Cipher suites vulnerable to logjam

Question

The following is a list of ciphers, how to know which ciphers are vulnerable to LogJam attack?

Client shared list of ciphers:

Server chosen cipher: TLS_RSA_WITH_AES_128_CBC_SHA

Don't use _DSS_ (it's not supported these days anyway), don't use _RC4_ (it's broken and deprecated), don't use _ECDH_ (nobody supports it anyway, but still, ECDHE is what you want). You've not listed AEAD (AES-GCM) cipher suites, these are the only ones that are considered secure. Add them. Reorder the list to be: ECDHE+ECDSA+AESGCM, ECDHE+aRSA+AESGCM, DHE+aRSA+AESGCM, ECDHE+ECDSA+AES, ECDHE+aRSA+AES, DHE+aRSA+AES, RSA+AES, RSA+3DES. The first three are secure, the next 3 at least provide PFS, the last 2 are for compatibility. DHE is really secure only if you use at least 2048 bit DHE. — Z.T., Jun 09 '15 at 19:19
Thanks for the reply, DH export cipher is vulnerable to logjam attack, but the list its being hard to find which are all DH export cipher — Prem M, Jun 10 '15 at 03:43

StackzOfZtuff · Answer 1 · 2015-06-10T07:31:41.497

6

Any with _DHE_ in them. Those are the ones that use Ephemeral Diffie-Hellman, _ECDHE_ is safe.

edited Jun 10 '15 at 07:31

answered Jun 09 '15 at 15:00

StackzOfZtuff

Thanks for the reply ,What i understood is anything starting with _DHE is vulnerable to logjam attack. ECDHE is safe, is that right? – Prem M Jun 10 '15 at 03:38
Yes. There is no known similar exploit for the Elliptic curve version of Diffie–Hellman (ECDH). – StackzOfZtuff Jun 10 '15 at 06:37
For more info see my answers to these questions: Securing Chrome against Logjam on Windows and How to Check if a server is not vulnerable to logjam? – StackzOfZtuff Jun 10 '15 at 07:33

1 Answers1