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cfb8.go
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cfb8.go
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package cipher
import (
"crypto/cipher"
"github.com/deatil/go-cryptobin/tool/alias"
)
// CFB stream with 8 bit segment size
// See http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
type cfb8 struct {
b cipher.Block
blockSize int
in []byte
out []byte
decrypt bool
}
func (x *cfb8) XORKeyStream(dst, src []byte) {
if len(dst) < len(src) {
panic("cryptobin/cfb8: output smaller than input")
}
if alias.InexactOverlap(dst[:len(src)], src) {
panic("cryptobin/cfb8: invalid buffer overlap")
}
for i := range src {
x.b.Encrypt(x.out, x.in)
copy(x.in[:x.blockSize-1], x.in[1:])
if x.decrypt {
x.in[x.blockSize-1] = src[i]
}
dst[i] = src[i] ^ x.out[0]
if !x.decrypt {
x.in[x.blockSize-1] = dst[i]
}
}
}
func NewCFB8(block cipher.Block, iv []byte, decrypt bool) cipher.Stream {
blockSize := block.BlockSize()
if len(iv) != blockSize {
// stack trace will indicate whether it was de or encryption
panic("cryptobin/cfb8: IV length must equal block size")
}
x := &cfb8{
b: block,
blockSize: blockSize,
out: make([]byte, blockSize),
in: make([]byte, blockSize),
decrypt: decrypt,
}
copy(x.in, iv)
return x
}
// NewCFB8Encrypter returns a Stream which encrypts with cipher feedback mode
// (segment size = 8), using the given Block. The iv must be the same length as
// the Block's block size.
func NewCFB8Encrypter(block cipher.Block, iv []byte) cipher.Stream {
return NewCFB8(block, iv, false)
}
// NewCFB8Decrypter returns a Stream which decrypts with cipher feedback mode
// (segment size = 8), using the given Block. The iv must be the same length as
// the Block's block size.
func NewCFB8Decrypter(block cipher.Block, iv []byte) cipher.Stream {
return NewCFB8(block, iv, true)
}