From 3ad91d3c8c06cf77e69b9a1c80fce236f660956b Mon Sep 17 00:00:00 2001
From: Jack Lloyd <jack@randombit.net>
Date: Mon, 11 Sep 2017 13:12:13 -0400
Subject: Add alternate form for matching OCB ref code

---
 src/lib/modes/aead/ocb/ocb.cpp | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

(limited to 'src/lib/modes/aead/ocb/ocb.cpp')

diff --git a/src/lib/modes/aead/ocb/ocb.cpp b/src/lib/modes/aead/ocb/ocb.cpp
index 7ebb0a5f0..4eb8089b5 100644
--- a/src/lib/modes/aead/ocb/ocb.cpp
+++ b/src/lib/modes/aead/ocb/ocb.cpp
@@ -210,7 +210,12 @@ OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
    secure_vector<uint8_t> nonce_buf(BS);
 
    copy_mem(&nonce_buf[BS - nonce_len], nonce, nonce_len);
+   #if 0
    nonce_buf[0] = ((tag_size()*8) % (BS*8)) << (BS <= 16 ? 1 : 0);
+   #else
+   nonce_buf[0] = (tag_size()*8) << (BS <= 16 ? 1 : 0);
+   #endif
+
    nonce_buf[BS - nonce_len - 1] ^= 1;
 
    const uint8_t bottom = nonce_buf[BS-1] & BOTTOM_MASK;
@@ -244,7 +249,7 @@ OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
                  |     1024 |  524355 |   352 |    9    |
                  +----------+---------+-------+---------+
       */
-
+#if 0
       if(BS == 16)
          {
          for(size_t i = 0; i != BS / 2; ++i)
@@ -265,12 +270,35 @@ OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)
          for(size_t i = 0; i != BS / 2; ++i)
             nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+22]);
          }
+#else
+      nonce_buf.insert(nonce_buf.end(), nonce_buf.begin(), nonce_buf.end());
+
+      if(BS == 16)
+         {
+         for(size_t i = BS; i != BS + (BS / 2); ++i)
+            nonce_buf[i] ^= nonce_buf[i+1];
+         }
+      else if(BS == 24)
+         {
+         for(size_t i = BS; i != BS + (BS / 2); ++i)
+            nonce_buf[i] ^= nonce_buf[i+5];
+         }
+      else if(BS == 32)
+         {
+         for(size_t i = BS; i != BS + (BS / 2); ++i)
+            nonce_buf[i] ^= (nonce_buf[i] << 1) ^ (nonce_buf[i+1] >> 7);
+         }
+      else if(BS == 64)
+         {
+         for(size_t i = BS; i != BS + (BS / 2); ++i)
+            nonce_buf[i] ^= nonce_buf[i+22];
+         }
+#endif
 
       m_stretch = nonce_buf;
       }
 
    // now set the offset from stretch and bottom
-
    const size_t shift_bytes = bottom / 8;
    const size_t shift_bits  = bottom % 8;
 
@@ -373,9 +401,7 @@ void OCB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
    secure_vector<uint8_t> mac = m_offset;
    mac ^= checksum;
    mac ^= m_L->dollar();
-
    m_cipher->encrypt(mac);
-
    mac ^= m_ad_hash;
 
    buffer += std::make_pair(mac.data(), tag_size());
-- 
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