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v/vlib/crypto/cipher/ctr.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.
//
// Counter (CTR) mode.
//
// CTR converts a block cipher into a stream cipher by
// repeatedly encrypting an incrementing counter and
// xoring the resulting stream of data with the input.
//
// See NIST SP 800-38A, pp 13-15
module cipher
import crypto.internal.subtle
struct Ctr {
mut:
b Block
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next []u8
out []u8
out_used int
}
// free the resources taken by the Ctr `c`
[unsafe]
pub fn (mut x Ctr) free() {
$if prealloc {
return
}
unsafe {
// x.b.free() TODO add?
x.out.free()
x.next.free()
}
}
// new_ctr returns a Ctr which encrypts/decrypts using the given Block in
// counter mode. The length of iv must be the same as the Block's block size.
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pub fn new_ctr(b Block, iv []u8) Ctr {
block_size := b.block_size
if iv.len != block_size {
panic('cipher.new_cfb: IV length must be equal block size')
}
return Ctr{
b: b
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out: []u8{len: b.block_size}
next: iv.clone()
out_used: block_size
}
}
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pub fn (x &Ctr) xor_key_stream(mut dst_ []u8, src_ []u8) {
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
}
n := xor_bytes(mut dst, src, x.out[x.out_used..])
// increment counter
for i := x.next.len - 1; i >= 0; i-- {
x.next[i]++
if x.next[i] != 0 {
break
}
}
dst = dst[n..]
src = src[n..]
x.out_used += n
}
}
}