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Data Encryption Standard
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Data Encryption Standard
The Feistel function (F function) of DES
General
Designers
IBM
First published
1975 (Federal Register) (standardized in January 1977)
Derived from
Lucifer
Successors
Triple DES, G-DES, DES-X, LOKI89, ICE
Cipher detail
Key sizes
56 bits (+8 parity bits)
Block sizes
64 bits
Structure
Balanced Feistel network
Rounds
16
Best public cryptanalysis
DES is now considered insecure because a brute-force attack is possible (see EFF DES cracker). As of 2008, the best analytical attack is linear cryptanalysis, which requires 243 known plaintexts and has a time complexity of 239–43 (Junod, 2001).
The Data Encryption Standard (DES, /ˌdiːˌiːˈɛs/ or /ˈdɛz/) is a symmetric-key algorithm for the encryption of electronic data. Although now considered insecure, it was highly influential in the advancement of modern cryptography.
Developed in the early 1970s at IBM and based on an earlier design by Horst Feistel, the algorithm was submitted to the National Bureau of Standards (NBS) following the agency's invitation to propose a candidate for the protection of sensitive, unclassified electronic government data. In 1976, after consultation with the National Security Agency (NSA), the NBS eventually selected a slightly modified version (strengthened against differential cryptanalysis, but weakened against brute-force attacks), which was published as an official Federal Information Processing Standard (FIPS) for the United States in 1977.
The publication of an NSA-approved encryption standard simultaneously resulted in its quick international adoption and widespread academic scrutiny. Controversies arose out of classified design elements, a relatively short key length of the symmetric-key block cipher design, and the involvement of the NSA, nourishing suspicions about a backdoor. The intense academic scrutiny the algorithm received over time led to the modern understanding of block ciphers and their cryptanalysis.
DES is now considered to be insecure for many applications. This is mainly due to the 56-bit key size being too small. In January 1999, distributed.net and the Electronic Frontier Foundation collaborated to publicly break a DES key in 22 hours and 15 minutes (see chronology). There are also some analytical results which demonstrate theoretical weaknesses in the cipher, although they are infeasible to mount in practice. The algorithm is believed to be practically secure in the form of Triple DES, although there are theoretical attacks. This cipher has been superseded by the Advanced Encryption Standard (AES). Furthermore, DES has been withdrawn as a standard by the National Institute of Standards and Technology.
Some documentation makes a distinction between DES as a standard and as an algorithm, referring to the algorithm as the DEA (Data Encryption Algorithm).
Contents
[hide]
1 History of DES
1.1 NSA's involvement in the design
1.2 The algorithm as a standard
1.3 Chronology
2 Description
2.1 Overall structure
2.2 The Feistel (F) function
2.3 Key schedule
3 Security and cryptanalysis
3.1 Brute-force attack
3.2 Attacks faster than brute force
3.3 Minor cryptanalytic properties
4 Simplified DES
5 Replacement algorithms
6 See also
7 Notes
8 References
9 External links
History of DES[edit]
The origins of DES go back to the early 1970s. In 1972, after concluding a study on the US government's computer security needs, the US standards body NBS (National Bureau of Standards)—now named NIST (National Institute of Standards and Technology)—identified a need for a government-wide standard for encrypting unclassified, sensitive information.[1] Accordingly, on 15 May 1973, after consulting with the NSA, NBS solicited proposals for a cipher that would meet rigorous design criteria. None of the submissions, however, turned out to be suitable. A second request was issued on 27 August 1974. This time, IBM submitted a candidate which was deemed acceptable—a cipher developed during the period 1973–1974 based on an earlier algorithm, Horst Feistel's Lucifer cipher. The team at IBM involved in cipher design and analysis included Feistel, Walter Tuchman, Don Coppersmith, Alan Konheim, Carl Meyer, Mike Matyas, Roy Adler, Edna Grossman, Bill Notz, Lynn Smith, and Bryant Tuckerman.
NSA's involvement in the design[edit]
On 17 March 1975, the proposed DES was published in the Federal Register. Public comments were requested, and in the following year two open workshops were held to discuss the proposed standard. There was some criticism from various parties, including from public-key cryptography pioneers Martin Hellman and Whitfield Diffie,[2] citing a shortened key length and the mysterious "S-boxes" as evidence of improper interference from the NSA. The suspicion was that the algorithm had been covertly weakened by the intelligence agency so that they—but no-one else—could easily read encrypted messages.[3] Alan Konheim (one of the designers of DES) commented, "We sent the S-boxes off to Washington. They came back and were all different."[4] The United States Senate Select Committee on Intelligence reviewed the NSA's actions to determine whether there had been any improper involvement. In the unclassified summary of their findings, published in 1978, the Committee wrote:
In the development of DES, NSA convinced IBM that a reduced key size was sufficient; indirectly assisted in the development of the S-box structures; and certified that the final DES algorithm was, to the best of their knowledge, free from any statistical or mathematical weakness.[5]
However, it also found that
NSA did not tamper with the design of the algorithm in any way. IBM invented and designed the algorithm, made all pertinent decisions regarding it, and concurred that the agreed upon key size was more than adequate for all commercial applications for which the DES was intended.[6]
Another member of the DES team, Walter Tuchman, stated "We developed the DES algorithm entirely within IBM using IBMers. The NSA did not dictate a single wire!"[7] In contrast, a declassified NSA book on cryptologic history states:
In 1973 NBS solicited private industry for a data encryption standard (DES). The first offerings were disappointing, so NSA began working on its own algorithm. Then Howard Rosenblum, deputy director for research and engineering, discovered that Walter Tuchman of IBM was working on a modification to Lucifer for general use. NSA gave Tuchman a clearance and brought him in to work jointly with the Agency on his Lucifer modification."[8]
and
NSA worked closely with IBM to strengthen the algorithm against all except brute-force attacks and to strengthen substitution tables, called S-boxes. Conversely, NSA tried to convince IBM to reduce the length of the key from 64 to 48 bits. Ultimately they compromised on a 56-bit key.[9][10]
Some of the suspicions about hidden weaknesses in the S-boxes were allayed in 1990, with the independent discovery and open publication by Eli Biham and Adi Shamir of differential cryptanalysis, a general method for breaking block ciphers. The S-boxes of DES were much more resistant to the attack than if they had been chosen at random, strongly suggesting that IBM knew about the technique in the 1970s. This was indeed the case; in 1994, Don Coppersmith published some of the original design criteria for the S-boxes.[11] According to Steven Levy, IBM Watson researchers discovered differential cryptanalytic attacks in 1974 and were asked by the NSA to keep the technique secret.[12] Coppersmith explains IBM's secrecy decision by saying, "that was because [differential cryptanalysis] can be a very powerful tool, used against many schemes, and there was concern that such information in the public domain could adversely affect national security." Levy quotes Walter Tuchman: "[t]hey asked us to stamp all our documents confidential... We actually put a number on each one and locked them up in safes, because they were considered U.S. government classified. They said do it. So I did it".[12] Bruce Schneier observed that "It took the academic community two decades to figure out that the NSA 'tweaks' actually improved the security of DES."[13]
The algorithm as a standard[edit]
Despite the criticisms, DES was approved as a federal standard in November 1976, and published on 15 January 1977 as FIPS PUB 46, authorized for use on all unclassified data. It was subsequently reaffirmed as the standard in 1983, 1988 (revised as FIPS-46-1), 1993 (FIPS-46-2), and again in 1999 (FIPS-46-3), the latter prescribing "Triple DES" (see below). On 26 May 2002, DES was finally superseded by the Advanced Encryption Standard (AES), following a public competition. On 19 May 2005, FIPS 46-3 was officially withdrawn, but NIST has approved Triple DES through the year 2030 for sensitive government information.[14]
The algorithm is also specified in ANSI X3.92 (Now, X3 is now known as INCITS and ANSI X3.92 as ANSI INCITS 92),[15] NIST SP 800-67[14] and ISO/IEC 18033-3[16] (as a component of TDEA).
Another theoretical attack, linear cryptanalysis, was published in 1994, but it was the Electronic Frontier Foundation's DES cracker in 1998 that demonstrated that DES could be attacked very practically, and highlighted the need for a replacement algorithm. These and other methods of cryptanalysis are discussed in more detail later in this article.
The introduction of DES is considered to have been a catalyst for the academic study of cryptography, particularly of methods to crack block ciphers. According to a NIST retrospective about DES,
The DES can be said to have "jump-started" the nonmilitary study and development of encryption algorithms. In the 1970s there were very few cryptographers, except for those in military or intelligence organizations, and little academic study of cryptography. There are now many active academic cryptologists, mathematics departments with strong programs in cryptography, and commercial information security companies and consultants. A generation of cryptanalysts has cut its teeth analyzing (that is, trying to "crack") the DES algorithm. In the words of cryptographer Bruce Schneier,[17] "DES did more to galvanize the field of cryptanalysis than anything else. Now there was an algorithm to study." An astonishing share of the open literature in cryptography in the 1970s and 1980s dealt with the DES, and the DES is the standard against which every symmetric key algorithm since has been compared.[18]
Chronology[edit]
Date
Year
Event
15 May 1973 NBS publishes a first request for a standard encryption algorithm
27 August 1974 NBS publishes a second request for encryption algorithms
17 March 1975 DES is published in the Federal Register for comment
August 1976 First workshop on DES
September 1976 Second workshop, discussing mathematical foundation of DES
November 1976 DES is approved as a standard
15 January 1977 DES is published as a FIPS standard FIPS PUB 46
1983 DES is reaffirmed for the first time
1986 Videocipher II, a TV satellite scrambling system based upon DES, begins use by HBO
22 January 1988 DES is reaffirmed for the second time as FIPS 46-1, superseding FIPS PUB 46
July 1991 Biham and Shamir rediscover differential cryptanalysis, and apply it to a 15-round DES-like cryptosystem.
1992 Biham and Shamir report the first theoretical attack with less complexity than brute force: differential cryptanalysis. However, it requires an unrealistic 247 chosen plaintexts.
30 December 1993 DES is reaffirmed for the third time as FIPS 46-2
1994 The first experimental cryptanalysis of DES is performed using linear cryptanalysis (Matsui, 1994).
June 1997 The DESCHALL Project breaks a message encrypted with DES for the first time in public.
July 1998 The EFF's DES cracker (Deep Crack) breaks a DES key in 56 hours.
January 1999 Together, Deep Crack and distributed.net break a DES key in 22 hours and 15 minutes.
25 October 1999 DES is reaffirmed for the fourth time as FIPS 46-3, which specifies the preferred use of Triple DES, with single DES permitted only in legacy systems.
26 November 2001 The Advanced Encryption Standard is published in FIPS 197
26 May 2002 The AES becomes effective
26 July 2004 The withdrawal of FIPS 46-3 (and a couple of related standards) is proposed in the Federal Register[19]
19 May 2005 NIST withdraws FIPS 46-3 (see Federal Register vol 70, number 96)
April 2006 The FPGA-based parallel machine COPACOBANA of the Universities of Bochum and Kiel, Germany, breaks DES in 9 days at a $10,000 hardware cost.[20] Within a year software improvements reduced the average time to 6.4 days.
Nov. 2008 The successor of COPACOBANA, the RIVYERA machine, reduced the average time to less than a single day.
July 2017 A chosen-plaintext attack utilizing a rainbow table can recover the DES key for a single specific chosen plaintext 1122334455667788 in 25 seconds. A new rainbow table has to be calculated per plaintext. A limited set of rainbow tables have been made available for download.[21]
Description[edit]
Figure 1— The overall Feistel structure of DES
For brevity, the following description omits the exact transformations and permutations which specify the algorithm; for reference, the details can be found in DES supplementary material.
DES is the archetypal block cipher—an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another ciphertext bitstring of the same length. In the case of DES, the block size is 64 bits. DES also uses a key to customize the transformation, so that decryption can supposedly only be performed by those who know the particular key used to encrypt. The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits.
The key is nominally stored or transmitted as 8 bytes, each with odd parity. According to ANSI X3.92-1981 (Now, known as ANSI INCITS 92-1981), section 3.5:
One bit in each 8-bit byte of the KEY may be utilized for error detection in key generation, distribution, and storage. Bits 8, 16,..., 64 are for use in ensuring that each byte is of odd parity.
Like other block ciphers, DES by itself is not a secure means of encryption, but must instead be used in a mode of operation. FIPS-81 specifies several modes for use with DES.[22] Further comments on the usage of DES are contained in FIPS-74.[23]
Decryption uses the same structure as encryption, but with the keys used in reverse order. (This has the advantage that the same hardware or software can be used in both directions.)
Overall structure[edit]
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The algorithm's overall structure is shown in Figure 1: there are 16 identical stages of processing, termed rounds. There is also an initial and final permutation, termed IP and FP, which are inverses (IP "undoes" the action of FP, and vice versa). IP and FP have no cryptographic significance, but were included in order to facilitate loading blocks in and out of mid-1970s 8-bit based hardware.[24]
Before the main rounds, the block is divided into two 32-bit halves and processed alternately; this criss-crossing is known as the Feistel scheme. The Feistel structure ensures that decryption and encryption are very similar processes—the only difference is that the subkeys are applied in the reverse order when decrypting. The rest of the algorithm is identical. This greatly simplifies implementation, particularly in hardware, as there is no need for separate encryption and decryption algorithms.
The ⊕ symbol denotes the exclusive-OR (XOR) operation. The F-function scrambles half a block together with some of the key. The output from the F-function is then combined with the other half of the block, and the halves are swapped before the next round. After the final round, the halves are swapped; this is a feature of the Feistel structure which makes encryption and decryption similar processes.
The Feistel (F) function[edit]
The F-function, depicted in Figure 2, operates on half a block (32 bits) at a time and consists of four stages:
Figure 2—The Feistel function (F-function) of DES
Expansion: the 32-bit half-block is expanded to 48 bits using the expansion permutation, denoted E in the diagram, by duplicating half of the bits. The output consists of eight 6-bit (8 * 6 = 48 bits) pieces, each containing a copy of 4 corresponding input bits, plus a copy of the immediately adjacent bit from each of the input pieces to either side.
Key mixing: the result is combined with a subkey using an XOR operation. Sixteen 48-bit subkeys—one for each round—are derived from the main key using the key schedule (described below).
Substitution: after mixing in the subkey, the block is divided into eight 6-bit pieces before processing by the S-boxes, or substitution boxes. Each of the eight S-boxes replaces its six input bits with four output bits according to a non-linear transformation, provided in the form of a lookup table. The S-boxes provide the core of the security of DES—without them, the cipher would be linear, and trivially breakable.
Permutation: finally, the 32 outputs from the S-boxes are rearranged according to a fixed permutation, the P-box. This is designed so that, after permutation, the bits from the output of each S-box in this round are spread across four different S-boxes in the next round.
The alternation of substitution from the S-boxes, and permutation of bits from the P-box and E-expansion provides so-called "confusion and diffusion" respectively, a concept identified by Claude Shannon in the 1940s as a necessary condition for a secure yet practical cipher.
Key schedule[edit]
Figure 3— The key-schedule of DES
Figure 3 illustrates the key schedule for encryption—the algorithm which generates the subkeys. Initially, 56 bits of the key are selected from the initial 64 by Permuted Choice 1 (PC-1)—the remaining eight bits are either discarded or used as parity check bits. The 56 bits are then divided into two 28-bit halves; each half is thereafter treated separately. In successive rounds, both halves are rotated left by one or two bits (specified for each round), and then 48 subkey bits are selected by Permuted Choice 2 (PC-2)—24 bits from the left half, and 24 from the right. The rotations (denoted by "<<<" in the diagram) mean that a different set of bits is used in each subkey; each bit is used in approximately 14 out of the 16 subkeys.
The key schedule for decryption is similar—the subkeys are in reverse order compared to encryption. Apart from that change, the process is the same as for encryption. The same 28 bits are passed to all rotation boxes.
Security and cryptanalysis[edit]
Although more information has been published on the cryptanalysis of DES than any other block cipher, the most practical attack to date is still a brute-force approach. Various minor cryptanalytic properties are known, and three theoretical attacks are possible which, while having a theoretical complexity less than a brute-force attack, require an unrealistic number of known or chosen plaintexts to carry out, and are not a concern in practice.
Brute-force attack[edit]
For any cipher, the most basic method of attack is brute force—trying every possible key in turn. The length of the key determines the number of possible keys, and hence the feasibility of this approach. For DES, questions were raised about the adequacy of its key size early on, even before it was adopted as a standard, and it was the small key size, rather than theoretical cryptanalysis, which dictated a need for a replacement algorithm. As a result of discussions involving external consultants including the NSA, the key size was reduced from 128 bits to 56 bits to fit on a single chip.[25]
The EFF's US$250,000 DES cracking machine contained 1,856 custom chips and could brute-force a DES key in a matter of days—the photo shows a DES Cracker circuit board fitted with several Deep Crack chips.
In academia, various proposals for a DES-cracking machine were advanced. In 1977, Diffie and Hellman proposed a machine costing an estimated US$20 million which could find a DES key in a single day. By 1993, Wiener had proposed a key-search machine costing US$1 million which would find a key within 7 hours. However, none of these early proposals were ever implemented—or, at least, no implementations were publicly acknowledged. The vulnerability of DES was practically demonstrated in the late 1990s. In 1997, RSA Security sponsored a series of contests, offering a $10,000 prize to the first team that broke a message encrypted with DES for the contest. That contest was won by the DESCHALL Project, led by Rocke Verser, Matt Curtin, and Justin Dolske, using idle cycles of thousands of computers across the Internet. The feasibility of cracking DES quickly was demonstrated in 1998 when a custom DES-cracker was built by the Electronic Frontier Foundation (EFF), a cyberspace civil rights group, at the cost of approximately US$250,000 (see EFF DES cracker). Their motivation was to show that DES was breakable in practice as well as in theory: "There are many people who will not believe a truth until they can see it with their own eyes. Showing them a physical machine that can crack DES in a few days is the only way to convince some people that they really cannot trust their security to DES." The machine brute-forced a key in a little more than 2 days' worth of searching.
The next confirmed DES cracker was the COPACOBANA machine built in 2006 by teams of the Universities of Bochum and Kiel, both in Germany. Unlike the EFF machine, COPACOBANA consists of commercially available, reconfigurable integrated circuits. 120 of these field-programmable gate arrays (FPGAs) of type XILINX Spartan-3 1000 run in parallel. They are grouped in 20 DIMM modules, each containing 6 FPGAs. The use of reconfigurable hardware makes the machine applicable to other code breaking tasks as well.[26] One of the more interesting aspects of COPACOBANA is its cost factor. One machine can be built for approximately $10,000.[27] The cost decrease by roughly a factor of 25 over the EFF machine is an example of the continuous improvement of digital hardware—see Moore's law. Adjusting for inflation over 8 years yields an even higher improvement of about 30x. Since 2007, SciEngines GmbH, a spin-off company of the two project partners of COPACOBANA has enhanced and developed successors of COPACOBANA. In 2008 their COPACOBANA RIVYERA reduced the time to break DES to less than one day, using 128 Spartan-3 5000's. SciEngines RIVYERA held the record in brute-force breaking DES, having utilized 128 Spartan-3 5000 FPGAs.[28] Their 256 Spartan-6 LX150 model has further lowered this time.
In 2012, David Hutton and Moxie Marlinspike announced a system with 48 Xilinx Virtex-6 LX240T FPGAs, each FPGA containing 40 fully pipelined DES cores running at 400MHz, for a total capacity of 768 gigakeys/sec. The system can exhaustively search the entire 56-bit DES key space in about 26 hours and this service is offered for a fee online.[29][30]
Attacks faster than brute force[edit]
There are three attacks known that can break the full 16 rounds of DES with less complexity than a brute-force search: differential cryptanalysis (DC), linear cryptanalysis (LC), and Davies' attack. However, the attacks are theoretical and are unfeasible to mount in practice[citation needed]; these types of attack are sometimes termed certificational weaknesses.
Differential cryptanalysis was rediscovered in the late 1980s by Eli Biham and Adi Shamir; it was known earlier to both IBM and the NSA and kept secret. To break the full 16 rounds, differential cryptanalysis requires 247 chosen plaintexts.[31] DES was designed to be resistant to DC.
Linear cryptanalysis was discovered by Mitsuru Matsui, and needs 243 known plaintexts (Matsui, 1993); the method was implemented (Matsui, 1994), and was the first experimental cryptanalysis of DES to be reported. There is no evidence that DES was tailored to be resistant to this type of attack. A generalization of LC—multiple linear cryptanalysis—was suggested in 1994 (Kaliski and Robshaw), and was further refined by Biryukov and others. (2004); their analysis suggests that multiple linear approximations could be used to reduce the data requirements of the attack by at least a factor of 4 (that is, 241 instead of 243). A similar reduction in data complexity can be obtained in a chosen-plaintext variant of linear cryptanalysis (Knudsen and Mathiassen, 2000). Junod (2001) performed several experiments to determine the actual time complexity of linear cryptanalysis, and reported that it was somewhat faster than predicted, requiring time equivalent to 239–241 DES evaluations.
Improved Davies' attack: while linear and differential cryptanalysis are general techniques and can be applied to a number of schemes, Davies' attack is a specialized technique for DES, first suggested by Donald Davies in the eighties, and improved by Biham and Biryukov (1997). The most powerful form of the attack requires 250 known plaintexts, has a computational complexity of 250, and has a 51% success rate.
There have also been attacks proposed against reduced-round versions of the cipher, that is, versions of DES with fewer than 16 rounds. Such analysis gives an insight into how many rounds are needed for safety, and how much of a "security margin" the full version retains. Differential-linear cryptanalysis was proposed by Langford and Hellman in 1994, and combines differential and linear cryptanalysis into a single attack. An enhanced version of the attack can break 9-round DES with 215.8 chosen plaintexts and has a 229.2 time complexity (Biham and others, 2002).
Minor cryptanalytic properties[edit]
DES exhibits the complementation property, namely that
E K ( P ) = C ⇔ E K ¯ ( P ¯ ) = C ¯ {\displaystyle E_{K}(P)=C\Leftrightarrow E_{\overline {K}}({\overline {P}})={\overline {C}}}
where x ¯ {\displaystyle {\overline {x}}} is the bitwise complement of x . {\displaystyle x.} E K {\displaystyle E_{K}} denotes encryption with key K . {\displaystyle K.} P {\displaystyle P} and C {\displaystyle C} denote plaintext and ciphertext blocks respectively. The complementation property means that the work for a brute-force attack could be reduced by a factor of 2 (or a single bit) under a chosen-plaintext assumption. By definition, this property also applies to TDES cipher.[citation needed]
DES also has four so-called weak keys. Encryption (E) and decryption (D) under a weak key have the same effect (see involution):
E K ( E K ( P ) ) = P {\displaystyle E_{K}(E_{K}(P))=P} or equivalently, E K = D K . {\displaystyle E_{K}=D_{K}.}
There are also six pairs of semi-weak keys. Encryption with one of the pair of semiweak keys, K 1 {\displaystyle K_{1}} , operates identically to decryption with the other, K 2 {\displaystyle K_{2}} :
E K 1 ( E K 2 ( P ) ) = P {\displaystyle E_{K_{1}}(E_{K_{2}}(P))=P} or equivalently, E K 2 = D K 1 . {\displaystyle E_{K_{2}}=D_{K_{1}}.}
It is easy enough to avoid the weak and semiweak keys in an implementation, either by testing for them explicitly, or simply by choosing keys randomly; the odds of picking a weak or semiweak key by chance are negligible. The keys are not really any weaker than any other keys anyway, as they do not give an attack any advantage.
DES has also been proved not to be a group, or more precisely, the set { E K } {\displaystyle \{E_{K}\}} (for all possible keys K {\displaystyle K} ) under functional composition is not a group, nor "close" to being a group.[32] This was an open question for some time, and if it had been the case, it would have been possible to break DES, and multiple encryption modes such as Triple DES would not increase the security, because encryption under one key would be equivalent to decryption under another key.[citation needed]
Simplified DES[edit]
Simplified DES (SDES) was designed for educational purposes only, to help students learn about modern cryptanalytic techniques. SDES has similar properties and structure as DES, but has been simplified to make it much easier to perform encryption and decryption by hand with pencil and paper. Some people feel that learning SDES gives insight into DES and other block ciphers, and insight into various cryptanalytic attacks against them.[33][34][35][36][37][38][39][40][41]
Replacement algorithms[edit]
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Concerns about security and the relatively slow operation of DES in software motivated researchers to propose a variety of alternative block cipher designs, which started to appear in the late 1980s and early 1990s: examples include RC5, Blowfish, IDEA, NewDES, SAFER, CAST5 and FEAL. Most of these designs kept the 64-bit block size of DES, and could act as a "drop-in" replacement, although they typically used a 64-bit or 128-bit key. In the Soviet Union the GOST 28147-89 algorithm was introduced, with a 64-bit block size and a 256-bit key, which was also used in Russia later.
DES itself can be adapted and reused in a more secure scheme. Many former DES users now use Triple DES (TDES) which was described and analysed by one of DES's patentees (see FIPS Pub 46-3); it involves applying DES three times with two (2TDES) or three (3TDES) different keys. TDES is regarded as adequately secure, although it is quite slow. A less computationally expensive alternative is DES-X, which increases the key size by XORing extra key material before and after DES. GDES was a DES variant proposed as a way to speed up encryption, but it was shown to be susceptible to differential cryptanalysis.
On January 2, 1997, NIST announced that they wished to choose a successor to DES.[42] In 2001, after an international competition, NIST selected a new cipher, the Advanced Encryption Standard (AES), as a replacement.[43] The algorithm which was selected as the AES was submitted by its designers under the name Rijndael. Other finalists in the NIST AES competition included RC6, Serpent, MARS, and Twofish.
See also[edit]
Cryptography portal
Brute Force: Cracking the Data Encryption Standard
DES supplementary material
Triple DES
Skipjack (cipher)
Symmetric key algorithm
GOST (block cipher)
Notes[edit]
Jump up ^ It was created by IBM's (International Business Machines) Walter Tuchman (1997). "A brief history of the data encryption standard". Internet besieged: countering cyberspace scofflaws. ACM Press/Addison-Wesley Publishing Co. New York, NY, USA. pp. 275–280.
Jump up ^ ^ Diffie, Whitfield; Hellman, Martin E. (June 1977). "Exhaustive Cryptanalysis of the NBS Data Encryption Standard" (PDF). Computer. 10 (6): 74–84. doi:10.1109/C-M.1977.217750. Archived from the original (PDF) on 2014-02-26.
Jump up ^ RSA Laboratories. "Has DES been broken?". Retrieved 2009-11-08.
Jump up ^ Schneier. Applied Cryptography (2nd ed.). p. 280.
Jump up ^ Davies, D.W.; W.L. Price (1989). Security for computer networks, 2nd ed. John Wiley & Sons.
Jump up ^ Robert Sugarman (editor) (July 1979). "On foiling computer crime". IEEE Spectrum. IEEE. CS1 maint: Extra text: authors list (link)
Jump up ^ P. Kinnucan (October 1978). "Data Encryption Gurus: Tuchman and Meyer". Cryptologia. 2 (4): 371. doi:10.1080/0161-117891853270.
Jump up ^ Thomas R. Johnson (2009-12-18). "American Cryptology during the Cold War, 1945-1989.Book III: Retrenchment and Reform, 1972-1980, page 232" (PDF). National Security Agency, DOCID 3417193 (file released on 2009-12-18, hosted at nsa.gov). Archived from the original (PDF) on 2013-09-18. Retrieved 2014-07-10.
Jump up ^ Thomas R. Johnson (2009-12-18). "American Cryptology during the Cold War, 1945-1989.Book III: Retrenchment and Reform, 1972-1980, page 232" (PDF). National Security Agency. Retrieved 2015-07-16 – via National Security Archive FOIA request. This version is differently redacted than the version on the NSA website.
Jump up ^ Thomas R. Johnson (2009-12-18). "American Cryptology during the Cold War, 1945-1989.Book III: Retrenchment and Reform, 1972-1980, page 232" (PDF). National Security Agency. Retrieved 2015-07-16 – via National Security Archive FOIA request. This version is differently redacted than the version on the NSA website.
Jump up ^ Konheim. Computer Security and Cryptography. p. 301.
^ Jump up to: a b Levy, Crypto, p. 55
Jump up ^ Schneier, Bruce (2004-09-27). "Saluting the data encryption legacy". CNet. Retrieved 2015-07-22.
^ Jump up to: a b National Institute of Standards and Technology, NIST Special Publication 800-67 Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher, Version 1.1
Jump up ^ American National Standards Institute, ANSI X3.92-1981 (Now, known as ANSI INCITS 92-1981)American National Standard, Data Encryption Algorithm
Jump up ^ "ISO/IEC 18033-3:2010 Information technology—Security techniques—Encryption algorithms—Part 3: Block ciphers". Iso.org. 2010-12-14. Retrieved 2011-10-21.
Jump up ^ Bruce Schneier, Applied Cryptography, Protocols, Algorithms, and Source Code in C, Second edition, John Wiley and Sons, New York (1996) p. 267
Jump up ^ William E. Burr, "Data Encryption Standard", in NIST's anthology "A Century of Excellence in Measurements, Standards, and Technology: A Chronicle of Selected NBS/NIST Publications, 1901–2000. HTML PDF
Jump up ^ "FR Doc 04-16894". Edocket.access.gpo.gov. Retrieved 2009-06-02.
Jump up ^ S. Kumar, C. Paar, J. Pelzl, G. Pfeiffer, A. Rupp, M. Schimmler, "How to Break DES for Euro 8,980". 2nd Workshop on Special-purpose Hardware for Attacking Cryptographic Systems—SHARCS 2006, Cologne, Germany, April 3–4, 2006.
Jump up ^ [1]
Jump up ^ "FIPS 81 - Des Modes of Operation". csrc.nist.gov. Retrieved 2009-06-02.
Jump up ^ "FIPS 74 - Guidelines for Implementing and Using the NBS Data". Itl.nist.gov. Retrieved 2009-06-02.
Jump up ^ Schneier. Applied Cryptography (1st ed.). p. 271.
Jump up ^ Stallings, W. Cryptography and network security: principles and practice. Prentice Hall, 2006. p. 73
Jump up ^ "Getting Started, COPACOBANA — Cost-optimized Parallel Code-Breaker" (PDF). December 12, 2006. Retrieved March 6, 2012.
Jump up ^ Reinhard Wobst (October 16, 2007). Cryptology Unlocked. John Wiley & Sons.
Jump up ^ Break DES in less than a single day [Press release of Firm, demonstrated on 2009 Workshop]
Jump up ^ The World's fastest DES cracker
Jump up ^ Think Complex Passwords Will Save You?, David Hulton, Ian Foster, BSidesLV 2017
Jump up ^ Biham, E. and Shamir, A. Differential Cryptanalysis of the Data Encryption Standard - Advances in Cryptology - CRYPTO '92, 12th Annual International Cryptology Conference, Santa Barbara, California, USA, August 16–20, 1992, Proceedings. 1992. pp. 487–496.
Jump up ^ Campbell and Wiener, 1992
Jump up ^ Sanjay Kumar; Sandeep Srivastava. "Image Encryption using Simplified Data Encryption Standard (S-DES)". 2014.
Jump up ^ Alasdair McAndrew. "Introduction to Cryptography with Open-Source Software". 2012. Section "8.8 Simplified DES: sDES". p. 183 to 190.
Jump up ^ William Stallings. "Appendix G: Simplified DES". 2010.
Jump up ^ Nalini N; G Raghavendra Rao. "Cryptanalysis of Simplified Data Encryption Standard via Optimisation Heuristics". 2006.
Jump up ^ Minh Van Nguyen. "Simplified DES". 2009.
Jump up ^ Dr. Manoj Kumar. "Cryptography and Network Security". Section 3.4: The Simplified Version of DES (S-DES). p. 96.
Jump up ^ Edward F. Schaefer. "A Simplified Data Encryption Standard Algorithm". doi:10.1080/0161-119691884799 1996.
Jump up ^ Lavkush Sharma; Bhupendra Kumar Pathak; and Nidhi Sharma. "Breaking of Simplified Data Encryption Standard Using Binary Particle Swarm Optimization". 2012.
Jump up ^ "Cryptography Research: Devising a Better Way to Teach and Learn the Advanced Encryption Standard".
Jump up ^ http://csrc.nist.gov/archive/aes/pre-round1/aes_9701.txt
Jump up ^ http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf November 26, 2001.
References[edit]
Biham, Eli and Shamir, Adi (1991). "Differential Cryptanalysis of DES-like Cryptosystems". Journal of Cryptology. 4 (1): 3–72. doi:10.1007/BF00630563. CS1 maint: Multiple names: authors list (link) (preprint)
Biham, Eli and Shamir, Adi, Differential Cryptanalysis of the Data Encryption Standard, Springer Verlag, 1993. ISBN 0-387-97930-1, ISBN 3-540-97930-1.
Biham, Eli and Alex Biryukov: An Improvement of Davies' Attack on DES. J. Cryptology 10(3): 195–206 (1997)
Biham, Eli, Orr Dunkelman, Nathan Keller: Enhancing Differential-Linear Cryptanalysis. ASIACRYPT 2002: pp254–266
Biham, Eli: A Fast New DES Implementation in Software
Cracking DES: Secrets of Encryption Research, Wiretap Politics, and Chip Design, Electronic Frontier Foundation
Biryukov, A, C. De Canniere and M. Quisquater (2004). Franklin, Matt, ed. "On Multiple Linear Approximations". Lecture Notes in Computer Science. Lecture Notes in Computer Science. 3152: 1–22. ISBN 978-3-540-22668-0. doi:10.1007/b99099. CS1 maint: Multiple names: authors list (link) (preprint).
Campbell, Keith W., Michael J. Wiener: DES is not a Group. CRYPTO 1992: pp512–520
Coppersmith, Don. (1994). The data encryption standard (DES) and its strength against attacks at the Wayback Machine (archived June 15, 2007). IBM Journal of Research and Development, 38(3), 243–250.
Diffie, Whitfield and Martin Hellman, "Exhaustive Cryptanalysis of the NBS Data Encryption Standard" IEEE Computer 10(6), June 1977, pp74–84
Ehrsam and others., Product Block Cipher System for Data Security, U.S. Patent 3,962,539, Filed February 24, 1975
Gilmore, John, "Cracking DES: Secrets of Encryption Research, Wiretap Politics and Chip Design", 1998, O'Reilly, ISBN 1-56592-520-3.
Junod, Pascal. "On the Complexity of Matsui's Attack." Selected Areas in Cryptography, 2001, pp199–211.
Kaliski, Burton S., Matt Robshaw: Linear Cryptanalysis Using Multiple Approximations. CRYPTO 1994: pp26–39
Knudsen, Lars, John Erik Mathiassen: A Chosen-Plaintext Linear Attack on DES. Fast Software Encryption - FSE 2000: pp262–272
Langford, Susan K., Martin E. Hellman: Differential-Linear Cryptanalysis. CRYPTO 1994: 17–25
Levy, Steven, Crypto: How the Code Rebels Beat the Government—Saving Privacy in the Digital Age, 2001, ISBN 0-14-024432-8.
Matsui, Mitsuru (1994). Helleseth, Tor, ed. "Linear Cryptanalysis Method for DES Cipher". Lecture Notes in Computer Science. Lecture Notes in Computer Science. 765: 386–397. CiteSeerX 10.1.1.50.8472  . ISBN 978-3-540-57600-6. doi:10.1007/3-540-48285-7.
Matsui, Mitsuru (1994). "The First Experimental Cryptanalysis of the Data Encryption Standard". Lecture Notes in Computer Science. Lecture Notes in Computer Science. 839: 1–11. ISBN 978-3-540-58333-2. doi:10.1007/3-540-48658-5_1.
National Bureau of Standards, Data Encryption Standard, FIPS-Pub.46. National Bureau of Standards, U.S. Department of Commerce, Washington D.C., January 1977.
Christof Paar, Jan Pelzl, "The Data Encryption Standard (DES) and Alternatives"[permanent dead link], free online lectures on Chapter 3 of "Understanding Cryptography, A Textbook for Students and Practitioners". Springer, 2009.
External links[edit]
Wikimedia Commons has media related to Data Encryption Standard.
FIPS 46-3: The official document describing the DES standard (PDF); An older version in HTML
COPACOBANA, a $10,000 DES cracker based on FPGAs by the Universities of Bochum and Kiel
DES step-by-step presentation and reliable message encoding application
A Fast New DES Implementation in Software - Biham
On Multiple Linear Approximations
RFC4772 : Security Implications of Using the Data Encryption Standard (DES)
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Eustace Scrubb
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Eustace Clarence Scrubb
Narnia character
Eustace Clarence Scrubb, as portrayed by Will Poulter in the 2010 movie, The Chronicles of Narnia: The Voyage of the Dawn Treader
Race
Human
Nation
England
Gender
Male
Birthplace
England, Earth
Family
Parents
Harold and Alberta Scrubb
Family
Peter, Susan, Edmund and Lucy Pevensie (cousins)
Major character in
The Voyage of the Dawn Treader
The Silver Chair
The Last Battle
Portrayals in adaptations
1989 BBC miniseries: David Thwaites
2010 Walden/Fox film: Will Poulter
Eustace Clarence Scrubb is a fictional character in C. S. Lewis's Chronicles of Narnia. He appears in The Voyage of the Dawn Treader, The Silver Chair, and The Last Battle. In The Voyage of the Dawn Treader, he is accompanied by Edmund and Lucy Pevensie, his cousins. In The Silver Chair and The Last Battle, he is accompanied by Jill Pole, a classmate from his school.
Contents
[hide]
1 Personality
2 Biography
2.1 Prior story
2.2 The Voyage of the Dawn Treader
2.3 The Silver Chair
2.4 The Last Battle
3 Themes
4 Portrayal
5 References
Personality[edit]
Eustace is portrayed at first as arrogant, whiny, and self-centred. It can be gathered from Eustace's behaviour, and the tone that Lewis used in describing his family and school, that Lewis thought such behaviour silly and disliked it a great deal. In fact, at the beginning of The Voyage of the Dawn Treader, Lucy and Edmund dislike visiting him and his parents, though that has mostly to do with Eustace's arrogant and unfriendly attitude. However, in the later books, Eustace is shown as an altogether better person, becoming a hero along with Jill Pole. It is mentioned in the Silver Chair that Eustace is afraid of heights, causing him to overreact when Jill goes too close to the edge of a cliff. In trying to stop her he falls. In other respects Eustace displays great courage and a fair degree of discernment in facing the challenges that confront him in the Narnian world.
Biography[edit]
Prior story[edit]
According to Lewis's Narnian timeline, Eustace was born in 1933 and is 10 years old when he appears in The Voyage of the Dawn Treader; and by The Last Battle he is 16 years old.
The Voyage of the Dawn Treader[edit]
We meet Eustace at the beginning of The Voyage of the Dawn Treader with the memorable opening line, "There was a boy called Eustace Clarence Scrubb, and he almost deserved it."
Eustace Scrubb, as portrayed by David Thwaites in the BBC production
He is the only child of what Lewis describes as "very up-to-date and advanced people," who send him to a progressive mixed school. Eustace calls his parents by their first names (Harold and Alberta); his parents are vegetarians, nonsmokers, teetotallers, pacifists, and wear an (unspecified) special kind of underclothes.
Much of the narrative of The Voyage of the Dawn Treader concerns the personal growth of Eustace, as he is drawn into Narnia and aboard the eponymous ship along with Lucy and Edmund, and into adventures that bring him to realize how self-centred his attitudes are. Part of the story is told with extracts from his diary, where we see how skewed his point of view is. He describes the ship sailing in perpetual storm (though the weather is fine), and portrays the others as foolishly denying the supposed rough seas and refusing to face the "truth" of the situation. He complains when Lucy is given Caspian's cabin, and comments to the crew that giving girls special treatment is actually "putting them down, and making them weaker". Moreover, he cannot accept that he is in the Narnian universe: he imagines that he can "lodge a disposition" (or "bring an action") at a British consulate or a British court; and he is beaten by Reepicheep for treating the mouse as one might a circus animal.
Eustace wanders off by himself when the ship puts ashore on an unexplored island. He falls asleep on a dragon's hoard and finds himself transformed into a dragon by "greedy, dragonish thoughts" in his heart (cf. Fafnir). Worse, he is now in constant agony from Lord Octesian's arm bracelet, which he put on as a boy but is too small for a dragon's leg. Upon return to the Dawn Treader, he is nearly attacked by the crew until Lucy asks if he is Eustace, to which he vigorously nods his head. Being a dragon changes Eustace; instead of behaving like his usual sulky self, he helps the travellers find food, shelter, and a tree to serve as a new mainmast. The problem comes when it is time to leave the island, as the ship cannot hold or maintain a dragon. Reepicheep displays sympathy to Eustace's plight despite the boy's prior cruelty to the mouse and they eventually become friends.
Eventually, Eustace meets Aslan, who returns him to human form by peeling off his dragon skin and sending him into a refreshing bath. Edmund shares with Eustace his own redemption story, observing that "you were only an ass, but I was a traitor." Eustace improves after this, though he still exhibits bad habits - "he began to be a different boy" is how the author puts it - and becomes a valuable member of the expedition. When the ship is in danger of being sunk by a giant sea-serpent, Eustace boldly if ineffectually attacks the monster, using only a sword. When Eustace returns home after his adventures, his mother thinks he has become tiresome and commonplace, blaming the change on the influence of "those Pevensie children"—though everyone else thinks he has become a much better person.
The Silver Chair[edit]
Eustace returns to his progressive school where he is now labelled a misfit, due to the changes in him wrought during The Voyage of The Dawn Treader. Where before he was a crony and tale-bearer to the gang of bullies who are given free rein at the school, he is now one of their targets, but has the courage to withstand them. He befriends fellow misfit Jill Pole, and their desire to leave the school draws them into Narnia. This unlikely friendship (given that Eustace had bullied Jill before his experience in Narnia) is strengthened throughout the story. Following the custom of their school, Eustace and Jill address each other by their surnames, "Scrubb" and "Pole".
The two journey to the far north of Narnia, and the world below it, to recover the lost heir to the throne and to thwart the plan of the Lady of the Green Kirtle to overthrow the kingdom. Though he still has faults, mainly stubbornness and rash decision-making, Eustace displays little of his former odiousness, and he and Jill begin to develop affection towards one another. He wholeheartedly rejects the insipid philosophy offered by the Lady in favour of the Narnian life he has grown to love. He helps Prince Rilian to escape the underworld and return to Narnia, just in time to meet Rillian's aged father before the latter's death. Caspian was now an old man, as 50 years had passed since Eustace had first been in Narnia.
Eustace and Jill return to Aslan's Country, where Caspian is resurrected and restored to the youth and strength that Eustace remembers from his earlier visit to this world. At the end of the story Caspian is briefly translated into Eustace's world, something Caspian has wanted ever since he met Eustace's cousins 53 years earlier. Here he helps the two friends scare off the school bullies and set in motion a train of events that leads to the school's becoming a well-managed place of learning.
The Last Battle[edit]
Eustace and Jill are sent to Narnia shortly before its destruction to help young King Tirian rally supporters for one last battle to save Narnia. The friends show great courage and wisdom but the Narnian forces ultimately go down to defeat.
Meanwhile, a railway accident in England results in the death of Eustace and Jill, along with Lucy, Edmund, and Peter, as well as Polly and Digory. They find themselves in Aslan's country, where Aslan directs Peter to end the world of Narnia. Thereafter they encounter many of the characters they had known in Narnia, as they climb "farther up and farther in" to live in eternal happiness.
Themes[edit]
Writer Philip Hensher objected to the description of Eustace and his family, regarding it as evidence of supposed anti-intellectual and anti-progressive leanings.[1] In Lewis' essay The Abolition of Man, he argues that modern education is producing "men without chests" – people whose lives are divided between the purely cerebral and the purely visceral, without any middle ground of sentiment or imagination—and Eustace (in his initial state) is clearly intended to be one of these. In the same essay, however, Lewis denies the suggestion that he is attacking intellect as such, and in his book on Miracles he even argues for the scholastic belief that the intellect is our participation in the supernatural world. Similarly, he was not against progress in the sense of objectively justifiable social improvement, but did oppose purely fashionable progressivism, and in particular what he called "chronological snobbery", the view that the superiority of modern values can always be assumed automatically and without investigation.
Portrayal[edit]
In the BBC production, Eustace was portrayed by David Thwaites.
In the 2014 BBC audiobook dramatisations of the books, he is portrayed by Marco Williamson.
Will Poulter plays Eustace in the Walden Media film adaptation, directed by Michael Apted. Among the alterations for the film is that when Eustace is turned into a dragon, he proves his true identity to Edmund by flying him to where he has used his fire breath to carve the sentence, "I am Eustace" on the ground. Once establishing his identity, the agonizingly undersized bracelet Eustace was wearing when he was transformed into a dragon is quickly removed with Lucy's help. Afterward and still in his dragon form Eustace accompanies the Dawn Treader on its quest to the next islands and earns the respect of the crew first by towing the ship when it is caught in magically imposed doldrums and later aiding the crew in battle against the sea serpent on the Dark Island, but gets injured. It is here that Aslan restores Eustace to normal, but only by scratching off the dragon's skin. Eustace's final redemption comes when he races to lay the seventh magic sword at Aslan's Table, unleashing the swords' power to defeat the evil of Dark Island and saving his friends.
The Oh Hellos, a folk rock band, wrote a song The Lament of Eustace Scrubb on their 2012 album Through the Deep, Dark Valley.
References[edit]
Jump up ^ Hensher, Philip (1998), "Don't let your children go to Narnia: C.S. Lewis's books are racist and misogynist", The Independent ; see also Goldthwaite, below.
Ford, Paul F. (2005-07-05). "Eustace Clarence Scrubb". The Companion to Narnia: A Complete Guide to the Magical World of C.S. Lewis' The Chronicles of Narnia. HarperOne. ISBN 0-06-079127-6.
Goldthwaite, John, The Natural History of Make-believe: A Guide to the Principal Works of Britain, Europe and America: OUP 1996, ISBN 0-19-503806-1, ISBN 978-0-19-503806-4
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