[openssl-users] Getting info on the ciphers supported by a client

[Christian Georg]

Hi all,

I am trying to get detailed info on the protocols and cipher suites supported by a client app. Main goal is to verify that the constraints on protocols versions and cipher suites we are using within an app are working correctly. (so it is not about the cipher suites that are theoretically available on a mobile device)
I was planning to use openssl s_server for this task. I am opening s_server on different ports each with a specific protocol version (-ssl2, -ssl3, -tls1...). On some of the ports a handshake should be successful on others not.

The tricky part are the supported cipher suites. When using the -www option I can return a website to the client showing the cipher suites that provide a match, which gets pretty close to what I want in a browser. Now here are my challenges.

Challenge 1: Getting a list of ALL Ciphersuites
I would like to get info on all cipher suites supported (preferred) by the client . The -www option does only show the cipher suites with a match. So any cipher suite not supported by openssl will not be listed. When checking my browser with qualys SSl Lab I noticed that the following three ciphersuites are showing up on the qualys report but not on the s_server page.

TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256

I do not see them as a risk, but what if some exotic weak ciphers are enabled within the app. It is my understanding that during a handshake a list of all preferred ciphers is send from the client to the server. How can I get access to this info?

Challenge 2: How do I get the info into a log file on the server rather than sending it back as a website?
The approach described above is working fine for browsers but what about consuming webservices? I am able to redirect the webservices to my openssl s_server and perform the handshake (even so the SOAP or REST Interface will then throw an error). But I could not find an option on getting the info written into the Logfile (in a human readable way) even with all logging I found enabled (-state -debug -msg -tlsextdebug -trace) I could not find the info in a human readable way.

Any recommendations on how I can solve my issues without changing the openssl code and add this manually?

Cheers

Chris

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