Sodium Functions
PHP Manual

sodium_crypto_stream_xchacha20_xor_ic

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

Description

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

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