From 941a184703fbdb979965d4ef9328a99535e692ae Mon Sep 17 00:00:00 2001
From: lloyd <lloyd@randombit.net>
Date: Sat, 17 Apr 2010 17:41:33 +0000
Subject: Add Comb4P hash combiner, as described in Anja Lehmann's thesis.

---
 src/hash/comb4p/comb4p.cpp | 104 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 src/hash/comb4p/comb4p.cpp

(limited to 'src/hash/comb4p/comb4p.cpp')

diff --git a/src/hash/comb4p/comb4p.cpp b/src/hash/comb4p/comb4p.cpp
new file mode 100644
index 000000000..ff6cb43a9
--- /dev/null
+++ b/src/hash/comb4p/comb4p.cpp
@@ -0,0 +1,104 @@
+/**
+* Comb4P hash combiner
+* (C) 2010 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/comb4p.h>
+#include <botan/internal/xor_buf.h>
+#include <stdexcept>
+
+namespace Botan {
+
+namespace {
+
+u32bit comb4p_block_size(const HashFunction* h1,
+                         const HashFunction* h2)
+   {
+   if(h1->HASH_BLOCK_SIZE == h2->HASH_BLOCK_SIZE)
+      return h1->HASH_BLOCK_SIZE;
+
+   /*
+   * Return LCM of the block sizes? This would probably be OK for
+   * HMAC, which is the main thing relying on knowing the block size.
+   */
+   return 0;
+   }
+
+void comb4p_round(MemoryRegion<byte>& out,
+                  const MemoryRegion<byte>& in,
+                  byte round_no,
+                  HashFunction* h1,
+                  HashFunction* h2)
+   {
+   h1->update(round_no);
+   h2->update(round_no);
+
+   h1->update(&in[0], in.size());
+   h2->update(&in[0], in.size());
+
+   SecureVector<byte> h_buf = h1->final();
+   xor_buf(&out[0], &h_buf[0], std::min(out.size(), h_buf.size()));
+
+   h_buf = h2->final();
+   xor_buf(&out[0], &h_buf[0], std::min(out.size(), h_buf.size()));
+   }
+
+}
+
+Comb4P::Comb4P(HashFunction* h1, HashFunction* h2) :
+   HashFunction(h1->OUTPUT_LENGTH + h2->OUTPUT_LENGTH,
+                comb4p_block_size(h1, h2)),
+   hash1(h1), hash2(h2)
+   {
+#if 0
+   if(hash1->OUTPUT_LENGTH != hash2->OUTPUT_LENGTH)
+      throw std::invalid_argument("Comb4P: Incompatible hashes " +
+                                  hash1->name() + " and " +
+                                  hash2->name());
+#endif
+
+   clear();
+   }
+
+void Comb4P::clear()
+   {
+   hash1->clear();
+   hash2->clear();
+
+   // Prep for processing next message, if any
+   hash1->update(0);
+   hash2->update(0);
+   }
+
+void Comb4P::add_data(const byte input[], u32bit length)
+   {
+   hash1->update(input, length);
+   hash2->update(input, length);
+   }
+
+void Comb4P::final_result(byte out[])
+   {
+   SecureVector<byte> h1 = hash1->final();
+   SecureVector<byte> h2 = hash2->final();
+
+   // First round
+   xor_buf(&h1[0], &h2[0], std::min(h1.size(), h2.size()));
+
+   // Second round
+   comb4p_round(h2, h1, 1, hash1, hash2);
+
+   // Third round
+   comb4p_round(h1, h2, 2, hash1, hash2);
+
+   copy_mem(out            , &h1[0], h1.size());
+   copy_mem(out + h1.size(), &h2[0], h2.size());
+
+   // Prep for processing next message, if any
+   hash1->update(0);
+   hash2->update(0);
+   }
+
+}
+
-- 
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