v/vlib/crypto/cipher/ofb.v

65 lines
1.4 KiB
V

// 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.
//
// OFB (Output Feedback) Mode.
// See NIST SP 800-38A, pp 13-15
module cipher
import crypto.internal.subtle
struct Ofb {
mut:
b Block
next []byte
out []byte
out_used int
}
// new_ofb returns a Ofb that encrypts or decrypts using the block cipher b
// in output feedback mode. The initialization vector iv's length must be equal
// to b's block size.
pub fn new_ofb(b Block, iv []byte) Ofb {
block_size := b.block_size
if iv.len != block_size {
panic('cipher.new_ofb: IV length must be equal block size')
}
mut x := Ofb{
b: b
out: []byte{len: b.block_size}
next: []byte{len: b.block_size}
out_used: block_size
}
copy(mut x.next, iv)
return x
}
pub fn (mut x Ofb) 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
}
copy(mut x.next, x.out)
n := xor_bytes(mut dst, src, x.out)
dst = dst[n..]
src = src[n..]
x.out_used += n
}
}
}