FastFlex (efflex)

Contributed by Ashish Sharma

FastFlex (pronounced efflex) is a New Cryptographic Function which can be used to construct Stream Ciphers, Hash Functions, Message Authentication Codes and Block Ciphers which perform considerably well in both hardware and software environments on Processors of varying word lengths. FastFlex uses a modified version of the Salsa20 [1] Hash Function as its core, along with a 256:256 bit mapping generated using a 256*256 virtual s-box. FastFlex only uses 4 primitive operations, Word Additions, Word Rotations, Word Multiplications and Word XORs, which gives it speed and flexibility. Furthermore Word Multiplications are used only in moderation where the advantages of using them outweigh the slight speed penalty induced by using multiplications over additions and xor. Finally, the design of FastFlex allows significant tradeoffs in Speed, Size and Security in both Hardware and Software. The cryptanalysis of FastFlex is in progress and initial results have been very encouraging. The Soucre Code for the same may be downloaded at

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