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can somebody explain to me if for example i use Server certificate, with 2048bit keys and client certificate with only 512bit strength, does this use in any way affect the security of the established SSL?

Why i'm asking is because using client certificate requires RSA decryption in ssl handshake and on embedded ARM5 devices using 2048 client cert negotiation takes 7 sec :S

So using a lesser client cert 512 is significantly faster...

Thank you and best regards, Lonko

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...if for example I use Server certificate, with 2048bit keys and client certificate with only 512bit strength, does this use in any way affect the security of the established SSL?

It does not affect the strength of encryption since this depends at most on the servers certificate (for RSA key exchange). But it will affect how easy the client certificate can be spoofed, so it does affect the credibility of the client authentication. 512 bit keys are considered broken since 1999 and might have been spoofed in 2011.

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  • But why is there then an rsa decryption going on in the handshake with the client cert ? I mean the decryption is the only thing what is slowing everything down...
    – Lonko
    Jan 3, 2015 at 18:06
  • It's not decryption, but signing. The client has to proof that it owns the private key to the public key inside the certificate. This is done by signing something within the CertificateVerify message.
    – Steffen Ullrich
    Jan 3, 2015 at 18:14
  • Finally i get it :D damm will see if the provider can give us a lesser strength, otherwise problem :) Catch is that this client cert identifies a solution nothing else...
    – Lonko
    Jan 3, 2015 at 18:23

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