v/vlib/crypto/rc4/rc4.v

84 lines
1.9 KiB
Go
Raw Normal View History

2019-07-26 16:48:49 +02:00
// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
// Package rc4 implements RC4 encryption, as defined in Bruce Schneier's
// Applied Cryptography.
//
// RC4 is cryptographically broken and should not be used for secure
// applications.
// Adapted from: https://github.com/golang/go/blob/master/src/crypto/rc4
module rc4
import crypto.internal.subtle
// A Cipher is an instance of RC4 using a particular key.
struct Cipher {
mut:
s []u32
i u8
j u8
}
// new_cipher creates and returns a new Cipher. The key argument should be the
// RC4 key, at least 1 byte and at most 256 bytes.
pub fn new_cipher(key []byte) ?Cipher {
if key.len < 1 || key.len > 256 {
return error('crypto.rc4: invalid key size ' + key.len.str())
}
mut c := Cipher{
s: [u32(0); 256]
}
for i := 0; i < 256; i++ {
c.s[i] = u32(i)
}
mut j := u8(0)
for i := 0; i < 256; i++ {
j += u8(c.s[i]) + u8(key[i%key.len])
tmp := c.s[i]
c.s[i] = c.s[j]
c.s[j] = tmp
}
return c
}
// reset zeros the key data and makes the Cipher unusable.
//
// Deprecated: Reset can't guarantee that the key will be entirely removed from
// the process's memory.
pub fn (c &Cipher) reset() {
for i in c.s {
c.s[i] = u32(0)
}
c.i = u8(0)
c.j = u8(0)
}
// xor_key_stream sets dst to the result of XORing src with the key stream.
// Dst and src must overlap entirely or not at all.
pub fn (c &Cipher) xor_key_stream(dst, src []byte) {
if src.len == 0 {
return
}
if subtle.inexact_overlap(dst.left(src.len), src) {
panic('crypto.rc4: invalid buffer overlap')
}
mut i := c.i
mut j := c.j
_ := dst[src.len-1]
dst = dst.left(src.len) // eliminate bounds check from loop
for k, v in src {
i += u8(1)
x := c.s[i]
j += u8(x)
y := c.s[j]
c.s[i] = y
c.s[j] = x
dst[k] = v ^ byte(c.s[u8(x+y)])
}
c.i = i
c.j = j
}