module rc4

// Copyright (c) 2019-2024 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.
// Based off:   https://github.com/golang/go/blob/master/src/crypto/rc4
// Last commit: https://github.com/golang/go/commit/b35dacaac57b039205d9b07ea24098e2c3fcb12e
import crypto.internal.subtle

// A Cipher is an instance of RC4 using a particular key.
struct Cipher {
mut:
    s []u32
    i u8
    j u8
}

// free the resources taken by the Cipher `c`
@[unsafe]
pub fn (mut c Cipher) free() {
    $if prealloc {
        return
    }
    unsafe { c.s.free() }
}

// 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.
@[direct_array_access]
pub fn new_cipher(key []u8) !&Cipher {
    if key.len < 1 || key.len > 256 {
        return error('crypto.rc4: invalid key size ' + key.len.str())
    }
    mut c := &Cipher{
        s: []u32{len: (256)}
    }
    for i in 0 .. 256 {
        c.s[i] = u32(i)
    }
    mut j := u8(0)
    for i in 0 .. 256 {
        j += u8(c.s[i]) + 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.good to com
//
// Deprecated: Reset can't guarantee that the key will be entirely removed from
// the process's memory.
pub fn (mut c Cipher) reset() {
    for i in c.s {
        c.s[i] = 0
    }
    c.i = 0
    c.j = 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.
@[direct_array_access]
pub fn (mut c Cipher) xor_key_stream(mut dst []u8, src []u8) {
    if src.len == 0 {
        return
    }
    if subtle.inexact_overlap(dst, src) {
        panic('crypto.rc4: invalid buffer overlap')
    }
    mut i := c.i
    mut j := c.j
    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 ^ u8(c.s[u8(x + y)])
    }
    c.i = i
    c.j = j
}