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Cipher Strength vs AEAD.

Question asked by porifera robert on Jan 3, 2015
Latest reply on May 31, 2015 by j-mailor

Hello,

 

in your rating guide, it  states that cipher strength is only based on key length : https://www.ssllabs.com/downloads/SSL_Server_Rating_Guide.pdf

 

This does not represent accurately the robustness of the cipher suite¸ since block cipher chaining mode with authenticated encryption provides a better security level than non-authenticated modes.

 

This might need to be revised in order to give priority/better rating for GCM based Cipher Suites vs CBC ones : it could be argued that AES-128-GCM is stronger than AES-256-CBC since it does not allow for ciphertext malleability.

 

Just to make things more complicated, there are theoretical attacks on AES-256 that do not apply to AES-128 and make key retreival "easier" on 256/192b keys so giving more points for AES-256 vs AES-128 might be questionable.

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