KeeLoq is a proprietary hardware-dedicated NLFSR

NLFSR

A NLFSR is a common component in modern stream ciphers, especially in RFID and smartcard applications. NLFSRs are known to be more resistant to cryptanalytic attacks than Linear Feedback Shift Registers , although construction of large NLFSRs with guaranteed long periods remains an open...

-based block cipher

Block cipher

In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...

. The uni-directional command transfer protocol was designed by Frederick Bruwer, PhD, CEO at Nanoteq (Pty) Ltd and the cryptographic algorithm was created by Professor Gideon Kuhn with the silicon implementation by Willem Smit, PhD, at Nanoteq Pty Ltd (South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

) in the mid 80's and sold to Microchip Technology Inc

Microchip Technology

Microchip Technology is an American manufacturer of microcontroller, memory and analog semiconductors. Its products include microcontrollers , Serial EEPROM devices, Serial SRAM devices, KEELOQ devices, radio frequency devices, thermal, power and battery management analog devices, as well as...

 in 1995 for $10 million. It's used in "code hopping" encoders and decoders such as NTQ105/106/115/125D/129D and HCS101/2XX/3XX/4XX/5XX.