sodium_crypto_stream_xchacha20_xor_ic

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

&reftitle.description; `string` `sodium_crypto_stream_xchacha20_xor_ic` `string` `message` `string` `nonce` `int` `counter` `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.

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`.

&reftitle.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`.

&reftitle.returnvalues;

Encrypted message, &return.falseforfailure;.

&reftitle.examples;

### `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);
    ?>

&example.outputs.similar;

    int(128)
    bool(true)

&reftitle.seealso;

- `sodium_crypto_stream_xchacha20_xor`