openssl_private_encrypt

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

openssl_private_encrypt — 秘密鍵でデータを暗号化する

説明

openssl_private_encrypt(
    #[\SensitiveParameter] string $data,
    string &$encrypted_data,
    #[\SensitiveParameter] OpenSSLAsymmetricKey|OpenSSLCertificate|array|string $private_key,
    int $padding = OPENSSL_PKCS1_PADDING
): bool

openssl_private_encrypt() は、data を秘密鍵 private_key で暗号化し、それを encrypted_data に格納します。暗号化されたデータは、 openssl_public_decrypt() を用いて復号可能です。

この関数を使用するのは、例えばデータ（あるいはその一部）に署名をし、それが他人によって書かれたものでないことを証明する場合です。

パラメータ

data
encrypted_data
private_key: private_key は、データの復号に使われる公開鍵と対になる秘密鍵である必要があります。
padding: padding には OPENSSL_PKCS1_PADDING あるいは OPENSSL_NO_PADDING が指定可能です。

戻り値

成功した場合に true を、失敗した場合に false を返します。

変更履歴

バージョン	説明
8.0.0	`private_key` は、 OpenSSLAsymmetricKey または OpenSSLCertificate クラスのインスタンスを受け入れるようになりました。これより前のバージョンでは、 `OpenSSL key` または `OpenSSL X.509` 型のリソースを受け入れていました。

参考

openssl_public_encrypt() - 公開鍵でデータを暗号化する
openssl_public_decrypt() - 公開鍵でデータを復号する

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User Contributed Notes 5 notes

down

Hernanibus ¶

8 years ago

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;
  }
?>

down

wfredkNOSPAM at L5DevelopmentNOSPAM dot com ¶

22 years ago

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";

?>

down

adityasingh at techknowtrends dot com ¶

12 years ago

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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down

P.Peyremorte ¶

8 years ago

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;
}
?>

down

billnet at tiscalinet dot it ¶

22 years ago

<?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 !

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