v/vlib/crypto/cipher/cfb.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.
//
// 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
		}
	}
}