(PHP 4 >= 4.0.6, PHP 5)
openssl_private_encrypt — Encrypts data with private key
$data
   , string &$crypted
   , mixed $key
   [, int $padding = OPENSSL_PKCS1_PADDING
  ] )
   openssl_private_encrypt() encrypts data
   with private key and stores the result into
   crypted. Encrypted data can be decrypted via
   openssl_public_decrypt(). 
  
This function can be used e.g. to sign data (or its hash) to prove that it is not written by someone else.
data
crypted
key
padding
       padding can be one of
       OPENSSL_PKCS1_PADDING,
       OPENSSL_NO_PADDING.
      
   Returns TRUE on success or FALSE on failure.