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openssl_seal

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

openssl_sealSeal (encrypt) data

Description

openssl_seal(
    string $data,
    string &$sealed_data,
    array &$encrypted_keys,
    array $public_key,
    string $cipher_algo,
    string &$iv = null
): int|false

openssl_seal() seals (encrypts) data by using the given cipher_algo with a randomly generated secret key. The key is encrypted with each of the public keys associated with the identifiers in public_key and each encrypted key is returned in encrypted_keys. This means that one can send sealed data to multiple recipients (provided one has obtained their public keys). Each recipient must receive both the sealed data and the envelope key that was encrypted with the recipient's public key.

Parameters

data

The data to seal.

sealed_data

The sealed data.

encrypted_keys

Array of encrypted keys.

public_key

Array of OpenSSLAsymmetricKey instances containing public keys.

cipher_algo

The cipher method.

Caution

The default value ('RC4') is considered insecure. It is strongly recommended to explicitly specify a secure cipher method.

iv

The initialization vector.

Return Values

Returns the length of the sealed data on success, or false on error. If successful the sealed data is returned in sealed_data, and the envelope keys in encrypted_keys.

Changelog

Version Description
8.0.0 public_key accepts an array of OpenSSLAsymmetricKey instances now; previously, an array of resources of type OpenSSL key was accepted.
8.0.0 cipher_algo is no longer an optional parameter.
8.0.0 iv is nullable now.

Examples

Example #1 openssl_seal() example

<?php
// $data is assumed to contain the data to be sealed

// fetch public keys for our recipients, and ready them
$fp fopen("/src/openssl-0.9.6/demos/maurice/cert.pem""r");
$cert fread($fp8192);
fclose($fp);
$pk1 openssl_get_publickey($cert);
// Repeat for second recipient
$fp fopen("/src/openssl-0.9.6/demos/sign/cert.pem""r");
$cert fread($fp8192);
fclose($fp);
$pk2 openssl_get_publickey($cert);

// seal message, only owners of $pk1 and $pk2 can decrypt $sealed with keys
// $ekeys[0] and $ekeys[1] respectively.
openssl_seal($data$sealed$ekeys, array($pk1$pk2));

// free the keys from memory
openssl_free_key($pk1);
openssl_free_key($pk2);
?>

See Also

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User Contributed Notes 6 notes

up
10
amer.alhabsi AT gmail DOT com
5 years ago
while the default is using RC4, it is possible to use other more secure algorithms. These are specified as the fifth parameter. Also, one needs to add an initialization vector (random bytes). Eg.

<?php
    $data
= "This is top secret.";
   
// fetch public keys for our recipients, and ready them
   
$cert = file_get_contents('./cert.pem');

   
$pk1 = openssl_get_publickey($cert);
   
$iv = openssl_random_pseudo_bytes(32);
   
openssl_seal($data, $sealed, $ekeys, array($pk1), "AES256", $iv);

   
// free the keys from memory
   
openssl_free_key($pk1);
    echo
base64_encode($sealed);
?>
up
6
devel@no-spam
16 years ago
"seals (encrypts) data by using RC4 with a randomly generated secret key"
It should be noted that the randomly generated secret key is 128 bits long (openssl: EVP_rc4(void):  RC4 stream cipher. This is a variable key length cipher with default key length 128 bits.)
up
4
Dominik M.
11 months ago
Please note that openssl_seal() cannot be used for EC encryption.
Took me literally two hours to find out because the OpenSSL documentation is so bad.
up
6
bowfingermail at gmx dot net
5 years ago
According to several sources (e.g. crypto101.io or Wikipedia) RC4 is not safe and not supposed to be used anymore.
So, shouldn't openssl_seal use another stream cipher in place of RC4?
up
0
aaron dot lawrence at umajin dot com
1 month ago
Some critical details that are not in the docs, nor widely written about elsewhere.

- The envelope key is a 128-bit RSA key, randomly generated.
- The data is encrypted with (A)RC4 using the envelope key.
- The envelope key is encrypted for transmission with PKCS1 v1.5. It is NOT the OAEP padding variant.  PKCS1 v1.5 is even older, and not widely supported anymore.

At least this was true for openssl_seal in PHP 7.2 that we are using.

(Note: In Python you can decrypt this envelope key with the Cryptography package, using padding.PKCS1v15())

The combination of RC4 and PKCS1 v1.5 make this function actually semi-obsolete for security use in my opinion.
up
-5
hfuecks at nospam dot org
13 years ago
openssl_seal() can work well when you need to pass data securely to other platforms / languages. What openssl_seal() does is;

1. Generate a random key
2. Encrypt the data symmetrically with RC4 using the random key
3. Encrypt the random key itself with RSA using the public key / certificate
4. Returns the encrypted data and the encrypted key

So to decrypt the steps are simply;

1. Decrypt the key using RSA and your private key
2. Decrypt the data using RC4 and the decrypted key

The trickiest part may be figuring out how handle the private key - BouncyCastle ( http://www.bouncycastle.org/ ) provides a PEMReader for Java and C# while Not Yet commons-ssl ( http://juliusdavies.ca/commons-ssl/ ) has a KeyStoreBuilder to build Java keystores out of a PEM certificate.

A complete example in Java is described at http://blog.local.ch/archive/2007/10/29/openssl-php-to-java.html
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