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Secure Science Corporation Advisory CSA-056
From: SSC Advisory Notice <bugtraq () securescience net>
Date: Mon, 02 May 2005 17:56:17 -0700

Secure Science Corporation Advisory CSA-056
http://www.securescience.net
e-response () securescience net
877-570-0455

---------------------------------------------------------

LibTomCrypt version <=1.02 contained weak signature scheme used
with ECC keys, allowing trivial signature forgeries.

---------------------------------------------------------

Vulnerability Classification: Cryptography - arbitrary message signing

Discovery Date: May 1, 2005
Vendor Reported Advisory
Discovery Published: May 2, 2005

Abstract:
---------
LibTomCrypt is a fairly comprehensive, modular and portable cryptographic toolkit that provides developers with a vast array of well known published block ciphers, one-way hash functions, chaining modes, pseudo-random number generators, public key cryptography and a plethora of other routines. A vulnerability was found by the author within the signature scheme used with the Elliptic Curve Cryptosystem routines that will allow arbitrary signatures to be created by an attacker.

Description:
------------
During recent cryptographic review by the author, a mathematical flaw was found within the implementation of the El Gamal signature algorithm used in LibTomCrypt versions <=1.02 An attacker can create a valid random signature by selecting a random value for a, and then computing (a^-1)C (where the inverse is modulo the order of the curve), essentially allowing an attacker to sign arbitrary messages without the private key.


Affected Vendors:
---------------
All vendors using LTC <=1.02 that apply ECC with signatures.

Vendor and Patch Information:
-----------------------------
Secure Science Corporation is distributing this advisory on behalf of the author. The author has stated that LibTomCrypt 1.03 will be released May 7, 2005 with X9.62 ECDSA implemented, a FIPS 180-2 standard.

Solution:
---------
X9.62 ECDSA implementation.


Credits:
--------
Secure Science Corporation - Tom St Denis

Disclaimer:
-----------
Secure Science Corporation is not responsible for the misuse of any of the information we provide on this website and/or through our security advisories. Our advisories are a service to our customers intended to promote secure installation and use of Secure Science Corporation products.



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