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I have an issue with the answer to Ch. 3 Review Question 9 - "Which of the following is a FIPS encryption standard that uses a single 56-bit symmetric key? (Choose all that apply.). My answer is C (DES) & D (3DES). The answer, according to the text, is C (DES). Would I be right if the question had stated "Which of the following is a FIPS encryption standard that has an effective key strength of 56-bits?”? I know that 3DES keying option 3 has all three keys being equal (K1=K2=K3) therefore it's really just a slower implementation of DES and has an effective key strength of 56-bits. Am I correct in saying this?

Thanks,

Because DES is  symmetric, step 2, decrypt with a second key, is really not a decryption.

3DES uses EDE - Encrypt,Decrypt,Encrypt  64-bits block encryption technique.

If K1 !=K2 !=K3 and K1 !=K3, then key entropy is 168 bits

IF K1=K3 !=K2, then key entropy is 112 bits.

3DES-EDE encryption with K1=K2=K3 equal DES encryption, which is prohibiterd in FIPS standard.

Good Luck!

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Vertigo

Thanks guys!

Kewl info!  Great discussion.  I'm a little rusty on this stuff. 

Darby Weaver