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Update comments in XTS

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This commit is contained in:
Jeffrey Walton 2019-10-13 10:42:10 -04:00
parent d36a0b1a54
commit 74f265aff3
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GPG Key ID: B36AB348921B1838
1 changed files with 16 additions and 13 deletions
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29
xts.cpp
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@ -1,4 +1,12 @@
// xts.cpp - written and placed in the public domain by Jeffrey Walton
//
// The best performance is achieved on machines with AES hardware acceleration.
// However, 64-bit machines without hardware acceleration profit the most with
// separate calls to ProcessBlock followed by XorBuffer rather than a single
// call to AdvancedProcessBlocks. That's because we did not parallelize, and
// XorBuffer uses SSE2 and ASIMD when available. Parallelizing slowed things
// down due to copying m_register for GF_Double. XorBuffer profits without
// AESNI and friends since XorBuffer only uses load, store and xor.
#include "pch.h"
@ -327,12 +335,10 @@ size_t XTS_ModeBase::ProcessLastPlainBlock(byte *outString, size_t outLength, co
// merge the tweak into the input block
XorBuffer(m_workspace, inString, m_register, blockSize);
// encrypt one block, merge the tweak into the output block
// GetBlockCipher().AdvancedProcessBlocks(m_workspace, m_register, outString, blockSize, 0);
// encrypt one block
GetBlockCipher().ProcessBlock(m_workspace);
// merge the tweak into the input block
// merge the tweak into the output block
XorBuffer(outString, m_workspace, m_register, blockSize);
// Multiply T by alpha
@ -354,8 +360,11 @@ size_t XTS_ModeBase::ProcessLastPlainBlock(byte *outString, size_t outLength, co
// merge the tweak into the input block
XorBuffer(m_workspace, m_register, blockSize);
// encrypt the final block, merge the tweak into the output block
GetBlockCipher().AdvancedProcessBlocks(m_workspace, m_register, outString-blockSize, blockSize, 0);
// encrypt one block
GetBlockCipher().ProcessBlock(m_workspace);
// merge the tweak into the previous output block
XorBuffer(outString-blockSize, m_workspace, m_register, blockSize);
return outLength;
}
@ -399,9 +408,6 @@ size_t XTS_ModeBase::ProcessLastCipherBlock(byte *outString, size_t outLength, c
// merge the tweak into the input block
XorBuffer(m_workspace, inString-blockSize, poly2, blockSize);
// encrypt one block, merge the tweak into the output block
// GetBlockCipher().AdvancedProcessBlocks(m_workspace, poly2, m_workspace, blockSize, 0);
// encrypt one block
GetBlockCipher().ProcessBlock(m_workspace);
@ -420,12 +426,9 @@ size_t XTS_ModeBase::ProcessLastCipherBlock(byte *outString, size_t outLength, c
inString -= blockSize;
outString -= blockSize;
// merge the tweak into the output block
// merge the tweak into the input block
XorBuffer(m_workspace, outString, poly1, blockSize);
// encrypt one block, merge the tweak into the input block
// GetBlockCipher().AdvancedProcessBlocks(m_workspace, poly1, outString, blockSize, 0);
// encrypt one block
GetBlockCipher().ProcessBlock(m_workspace);