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v/vlib/crypto/cipher/cfb.v

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// The source code refers to the go standard library, which will be combined with AES in the future.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
//
// Cipher Feedback Mode (CFB).
// See NIST SP 800-38A, pp 11-13
module cipher
import crypto.internal.subtle
struct Cfb {
mut:
b Block
next []byte
out []byte
out_used int
decrypt bool
}
// new_cfb_encrypter returns a `Cfb` which encrypts with cipher feedback mode,
// using the given Block. The iv must be the same length as the Block's block
// size
pub fn new_cfb_encrypter(b Block, iv []byte) Cfb {
return new_cfb(b, iv, false)
}
// new_cfb_decrypter returns a `Cfb` which decrypts with cipher feedback mode,
// using the given Block. The iv must be the same length as the Block's block
// size
pub fn new_cfb_decrypter(b Block, iv []byte) Cfb {
return new_cfb(b, iv, true)
}
fn new_cfb(b Block, iv []byte, decrypt bool) Cfb {
block_size := b.block_size
if iv.len != block_size {
panic('cipher.new_cfb: IV length must be equal block size')
}
x := Cfb{
b: b
out: []byte{len: b.block_size}
next: []byte{len: b.block_size}
out_used: block_size
decrypt: decrypt
}
copy(x.next, iv)
return x
}
pub fn (x &Cfb) xor_key_stream(mut dst_ []byte, src_ []byte) {
unsafe {
mut dst := *dst_
mut src := src_
if dst.len < src.len {
panic('crypto.cipher.xor_key_stream: output smaller than input')
}
if subtle.inexact_overlap(dst[..src.len], src) {
panic('crypto.cipher.xor_key_stream: invalid buffer overlap')
}
for src.len > 0 {
if x.out_used == x.out.len {
x.b.encrypt(mut x.out, x.next)
x.out_used = 0
}
if x.decrypt {
copy(x.next[x.out_used..], src)
}
n := xor_bytes(mut dst, src, x.out[x.out_used..])
if !x.decrypt {
copy(x.next[x.out_used..], dst)
}
dst = dst[n..]
src = src[n..]
x.out_used += n
}
}
}