h \
   crypto/sha256.h \
   crypto/sha512.h \
   crypto/hmac_sha256.h \
+  crypto/rfc6979_hmac_sha256.h \
   crypto/hmac_sha512.h \
   crypto/sha1.h \
   crypto/ripemd160.h
diff --git a/src/crypto/rfc6979_hmac_sha256.cpp b/src/crypto/rfc6979_hmac_sha256.cpp
new file mode 100644
index 0000000000..3f935abfea
--- /dev/null
+++ b/src/crypto/rfc6979_hmac_sha256.cpp
@@ -0,0 +1,47 @@
+// Copyright (c) 2014 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "crypto/rfc6979_hmac_sha256.h"
+
+#include <string.h>
+
+#include <algorithm>
+
+static const unsigned char zero[1] = {0x00};
+static const unsigned char one[1] = {0x01};
+
+RFC6979_HMAC_SHA256::RFC6979_HMAC_SHA256(const unsigned char* key, size_t keylen, const unsigned char* msg, size_t msglen) : retry(false)
+{
+    memset(V, 0x01, sizeof(V));
+    memset(K, 0x00, sizeof(K));
+
+    CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Write(zero, sizeof(zero)).Write(key, keylen).Write(msg, msglen).Finalize(K);
+    CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Finalize(V);
+    CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Write(one, sizeof(one)).Write(key, keylen).Write(msg, msglen).Finalize(K);
+    CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Finalize(V);
+}
+
+RFC6979_HMAC_SHA256::~RFC6979_HMAC_SHA256()
+{
+    memset(V, 0x01, sizeof(V));
+    memset(K, 0x00, sizeof(K));
+}
+
+void RFC6979_HMAC_SHA256::Generate(unsigned char* output, size_t outputlen)
+{
+    if (retry) {
+        CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Write(zero, sizeof(zero)).Finalize(K);
+        CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Finalize(V);
+    }
+
+    while (outputlen > 0) {
+        CHMAC_SHA256(K, sizeof(K)).Write(V, sizeof(V)).Finalize(V);
+        size_t len = std::min(outputlen, sizeof(V));
+        memcpy(output, V, len);
+        output += len;
+        outputlen -= len;
+    }
+
+    retry = true;
+}
diff --git a/src/crypto/rfc6979_hmac_sha256.h b/src/crypto/rfc6979_hmac_sha256.h
new file mode 100644
index 0000000000..e67ddcf8fe
--- /dev/null
+++ b/src/crypto/rfc6979_hmac_sha256.h
@@ -0,0 +1,36 @@
+// Copyright (c) 2014 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_RFC6979_HMAC_SHA256_H
+#define BITCOIN_RFC6979_HMAC_SHA256_H
+
+#include "crypto/hmac_sha256.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+
+/** The RFC 6979 PRNG using HMAC-SHA256. */
+class RFC6979_HMAC_SHA256
+{
+private:
+    unsigned char V[CHMAC_SHA256::OUTPUT_SIZE];
+    unsigned char K[CHMAC_SHA256::OUTPUT_SIZE];
+    bool retry;
+
+public:
+    /**
+     * Construct a new RFC6979 PRNG, using the given key and message.
+     * The message is assumed to be already hashed.
+     */
+    RFC6979_HMAC_SHA256(const unsigned char* key, size_t keylen, const unsigned char* msg, size_t msglen);
+
+    /**
+     * Generate a byte array.
+     */
+    void Generate(unsigned char* output, size_t outputlen);
+
+    ~RFC6979_HMAC_SHA256();
+};
+
+#endif // BITCOIN_RFC6979_HMAC_SHA256_H
diff --git a/src/test/crypto_tests.cpp b/src/test/crypto_tests.cpp
index 466b38fca9..26708f5071 100644
--- a/src/test/crypto_tests.cpp
+++ b/src/test/crypto_tests.cpp
@@ -2,6 +2,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include "crypto/rfc6979_hmac_sha256.h"
 #include "crypto/ripemd160.h"
 #include "crypto/sha1.h"
 #include "crypto/sha256.h"
@@ -13,6 +14,7 @@
 
 #include <vector>
 
+#include <boost/assign/list_of.hpp>
 #include <boost/test/unit_test.hpp>
 
 BOOST_AUTO_TEST_SUITE(crypto_tests)
@@ -246,4 +248,38 @@ BOOST_AUTO_TEST_CASE(hmac_sha512_testvectors) {
                    "b6022cac3c4982b10d5eeb55c3e4de15134676fb6de0446065c97440fa8c6a58");
 }
 
+void TestRFC6979(const std::string& hexkey, const std::string& hexmsg, const std::vector<std::string>& hexout)
+{
+    std::vector<unsigned char> key = ParseHex(hexkey);
+    std::vector<unsigned char> msg = ParseHex(hexmsg);
+    RFC6979_HMAC_SHA256 rng(&key[0], key.size(), &msg[0], msg.size());
+
+    for (unsigned int i = 0; i < hexout.size(); i++) {
+        std::vector<unsigned char> out = ParseHex(hexout[i]);
+        std::vector<unsigned char> gen;
+        gen.resize(out.size());
+        rng.Generate(&gen[0], gen.size());
+        BOOST_CHECK(out == gen);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(rfc6979_hmac_sha256)
+{
+    TestRFC6979(
+        "0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f00",
+        "4bf5122f344554c53bde2ebb8cd2b7e3d1600ad631c385a5d7cce23c7785459a",
+        boost::assign::list_of
+            ("4fe29525b2086809159acdf0506efb86b0ec932c7ba44256ab321e421e67e9fb")
+            ("2bf0fff1d3c378a22dc5de1d856522325c65b504491a0cbd01cb8f3aa67ffd4a")
+            ("f528b410cb541f77000d7afb6c5b53c5c471eab43e466d9ac5190c39c82fd82e"));
+
+    TestRFC6979(
+        "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
+        "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+        boost::assign::list_of
+            ("9c236c165b82ae0cd590659e100b6bab3036e7ba8b06749baf6981e16f1a2b95")
+            ("df471061625bc0ea14b682feee2c9c02f235da04204c1d62a1536c6e17aed7a9")
+            ("7597887cbd76321f32e30440679a22cf7f8d9d2eac390e581fea091ce202ba94"));
+}
+
 BOOST_AUTO_TEST_SUITE_END()