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.
(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)
openssl_seal — Sellar (encriptar) información
$data,&$sealed_data,&$env_keys,$pub_key_ids,$method = "RC4"
openssl_seal() sella (encripta)
la información dada por data mediante el método dado por method con una clave secreta
generada aleatoriamente. La clave es encriptada con cada clave pública
asociada con los identificadores de pub_key_ids
y cada clave encriptada es devuelta
en env_keys. Esto significa que se puede enviar
información sellada a múltiples destinatarios (siempre que se hayan obtenido sus
claves públicas). Cada destinatario debe recibir tanto la información sellada como
la clave de sobre que fue encriptada con la clave publica del destinatario.
dataLos datos a sellar.
sealed_dataLos datos sellados.
env_keysUn array de claves encriptadas.
pub_key_idsUn array de identificadores de recursos de clave pública.
methodEl método de cifrado.
Devuelve la longitud de la información sellada si se tuvo éxito, o false si se produjo un error.
Si se tuvo éxito, la información sellada es devuelta en
sealed_data, y las claves de sobre en
env_keys.
Ejemplo #1 Ejemplo de openssl_seal()
<?php
// se asume que $data contiene la información que va a ser sellada
// traer las claves públicas para nuestros destinatarios, y prepararlas
$fp = fopen("/src/openssl-0.9.6/demos/maurice/cert.pem", "r");
$cert = fread($fp, 8192);
fclose($fp);
$pk1 = openssl_get_publickey($cert);
// Repetir para el segundo destinatario
$fp = fopen("/src/openssl-0.9.6/demos/sign/cert.pem", "r");
$cert = fread($fp, 8192);
fclose($fp);
$pk2 = openssl_get_publickey($cert);
// sellar el mensaje, sólo los propietarios de $pk1 y $pk2 pueden desencriptar $sealed
// con las claves $ekeys[0] y $ekeys[1] respectivamente.
openssl_seal($data, $sealed, $ekeys, array($pk1, $pk2));
// liberar las claves de la memoria
openssl_free_key($pk1);
openssl_free_key($pk2);
?>| Versión | Descripción |
|---|---|
| 5.3.0 |
Se añadió el parámetro method.
|
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.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);
?>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."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