1 files changed, 229 insertions, 0 deletions
diff --git a/src/aead/gcm/gcm.cpp b/src/aead/gcm/gcm.cpp
new file mode 100644
index 000000000..0ff73b034
--- /dev/null
+++ b/src/aead/gcm/gcm.cpp
@@ -0,0 +1,229 @@
+/*
+* GCM Mode Encryption
+* (C) 2013 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/gcm.h>
+#include <botan/ctr.h>
+#include <botan/internal/xor_buf.h>
+#include <botan/loadstor.h>
+
+namespace Botan {
+
+namespace {
+
+secure_vector<byte>
+gcm_multiply(const secure_vector<byte>& x,
+             const secure_vector<byte>& y)
+   {
+   static const u64bit R = 0xE100000000000000;
+
+   u64bit V[2] = {
+      load_be<u64bit>(&y[0], 0),
+      load_be<u64bit>(&y[0], 1)
+   };
+
+   u64bit Z[2] = { 0, 0 };
+
+   for(size_t i = 0; i != 2; ++i)
+      {
+      u64bit X = load_be<u64bit>(&x[0], i);
+
+      for(size_t j = 0; j != 64; ++j)
+         {
+         if(X >> 63)
+            {
+            Z[0] ^= V[0];
+            Z[1] ^= V[1];
+            }
+
+         const u64bit r = (V[1] & 1) ? R : 0;
+
+         V[1] = (V[0] << 63) | (V[1] >> 1);
+         V[0] = (V[0] >> 1) ^ r;
+
+         X <<= 1;
+         }
+      }
+
+   secure_vector<byte> out(16);
+   store_be<u64bit>(&out[0], Z[0], Z[1]);
+   return out;
+   }
+
+void ghash_update(const secure_vector<byte>& H,
+                  secure_vector<byte>& ghash,
+                  const byte input[], size_t length)
+   {
+   const size_t BS = 16;
+
+   /*
+   This assumes if less than block size input then we're just on the
+   final block and should pad with zeros
+   */
+   while(length)
+      {
+      const size_t to_proc = std::min(length, BS);
+
+      xor_buf(&ghash[0], &input[0], to_proc);
+
+      ghash = gcm_multiply(ghash, H);
+
+      input += to_proc;
+      length -= to_proc;
+      }
+   }
+
+void ghash_finalize(const secure_vector<byte>& H,
+                    secure_vector<byte>& ghash,
+                    size_t ad_len, size_t text_len)
+   {
+   secure_vector<byte> final_block(16);
+   store_be<u64bit>(&final_block[0], 8*ad_len, 8*text_len);
+   ghash_update(H, ghash, &final_block[0], final_block.size());
+   }
+
+}
+
+/*
+* GCM_Mode Constructor
+*/
+GCM_Mode::GCM_Mode(BlockCipher* cipher, size_t tag_size) :
+   m_tag_size(tag_size),
+   m_cipher_name(cipher->name()),
+   m_H(16), m_H_ad(16), m_mac(16),
+   m_ad_len(0), m_text_len(0)
+   {
+   if(cipher->block_size() != BS)
+      throw std::invalid_argument("OCB requires a 128 bit cipher so cannot be used with " +
+                                  cipher->name());
+
+   m_ctr.reset(new CTR_BE(cipher)); // CTR_BE takes ownership of cipher
+
+   if(m_tag_size < 8 || m_tag_size > 16)
+      throw Invalid_Argument(name() + ": Bad tag size " + std::to_string(m_tag_size));
+   }
+
+void GCM_Mode::clear()
+   {
+   zeroise(m_H);
+   zeroise(m_H_ad);
+   zeroise(m_mac);
+   zeroise(m_enc_y0);
+   m_ad_len = 0;
+   m_text_len = 0;
+   m_ctr.reset();
+   }
+
+std::string GCM_Mode::name() const
+   {
+   return (m_cipher_name + "/GCM");
+   }
+
+size_t GCM_Mode::update_granularity() const
+   {
+   return 4096; // CTR-BE's internal block size
+   }
+
+Key_Length_Specification GCM_Mode::key_spec() const
+   {
+   return m_ctr->key_spec();
+   }
+
+void GCM_Mode::key_schedule(const byte key[], size_t keylen)
+   {
+   m_ctr->set_key(key, keylen);
+
+   const std::vector<byte> zeros(BS);
+   m_ctr->set_iv(&zeros[0], zeros.size());
+
+   zeroise(m_H);
+   m_ctr->cipher(&m_H[0], &m_H[0], m_H.size());
+   }
+
+void GCM_Mode::set_associated_data(const byte ad[], size_t ad_len)
+   {
+   zeroise(m_H_ad);
+
+   ghash_update(m_H, m_H_ad, ad, ad_len);
+   m_ad_len = ad_len;
+   }
+
+secure_vector<byte> GCM_Mode::start(const byte nonce[], size_t nonce_len)
+   {
+   secure_vector<byte> y0(BS);
+
+   if(nonce_len == 12)
+      {
+      copy_mem(&y0[0], nonce, nonce_len);
+      y0[15] = 1;
+      }
+   else
+      {
+      ghash_update(m_H, y0, nonce, nonce_len);
+      ghash_finalize(m_H, y0, 0, nonce_len);
+      }
+
+   m_ctr->set_iv(&y0[0], y0.size());
+
+   m_enc_y0.resize(BS);
+   m_ctr->encipher(m_enc_y0);
+
+   m_text_len = 0;
+   m_mac = m_H_ad;
+
+   return secure_vector<byte>();
+   }
+
+void GCM_Encryption::update(secure_vector<byte>& buffer)
+   {
+   m_ctr->cipher(&buffer[0], &buffer[0], buffer.size());
+   ghash_update(m_H, m_mac, &buffer[0], buffer.size());
+   m_text_len += buffer.size();
+   }
+
+void GCM_Encryption::finish(secure_vector<byte>& buffer)
+   {
+   update(buffer);
+
+   ghash_finalize(m_H, m_mac, m_ad_len, m_text_len);
+
+   m_mac ^= m_enc_y0;
+
+   buffer += m_mac;
+   }
+
+void GCM_Decryption::update(secure_vector<byte>& buffer)
+   {
+   ghash_update(m_H, m_mac, &buffer[0], buffer.size());
+   m_ctr->cipher(&buffer[0], &buffer[0], buffer.size());
+   m_text_len += buffer.size();
+   }
+
+void GCM_Decryption::finish(secure_vector<byte>& buffer)
+   {
+   BOTAN_ASSERT(buffer.size() >= tag_size(),
+                "Have the tag as part of final input");
+
+   // handle any final input before the tag
+   if(size_t input_length = buffer.size() - tag_size())
+      {
+      ghash_update(m_H, m_mac, &buffer[0], input_length);
+      m_ctr->cipher(&buffer[0], &buffer[0], input_length);
+      m_text_len += input_length;
+      }
+
+   ghash_finalize(m_H, m_mac, m_ad_len, m_text_len);
+
+   m_mac ^= m_enc_y0;
+
+   const byte* included_tag = &buffer[buffer.size() - tag_size()];
+
+   if(!same_mem(&m_mac[0], included_tag, tag_size()))
+      throw Integrity_Failure("GCM tag check failed");
+   }
+
+
+}