Short for DNS SECurity, this feature allows for zones to be cryptographically signed with a zone key.

In this way, the information about a specific zone can be verified as coming from a nameserver that has signed it with a particular private key, as long as the recipient has that nameserver's public key.

BIND version 9 also supports the SIG(0) public/private key method of message authentication.

Short for Transaction SIGnatures, this feature allows a transfer from master to slave only after verifying that a shared secret key exists on both nameservers.

This feature strengthens the standard IP address-based method of transfer authorization. An attacker would not only need to have access to the IP address to transfer the zone, but they would also need to know the secret key.

BIND version 9 also supports TKEY, which is another shared secret key method of authorizing zone transfers.