View source for NewDES

{{Short description|Block cipher}}
{{Infobox block cipher
| name          = NewDES
| designers     = Robert Scott
| publish date  = 1985
| derived from  = 
| derived to    =
| related to    =
| key size      = 120 bits
| block size    = 64 bits
| structure     =
| rounds        = 17
| cryptanalysis = A [[related-key attack]] succeeds with 2<sup>32</sup> known plaintexts
}}
In [[cryptography]], '''NewDES''' is a [[symmetric key cryptography|symmetric key]] [[block cipher]]. It was created in 1984–1985 by Robert Scott as a potential [[Data Encryption Standard|DES]] replacement.

Despite its name, it is not derived from DES and has quite a different structure. Its intended niche as a DES replacement has now mostly been filled by [[Advanced Encryption Standard|AES]]. The algorithm was revised with a modified [[key schedule]] in 1996 to counter a [[related-key attack]]; this version is sometimes referred to as '''NewDES-96'''.

In 2004, Scott posted some comments on [[sci.crypt]] reflecting on the motivation behind NewDES's design and what he might have done differently so as to make the cipher more secure.<ref>{{cite newsgroup
 | title = newdes
 | author = Robert Scott
 | date = 2004-10-28
 | newsgroup = sci.crypt
 | message-id = 418062d6.30341101@news.provide.net
 | url = https://groups.google.com/d/msg/sci.crypt/f72Hos33cfA/oZ16sMgmCKkJ
 | access-date = 2018-10-10
 }}</ref>

==Algorithm==
NewDES, unlike DES, has no bit-level permutations, making it easy to implement in software. All operations are performed on whole bytes. It is a [[product cipher]], consisting of 17 rounds performed on a 64-bit data block and makes use of a 120-bit [[key (cryptography)|key]].

In each round, subkey material is [[XOR]]ed with the 1-byte sub-blocks of data, then fed through an [[substitution box|S-box]], the output of which is then XORed with another sub-block of data. In total, 8 XORs are performed in each round. The S-box is derived from the [[Declaration of Independence (United States)|United States Declaration of Independence]] (used as a [[nothing-up-my-sleeve number]]).

Each set of two rounds uses seven 1-byte subkeys, which are derived by splitting 56 bits of the key into bytes. The key is then rotated 56 bits for use in the next two rounds.

==Cryptanalysis==
Only a small amount of [[cryptanalysis]] has been published on NewDES. The designer showed that NewDES exhibits the full [[avalanche effect]] after seven rounds: every [[ciphertext]] bit depends on every [[plaintext]] bit and key bit.

NewDES has the same complementation property that DES has: namely, that if

:<math>E_K(P)=C,</math>

then

:<math>E_{\overline{K}}(\overline{P})=\overline{C},</math>

where

:<math>\overline{x}</math>

is the [[bitwise complement]] of ''x''. This means that the work factor for a [[brute force attack]] is reduced by a factor of 2. [[Eli Biham]] also noticed that changing a full byte in all the key and data bytes leads to another complementation property. This reduces the work factor by 2<sup>8</sup>.

Biham's related-key attack can break NewDES with 2<sup>33</sup> chosen-key chosen plaintexts, meaning that NewDES is not as secure as DES.

[[John Kelsey (cryptanalyst)|John Kelsey]], [[Bruce Schneier]], and [[David A. Wagner|David Wagner]] used related-key cryptanalysis to develop another attack on NewDES; it requires 2<sup>32</sup> known plaintexts and one related key.<ref>{{cite book |last1=Kelsey |first1=John |author-link1=John Kelsey (cryptanalyst) |last2=Schneier |first2=Bruce |author-link2=Bruce Schneier |last3=Wagner |first3=David |title=Information and Communications Security |chapter=Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X, NewDES, RC2, and TEA |series=Lecture Notes in Computer Science |author-link3=David A. Wagner |editor1-last=Han |editor1-first=Y. |editor2-last=Okamoto |editor2-first=T. |editor3-last=Qing |editor3-first=S. |date=1997 |volume=1334 |pages=233–246 |doi=10.1007/BFb0028479 |url=https://www.schneier.com/academic/archives/1997/11/related-key_cryptana.html |access-date=2018-10-10 |isbn=978-3-540-63696-0 |citeseerx=10.1.1.35.8112 }}</ref>

==References==
{{reflist}}
* {{cite journal |last1=Scott |first1=Robert |title=Wide Open Encryption Design Offers Flexible Implementations |journal=Cryptologia |date=January 1985 |volume=9 |issue=1 |pages=75–91 |doi=10.1080/0161-118591859799 }}
* {{cite book
  | last = Schneier
  | first = Bruce
  | author-link  = Bruce Schneier
  | title = Applied Cryptography, Second Edition
  | publisher = [[John Wiley & Sons]]
  | year = 1996
  | pages = 306–308
  | isbn = 978-0-471-11709-4 }}

==External links==
* {{cite newsgroup
 | title = Revision of NEWDES
 | last1 = Scott
 | first1 = Robert
 | date = 1996-03-02
 | newsgroup = sci.crypt
 | message-id = 4hafm9$r51@condor.ic.net
 | url = https://groups.google.com/d/msg/sci.crypt/DFmZzBcgF2M/xZ36MbKGuX8J
 | access-date = 2018-10-10
 }}
* [https://web.archive.org/web/20080506105359/http://www.mirrors.wiretapped.net/security/cryptography/algorithms/newdes/ NewDES source code implementations]

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