73 lines
1.6 KiB
V
73 lines
1.6 KiB
V
// The source code refers to the go standard library, which will be combined with AES in the future.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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//
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// Counter (CTR) mode.
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//
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// CTR converts a block cipher into a stream cipher by
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// repeatedly encrypting an incrementing counter and
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// xoring the resulting stream of data with the input.
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//
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// See NIST SP 800-38A, pp 13-15
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module cipher
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import crypto.internal.subtle
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struct Ctr {
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mut:
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b Block
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next []byte
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out []byte
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out_used int
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}
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// new_ctr returns a Ctr which encrypts/decrypts using the given Block in
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// 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 []byte) Ctr {
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block_size := b.block_size
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if iv.len != block_size {
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panic('cipher.new_cfb: IV length must be equal block size')
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}
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return Ctr{
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b: b
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out: []byte{len: b.block_size}
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next: iv.clone()
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out_used: block_size
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}
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}
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pub fn (x &Ctr) xor_key_stream(mut dst_ []byte, src_ []byte) {
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unsafe {
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mut dst := *dst_
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mut src := src_
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if dst.len < src.len {
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panic('crypto.cipher.xor_key_stream: output smaller than input')
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}
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if subtle.inexact_overlap(dst[..src.len], src) {
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panic('crypto.cipher.xor_key_stream: invalid buffer overlap')
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}
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for src.len > 0 {
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if x.out_used == x.out.len {
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x.b.encrypt(mut x.out, x.next)
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x.out_used = 0
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}
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n := xor_bytes(mut dst, src, x.out[x.out_used..])
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// increment counter
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for i := x.next.len - 1; i >= 0; i-- {
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x.next[i]++
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if x.next[i] != 0 {
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break
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}
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}
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dst = dst[n..]
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src = src[n..]
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x.out_used += n
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}
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}
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}
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