## Cryptology ePrint Archive: Report 2003/142

**A New Tree based Domain Extension of UOWHF**

*Mridul Nandi*

**Abstract: **We present a new binary tree based parallel algorithm for extending the domain of a UOWHF. The key length expansion is m(t+O(log*(t))) bits. In particular, the key length expansion is 2m bits for t=2; m(t+1) bits for 3\leq t\leq 6 and m(t+2) bits for 7\leq t\leq 134, where m is the length of the message digest and t\geq 2 is the height of the binary tree. The previously best known binary tree algorithm required a key length expansion of m(t+[log_2 (t-1)]) bits. We also give a sufficient condition for valid domain extension in sequental domain extension.

**Category / Keywords: **public-key cryptography /

**Date: **received 22 Jul 2003, last revised 26 Aug 2003

**Contact author: **hi_mridul at yahoo com

**Available format(s): **Postscript (PS) | Compressed Postscript (PS.GZ) | BibTeX Citation

**Version: **20030826:091342 (All versions of this report)

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