Used with openssl_encrypt() and
openssl_decrypt() to indicate that data
should be in raw binary format rather than base64-encoded.
See the respective function descriptions for details.
By default encryption operations are padded using standard block
padding and the padding is checked and removed when decrypting.
If OPENSSL_ZERO_PADDING is set in the
openssl_encrypt() or openssl_decrypt()options then no padding is performed, the total
amount of data encrypted or decrypted must then be a multiple of the
block size or an error will occur.