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Dec
14
answered What is the impact of different modes on pseudo randomness of AES?
Dec
13
comment collision resistant summarizer for long hash values
@user10851: there's no known way to make SHA-256 'invertable'; I just listed that because a restriction to short inputs is one way to get around the lack-of-collision resistance of 128 bit hashes. One obvious way to make such an invertable hash would be to use the identity function; the hash is the input padded out to 128 bits. You don't get preimage resistance; however you do get excellent collision resistance (as long as the inputs are no longer than 128 bits)
Dec
13
answered ECC key size and signature size
Dec
12
comment collision resistant summarizer for long hash values
@user10851: if you use a keyed hash (where the attacker doesn't know the key), then the attacker obviously cannot perform an offline collision attack. And, if you limit the messages being hashed to no longer than 128 bits, you could conceivably use an invertable function for your hash; that obviously doesn't have any collisions. Other than that, there's not much you can do (other than increasing the length of the hash output)
Dec
12
comment collision resistant summarizer for long hash values
@user10851: I'd say know, but I don't know exactly what you mean by entropy; that certainly isn't true for the standard (Shannon) definition of entropy. Do you mean 'making the output a more complex function of the input'? If so, well, as far as we know, a SHA256 output is already a complex function of the input; it's unclear how making the function more complex adds to security (except for making the attacker's job incrementally harder).
Dec
12
answered collision resistant summarizer for long hash values
Dec
11
comment In RSA, why is it important choosing e so that it is coprime to φ(n)?
@CodesInChaos: doh! I knew that; however since I personally use prime $e$, it slipped my mind...
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
added 17 characters in body
Dec
11
awarded  Enlightened
Dec
11
awarded  Nice Answer
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
Grumble typo...
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
Expanded explination
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
typo
Dec
11
revised In RSA, why is it important choosing e so that it is coprime to φ(n)?
English fixup; added final note
Dec
11
answered In RSA, why is it important choosing e so that it is coprime to φ(n)?
Dec
10
comment Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
@user10800: well, I'm not sure what you should call it (stream cipher really doesn't apply either, come to think of it; it uses inputs from both sides; it appears to be closest to El Gammal, but it's not that either). The term OTP doesn't apply, because the one point that you're missing is a very important point about OTPs. As for exhaustive search, well, you're secure computationally, and so the correct protection against exhaustive search is to make it computationally to difficult to consider. As for each character getting its own random shift, we have better ways to protect plaintext.
Dec
10
answered What are the pros/cons of using symmetric crypto vs. hash in a commitment scheme?
Dec
10
comment Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
@RickyDemer: thanks; if you go through my answers, you'll find that I often think one word, but type something else...
Dec
10
revised Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?
Rewording
Dec
10
answered Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?