(PHP 4 >= 4.0.4, PHP 5, PHP 7)
openssl_seal — Seal (encrypt) data
$data
, string &$sealed_data
, array &$env_keys
, array $pub_key_ids
[, string $method = "RC4"
] )
openssl_seal() seals (encrypts)
data by using the given method with a randomly generated
secret key. The key is encrypted with each of the public keys
associated with the identifiers in pub_key_ids
and each encrypted key is returned
in env_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.
dataThe data to seal.
sealed_dataThe sealed data.
env_keysArray of encrypted keys.
pub_key_idsArray of public key resource identifiers.
methodThe cipher method.
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
env_keys.
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");
$cert = fread($fp, 8192);
fclose($fp);
$pk1 = openssl_get_publickey($cert);
// Repeat for second recipient
$fp = fopen("/src/openssl-0.9.6/demos/sign/cert.pem", "r");
$cert = fread($fp, 8192);
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);
?>
| Version | Description |
|---|---|
| 5.3.0 |
The method parameter was added.
|
"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.)
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?
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
