Description
bool 
openssl_private_encrypt ( string data, string &crypted, mixed key [, int padding] )
     openssl_private_encrypt() encrypts data
     with private key and stores the result into
     crypted. Encrypted data can be decrypted via
     openssl_public_decrypt(). padding
     defaults to OPENSSL_PKCS1_PADDING, but can also be
     OPENSSL_NO_PADDING.
    
     Returns TRUE on success or FALSE on failure.
    
     This function can be used e.g. to sign data (or its hash) to prove that it
     is not written by someone else.
    
     See also openssl_public_decrypt() and
     openssl_public_encrypt().