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().