openssl_private_encrypt

Just a little note on [P.Peyremorte]'s note.
"- openssl_private_encrypt can encrypt a maximum of 117 chars at one time."
This depends on the length of $key:
- For a 1024 bit key length => max number of chars (bytes) to encrypt = 1024/8 - 11(when padding used) = 117 chars (bytes).
- For a 2048 bit key length => max number of chars (bytes) to encrypt = 2048/8 - 11(when padding used) = 245 chars (bytes).
... and so on
By the way, if openssl_private_encrypt fails because of data size you won't get anything but just false as returned value, the same for openssl_public_decrypt() on decryption.
"- the encrypted output string is always 129 char length. If you use base64_encode on the encrypted output, it will give always 172 chars, with the last always "=" (filler)"
This again depends on the length of $key:
- For a 1024 bit key length => encrypted number of raw bytes is always a block of 128 bytes (1024 bits) by RSA design.
- For a 2048 bit key length => encrypted number of raw bytes is always a block of 256 bytes (2048 bits) by RSA design.
... and so on
About base64_encode output length, it depends on what you encode (meaning it depends on the bytes resulting after encryption), but in general the resulting encoded string will be about a 33% bigger (for 128 bytes bout 170 bytes and for 256 bytes about 340 bytes).
I would then generalize a little [P.Peyremorte]'s note by:
<?php
// given the variables as constants:
 //Block size for encryption block cipher
 private $ENCRYPT_BLOCK_SIZE = 200;// this for 2048 bit key for example, leaving some room
 //Block size for decryption block cipher
 private $DECRYPT_BLOCK_SIZE = 256;// this again for 2048 bit key
 //For encryption we would use:
 function encrypt_RSA($plainData, $privatePEMKey)
 {
 $encrypted = '';
 $plainData = str_split($plainData, $this->ENCRYPT_BLOCK_SIZE);
 foreach($plainData as $chunk)
 {
 $partialEncrypted = '';
 //using for example OPENSSL_PKCS1_PADDING as padding
 $encryptionOk = openssl_private_encrypt($chunk, $partialEncrypted, $privatePEMKey, OPENSSL_PKCS1_PADDING);
 if($encryptionOk === false){return false;}//also you can return and error. If too big this will be false
 $encrypted .= $partialEncrypted;
 }
 return base64_encode($encrypted);//encoding the whole binary String as MIME base 64
 }
 //For decryption we would use:
 protected function decrypt_RSA($publicPEMKey, $data)
 {
 $decrypted = '';
 //decode must be done before spliting for getting the binary String
 $data = str_split(base64_decode($data), $this->DECRYPT_BLOCK_SIZE);
 foreach($data as $chunk)
 {
 $partial = '';
 //be sure to match padding
 $decryptionOK = openssl_public_decrypt($chunk, $partial, $publicPEMKey, OPENSSL_PKCS1_PADDING);
 if($decryptionOK === false){return false;}//here also processed errors in decryption. If too big this will be false
 $decrypted .= $partial;
 }
 return $decrypted;
 }
?>

Encrypt using private key, decrypt using public key.
Use this for posting signed messages: Anyone with access to
your public key can read it, but they can't create one with
your signature.
<?php
echo "Source: $source";
$fp=fopen("/path/to/private.key","r");
$priv_key=fread($fp,8192);
fclose($fp);
// $passphrase is required if your key is encoded (suggested)
$res = openssl_get_privatekey($priv_key,$passphrase);
/*
 * NOTE: Here you use the returned resource value
 */
openssl_private_encrypt($source,$crypttext,$res);
echo "String crypted: $crypttext";
$fp=fopen ("/path/to/certificate.crt","r");
$pub_key=fread($fp,8192);
fclose($fp);
openssl_get_publickey($pub_key);
/*
 * NOTE: Here you use the $pub_key value (converted, I guess)
 */
openssl_public_decrypt($crypttext,$newsource,$pub_key);
echo "String decrypt : $newsource";
?>

Here is a over simplified version of using the crypt capabilities for getting started:
$res = openssl_pkey_new();
// Get private key
openssl_pkey_export($res, $privkey);
// Get public key
$pubkey = openssl_pkey_get_details($res);
$pubkey = $pubkey["key"];
var_dump($privkey);
var_dump($pubkey);
// get some text from command line to work with
$tocrypt = trim(fgets(STDIN));
// some variables to work with
$encryptedviaprivatekey = ""; //holds text encrypted with the private key
$decryptedviapublickey = ""; // holds text which was decrypted by the public key after being encrypted with the private key, should be same as $tocrypt
$encryptedviapublickey = ""; // holds text that was encrypted with the public key
$decryptedviaprivatekey = ""; // holds text that was decrypted with the private key after being encrypted with the public key, should be the same as $tocrypt
openssl_private_encrypt($tocrypt, $encryptedviaprivatekey, $privkey);
echo $tocrypt . "->" . $encryptedviaprivatekey;
echo "\n\n";
openssl_public_decrypt($encryptedviaprivatekey, $decryptedviapublickey, $pubkey);
echo $encryptedviaprivatekey . "->" . $decryptedviapublickey;
echo "\n\n";
openssl_public_encrypt($tocrypt,$encryptedviapublickey, $pubkey);
echo $tocrypt . "->" . $encryptedviapublickey;
echo "\n\n";
openssl_private_decrypt($encryptedviapublickey, $decryptedviaprivatekey, $privkey);
echo $encryptedviapublickey . "->" . $decryptedviaprivatekey;
Output:
string(887) "-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
"
string(272) "-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCy745x8AqGKlTWBu2Ub80boPaQ
xo/midZ4LHZ0zbPpiCAfkADNVYSe8OckPKutdjPX7SNAx66PgQRH1xrz1gysbRrf
8K/mA0LQ00MKBFaFottWt5cCIaUS9zvCgPw7prwng3hkGShnvTSMXiKFyt1E3RTv
pXRk0u46D6hKiy+TSQIDAQAB
-----END PUBLIC KEY-----
"
this is a test for crypting
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A trick not mentioned in manual to know :
- openssl_private_encrypt can encrypt a maximum of 117 chars at one time.
- the encrypted output string is always 129 char length. If you use base64_encode on the encrypted output, it will give always 172 chars, with the last always "=" (filler).
So, to encode a longer stream input you have to use something like :
<?php
$RawData = ... ; //Your input data to encode
$PartialData = '';
$EncodedData = '';
$Split = str_split($RawData , 117);
ForEach($Split as $Part)
{
 openssl_private_encrypt($Part, $PartialData, $PrivateKey);
 $EncodedData .= base64_encode($PartialData);
}
?> 
and then, to decode :
<?php
$OriginalData = '';
$Split = str_split($EncodedData , 172);
ForEach($Split as $Part)
{
 openssl_private_decrypt(base64_decode($Part), $PartialData, $PublicKey);
 $OriginalData .= $PartialData;
}
?>

<?php
$fp=fopen ("/path/to/key.pem","r");
$priv_key=fread ($fp,8192);
fclose($fp);
openssl_get_privatekey ($priv_key);
openssl_private_encrypt($source,$finaltext,$priv_key);
echo "String crypted: $finaltext";
?>

CIAO !