Secure Science Corporation Advisory CSA-056 http://www.securescience.net e-response@xxxxxxxxxxxxxxxxx 877-570-0455
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LibTomCrypt version <=1.02 contained weak signature scheme used with ECC keys, allowing trivial signature forgeries.
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Vulnerability Classification: Cryptography - arbitrary message signing
Discovery Date: May 1, 2005 Vendor Reported Advisory Discovery Published: May 2, 2005
Abstract:
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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:
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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:
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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:
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