On 13.11.2013 16:41, Jonas Wielicki wrote: > On 13.11.2013 16:31, Fedor Brunner wrote:> This information is quite > important because during DHE key exchange a >> temporary key is generated. This temporary key is used for encryption of >> the communication and the server public RSA key is used ONLY for signing >> of this temporary key and NOT for encryption of the communication. The >> problem is that in many cases the temporary key much shorter than the >> server RSA key. >> >> For example the server jabber.ccc.de uses 2048 bit RSA public key, but >> the length of the temporary key is only 1024 bit. The public key score >> is 90, cipher score is 90 >> http://xmpp.net/result.php?domain=jabber.ccc.de&type=server > I agree that this information is important, however, there are > implementations which do not support more than 1024 bits of DH and are > unable to negotiate an TLS connection if the 1024 are exceeded, without > the app or the user knowing why it failed. This means, if you have > 1024bit EDH and the client and server agree on negotiating EDH (likely > if the client prefers it, as it should), they're unable to connect. > > This seems to affect primarily java and some versions of openssl, as > I've learnt on this list. > > regards, > jw There is already bug report on Java and will be fixed. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6521495 New versions of OpenSSL have no problem with longer EDH keys
http://www.keylength.com/en/compare/ " The Finite Field Diffie-Hellman <https://en.wikipedia.org/wiki/Diffie-Hellman> algorithm has roughly the same key strength as RSA for the same key sizes. The work factor for breaking Diffie-Hellman is based on the discrete logarithm problem <https://en.wikipedia.org/wiki/Discrete_logarithm_problem>, which is related to the integer factorization problem on which RSA's strength is based. Thus, a 3072-bit Diffie-Hellman key has about the same strength as a 3072-bit RSA key. " https://en.wikipedia.org/wiki/Key_sizes RSA 1024-bit Encryption not Enough http://www.pcworld.com/article/132184/article.html
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