poncho
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 Aug 6 awarded Enlightened Aug 6 awarded Nice Answer Aug 5 comment Is the encryption of a hash a good MAC? @cooky451: why would it fail? What if the attacker intercepted the original $(M, Mac)$, so the receiver never got it, and replaced it with $(M', Mac')$? Aug 4 awarded Excavator Aug 4 revised How to build an electro-mechanical public key cipher machine? Fixed explanation of Rabin Aug 4 comment Is the encryption of a hash a good MAC? @cooky451: I believe you're misunderstand what I'm trying to say; we have $Mac = E(Hash(M))$, can the attacker find a second message, MAC pair for which $Mac' = E(Hash(M'))$. It's not the valid sender which is trying to generate $E(Hash(M'))$, it's an attacker. Unless the attacker is forced to modify the $IV$ when he modifies $M$, he (unlike the valid sender) has no issue with reusing an IV. Aug 4 awarded Enlightened Aug 3 awarded Nice Answer Aug 3 comment RSA signature attack check on lowest 16 bytes - Implementation @Seed3Key: look at what I wrote; not y = y.add(two) but y = y.add(two.pow(i-1)) Aug 3 reviewed Leave Open How to reconstruct hash value to the original format? Aug 3 comment RSA signature attack check on lowest 16 bytes - Implementation That's wrong as well. If the $y^3$ and $hash$ agree in the lower $i$ bits, then you don't need to update $y$ at all (because you know that the lower $i$ bits are correct. If they don't agree, then you know you need to flip bit $i-1$ of $y$ (and since you initialize that bit to 0, that's the same as adding two,pow(i-1) to it. Aug 3 answered RSA signature attack check on lowest 16 bytes - Implementation Aug 3 revised Why do crypto libs use table lookups when they're vulnerable to timing attacks? added 1123 characters in body Aug 3 answered Why do crypto libs use table lookups when they're vulnerable to timing attacks? Aug 2 comment Can non-assembly crypto libraries truly be secure against timing attacks? You can't really control what's in the L1/L2 cache with assembly; that also depends on interrupts the CPU takes, and what the other cores are doing (neither of which are under the user's control). If you controlled the operating system as well, you would have hope; however I believe that's focusing in on the wrong question; the answer to timing attacks isn't having precisely consistent timing, but have any variation in the timing uncorrelated to any secret we have. Aug 2 reviewed No Action Needed Signature Verification: High level Aug 2 reviewed No Action Needed Understanding elliptic curve encryption Aug 1 revised Implementing CBC Encryption Using Decryption edited tags Aug 1 answered Implementing CBC Encryption Using Decryption Jul 31 comment Encryption algorithms larger than 256 Bit for “big data” encryption? Are you asking "why do we generally restrict our (symmetric) keys to 256 bits"? If you aren't asking that, what are you asking?