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I've been benchmarking my TLS performance, and I noticed that during the "write client key exchange" phase, there's significant overhead compared to all other actions. I'm wondering if there's anything I can do to speed this up?

40348.989720O ssl_info_callback SSL_connect SSLv3 read server certificate A
140348.989934O ssl_info_callback SSL_connect SSLv3 read server key exchange A
140348.989954O ssl_info_callback SSL_connect SSLv3 read server certificate request A
140348.989968O ssl_info_callback SSL_connect SSLv3 read server done A
140348.990606O ssl_info_callback SSL_connect SSLv3 write client certificate A
140349.29131O ssl_info_callback SSL_connect SSLv3 write client key exchange A
140349.35914O ssl_info_callback SSL_connect SSLv3 write certificate verify A
140349.36013O ssl_info_callback SSL_connect SSLv3 write change cipher spec A
140349.36062O ssl_info_callback SSL_connect SSLv3 write finished A
140349.36077O ssl_info_callback SSL_connect SSLv3 flush data
140349.36094O ssl_info_callback SSL_connect error in SSLv3 read server session ticket A

Based on this, it looks like the client key exchange takes ~300ms

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You really should include some data on the hardware and software platforms involved here. A client key exchange in only 300ms would be extremely fast if the client uses, say, a 33 MHz ARM processor -- and quite slow if the client is a 2 GHz PC. –  Thomas Pornin Aug 3 '11 at 23:22
    
Please provide more information. It looks like OpenSSL. What version is it, can you reproduce that behavior with openssl s_client ? Do you have a public URL we can try ? –  ixe013 Aug 5 '11 at 12:56
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1 Answer

After your client receives the server's certificate, It could be that the client tries to check certificate revocation.

Save the server's CA certificates to a file and use the -CACert argument (or -CAPath).

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and or is checking the certificate chain, especially if the chain is long –  this.josh Aug 5 '11 at 6:18
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