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Lucifer (cipher)

 

 
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Lucifer (cipher)
 
 
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In cryptography
Cryptography

Cryptography is the practice and study of hiding information. In modern times cryptography is considered a branch of both mathematics and computer science and is affiliated closely with information theory, computer security and engineering....
, Lucifer was the name given to several of the earliest civilian block cipher
Block cipher

In cryptography, a block cipher is a symmetric key algorithm cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation....
s, developed by Horst Feistel
Horst Feistel

Horst Feistel was a cryptographer who worked on the design of ciphers at IBM, initiating research that would culminate in the development of the Data Encryption Standard in the 1970s....
 and his colleagues at IBM
IBM

International Business Machines Corporation, abbreviated IBM and nicknamed "Big Blue" , is a multinational corporation computer technology and consulting corporation headquartered in Armonk, New York, New York, United States....
. Lucifer was a direct precursor to the Data Encryption Standard
Data Encryption Standard

The Data Encryption Standard is a block cipher that was selected by National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally....
. One version, alternatively named DTD-1, saw commercial use in the 1970s for electronic banking.

Overview
One variant, described in (US Patent 3,798,359; June 1971), uses a 48-bit key and operates on 48-bit blocks.






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In cryptography
Cryptography

Cryptography is the practice and study of hiding information. In modern times cryptography is considered a branch of both mathematics and computer science and is affiliated closely with information theory, computer security and engineering....
, Lucifer was the name given to several of the earliest civilian block cipher
Block cipher

In cryptography, a block cipher is a symmetric key algorithm cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation....
s, developed by Horst Feistel
Horst Feistel

Horst Feistel was a cryptographer who worked on the design of ciphers at IBM, initiating research that would culminate in the development of the Data Encryption Standard in the 1970s....
 and his colleagues at IBM
IBM

International Business Machines Corporation, abbreviated IBM and nicknamed "Big Blue" , is a multinational corporation computer technology and consulting corporation headquartered in Armonk, New York, New York, United States....
. Lucifer was a direct precursor to the Data Encryption Standard
Data Encryption Standard

The Data Encryption Standard is a block cipher that was selected by National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally....
. One version, alternatively named DTD-1, saw commercial use in the 1970s for electronic banking.

Overview


One variant, described in (US Patent 3,798,359; June 1971), uses a 48-bit key and operates on 48-bit blocks. The cipher is a Substitution-permutation network
Substitution-permutation network

In cryptography, an SP-network, or substitution-permutation network , is a series of linked mathematical operations used in block cipher algorithms such as Advanced Encryption Standard....
 and uses two 4-bit S-boxes. The key selects which S-boxes are used. The patent describes the execution of the cipher operating on 24-bits at a time, and also a sequential version operating on 8-bits at a time.

Another variant, described in (US Patent 3,796,830; Nov 1971), uses a 64-bit key operating on a 32-bit block, using one addition mod 4 and a singular 4-bit S-box. The construction is designed to operate on 4 bits per clock cycle. This may be one of the smallest block-cipher implementations known.

A stronger variant, described in (Feistel, 1973), uses a 128-bit key and operates on 128-bit blocks. The cipher is a Substitution-permutation network
Substitution-permutation network

In cryptography, an SP-network, or substitution-permutation network , is a series of linked mathematical operations used in block cipher algorithms such as Advanced Encryption Standard....
 and uses two 4-bit S-boxes. The key selects which S-boxes are used.

A later Lucifer was a 16-round Feistel network, also on 128-bit blocks and 128-bit keys, described in (Sorkin, 1984). This version was shown to be susceptible to differential cryptanalysis
Differential cryptanalysis

Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions....
; for about half the keys, the cipher can be broken with 236 chosen plaintexts and 236 time complexity (Ben-Aroya and Biham, 1996).

IBM submitted the Feistel-network version of Lucifer as a candidate for DES
Data Encryption Standard

The Data Encryption Standard is a block cipher that was selected by National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally....
 (compare the more recent AES process
Advanced Encryption Standard process

The Advanced Encryption Standard , the block cipher ratified as a standard by National Institute of Standards and Technology of the United States , was chosen using a process markedly more open and transparent than its predecessor, the aging Data Encryption Standard ....
). After some redesign (a reduction to a 56-bit key and 64-bit block, but strengthened against differential cryptanalysis
Differential cryptanalysis

Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions....
) it became the Data Encryption Standard
Data Encryption Standard

The Data Encryption Standard is a block cipher that was selected by National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally....
 in 1977.

The name "Lucifer" was apparently a pun on "Demon". This was in turn a truncation of "Demonstration", the name for a privacy system Feistel was working on. The operating system used could not handle the longer name.

Description of the Sorkin variant

The variant described in (Sorkin, 1984) has 16 Feistel rounds, like DES, but no initial or final permutations. The key and block sizes are both 128 bits. The Feistel function operates on a 64-bit half-block of data, together with a 64-bit subkey and 8 "interchange control bits" (ICBs). The ICBs control a swapping operation. The 64-bit data block is considered as a series of eight 8-bit bytes, and if the ICB corresponding to a particular byte is zero, the left and right 4-bit halves (nibble
Nibble

A nibble is the computing term for a four-bit aggregation, or half an octet . As a nibble contains 4 bits, there are sixteen possible values, so a nibble corresponds to a single hexadecimal digit ....
s) are swapped. If the ICB is one, the byte is left unchanged. Each byte is then operated on by two 4×4-bit S-boxes, denoted S0 and S1 — S0 operates on the left 4-bit nibble and S1 operates on the right. The resultant outputs are concatenated and then combined with the subkey using exclusive or (XOR); this is termed "key interruption". This is followed by a permutation operation in two stages; the first permutes each byte under a fixed permutation. The second stage mixes bits between the bytes.

The key-scheduling algorithm is relatively simple. Initially, the 128 key bits are loaded into a shift register
Shift register

In digital circuits, a shift register is a group of flip-flop s set up in a linear fashion which have their inputs and outputs connected together in such a way that the data is shifted down the line when the circuit is activated....
. Each round, the left 64 bits of the register form the subkey, and right eight bits form the ICB bits. After each round, the register is rotated 56 bits to the left.

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