Add Comb4P hash combiner, as described in Anja Lehmann's thesis.

3 files changed, 152 insertions, 0 deletions

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);
+   }
+
+}
+
diff --git a/src/hash/comb4p/comb4p.h b/src/hash/comb4p/comb4p.h
new file mode 100644
index 000000000..ce66bb9c9
--- /dev/null
+++ b/src/hash/comb4p/comb4p.h
@@ -0,0 +1,47 @@
+/**
+* Comb4P hash combiner
+* (C) 2010 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#ifndef BOTAN_COMB4P_H__
+#define BOTAN_COMB4P_H__
+
+#include <botan/hash.h>
+
+namespace Botan {
+
+/**
+* Combines two hash functions using a Feistel scheme. Described in
+* "On the Security of Hash Function Combiners", Anja Lehmann
+*/
+class Comb4P : public HashFunction
+   {
+   public:
+      Comb4P(HashFunction* h1, HashFunction* h2);
+
+      ~Comb4P() { delete hash1; delete hash2; }
+
+      HashFunction* clone() const
+         {
+         return new Comb4P(hash1->clone(), hash2->clone());
+         }
+
+      std::string name() const
+         {
+         return "Comb4P(" + hash1->name() + "," + hash2->name() + ")";
+         }
+
+      void clear();
+   private:
+      void add_data(const byte input[], u32bit length);
+      void final_result(byte out[]);
+
+      HashFunction* hash1;
+      HashFunction* hash2;
+   };
+
+}
+
+#endif
diff --git a/src/hash/comb4p/info.txt b/src/hash/comb4p/info.txt
new file mode 100644
index 000000000..9ccf0223a
--- /dev/null
+++ b/src/hash/comb4p/info.txt
@@ -0,0 +1 @@
+define COMB4P