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Deltavista_1797's avatar
Deltavista_1797
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Dec 10, 2014

DHE key exchange: why is ephemeral key only 1024bit long?

Hello,   during a recent analysis comparing security options provided by Apache httpd and F5 LTM we discovered that while Apache for RHEL/CentOS has lifted a limitation of 1024 bits for ephemeral ...
application delivery
LTM
security
Joe_M's avatar
Joe_M
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Mar 10, 2015

It is possible, I might be getting confused. But for clarification, the cert and key pair is signed with SHA2. What I am getting at is this, below are 2 snippets taken from SSL Labs reports. The first from our F5 indicating that the 1024 bit DH key is weak. 2nd is from the report of a linux box with the same ciphers using strong keys.

 

F5 VIP:

 

TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) DH 1024 bits (p: 128, g: 1, Ys: 128) FS WEAK256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 (0x6b) DH 1024 bits (p: 128, g: 1, Ys: 128) FS WEAK256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA (0x39) DH 1024 bits (p: 128, g: 1, Ys: 128) FS WEAK256

 

Linux box:

 

TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) DH 4096 bits (p: 512, g: 1, Ys: 512) FS256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 (0x6b) DH 4096 bits (p: 512, g: 1, Ys: 512) FS256 TLS_DHE_RSA_WITH_AES_256_CBC_SHA (0x39) DH 4096 bits (p: 512, g: 1, Ys: 512) FS256

 

So how do I get the F5 to not use 1024?