openssl_seal
(PHP 4 >= 4.0.4, PHP 5)
openssl_seal — Seal (encrypt) data
Description
$data
, string &$sealed_data
, array &$env_keys
, array $pub_key_ids
[, string $method
] )
openssl_seal() seals (encrypts)
data by using RC4 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.
Parameters
-
data -
-
sealed_data -
-
env_keys -
-
pub_key_ids -
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
env_keys.
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");
$cert = fread($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);
?>
- PHP Руководство
- Функции по категориям
- Индекс функций
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- Криптографические расширения
- OpenSSL
- openssl_cipher_iv_length
- openssl_csr_export_to_file
- openssl_csr_export
- openssl_csr_get_public_key
- openssl_csr_get_subject
- openssl_csr_new
- openssl_csr_sign
- openssl_decrypt
- openssl_dh_compute_key
- openssl_digest
- openssl_encrypt
- openssl_error_string
- openssl_free_key
- openssl_get_cert_locations
- openssl_get_cipher_methods
- openssl_get_md_methods
- openssl_get_privatekey
- openssl_get_publickey
- openssl_open
- openssl_pbkdf2
- openssl_pkcs12_export_to_file
- openssl_pkcs12_export
- openssl_pkcs12_read
- openssl_pkcs7_decrypt
- openssl_pkcs7_encrypt
- openssl_pkcs7_sign
- openssl_pkcs7_verify
- openssl_pkey_export_to_file
- openssl_pkey_export
- openssl_pkey_free
- openssl_pkey_get_details
- openssl_pkey_get_private
- openssl_pkey_get_public
- openssl_pkey_new
- openssl_private_decrypt
- openssl_private_encrypt
- openssl_public_decrypt
- openssl_public_encrypt
- openssl_random_pseudo_bytes
- openssl_seal
- openssl_sign
- openssl_spki_export_challenge
- openssl_spki_export
- openssl_spki_new
- openssl_spki_verify
- openssl_verify
- openssl_x509_check_private_key
- openssl_x509_checkpurpose
- openssl_x509_export_to_file
- openssl_x509_export
- openssl_x509_fingerprint
- openssl_x509_free
- openssl_x509_parse
- openssl_x509_read
Коментарии
"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.)
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
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?
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);
?>
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.
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.