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 — 密封 (加密) 数据
$data
, string &$sealed_data
, array &$env_keys
, array $pub_key_ids
, string $method = "RC4"
, string &$iv = ?
) : int
openssl_seal() 使用随机生成的密钥和给定的 method 方法密封 (加密)
data 数据。 密钥用与pub_key_ids中的标识符相关联的每个公共密钥加密，并且每个加密密钥在env_keys中返回。 这意味着一个人可以将密封的数据发送给多个接收者(如果一个人已经获得了他们的公钥)。每个接收方都必须同时接收加密的数据和用接收方的公钥加密的信封密钥。
data要密封的数据。
sealed_data被密封后的数据。
env_keys已被加密的密钥数组。
pub_key_ids公钥资源标识符组成的数组。
method加密算法。
iv初始化向量。
成功，返回密封后数据的长度，错误，返回 false .
如果密封后的数据成功地通过sealed_data变量返回，那么信封密钥也将会通过 env_keys 变量返回。
| 版本 | 说明 |
|---|---|
| 7.0.0 |
添加 iv 变量。
|
| 5.3.0 |
添加 method 变量。
|
Example #1 openssl_seal() 范例：
<?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);
?>
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);
?>
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
"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.)