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*To*: [email protected], [email protected], [email protected]*Subject*: WEAK3-EX -- A Layman's 56-bit Data Encryption Algorithm*From*: Mok-Kong Shen <[email protected]>*Date*: Tue, 15 Dec 1998 20:17:07 +0100*Organization*: Studenten; LRZ; Universitaet Muenchen*Sender*: [email protected]

In the previous products of my WEAK series of data encryption algorithms I have very strongly exploited the possibility of using arbitrarily long keys. Since this conflicts with the recent requirement of using 56-bit keys, a new program, WEAK3-EX, has been designed specifically for users that can only use 56-bit encryption keys. The design draws upon various techniques that have been accumulated in the course of the development of the previous WEAK3-E. Besides employing constant length 56-bit keys, a new feature that is introduced in WEAK3-EX is a user choosable scaling factor for the initialization time of the algorithm. Normally the initialization time of crypto algorithms are small and is for obvious reasons to be reduced as far as technically possible. In fact, the initialization time of almost all known encryption algorithms is negligible compared to the proper record processing time. Our algorithm, which contains author's compound PRNG, is however an exception to the rule. For, depending on the number of the constituent generators of the compound PRNG used, this can under circumstances indeed attain a non-trivial value. This is till present a necessary evil of our WEAK3-E which now fortunately in the special case of key length restriction (with the obvious accompanying unfavourable strength reduction effect) can be turned into a virtue of our new WEAK3-EX. In fact, if the (variable) parameters to be chosen by the user (in particular the number of rounds) of our algorithm are adequate, brute force would be the only feasible method of attack. Now the average time for brute force is equal to the time of running a single encryption/decryption process multiplied by one half of the size of the key space. If the initialization time of the algorithm is increased, the time for brute forcing correspondingly increases so that through suitable choice of the said scaling factor it can reach practically infeasible value for analysis without however on the other hand rendering the total processing time of the user (which of course also augments) to amounts entirely inacceptable for him. (The multiplying factor of one half of the key space is the leverage we exploit here.) Technically, the scaling factor determines the number of pseudo-random numbers retrieved from the shuffling buffer (of Bays and Duncan) that are to be combined into one pseudo-random number through the addition mod 1 operation (device of Wichmann and Hill) for subsequent utilization in building up the constituent generators of author's compound PRNG. The larger the scaling factor, the longer it will take to build up the compound PRNG. The multiple-seed standard PRNG employed in WEAK3-E is abandoned in WEAK3-EX in order to comply with the 56-bit key restriction. In its place is a standard PRNG that consists of two internal (single-seed) PRNGs which are activated alternatingly and which each accepts a seed of 28 bits, totalling 56 bits. An implementation in Fortran 90 is given in http://www.stud.uni-muenchen.de/~mok-kong.shen/#paper13 Both source and a binary executable file for PC can be downloaded via my main Web page. I wish to thank CWL and ZFS for suggesting the use of the scaling factor. Constructive critiques, comments and suggestions for improvements are sincerely solicited. M. K. Shen P.S. For space and obvious reasons, I plan to remove the code and binaries of WEAK1, WEAK2, WEAK3 and WEAK3-E from my Web page this Friday, leaving in future WEAK3-EX the single encryption software accessible.

**Follow-Ups**:**Re: WEAK3-EX -- A Layman's 56-bit Data Encryption Algorithm***From:*Ben Laurie <[email protected]>

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