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May
27
comment Effective security of block cipher – equal the key size, or half the key size?
Maybe the algorithm would be clearer if the first loop used $X$ instead of $T$ as a variable name? (Also, the hash table access is likely not O(1), but $O(\log(2^{n/2})) = O(n)$. Still almost negligible compared to $O(2^{n/2})$.)
May
26
comment Effective security of block cipher – equal the key size, or half the key size?
@J.D. Please add this as an answer (with some details of how this attack works and a reference to a paper or similar).
May
25
comment Is it practical to use a stream cipher in a block cipher mode?
@J.D. consider adding an answer to the question linked in my previous comment, if that is not already covered by one of the answers there.
May
25
comment Can you make a hash out of a stream cipher?
If you have a PRF, why can't we use that directly as the compression function? It looks like unnecessary overhead to first build a PRP from a PRF, and then use Davies-Meyer to remove the P aspect from it?
May
25
revised Can you make a hash out of a stream cipher?
Fiestel → Feistel
May
25
comment Is it practical to use a stream cipher in a block cipher mode?
In Converting a stream cipher into a block cipher, this is discussed in a more general way – it looks like there is no way to build a block cipher from just a stream cipher, though if you additionally can use a keyed hash function, it might work. (You'll get a block cipher for much larger blocks, though.)
May
25
answered Is it practical to use a stream cipher in a block cipher mode?
May
25
comment Is it possible to have identical public keys for different ciphers?
@Nayef it looks like you misunderstood the question ... it is about public keys from different schemes colliding, not about collisions within one scheme (RSA and DSA in your example).
May
19
comment How do we know one-way functions can be iterated?
@fkraiem in a general mathematical point of view, both "input" and "output" of a function can elements of some arbitrary sets. Nothing stringy here. The set of (finite) bit-strings and its subsets are important examples, but not really exclusive ones.
May
19
revised How do we know one-way functions can be iterated?
recursion would be g(n) = g(h(n)) or similar. Using the output of a function as its input is named iterating it.
May
1
comment PGP digital signature vs SHA256 HMAC Comparison
keylength.com has some comparisons of key sizes for algorithms.
May
1
revised PGP digital signature vs SHA256 HMAC Comparison
adding some paragraph breaks
Apr
25
revised SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
edited tags
Apr
25
revised SHACAL in SHA-256
edited tags
Apr
25
comment SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
Also, you would need to do the key-schedule for each block again, which also adds to the execution time.
Apr
21
awarded  Nice Answer
Apr
19
comment Why does applying 56-bit DES twice only give 57 bits of security?
@fgrieu I guess we could build the table with only one block of plaintext-ciphertext, and for each of the $2^{48}$ found matches check the second block. This would have work of $2^{57} + 2^{49}$, which I would still consider as 57-bit security.
Apr
15
comment Why is Diffie-Hellman considered in the context of public key cryptography?
@i486 Diffie-Hellman does not directly allow encryption, it is just a key-exchange algorithm (and usually the resulting key should be hashed before being used for anything). You could use that key as a "stream cipher" key stream (i.e. XOR it with a plaintext) and send the result as ciphertext, but then you are actually doing more than just DH.
Apr
12
comment Encryption in which ciphertext is bigger than plaintext?
In cipher designs one usually tries to avoid a (more than constant) increase of the ciphertext.
Apr
10
revised How to encrypt a vector $e\in Z^{m}$ using LWE
fix wikipedia link