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.
如果成功则返回 TRUE，失败则返回 FALSE。
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().