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sm4: improve cbc decrypt performance

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Sun Yimin 2022-07-20 11:43:49 +08:00 committed by GitHub
parent 54a06d72e1
commit 572bf6574e
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1 changed files with 14 additions and 12 deletions
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26
sm4/cbc_cipher_asm.go
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@ -43,28 +43,30 @@ func (x *cbc) CryptBlocks(dst, src []byte) {
if len(src) == 0 {
return
}
// For each block, we need to xor the decrypted data with the previous block's ciphertext (the iv).
// To avoid making a copy each time, we loop over the blocks BACKWARDS.
end := len(src)
// Copy the last block of ciphertext in preparation as the new iv.
copy(x.tmp, src[end-BlockSize:end])
start := end - x.b.blocksSize
var temp []byte = make([]byte, x.b.blocksSize)
var batchSrc []byte = make([]byte, x.b.blocksSize)
var batchSrc []byte = make([]byte, x.b.blocksSize+BlockSize)
for start > 0 {
x.b.DecryptBlocks(temp, src[start:end])
for i := 0; i < x.b.batchBlocks; i++ {
xor.XorBytes(dst[end-(i+1)*BlockSize:end-i*BlockSize], temp[x.b.blocksSize-(i+1)*BlockSize:x.b.blocksSize-i*BlockSize], src[end-(i+2)*BlockSize:end-(i+1)*BlockSize])
}
copy(batchSrc, src[start-BlockSize:])
xor.XorBytes(dst[start:], temp, batchSrc)
end = start
start -= x.b.blocksSize
}
copy(batchSrc, src[:end])
x.b.DecryptBlocks(temp, batchSrc)
count := end / BlockSize
for i := count; i > 1; i-- {
xor.XorBytes(dst[end-BlockSize:end], temp[end-BlockSize:end], src[end-2*BlockSize:end-BlockSize])
end -= BlockSize
}
xor.XorBytes(dst[0:end], temp[0:end], x.iv[:])
// Handle remain first blocks
copy(batchSrc[BlockSize:], src[:end])
x.b.DecryptBlocks(temp, batchSrc[BlockSize:])
copy(batchSrc, x.iv)
xor.XorBytes(dst, temp[:end], batchSrc)
// Set the new iv to the first block we copied earlier.
x.iv, x.tmp = x.tmp, x.iv
}