full-disclosure - [FD] Should openssl accept weak DSA/DH keys with g = +/- 1 ?

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Date: Tue, 15 Apr 2014 17:06:13 +0300
From: Georgi Guninski <guninski@...inski.com>
To: fulldisclosure@...lists.org
Subject: [FD] Should openssl accept weak DSA/DH keys with g = +/- 1 ?

openssl accepts DSA (and probably DH) keys with
g=1 (or g= -1). Both are extremely weak, in
practice plaintext.

g=1 works all the time
g= -1 works about half the time in DSA
(on vanilla openssl).

Is there a MITM implication in this,
e.g. can a MITM convince both parties
that g=1 -- in this case the private keys
won't matter in DH.

Attached are certs.
$ openssl x509 -text -in certg=1.pem
G:    1 (0x1)

#server
$openssl s_server -accept 8888 -cert ./certg=1.pem -key certg=1.key -CAfile ./cacert.pem -www

#client
$ openssl s_client -connect localhost:8888 -showcerts -CAfile cacert.pem
Verify return code: 0 (ok)

-- 
blog:  https://j.ludost.net/blog

View attachment "cacert.pem" of type "text/plain" (3073 bytes)

View attachment "certg=1.pem" of type "text/plain" (3147 bytes)

Download attachment "certg=1.key" of type "application/pgp-keys" (322 bytes)

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