Send data to the cube to be decrypted. Discovered by trial and error; algorithm and purpose are unknown.
d:encrypted-base64
The response will contain the cleartext data, padded at the end with nullbytes.
D:ZXhhbXBsZQoAAAAAAAAAAA==
65 78 61 6d 70 6c 65 0a 00 00 00 00 00 00 00 00 example.........