Horst Feistel's paper [Feistel, 1973] described the role cryptography might play in providing privacy in computer systems. The importance of this paper cannot be underestimated; first, it suggested a template for the design of cryptographic algorithms and second, it challenged the Government's undisputed role as master in the area of cryptology. It initiated a new era in cryptography that would lead to public-key cryptography. It was also of benefit to NSA, forcing it to re-examine its relationship with universities and business organizations.
Feistel's paper described LUCIFER, a product block-cipher enciphering plaintext data in blocks of M bits:
Feistel used the APL programming language to experiment with and test LUCIFER. The program was stored in an APL-workspace, the analogue of a PC/MAC-folder and a UNIX-directory. The APL implementation, available at this time, imposed a limit on the number of letters in a workspace name. Feistel's original choice of DEMONSTRATION for the workspace name had to be shortened to DEMON; ultimately, someone suggested the sexier name LUCIFER.
A description of one version of LUCIFER may be found in Sorkin's paper . Outerbridge  referred to LUCIFER as a Feistel-like block product cipher.