OCB cleanup and additional tests

2 files changed, 46 insertions, 51 deletions

diff --git a/src/lib/modes/aead/ocb/ocb.cpp b/src/lib/modes/aead/ocb/ocb.cpp
index 8bb45f217..f3aa8e06c 100644
--- a/src/lib/modes/aead/ocb/ocb.cpp
+++ b/src/lib/modes/aead/ocb/ocb.cpp
@@ -13,12 +13,6 @@
 
 namespace Botan {
 
-namespace {
-
-const size_t BS = 16; // intrinsic to OCB definition
-
-}
-
 // Has to be in Botan namespace so unique_ptr can reference it
 class L_computer
    {
@@ -41,7 +35,8 @@ class L_computer
                                                  size_t block_index,
                                                  size_t blocks) const
          {
-         m_offset_buf.resize(blocks*BS);
+         const size_t BS = m_L_star.size();
+         m_offset_buf.resize(blocks * BS);
 
          for(size_t i = 0; i != blocks; ++i)
             { // could be done in parallel
@@ -80,6 +75,8 @@ secure_vector<byte> ocb_hash(const L_computer& L,
                              const BlockCipher& cipher,
                              const byte ad[], size_t ad_len)
    {
+   const size_t BS = cipher.block_size();
+
    secure_vector<byte> sum(BS);
    secure_vector<byte> offset(BS);
 
@@ -121,16 +118,16 @@ secure_vector<byte> ocb_hash(const L_computer& L,
 
 OCB_Mode::OCB_Mode(BlockCipher* cipher, size_t tag_size) :
    m_cipher(cipher),
+   m_BS(m_cipher->block_size()),
    m_checksum(m_cipher->parallel_bytes()),
-   m_offset(BS),
-   m_ad_hash(BS),
+   m_offset(m_BS),
+   m_ad_hash(m_BS),
    m_tag_size(tag_size)
    {
-   if(m_cipher->block_size() != BS)
-      throw std::invalid_argument("OCB requires a 128 bit cipher so cannot be used with " +
-                                  m_cipher->name());
+   if(BS() != 16)
+      throw std::invalid_argument("OCB is not compatible with " + m_cipher->name());
 
-   if(m_tag_size != 8 && m_tag_size != 12 && m_tag_size != 16)
+   if(m_tag_size % 4 != 0 || m_tag_size < 8 || m_tag_size > BS())
       throw std::invalid_argument("OCB cannot produce a " + std::to_string(m_tag_size) +
                                   " byte tag");
 
@@ -150,7 +147,7 @@ void OCB_Mode::clear()
 
 bool OCB_Mode::valid_nonce_length(size_t length) const
    {
-   return (length > 0 && length < 16);
+   return (length > 0 && length < m_cipher->block_size());
    }
 
 std::string OCB_Mode::name() const
@@ -183,16 +180,16 @@ void OCB_Mode::set_associated_data(const byte ad[], size_t ad_len)
 secure_vector<byte>
 OCB_Mode::update_nonce(const byte nonce[], size_t nonce_len)
    {
-   BOTAN_ASSERT(nonce_len < BS, "Nonce is less than 128 bits");
+   BOTAN_ASSERT(nonce_len < BS(), "OCB nonce is less than cipher block size");
 
-   secure_vector<byte> nonce_buf(BS);
+   secure_vector<byte> nonce_buf(BS());
 
-   copy_mem(&nonce_buf[BS - nonce_len], nonce, nonce_len);
+   copy_mem(&nonce_buf[BS() - nonce_len], nonce, nonce_len);
    nonce_buf[0] = ((tag_size() * 8) % 128) << 1;
-   nonce_buf[BS - nonce_len - 1] = 1;
+   nonce_buf[BS() - nonce_len - 1] = 1;
 
-   const byte bottom = nonce_buf[15] & 0x3F;
-   nonce_buf[15] &= 0xC0;
+   const byte bottom = nonce_buf[BS()-1] & 0x3F;
+   nonce_buf[BS()-1] &= 0xC0;
 
    const bool need_new_stretch = (m_last_nonce != nonce_buf);
 
@@ -202,7 +199,7 @@ OCB_Mode::update_nonce(const byte nonce[], size_t nonce_len)
 
       m_cipher->encrypt(nonce_buf);
 
-      for(size_t i = 0; i != 8; ++i)
+      for(size_t i = 0; i != BS() / 2; ++i)
          nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+1]);
 
       m_stretch = nonce_buf;
@@ -213,8 +210,8 @@ OCB_Mode::update_nonce(const byte nonce[], size_t nonce_len)
    const size_t shift_bytes = bottom / 8;
    const size_t shift_bits  = bottom % 8;
 
-   secure_vector<byte> offset(BS);
-   for(size_t i = 0; i != BS; ++i)
+   secure_vector<byte> offset(BS());
+   for(size_t i = 0; i != BS(); ++i)
       {
       offset[i]  = (m_stretch[i+shift_bytes] << shift_bits);
       offset[i] |= (m_stretch[i+shift_bytes+1] >> (8-shift_bits));
@@ -239,16 +236,14 @@ secure_vector<byte> OCB_Mode::start_raw(const byte nonce[], size_t nonce_len)
 
 void OCB_Encryption::encrypt(byte buffer[], size_t blocks)
    {
-   const L_computer& L = *m_L; // convenient name
-
-   const size_t par_blocks = m_checksum.size() / BS;
+   const size_t par_blocks = m_checksum.size() / BS();
 
    while(blocks)
       {
       const size_t proc_blocks = std::min(blocks, par_blocks);
-      const size_t proc_bytes = proc_blocks * BS;
+      const size_t proc_bytes = proc_blocks * BS();
 
-      const auto& offsets = L.compute_offsets(m_offset, m_block_index, proc_blocks);
+      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
 
       xor_buf(&m_checksum[0], &buffer[0], proc_bytes);
 
@@ -268,9 +263,8 @@ void OCB_Encryption::update(secure_vector<byte>& buffer, size_t offset)
    const size_t sz = buffer.size() - offset;
    byte* buf = &buffer[offset];
 
-   BOTAN_ASSERT(sz % BS == 0, "Input length is an even number of blocks");
-
-   encrypt(buf, sz / BS);
+   BOTAN_ASSERT(sz % BS() == 0, "Input length is an even number of blocks");
+   encrypt(buf, sz / BS());
    }
 
 void OCB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
@@ -281,14 +275,14 @@ void OCB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
 
    if(sz)
       {
-      const size_t final_full_blocks = sz / BS;
-      const size_t remainder_bytes = sz - (final_full_blocks * BS);
+      const size_t final_full_blocks = sz / BS();
+      const size_t remainder_bytes = sz - (final_full_blocks * BS());
 
       encrypt(buf, final_full_blocks);
 
       if(remainder_bytes)
          {
-         BOTAN_ASSERT(remainder_bytes < BS, "Only a partial block left");
+         BOTAN_ASSERT(remainder_bytes < BS(), "Only a partial block left");
          byte* remainder = &buf[sz - remainder_bytes];
 
          xor_buf(&m_checksum[0], &remainder[0], remainder_bytes);
@@ -296,13 +290,13 @@ void OCB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
 
          m_offset ^= m_L->star(); // Offset_*
 
-         secure_vector<byte> zeros(BS);
+         secure_vector<byte> zeros(BS());
          m_cipher->encrypt(m_offset, zeros);
          xor_buf(&remainder[0], &zeros[0], remainder_bytes);
          }
       }
 
-   secure_vector<byte> checksum(BS);
+   secure_vector<byte> checksum(BS());
 
    // fold checksum
    for(size_t i = 0; i != m_checksum.size(); ++i)
@@ -326,20 +320,18 @@ void OCB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
 
 void OCB_Decryption::decrypt(byte buffer[], size_t blocks)
    {
-   const L_computer& L = *m_L; // convenient name
-
    const size_t par_bytes = m_cipher->parallel_bytes();
 
-   BOTAN_ASSERT(par_bytes % BS == 0, "Cipher is parallel in full blocks");
+   BOTAN_ASSERT(par_bytes % BS() == 0, "Cipher is parallel in full blocks");
 
-   const size_t par_blocks = par_bytes / BS;
+   const size_t par_blocks = par_bytes / BS();
 
    while(blocks)
       {
       const size_t proc_blocks = std::min(blocks, par_blocks);
-      const size_t proc_bytes = proc_blocks * BS;
+      const size_t proc_bytes = proc_blocks * BS();
 
-      const auto& offsets = L.compute_offsets(m_offset, m_block_index, proc_blocks);
+      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
 
       xor_buf(&buffer[0], &offsets[0], proc_bytes);
       m_cipher->decrypt_n(&buffer[0], &buffer[0], proc_blocks);
@@ -359,9 +351,9 @@ void OCB_Decryption::update(secure_vector<byte>& buffer, size_t offset)
    const size_t sz = buffer.size() - offset;
    byte* buf = &buffer[offset];
 
-   BOTAN_ASSERT(sz % BS == 0, "Input length is an even number of blocks");
+   BOTAN_ASSERT(sz % BS() == 0, "Input length is an even number of blocks");
 
-   decrypt(buf, sz / BS);
+   decrypt(buf, sz / BS());
    }
 
 void OCB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
@@ -376,20 +368,20 @@ void OCB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
 
    if(remaining)
       {
-      const size_t final_full_blocks = remaining / BS;
-      const size_t final_bytes = remaining - (final_full_blocks * BS);
+      const size_t final_full_blocks = remaining / BS();
+      const size_t final_bytes = remaining - (final_full_blocks * BS());
 
       decrypt(&buf[0], final_full_blocks);
 
       if(final_bytes)
          {
-         BOTAN_ASSERT(final_bytes < BS, "Only a partial block left");
+         BOTAN_ASSERT(final_bytes < BS(), "Only a partial block left");
 
          byte* remainder = &buf[remaining - final_bytes];
 
          m_offset ^= m_L->star(); // Offset_*
 
-         secure_vector<byte> pad(BS);
+         secure_vector<byte> pad(BS());
          m_cipher->encrypt(m_offset, pad); // P_*
 
          xor_buf(&remainder[0], &pad[0], final_bytes);
@@ -399,7 +391,7 @@ void OCB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
          }
       }
 
-   secure_vector<byte> checksum(BS);
+   secure_vector<byte> checksum(BS());
 
    // fold checksum
    for(size_t i = 0; i != m_checksum.size(); ++i)
diff --git a/src/lib/modes/aead/ocb/ocb.h b/src/lib/modes/aead/ocb/ocb.h
index a7293ffcb..02ea0b0a1 100644
--- a/src/lib/modes/aead/ocb/ocb.h
+++ b/src/lib/modes/aead/ocb/ocb.h
@@ -1,6 +1,6 @@
 /*
 * OCB Mode
-* (C) 2013 Jack Lloyd
+* (C) 2013,2014 Jack Lloyd
 *
 * Distributed under the terms of the Botan license
 */
@@ -50,12 +50,13 @@ class BOTAN_DLL OCB_Mode : public AEAD_Mode
       */
       OCB_Mode(BlockCipher* cipher, size_t tag_size);
 
-      void key_schedule(const byte key[], size_t length) override;
+      size_t BS() const { return m_BS; }
 
       // fixme make these private
       std::unique_ptr<BlockCipher> m_cipher;
       std::unique_ptr<L_computer> m_L;
 
+      size_t m_BS;
       size_t m_block_index = 0;
 
       secure_vector<byte> m_checksum;
@@ -64,6 +65,8 @@ class BOTAN_DLL OCB_Mode : public AEAD_Mode
    private:
       secure_vector<byte> start_raw(const byte nonce[], size_t nonce_len) override;
 
+      void key_schedule(const byte key[], size_t length) override;
+
       secure_vector<byte> update_nonce(const byte nonce[], size_t nonce_len);
 
       size_t m_tag_size = 0;