Encrypts a message using a nonce and a secret key (no authentication)

# sodium_crypto_stream_xchacha20_xor_ic

(PHP 8 >= 8.2.0)

sodium_crypto_stream_xchacha20_xor_ic — Encrypts a message using a nonce and a secret key (no authentication)

### Description

sodium_crypto_stream_xchacha20_xor_ic(
#[\SensitiveParameter] string `$message`,
string `$nonce`,
int `$counter`,
#[\SensitiveParameter] string `$key`
): string

The function is similar to sodium_crypto_stream_xchacha20_xor() but adds the ability to set the initial value of the block counter to a non-zero value. This permits direct access to any block without having to compute the previous ones.

Caution

This encryption is unauthenticated, and does not prevent chosen-ciphertext attacks. Make sure to combine the ciphertext with a Message Authentication Code, for example with sodium_crypto_aead_xchacha20poly1305_ietf_encrypt() function, or sodium_crypto_auth().

### Parameters

`message`
  The message to encrypt.
`nonce`
  24-byte nonce.
`counter`
  The initial value of the block counter.
`key`
  Key, possibly generated from sodium_crypto_stream_xchacha20_keygen().

### Return Values

Encrypted message, or `false` on failure.

### Examples

Example #1 sodium_crypto_stream_xchacha20_xor_ic() example

`<?php
$n2 = random_bytes(SODIUM_CRYPTO_STREAM_XCHACHA20_NONCEBYTES);
$left = str_repeat("\x01", 64);
$right = str_repeat("\xfe", 64);
// All at once:
$stream7_unified = sodium_crypto_stream_xchacha20_xor($left . $right, $n2, $key);
// Piecewise, with initial counter:
$stream7_left = sodium_crypto_stream_xchacha20_xor_ic($left, $n2, 0, $key);
$stream7_right = sodium_crypto_stream_xchacha20_xor_ic($right, $n2, 1, $key);
$stream7_concat = $stream7_left . $stream7_right;
var_dump(strlen($stream7_concat));
var_dump($stream7_unified === $stream7_concat);
?>`

The above example will output something similar to:

    int(128)
    bool(true)

### See Also

- sodium_crypto_stream_xchacha20_xor() - Encrypts a message using a nonce and a secret key (no authentication)

`↑` and `↓` to navigate • `Enter` to select • `Esc` to close • `/` to open