openssl_public_encrypt

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

openssl_public_encrypt — Encrypts data with public key

Description

openssl_public_encrypt(
    string $data,
    string &$encrypted_data,
    OpenSSLAsymmetricKey|OpenSSLCertificate|array|string $public_key,
    int $padding = OPENSSL_PKCS1_PADDING
): bool

openssl_public_encrypt() encrypts data with public public_key and stores the result into encrypted_data. Encrypted data can be decrypted via openssl_private_decrypt().

This function can be used e.g. to encrypt message which can be then read only by owner of the private key. It can be also used to store secure data in database.

Parameters

data
encrypted_data: This will hold the result of the encryption.
public_key: The public key.
padding: padding can be one of OPENSSL_PKCS1_PADDING, OPENSSL_SSLV23_PADDING, OPENSSL_PKCS1_OAEP_PADDING, OPENSSL_NO_PADDING.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
8.0.0	`public_key` accepts an OpenSSLAsymmetricKey or OpenSSLCertificate instance now; previously, a resource of type `OpenSSL key` or `OpenSSL X.509` was accepted.

User Contributed Notes 19 notes

down

Jeff ¶

20 years ago


I figured it out.  This function is not intended for general encryption and decryption.  For that, you want openssl_seal() and openssl_open().

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security at paragonie dot com ¶

8 years ago


We can't guarantee that RSA will still be trusted for security in 2016, but this is the current best practice for RSA. The rest of the world is moving on to ECDH and EdDSA (e.g. Ed25519).

That said, make sure you are using OPENSSL_PKCS1_OAEP_PADDING or else you're vulnerable to a chosen-ciphertext attack (Google: "Daniel Bleichenbacher 1998 RSA padding oracle" and you'll find plenty of material on it.)

The only fix is to use OAEP (preferably with MGF1-SHA256, but this function doesn't let you specify that detail and defaults to MGF1+SHA1).

Phpseclib offers RSAES-OAEP + MGF1-SHA256 for encryption and RSASS-PSS + MGF1-SHA256 for signatures.

http://phpseclib.sourceforge.net/rsa/examples.html#encrypt,enc1

If you don't want to hassle with these details yourself,  check out https://github.com/paragonie/EasyRSA

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Thomas Horsten ¶

19 years ago


chsnyder writes that the data is limited to 936 bits in his implementation.

Actually, it has nothing to do with RSA being CPU intensive, RAM or anything of the sort.

Basically when you encrypt something using an RSA key (whether public or private), the encrypted value must be smaller than the key (due to the maths used to do the actual encryption). So if you have a 1024-bit key, in theory you could encrypt any 1023-bit value (or a 1024-bit value smaller than the key) with that key.

However, the PKCS#1 standard, which OpenSSL uses, specifies a padding scheme (so you can encrypt smaller quantities without losing security), and that padding scheme takes a minimum of 11 bytes (it will be longer if the value you're encrypting is smaller). So the highest number of bits you can encrypt with a 1024-bit key is 936 bits because of this (unless you disable the padding by adding the OPENSSL_NO_PADDING flag, in which case you can go up to 1023-1024 bits). With a 2048-bit key it's 1960 bits instead.

But as chsnyder correctly wrote, the normal application of a public key encryption algorithm is to store a key or a hash of the data you want to respectively encrypt or sign. A hash is typically 128-256 bits (the PHP sha1() function returns a 160 bit hash). And an AES key is 128 to 256 bits. So either of those will comfortably fit inside a single RSA encryption.

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AoK ¶

10 years ago


Very important to recognize the maximum size $data string constraint and its relation to SSL bit size as pointed out by others.  Before I addressed the maximum size limit through blocking the data, I was receiving these types of errors from openssl_error_string():
- error:0906D06C:PEM routines:PEM_read_bio:no start line  OR
- error:0E06D06C:configuration file routines:NCONF_get_string:no value
Using a key (sha512, OPENSSL_KEYTYPE_RSA) with 2048 bits, I had a maximum message size of 245 bytes and 4096 bits yielded a max size of 502 bytes.  So if you change your key size later, in particular if you reduce the size of it, be aware it affects your maximum encryption length.

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adrian ¶

19 years ago


T. Horsten explained the size limits on raw encryption. Here are two functions to encrypt/decrypt larger data when you can't use the envelope functions:

function ssl_encrypt($source,$type,$key){
//Assumes 1024 bit key and encrypts in chunks.

$maxlength=117;
$output='';
while($source){
  $input= substr($source,0,$maxlength);
  $source=substr($source,$maxlength);
  if($type=='private'){
    $ok= openssl_private_encrypt($input,$encrypted,$key);
  }else{
    $ok= openssl_public_encrypt($input,$encrypted,$key);
  }
        
  $output.=$encrypted;
}
return $output;
}

function ssl_decrypt($source,$type,$key){
// The raw PHP decryption functions appear to work
// on 128 Byte chunks. So this decrypts long text
// encrypted with ssl_encrypt().

$maxlength=128;
$output='';
while($source){
  $input= substr($source,0,$maxlength);
  $source=substr($source,$maxlength);
  if($type=='private'){
    $ok= openssl_private_decrypt($input,$out,$key);
  }else{
    $ok= openssl_public_decrypt($input,$out,$key);
  }
        
  $output.=$out;
}
return $output;

}

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ppostma1 ¶

13 years ago


The confusion most have seems to be on "mixed $key"



The $key is explained in, and mostly the same as the parameter of http://www.php.net/manual/en/function.openssl-pkey-get-public.php



It can take the resource $key returned from openssl_pkey_get_public() OR find the value is text and passes the text to openssl_pkey_get_public() to get a valid resource.



To better break down rstinnett's example:

(and where the flaw is)



<?php

function EncryptData($source)

{

  $fp=fopen("/etc/httpd/conf/ssl.crt/server.crt","r");

  $pub_key_string=fread($fp,8192);

  fclose($fp);

  openssl_get_publickey($pub_key);



  openssl_public_encrypt($source,$crypttext,$pub_key_string);

  /*this simply passes the string contents of pub_key_string back to be decoded*/

  return(base64_encode($crypttext));

}

?>



is more efficient:



<?php

function EncryptData($source)

{

  $fp=fopen("/etc/httpd/conf/ssl.crt/server.crt","r");

  $pub_key_string=fread($fp,8192);

  fclose($fp);

  $key_resource = openssl_get_publickey($pub_key);



  openssl_public_encrypt($source,$crypttext, $key_resource );

  /*uses the already existing key resource*/

  return(base64_encode($crypttext));

}

?>



shorter:



<?php

function EncryptData($source)

{

  $fp=fopen("/etc/httpd/conf/ssl.crt/server.crt","r");

  $pub_key=fread($fp,8192);

  fclose($fp);



  openssl_public_encrypt($source,$crypttext, $pub_key );



  return(base64_encode($crypttext));

}

?>

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Mark Seecof ¶

14 years ago


If you need a message key, obtain it from the openssl_random_pseudo_bytes() function.

DO NOT just hash the current time-- an attacker will guess any such key very easily (he'll just hash a bunch of likely time values and try them until he finds the right one.  The attacker can generate and test many millions of candidate hashes every minute using an ordinary PC).

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pigo at ms5 dot url dot com dot tw ¶

20 years ago


openssl_public_encrypt and openssl_private_encrypt can't encrypt large data . so I write a class . this class can encrypt large data and decrypt.

look url : http://pigo.pigo.idv.tw/opensslcrypt.phps

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Jeff ¶

20 years ago


It looks like there is a limit on the size of the string to be encrypted: about 50 characters.

This is due to the fact that the implementation allocates an output buffer of size EVP_PKEY_size(pkey), which is totally arbitrary and unrelated to the size of the input.  Also, it's not using a cipher envelope approach.  It's just RSAing the input string.

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webmaster at costarica-travelinfo dot com ¶

21 years ago


This example worked for me:

RedHat 7.2 / php 4.2.2 / Apache 1.3.7

// STEP 1: Encryption with Public Key (you will need Private Key to decrypt - see step2).

$string="Some Important Data";
$fp=fopen ("cert.pem","r");
$pub_key=fread ($fp,8192);
fclose($fp);
$PK="";
$PK=openssl_get_publickey($pub_key);
if (!$PK) {
    echo "Cannot get public key";
}
$finaltext="";
openssl_public_encrypt($string,$finaltext,$PK);
if (!empty($finaltext)) {
    openssl_free_key($PK);
    echo "Encryption OK!";
}else{
    echo "Cannot Encrypt";
}

// STEP 2: Decription (Using Private Key)

$fp=fopen ("pk.pem","r");
$priv_key2=fread ($fp,8192);
fclose($fp);
$PK2=openssl_get_privatekey($priv_key2);
$Crypted=openssl_private_decrypt($Data,$Decrypted,$PK2);
if (!$Crypted) {
    $MSG.="<p class='error'>Cannot Decrypt ($CCID).</p>";
}else{
    echo "Decrypted Data: " . $Decrypted;
}

down

-1

sumadhuracool at gmail dot com ¶

13 years ago


length of the data < length of the private key ..so i divided the message while taking it,put a ":::".then again encrpt it. look at the pgm to get an idea about this..



<?php

    class cry

    {

            # generate a 1024 bit rsa private key, ask for a passphrase to encrypt it and save to file

            //openssl genrsa -des3 -out /path/to/privatekey 1024

 

            # generate the public key for the private key and save to file

            //openssl rsa -in /path/to/privatekey -pubout -out /path/to/publickey

            //programatically using php-openssll



            //This will call while registration

            function gen_cert($userid)

            {

                $dn = array("countryName" => 'XX', "stateOrProvinceName" => 'State', "localityName" => 'SomewhereCity', "organizationName" =>'MySelf', "organizationalUnitName" => 'Whatever', "commonName" => 'mySelf', "emailAddress" => 'user@example.com');

                //Passphrase can be taken during registration 

                //Here its initialized to 1234 for sample                

                $privkeypass = 'root';

                $numberofdays = 365;

                //RSA encryption and 1024 bits length

                $privkey = openssl_pkey_new(array('private_key_bits' => 1024,'private_key_type' => OPENSSL_KEYTYPE_RSA));

                $csr = openssl_csr_new($dn, $privkey);

                $sscert = openssl_csr_sign($csr, null, $privkey, $numberofdays);

                openssl_x509_export($sscert, $publickey);

                openssl_pkey_export($privkey, $privatekey, $privkeypass);

                openssl_csr_export($csr, $csrStr);

                //Generated keys are stored into files

                $fp=fopen("../PKI/private/$userid.key","w");

                fwrite($fp,$privatekey);

                fclose($fp); 

                $fp=fopen("../PKI/public/$userid.crt","w");

                fwrite($fp,$publickey);

                fclose($fp);        

            }

            //Encryption with public key

            function encrypt($source,$rc)

            {

                //path holds the certificate path present in the system                

                $path="../PKI/public/server.crt";

                $fp=fopen($path,"r");

                $pub_key=fread($fp,8192);

                fclose($fp);

                openssl_get_publickey($pub_key);

            //$source='';

                //$source="sumanth ahoiadodakjaksdsa;ldadkkllksdalkalsdl;asld;ls sumanthasddddddddddddddddddddddddddddddddfsdfsffdfsdfsumanth";

                $j=0;

                $x=strlen($source)/10;

                $y=floor($x);

                for($i=0;$i<$y;$i++)

                {

                $crypttext='';

                

                openssl_public_encrypt(substr($source,$j,10),$crypttext,$pub_key);$j=$j+10;

                $crt.=$crypttext;

                $crt.=":::";

                }

                if((strlen($source)%10)>0)

                {

                openssl_public_encrypt(substr($source,$j),$crypttext,$pub_key);

                $crt.=$crypttext;

                }    

                return($crt);

                

            }

            //Decryption with private key

            function decrypt($crypttext,$userid)

            {

                $passphrase="root";

                $path="../PKI/private/server.key";

                $fpp1=fopen($path,"r");

                $priv_key=fread($fpp1,8192);

                fclose($fpp1);

                $res1= openssl_get_privatekey($priv_key,$passphrase);

                $tt=explode(":::",$crypttext);

                $cnt=count($tt);

                $i=0;

                while($i<$cnt)

                {

                openssl_private_decrypt($tt[$i],$str1,$res1);

                $str.=$str1;

                $i++;

                }

                return $str;      

        }

            function sign($source,$rc)

            {

                $has=sha1($source);

                $source.="::";

                $source.=$has;

                $path="../PKI/public/$rc.crt";

                $fp=fopen($path,"r");

                $pub_key=fread($fp,8192);

                fclose($fp);

                openssl_get_publickey($pub_key);

                openssl_public_encrypt($source,$mese,$pub_key);

                return $mese;

            

            }

            function verify($crypttext,$userid)

            {

                $passphrase="root";

                $path="../PKI/private/$userid.key";

                $fpp1=fopen($path,"r");

                $priv_key=fread($fpp1,8192);

                fclose($fpp1);

                $res1= openssl_get_privatekey($priv_key,$passphrase);

                openssl_private_decrypt($crypttext,$has1,$res1);

                list($c1,$c2)=split("::",$has1);

                $has=sha1($c1);

                if($has==$c2)

                {

                    $message=$c1;

                    return $message;

                }                 

            }



    }

?>

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-1

lonewolf at greyskydesigns dot com ¶

21 years ago


Easy way:

<?php

$publicKey = "file://path/to/public/key-crt.pem";
$plaintext = "String to encrypt";

openssl_public_encrypt($plaintext, $encrypted, $publicKey);

echo $encrypted;   //encrypted string

?>

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-2

public at grik dot net ¶

14 years ago


openssl_private_encrypt() has a low limit for the length of the data it can encrypt due to the nature of the algorithm.

To encrypt the larger data you can use openssl_encrypt() with a random password (like sha1(microtime(true))), and encrypt the password with openssl_public_encrypt().
This way the data can be encrypted with a public key and decrypted with the private one.

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-3

1520667045 at qq dot com ¶

4 years ago


<?php
$value =<<<EOL
some long long text
EOL;
$data = str_split($value, 214); // max is 214
$result = '';
foreach($data as $d){
    if(openssl_public_encrypt($d, $encrypted, $publickey, OPENSSL_PKCS1_OAEP_PADDING)){
        $result .= $encrypted;
    }
}
var_dump($result);
$result = base64_encode($result);
$data = str_split(base64_decode($result), 256); //every strlen($encrypted) == 256
$result = '';
foreach($data as $d){
    if(openssl_private_decrypt($d, $decrypted, $privatekey, OPENSSL_PKCS1_OAEP_PADDING)){
        $result .= $decrypted;
    }
}
var_dump($result);
?>

down

-3

chsnyder at gmail dot com ¶

19 years ago


In comment below, Jeff says the input to this function is limited to "about 50 characters". On my PHP5 build, the limit is 117 characters (936 bits, strange number).

That's because public key encryption is CPU intensive, and meant to be used on short values. The idea is to use this function to encrypt a secret key that is in turn used to encrypt data using a more efficient algorithm, such as RC4 or TripleDES. The recipient uses their private key to decrypt the secret, and can then decrypt the data.

The openssl_seal() and openssl_open() functions do this internally, and are very well documented. You should probably use them instead.

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-3

kenashkov at gmail dot com ¶

19 years ago


The encrypted data can be stored in MySQL without use of base64. It must be properly escaped with mysql_real_escape_string(), and then saved to BLOB column. (In fact - this function must be used every time when you insert binary data in MySQL).

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-4

rstinnett at bfmhconsulting dot com ¶

20 years ago


To store the encrypted data in a MySQL database, you first have to encode the data so it can safely be written. You can use a blob type for this, but it can make SELECTs really nasty. The easiest way I have found to do this is with base64_encode and base64_decode. The following example using code from a previous example and split into encrypt and decrypt functions.

function EncryptData($source)
{
  $fp=fopen("/etc/httpd/conf/ssl.crt/server.crt","r");
  $pub_key=fread($fp,8192);
  fclose($fp);
  openssl_get_publickey($pub_key);
  /*
   * NOTE:  Here you use the $pub_key value (converted, I guess)
   */
  openssl_public_encrypt($source,$crypttext,$pub_key);
  return(base64_encode($crypttext));
}

function DecryptData($source)
{
  #print("number : $number");
  $fp=fopen("/etc/httpd/conf/ssl.key/server.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
   */
  $decoded_source = base64_decode($source);
  openssl_private_decrypt($decoded_source,$newsource,$res);
  return($newsource);
}

Just use the return values to store the encrypted data or display the decrypted data.

down

-6

wfredkNOSPAM at L5DevelopmentNOSPAM dot com ¶

22 years ago


Encrypt using public key, decrypt using private key.

Use this to store stuff in your database: Unless someone
has your private key, the database contents are useless.

Also, use this for sending to a specific individual:  Get
their public key, encrypt the message, only they can use
their private key to decode it.

<?php
echo "Source: $source";
$fp=fopen ("/path/to/certificate.crt","r");
$pub_key=fread($fp,8192);
fclose($fp);
openssl_get_publickey($pub_key);
/*
 * NOTE:  Here you use the $pub_key value (converted, I guess)
 */
openssl_public_encrypt($source,$crypttext,$pub_key);
echo "String crypted: $crypttext";

$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,$passphrase);
/*
 * NOTE:  Here you use the returned resource value
 */
openssl_private_decrypt($crypttext,$newsource,$res);
echo "String decrypt : $newsource";
?>

down

-15

hromi at kyberia dot sk ¶

22 years ago


function description is wrong, you have to switch crypttext and text if you want it to work
this is correct:
bool openssl_public_encrypt ( string crypted, string data, mixed key [, int padding])

add a note

openssl_public_encrypt

Description

Parameters

Return Values

Changelog

See Also

User Contributed Notes 19 notes