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78 lines
1.9 KiB
Go
78 lines
1.9 KiB
Go
//go:build (amd64 && !generic) || (arm64 && !generic)
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// +build amd64,!generic arm64,!generic
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package sm4
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import (
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"crypto/cipher"
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"github.com/emmansun/gmsm/internal/subtle"
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"github.com/emmansun/gmsm/internal/xor"
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)
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// Assert that sm4CipherAsm implements the cbcDecAble interfaces.
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var _ cbcDecAble = (*sm4CipherAsm)(nil)
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type cbc struct {
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b *sm4CipherAsm
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iv []byte
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tmp []byte
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}
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func (b *sm4CipherAsm) NewCBCDecrypter(iv []byte) cipher.BlockMode {
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var c cbc
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c.b = b
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c.iv = make([]byte, BlockSize)
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c.tmp = make([]byte, BlockSize)
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copy(c.iv, iv)
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return &c
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}
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func (x *cbc) BlockSize() int { return BlockSize }
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func (x *cbc) CryptBlocks(dst, src []byte) {
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if len(src)%BlockSize != 0 {
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panic("cipher: input not full blocks")
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}
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if len(dst) < len(src) {
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panic("cipher: output smaller than input")
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}
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if subtle.InexactOverlap(dst[:len(src)], src) {
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panic("cipher: invalid buffer overlap")
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}
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if len(src) == 0 {
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return
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}
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end := len(src)
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copy(x.tmp, src[end-BlockSize:end])
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start := end - x.b.blocksSize
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var temp []byte = make([]byte, x.b.blocksSize)
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var batchSrc []byte = make([]byte, x.b.blocksSize)
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for start > 0 {
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x.b.DecryptBlocks(temp, src[start:end])
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for i := 0; i < x.b.batchBlocks; i++ {
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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])
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}
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end = start
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start -= x.b.blocksSize
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}
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copy(batchSrc, src[:end])
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x.b.DecryptBlocks(temp, batchSrc)
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count := end / BlockSize
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for i := count; i > 1; i-- {
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xor.XorBytes(dst[end-BlockSize:end], temp[end-BlockSize:end], src[end-2*BlockSize:end-BlockSize])
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end -= BlockSize
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}
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xor.XorBytes(dst[0:end], temp[0:end], x.iv[:])
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// Set the new iv to the first block we copied earlier.
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x.iv, x.tmp = x.tmp, x.iv
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}
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func (x *cbc) SetIV(iv []byte) {
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if len(iv) != BlockSize {
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panic("cipher: incorrect length IV")
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}
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copy(x.iv[:], iv)
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}
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