openssl_encrypt

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

openssl_encrypt — Encrypts data

Description

openssl_encrypt(
    string$data,
    string$cipher_algo,
    string$passphrase,
    int$options = 0,
    string$iv = "",
    string&$tag = null,
    string$aad = "",
    int$tag_length = 16
): string|false

Encrypts given data with given method and key, returns a raw or base64 encoded string

Parameters

data: The plaintext message data to be encrypted.
cipher_algo: The cipher method. For a list of available cipher methods, use openssl_get_cipher_methods().
passphrase: The passphrase. If the passphrase is shorter than expected, it is silently padded with NUL characters; if the passphrase is longer than expected, it is silently truncated.
options: options is a bitwise disjunction of the flags OPENSSL_RAW_DATA and OPENSSL_ZERO_PADDING.
iv: A non-NULL Initialization Vector.
tag: The authentication tag passed by reference when using AEAD cipher mode (GCM or CCM).
aad: Additional authenticated data.
tag_length: The length of the authentication tag. Its value can be between 4 and 16 for GCM mode.

Return Values

Returns the encrypted string on success or false on failure.

Errors/Exceptions

Emits an E_WARNING level error if an unknown cipher algorithm is passed in via the cipher_algo parameter.

Emits an E_WARNING level error if an empty value is passed in via the iv parameter.

Changelog

Version	Description
7.1.0	The `tag`, `aad` and `tag_length` parameters were added.

Examples

Example #1 AES Authenticated Encryption in GCM mode example for PHP 7.1+

<?php
//$key should have been previously generated in a cryptographically safe way, like openssl_random_pseudo_bytes
$plaintext = "message to be encrypted";
$cipher = "aes-128-gcm";
if (in_array($cipher, openssl_get_cipher_methods()))
{
$ivlen = openssl_cipher_iv_length($cipher);
$iv = openssl_random_pseudo_bytes($ivlen);
$ciphertext = openssl_encrypt($plaintext, $cipher, $key, $options=0, $iv, $tag);
//store $cipher, $iv, and $tag for decryption later
$original_plaintext = openssl_decrypt($ciphertext, $cipher, $key, $options=0, $iv, $tag);
 echo $original_plaintext."\n";
}
?>

Example #2 AES Authenticated Encryption example prior to PHP 7.1

<?php
//$key previously generated safely, ie: openssl_random_pseudo_bytes
$plaintext = "message to be encrypted";
$ivlen = openssl_cipher_iv_length($cipher="AES-128-CBC");
$iv = openssl_random_pseudo_bytes($ivlen);
$ciphertext_raw = openssl_encrypt($plaintext, $cipher, $key, $options=OPENSSL_RAW_DATA, $iv);
$hmac = hash_hmac('sha256', $ciphertext_raw, $key, $as_binary=true);
$ciphertext = base64_encode( $iv.$hmac.$ciphertext_raw );

//decrypt later....
$c = base64_decode($ciphertext);
$ivlen = openssl_cipher_iv_length($cipher="AES-128-CBC");
$iv = substr($c, 0, $ivlen);
$hmac = substr($c, $ivlen, $sha2len=32);
$ciphertext_raw = substr($c, $ivlen+$sha2len);
$original_plaintext = openssl_decrypt($ciphertext_raw, $cipher, $key, $options=OPENSSL_RAW_DATA, $iv);
$calcmac = hash_hmac('sha256', $ciphertext_raw, $key, $as_binary=true);
if (hash_equals($hmac, $calcmac))// timing attack safe comparison
{
 echo $original_plaintext."\n";
}
?>