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Nov
14
comment Complexity to find an preimage of a hash function
One note: while the lecturer was correct as regards to a Merke-Daamgard hash function with an inverible compression function, however all real MD hash functions (SHA-1, SHA-2) use a noninvertible compression function. What the lecturer was likely trying to point out why this is the case; why a compression function that is invertible is a bad idea.
Nov
14
comment Consequences of AES without any one of its operations
Yup, except for one glitch; the cipher is affine rather than linear (hence, there's this constant c sitting in the relationship); this is actually pretty easy to workaround; one way is adding an extra implied bit to each plaintext/ciphertext, which is set on every plaintext/ciphertext you have, and solve it as a set of GF(2) linear equations over 129 variables.
Nov
14
comment Consequences of AES without any one of its operations
Suppose you knew the plaintexts the correspond to the ciphertexts 1000...00, 0100...00, 0010...00, ..., 0000...001, and finally 0000...00 (all zeros). How could you use that to decrypt an arbitrary ciphertext? Extra credit question: how could you use that technique if you were given 129+ random plaintext/ciphertext pairs?
Nov
14
comment Consequences of AES without any one of its operations
No, that is not correct. However, suppose we had a large pile of plaintext/ciphertext pairs, what could we do with them to decrypt other ciphertexts?
Nov
14
reviewed Close CCA security of a system that splits messages and encrypts each packet
Nov
13
revised What is primary security in ECC?
Tried to make the questions clearer
Nov
13
reviewed Looks OK Condition on Vector Boolean Function to be Bijective
Nov
13
reviewed Close Modern integer factorization software
Nov
13
reviewed No Action Needed Verifiable, Distributed Secret Santa Assignments
Nov
13
reviewed No Action Needed Perfectly secret cipher can leak about the key?
Nov
13
reviewed No Action Needed Strange MAC algorithm
Nov
13
comment Consequences of AES without any one of its operations
Hint: what does linearity mean? If $AES(x) \oplus AES(y) = AES(x \oplus y) \oplus c$, for any $x$ and $y$ (and a fixed, key-dependent $c$), how could this be exploited?
Nov
13
comment What is the use of segments in Cipher Feedback Mode (CFB)
@owlstead: ok, universally recognized by the cryptographically clueful. In any case, while I can come up with plausible scenarios where CFB mode with s=8 is the best solution, I cannot think of any scenario where OFB mode with s=8 is any better than, say, OFB mode with s=n.
Nov
13
revised What is the use of segments in Cipher Feedback Mode (CFB)
Made things a bit more explicit
Nov
13
revised Condition on Vector Boolean Function to be Bijective
added 2 characters in body
Nov
13
answered What is the use of segments in Cipher Feedback Mode (CFB)
Nov
13
answered Condition on Vector Boolean Function to be Bijective
Nov
13
reviewed No Action Needed Blowfish ECB mode: Tools for known-plaintext attack?
Nov
13
reviewed No Action Needed Verifiable, Distributed Secret Santa Assignments
Nov
12
reviewed Leave Closed RSA: Fermat-Euler Theorem - coprimality of message and modulus