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7

I suspect that KCV's are in general not used because they don't add enough to be worth the small overhead. There are a number of cryptographical attacks on encrypted methods that involve the attacker modifying a valid ciphertext, and then having the receiver decrypt the modified message (and watch how the receiver reacts). Because of these attacks, it is ...


4

In order for a symmetric block cipher to be considered secure by modern standards, it has to be IND-CPA, that is indistinguishable from a random oracle under a chosen plain text attack. It also has to be IND-CCA and IND-CCA2, but IND-CPA is sufficient for it to also be secure under a known plain text attack. Presuming TwoFish is still unbroken, it should ...


3

I've thought quite a lot about this, and I think in general the answer is no, it would not be a good idea to use a KCV for those kind of situations. Using a hash or even better a MAC (using the key as MAC Key) would be a much better idea if a KCV is required. Instead of zero's, it would be much better to use a block of bytes that is not likely to be of use ...


1

Owlstead already gave a good answer, but I just wanted to point to a [very] relevant recent paper: Impact of ANSI X9.24-1:2009 Key Check Value on ISO/IEC 9797-1:2011 MACs After a brief discussion of some general issues, the paper goes on to prove tight bounds on the security of the IEC MACs once the Key-Check-Value has been released. To quote the abstract: ...


1

To calculate the KCV for AES, you take the first three bytes of the encryption of zero under your key. Indeed, the case you've given is precisely this - the zero vector encrypted under the key 48C3B4286FF421A4A328E68AD9E542A4 is 77dc841daeb43315fed9acdf2f965f45, which restricts to 77dc84. In your question you say you already have AES-128 encryption, at ...



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