[openssl-users] DTLS handshake in WebRTC

Suman Paul sumanpaul1987 at gmail.com
Wed Mar 1 09:39:30 UTC 2017

Sorry, I meant to say when the client sends its certificate, firefox in this case, it has a key of type ECDSA. How does a key of this type work when the  cipher selected is of type RSA?

> On Mar 1, 2017, at 1:33 AM, Matt Caswell <matt at openssl.org> wrote:
> On 01/03/17 05:55, Suman Paul wrote:
>> I have been looking at WebRTC DTLS handshake and don’t understand the
>> logic of how it works.
>> My Firefox client has support for both RSA and ECDSA ciphers while my
>> DTLS server only supports DHE-RSA-AES128-SHA and has a RSA key. I see
>> that Firefox sends a ECDSA key during client hello. What ends up
>> happening is that DHE-RSA-AES128-SHA is selected. I would have
>> expected the negotiation to fail due to there being no common
>> ciphers.
>> I also verified this behavior using the OpenSSL s_server and s_client
>> utilities. Seems to me that as long as s_server has a cert and key of
>> the type of cipher I enforce with ‘-cipher’ option the negotiation
>> succeeds irrespective of the type of key the s_client (provided that
>> cipher is also supported by the client).
> Your terminology is slightly confusing. No keys are sent in the
> ClientHello at all. You should see a list of all the ciphersuites that
> the client supports being sent in the ClientHello and then the server
> should respond with a ServerHello which picks a ciphersuite from that list.
> Matt
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