# sodium_crypto_secretstream_xchacha20poly1305_init_push

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_secretstream_xchacha20poly1305_init_push — Initialize a secretstream context for encryption

### Descripción

sodium_crypto_secretstream_xchacha20poly1305_init_push(string `$key`): array

Initialize a secretstream context for encryption.

### Parámetros

`key`

  Cryptography key. See sodium_crypto_secretstream_xchacha20poly1305_keygen().

### Valores devueltos

An array with two string values:

- The secretstream state, needed for further pushes
- The secretstream header, which needs to be provided to the recipient so they can pull data

### Ejemplos

Ejemplo #1 sodium_crypto_secretstream_xchacha20poly1305_init_push() example

`<?php
function encrypt_file(string $inputFilePath, string $outputFilePath, string $key): void
{
[$state, $header] = sodium_crypto_secretstream_xchacha20poly1305_init_push($key);
$inputFile = fopen($inputFilePath, 'rb');
$outputFile = fopen($outputFilePath, 'wb');
// Write the header:
fwrite($outputFile, $header);
$inputFileSize = fstat($inputFile)['size'];
// Encrypt the file and write its contents to the output file:
for ($i = 0; $i < $inputFileSize; $i += 8175) {
$ptxt_chunk = fread($inputFile, 8175);
$ctxt_chunk = sodium_crypto_secretstream_xchacha20poly1305_push($state, $ptxt_chunk);
fwrite($outputFile, $ctxt_chunk);
}
sodium_memzero($state);
fclose($inputFile);
fclose($outputFile);
}
// sodium_crypto_secretstream_xchacha20poly1305_keygen()
$key = sodium_base642bin('MS0lzb7HC+thY6jY01pkTE/cwsQxnRq0/2L1eL4Hxn8=', SODIUM_BASE64_VARIANT_ORIGINAL);
file_put_contents('hello.txt', 'Hello world!');
encrypt_file('hello.txt', 'hello.txt.encrypted', $key);
var_dump(sodium_bin2hex(file_get_contents('hello.txt.encrypted')));
?>`

El resultado del ejemplo sería algo similar a:

    string(106) "971e33b255f0990ef3931caf761c59136efa77b434832f28ec719e3ff73f5aec38b3bba1574ab5b70a8844d8da36a668e802cfea2c"