Hardware Encryption for LTO4 Tapes
Attached is a whitepaper on how hardware encryption is done for LTO4 tapes. Hardware encryption is part of the specs for LTO4 tapes. Thus it is not available for LTO3 tapes although LTO4 tape drives can write to LTO3 tapes.
The part that I find particularly interesting is how an encrypted LTO4 is protected against low level copying.