Add RFC 6979 nonce generator. Also some HMAC_DRBG cleanups.

1 files changed, 48 insertions, 0 deletions

diff --git a/src/lib/pubkey/rfc6979/rfc6979.cpp b/src/lib/pubkey/rfc6979/rfc6979.cpp
new file mode 100644
index 000000000..634b3bcb0
--- /dev/null
+++ b/src/lib/pubkey/rfc6979/rfc6979.cpp
@@ -0,0 +1,48 @@
+/*
+* RFC 6979 Deterministic Nonce Generator
+* (C) 2014 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/rfc6979.h>
+#include <botan/hmac_drbg.h>
+#include <botan/libstate.h>
+
+#include <botan/hex.h>
+#include <iostream>
+
+namespace Botan {
+
+BigInt generate_rfc6979_nonce(const BigInt& x,
+                              const BigInt& q,
+                              const BigInt& h,
+                              const std::string& hash)
+   {
+   Algorithm_Factory& af = global_state().algorithm_factory();
+
+   HMAC_DRBG rng(af.make_mac("HMAC(" + hash + ")"), nullptr);
+
+   const size_t qlen = q.bits();
+   const size_t rlen = qlen / 8 + (qlen % 8 ? 1 : 0);
+
+   secure_vector<byte> input = BigInt::encode_1363(x, rlen);
+
+   input += BigInt::encode_1363(h, rlen);
+
+   rng.add_entropy(&input[0], input.size());
+
+   BigInt k;
+
+   secure_vector<byte> kbits(rlen);
+
+   while(k == 0 || k >= q)
+      {
+      rng.randomize(&kbits[0], kbits.size());
+      k = BigInt::decode(kbits) >> (8*rlen - qlen);
+      }
+
+   return k;
+   }
+
+}