(Qualsys has an excellent tool that simulates major browser negotiation with websites.)Įssentially all the other major browsers (Chrome, Firefox, Safari, etc) generally choose forward security if the server supports it, so decryption with just the private key of the server isn't possible. So if you're very careful in setting up your SSL options on the server, AND your server supports prioritizing one algorithm over another, then it's possible to get Forward Security negotiated on even IE. IE is notoriously bad at choosing a FS algorithm, and relies on the server to prioritize the various options. There's no guarantee that the client negotiates a forward security algorithm. It really depends on if Forward Security (FS) was negotiated between client and server. Have to always work) having the servers private key should still notĪllow you to decrypt any traffic unless you are performing an active ![]() The server (or theoretically client, but that is harder and doesn't Therefore it is not necessary for session decryption.Īssuming an appropriate setup of the SSL/TLS parameters on the side of The client or server never uses the client's public key to encrypt any information in the handshake. Thanks to Wireshark, we can decrypt Kerberos packets partially with help of. The server then uses this signature to verify the client. It only has the shared secret key derived from the clients password to. It responds with the ClientKeyExchange message as it does in a typical handshake, and then sends a ClientVerify message which signs the hashed key exchange data. This message asks the client for its public certificate. In the above exchange we see that after the server sends its certificate it also provides a CertificateRequest message. ![]() SSL/TLS Key Exchange w/ Client Authentication The client key exchange message is the pre-master secret encrypted with the server's public key. Notice how in the above exchange only the server sends its certificate. This is why you need the server's private key, not the client's. The pre-master secret is what's used to generate the session keys. ![]() A client certificate is only used for client authentication if the server requests it. This is because in an SSL/TLS connection the asymmetric key exchange uses the server's public key to exchange the pre-master secret.
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