Secure Science Corporation Advisory CSA-056
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:
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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:
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X9.62 ECDSA implementation.
Credits:
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Secure Science Corporation - Tom St Denis
Disclaimer:
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advisories. Our advisories are a service to our customers intended to
promote secure installation and use of Secure Science Corporation products.