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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// 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.
package rc4
import (
"crypto/internal/alias"
"strconv"
)
// A Cipher is an instance of RC4 using a particular key.
type Cipher struct {
s [256]uint32
i, j uint8
}
type KeySizeError int
func (k KeySizeError) Error() string {
return "crypto/rc4: invalid key size " + strconv.Itoa(int(k))
}
// NewCipher creates and returns a new [Cipher]. The key argument should be the
// RC4 key, at least 1 byte and at most 256 bytes.
func NewCipher(key []byte) (*Cipher, error) {
k := len(key)
if k < 1 || k > 256 {
return nil, KeySizeError(k)
}
var c Cipher
for i := 0; i < 256; i++ {
c.s[i] = uint32(i)
}
var j uint8 = 0
for i := 0; i < 256; i++ {
j += uint8(c.s[i]) + key[i%k]
c.s[i], c.s[j] = c.s[j], c.s[i]
}
return &c, nil
}
// 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.
func (c *Cipher) Reset() {
for i := range c.s {
c.s[i] = 0
}
c.i, c.j = 0, 0
}
// XORKeyStream sets dst to the result of XORing src with the key stream.
// Dst and src must overlap entirely or not at all.
func (c *Cipher) XORKeyStream(dst, src []byte) {
if len(src) == 0 {
return
}
if alias.InexactOverlap(dst[:len(src)], src) {
panic("crypto/rc4: invalid buffer overlap")
}
i, j := c.i, c.j
_ = dst[len(src)-1]
dst = dst[:len(src)] // eliminate bounds check from loop
for k, v := range src {
i += 1
x := c.s[i]
j += uint8(x)
y := c.s[j]
c.s[i], c.s[j] = y, x
dst[k] = v ^ uint8(c.s[uint8(x+y)])
}
c.i, c.j = i, j
}