Support larger block sizes in OCB

This doesn't match the draft-3 test vectors and may be bogus.

[ci skip]

2 files changed, 134 insertions, 59 deletions

diff --git a/src/lib/modes/aead/ocb/ocb.cpp b/src/lib/modes/aead/ocb/ocb.cpp
index aa8532526..7ebb0a5f0 100644
--- a/src/lib/modes/aead/ocb/ocb.cpp
+++ b/src/lib/modes/aead/ocb/ocb.cpp
@@ -1,6 +1,6 @@
 /*
 * OCB Mode
-* (C) 2013 Jack Lloyd
+* (C) 2013,2017 Jack Lloyd
 * (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
@@ -30,16 +30,18 @@ class L_computer
 
       const secure_vector<uint8_t>& operator()(size_t i) const { return get(i); }
 
-      const secure_vector<uint8_t>& compute_offsets(secure_vector<uint8_t>& offset,
-                                                 size_t block_index,
-                                                 size_t blocks) const
+      const secure_vector<uint8_t>&
+      compute_offsets(secure_vector<uint8_t>& offset,
+                      size_t block_index,
+                      size_t blocks,
+                      size_t BS) const
          {
-         m_offset_buf.resize(blocks * 16);
+         m_offset_buf.resize(blocks * BS);
 
          for(size_t i = 0; i != blocks; ++i)
             { // could be done in parallel
             offset ^= get(ctz(block_index + 1 + i));
-            copy_mem(&m_offset_buf[16*i], offset.data(), 16);
+            copy_mem(&m_offset_buf[BS*i], offset.data(), BS);
             }
 
          return m_offset_buf;
@@ -72,16 +74,17 @@ namespace {
 * OCB's HASH
 */
 secure_vector<uint8_t> ocb_hash(const L_computer& L,
-                             const BlockCipher& cipher,
-                             const uint8_t ad[], size_t ad_len)
+                                const BlockCipher& cipher,
+                                const uint8_t ad[], size_t ad_len)
    {
-   secure_vector<uint8_t> sum(16);
-   secure_vector<uint8_t> offset(16);
+   const size_t BS = cipher.block_size();
+   secure_vector<uint8_t> sum(BS);
+   secure_vector<uint8_t> offset(BS);
 
-   secure_vector<uint8_t> buf(16);
+   secure_vector<uint8_t> buf(BS);
 
-   const size_t ad_blocks = (ad_len / 16);
-   const size_t ad_remainder = (ad_len % 16);
+   const size_t ad_blocks = (ad_len / BS);
+   const size_t ad_remainder = (ad_len % BS);
 
    for(size_t i = 0; i != ad_blocks; ++i)
       {
@@ -89,7 +92,7 @@ secure_vector<uint8_t> ocb_hash(const L_computer& L,
       offset ^= L(ctz(i+1));
 
       buf = offset;
-      xor_buf(buf.data(), &ad[16*i], 16);
+      xor_buf(buf.data(), &ad[BS*i], BS);
 
       cipher.encrypt(buf);
 
@@ -101,8 +104,8 @@ secure_vector<uint8_t> ocb_hash(const L_computer& L,
       offset ^= L.star();
 
       buf = offset;
-      xor_buf(buf.data(), &ad[16*ad_blocks], ad_remainder);
-      buf[ad_len % 16] ^= 0x80;
+      xor_buf(buf.data(), &ad[BS*ad_blocks], ad_remainder);
+      buf[ad_len % BS] ^= 0x80;
 
       cipher.encrypt(buf);
 
@@ -117,14 +120,21 @@ secure_vector<uint8_t> ocb_hash(const L_computer& L,
 OCB_Mode::OCB_Mode(BlockCipher* cipher, size_t tag_size) :
    m_cipher(cipher),
    m_checksum(m_cipher->parallel_bytes()),
-   m_offset(16),
-   m_ad_hash(16),
+   m_offset(m_cipher->block_size()),
+   m_ad_hash(m_cipher->block_size()),
    m_tag_size(tag_size)
    {
-   if(m_cipher->block_size() != 16)
-      throw Invalid_Argument("OCB requires 128 bit cipher");
+   const size_t BS = m_cipher->block_size();
 
-   if(m_tag_size % 4 != 0 || m_tag_size < 8 || m_tag_size > 16)
+   /*
+   * draft-krovetz-ocb-wide-d1 specifies OCB for several other block
+   * sizes but only 128, 192, 256 and 512 bit are currently supported
+   * by this implementation.
+   */
+   if(BS != 16 && BS != 24 && BS != 32 && BS != 64)
+      throw Invalid_Argument("OCB does not support cipher " + m_cipher->name());
+
+   if(m_tag_size % 4 != 0 || m_tag_size < 8 || m_tag_size > BS || m_tag_size > 32)
       throw Invalid_Argument("Invalid OCB tag length");
    }
 
@@ -149,12 +159,17 @@ void OCB_Mode::reset()
 
 bool OCB_Mode::valid_nonce_length(size_t length) const
    {
-   return (length > 0 && length < m_cipher->block_size());
+   if(length == 0)
+      return false;
+   if(m_cipher->block_size() == 16)
+      return length < 16;
+   else
+      return length < (m_cipher->block_size() - 1);
    }
 
 std::string OCB_Mode::name() const
    {
-   return m_cipher->name() + "/OCB"; // include tag size
+   return m_cipher->name() + "/OCB"; // include tag size?
    }
 
 size_t OCB_Mode::update_granularity() const
@@ -182,16 +197,24 @@ void OCB_Mode::set_associated_data(const uint8_t ad[], size_t ad_len)
 secure_vector<uint8_t>
 OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
    {
-   BOTAN_ASSERT(nonce_len < 16, "OCB nonce is less than cipher block size");
+   const size_t BS = m_cipher->block_size();
+
+   BOTAN_ASSERT(BS == 16 || BS == 24 || BS == 32 || BS == 64,
+                "OCB block size is supported");
+
+   const size_t MASKLEN = (BS == 16 ? 6 : ((BS == 24) ? 7 : 8));
+
+   const uint8_t BOTTOM_MASK =
+      static_cast<uint8_t>((static_cast<uint16_t>(1) << MASKLEN) - 1);
 
-   secure_vector<uint8_t> nonce_buf(16);
+   secure_vector<uint8_t> nonce_buf(BS);
 
-   copy_mem(&nonce_buf[16 - nonce_len], nonce, nonce_len);
-   nonce_buf[0] = ((tag_size() * 8) % 128) << 1;
-   nonce_buf[16 - nonce_len - 1] = 1;
+   copy_mem(&nonce_buf[BS - nonce_len], nonce, nonce_len);
+   nonce_buf[0] = ((tag_size()*8) % (BS*8)) << (BS <= 16 ? 1 : 0);
+   nonce_buf[BS - nonce_len - 1] ^= 1;
 
-   const uint8_t bottom = nonce_buf[16-1] & 0x3F;
-   nonce_buf[16-1] &= 0xC0;
+   const uint8_t bottom = nonce_buf[BS-1] & BOTTOM_MASK;
+   nonce_buf[BS-1] &= ~BOTTOM_MASK;
 
    const bool need_new_stretch = (m_last_nonce != nonce_buf);
 
@@ -201,8 +224,47 @@ OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
 
       m_cipher->encrypt(nonce_buf);
 
-      for(size_t i = 0; i != 16 / 2; ++i)
-         nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+1]);
+      /*
+      The loop bounds (BS vs BS/2) are derived from the relation
+      between the block size and the MASKLEN. Using the terminology
+      of draft-krovetz-ocb-wide, we have to derive enough bits in
+      ShiftedKtop to read up to BLOCKLEN+bottom bits from Stretch.
+
+                 +----------+---------+-------+---------+
+                 | BLOCKLEN | RESIDUE | SHIFT | MASKLEN |
+                 +----------+---------+-------+---------+
+                 |       32 |     141 |    17 |    4    |
+                 |       64 |      27 |    25 |    5    |
+                 |       96 |    1601 |    33 |    6    |
+                 |      128 |     135 |     8 |    6    |
+                 |      192 |     135 |    40 |    7    |
+                 |      256 |    1061 |     1 |    8    |
+                 |      384 |    4109 |    80 |    8    |
+                 |      512 |     293 |   176 |    8    |
+                 |     1024 |  524355 |   352 |    9    |
+                 +----------+---------+-------+---------+
+      */
+
+      if(BS == 16)
+         {
+         for(size_t i = 0; i != BS / 2; ++i)
+            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+1]);
+         }
+      else if(BS == 24)
+         {
+         for(size_t i = 0; i != 16; ++i)
+            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+5]);
+         }
+      else if(BS == 32)
+         {
+         for(size_t i = 0; i != BS; ++i)
+            nonce_buf.push_back(nonce_buf[i] ^ (nonce_buf[i] << 1) ^ (nonce_buf[i+1] >> 7));
+         }
+      else if(BS == 64)
+         {
+         for(size_t i = 0; i != BS / 2; ++i)
+            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+22]);
+         }
 
       m_stretch = nonce_buf;
       }
@@ -212,8 +274,10 @@ OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
    const size_t shift_bytes = bottom / 8;
    const size_t shift_bits  = bottom % 8;
 
-   secure_vector<uint8_t> offset(16);
-   for(size_t i = 0; i != 16; ++i)
+   BOTAN_ASSERT(m_stretch.size() >= BS + shift_bytes + 1, "Size ok");
+
+   secure_vector<uint8_t> 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));
@@ -236,16 +300,17 @@ void OCB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
 
 void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)
    {
-   const size_t par_blocks = m_checksum.size() / 16;
+   const size_t BS = m_cipher->block_size();
+   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 * 16;
+      const size_t proc_bytes = proc_blocks * BS;
 
       BOTAN_ASSERT(m_L, "A key was set");
 
-      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
+      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks, BS);
 
       xor_buf(m_checksum.data(), buffer, proc_bytes);
 
@@ -261,27 +326,30 @@ void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)
 
 size_t OCB_Encryption::process(uint8_t buf[], size_t sz)
    {
-   BOTAN_ASSERT(sz % 16 == 0, "Invalid OCB input size");
-   encrypt(buf, sz / 16);
+   const size_t BS = m_cipher->block_size();
+   BOTAN_ASSERT(sz % BS == 0, "Invalid OCB input size");
+   encrypt(buf, sz / BS);
    return sz;
    }
 
 void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
    {
+   const size_t BS = m_cipher->block_size();
+
    BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
    const size_t sz = buffer.size() - offset;
    uint8_t* buf = buffer.data() + offset;
 
    if(sz)
       {
-      const size_t final_full_blocks = sz / 16;
-      const size_t remainder_bytes = sz - (final_full_blocks * 16);
+      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 < 16, "Only a partial block left");
+         BOTAN_ASSERT(remainder_bytes < BS, "Only a partial block left");
          uint8_t* remainder = &buf[sz - remainder_bytes];
 
          xor_buf(m_checksum.data(), remainder, remainder_bytes);
@@ -289,13 +357,13 @@ void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
 
          m_offset ^= m_L->star(); // Offset_*
 
-         secure_vector<uint8_t> zeros(16);
+         secure_vector<uint8_t> zeros(BS);
          m_cipher->encrypt(m_offset, zeros);
          xor_buf(remainder, zeros.data(), remainder_bytes);
          }
       }
 
-   secure_vector<uint8_t> checksum(16);
+   secure_vector<uint8_t> checksum(BS);
 
    // fold checksum
    for(size_t i = 0; i != m_checksum.size(); ++i)
@@ -319,18 +387,19 @@ void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
 
 void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)
    {
+   const size_t BS = m_cipher->block_size();
    const size_t par_bytes = m_cipher->parallel_bytes();
 
-   BOTAN_ASSERT(par_bytes % 16 == 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 / 16;
+   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 * 16;
+      const size_t proc_bytes = proc_blocks * BS;
 
-      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks);
+      const auto& offsets = m_L->compute_offsets(m_offset, m_block_index, proc_blocks, BS);
 
       xor_buf(buffer, offsets.data(), proc_bytes);
       m_cipher->decrypt_n(buffer, buffer, proc_blocks);
@@ -346,13 +415,16 @@ void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)
 
 size_t OCB_Decryption::process(uint8_t buf[], size_t sz)
    {
-   BOTAN_ASSERT(sz % 16 == 0, "Invalid OCB input size");
-   decrypt(buf, sz / 16);
+   const size_t BS = m_cipher->block_size();
+   BOTAN_ASSERT(sz % BS == 0, "Invalid OCB input size");
+   decrypt(buf, sz / BS);
    return sz;
    }
 
 void OCB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
    {
+   const size_t BS = m_cipher->block_size();
+
    BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
    const size_t sz = buffer.size() - offset;
    uint8_t* buf = buffer.data() + offset;
@@ -363,20 +435,20 @@ void OCB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
 
    if(remaining)
       {
-      const size_t final_full_blocks = remaining / 16;
-      const size_t final_bytes = remaining - (final_full_blocks * 16);
+      const size_t final_full_blocks = remaining / BS;
+      const size_t final_bytes = remaining - (final_full_blocks * BS);
 
       decrypt(buf, final_full_blocks);
 
       if(final_bytes)
          {
-         BOTAN_ASSERT(final_bytes < 16, "Only a partial block left");
+         BOTAN_ASSERT(final_bytes < BS, "Only a partial block left");
 
          uint8_t* remainder = &buf[remaining - final_bytes];
 
          m_offset ^= m_L->star(); // Offset_*
 
-         secure_vector<uint8_t> pad(16);
+         secure_vector<uint8_t> pad(BS);
          m_cipher->encrypt(m_offset, pad); // P_*
 
          xor_buf(remainder, pad.data(), final_bytes);
@@ -386,7 +458,7 @@ void OCB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
          }
       }
 
-   secure_vector<uint8_t> checksum(16);
+   secure_vector<uint8_t> 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 174812ee3..69f5fde60 100644
--- a/src/lib/modes/aead/ocb/ocb.h
+++ b/src/lib/modes/aead/ocb/ocb.h
@@ -22,6 +22,9 @@ class L_computer;
 *
 * @see "The OCB Authenticated-Encryption Algorithm" RFC 7253
 *      https://tools.ietf.org/html/rfc7253
+* @see "OCB For Block Ciphers Without 128-Bit Blocks"
+*      (draft-krovetz-ocb-wide-d3) for the extension of OCB to
+*      block ciphers with larger block sizes.
 * @see Free Licenses http://www.cs.ucdavis.edu/~rogaway/ocb/license.htm
 * @see OCB home page http://www.cs.ucdavis.edu/~rogaway/ocb
 */
@@ -47,7 +50,7 @@ class BOTAN_DLL OCB_Mode : public AEAD_Mode
       ~OCB_Mode();
    protected:
       /**
-      * @param cipher the 128-bit block cipher to use
+      * @param cipher the block cipher to use
       * @param tag_size is how big the auth tag will be
       */
       OCB_Mode(BlockCipher* cipher, size_t tag_size);
@@ -68,7 +71,7 @@ class BOTAN_DLL OCB_Mode : public AEAD_Mode
 
       secure_vector<uint8_t> update_nonce(const uint8_t nonce[], size_t nonce_len);
 
-      size_t m_tag_size = 0;
+      const size_t m_tag_size = 0;
       secure_vector<uint8_t> m_last_nonce;
       secure_vector<uint8_t> m_stretch;
    };
@@ -77,7 +80,7 @@ class BOTAN_DLL OCB_Encryption final : public OCB_Mode
    {
    public:
       /**
-      * @param cipher the 128-bit block cipher to use
+      * @param cipher the block cipher to use
       * @param tag_size is how big the auth tag will be
       */
       OCB_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
@@ -99,7 +102,7 @@ class BOTAN_DLL OCB_Decryption final : public OCB_Mode
    {
    public:
       /**
-      * @param cipher the 128-bit block cipher to use
+      * @param cipher the block cipher to use
       * @param tag_size is how big the auth tag will be
       */
       OCB_Decryption(BlockCipher* cipher, size_t tag_size = 16) :