Which of the following is not an encryption technology?

Blowfish is a legitimate symmetric-key block cipher designed by Bruce Schneier, widely used for password hashing and file encryption.

KILL does not exist as any recognized encryption algorithm, cipher suite, or cryptographic standard. It is a nonsense term inserted as a distractor. All other choices represent real technologies used in cryptographic contexts, making KILL the only option that is definitively not an encryption technology.

3DES (Triple DES) is a real symmetric encryption algorithm that applies the DES cipher three times to each data block, and was a NIST-approved standard.

MD5 is a real cryptographic function (a hash algorithm rather than symmetric encryption), but it exists as a recognized security technology unlike KILL.