openssl_public_decrypt

(PHP 4 >= 4.0.6, PHP 5)

openssl_public_decrypt — Decrypts data with public key

Description

bool openssl_public_decrypt ( string $data , string &$decrypted , mixed $key [, int $padding = OPENSSL_PKCS1_PADDING ] )

openssl_public_decrypt() decrypts data that was previous encrypted via openssl_private_encrypt() and stores the result into decrypted.

You can use this function e.g. to check if the message was written by the owner of the private key.

Parameters

data
decrypted
key: key must be the public key corresponding that was used to encrypt the data.
padding: padding can be one of OPENSSL_PKCS1_PADDING, OPENSSL_NO_PADDING.

Return Values

Returns TRUE on success or FALSE on failure.

Коментарии

Aug 31

Автор: Hernanibus


Just a little note on  [P.Peyremorte]'s note in manual's openssl_private_encrypt.



"- 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;

  }

?>