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Apr
4
answered HMAC-SHA1 vs HMAC-SHA256
Apr
3
comment TLS Key Block calculation - What is a PRF?
@Eddie: you are correct, except that PRFs in general do not produce arbitrary long outputs; that is a special property of the PRF that TLS uses
Apr
2
answered TLS Key Block calculation - What is a PRF?
Apr
2
comment What is h in this RSA variant?
Well, given a public key $(N,e)$ and plaintext/ciphertext pairs $(P,C)$, an attacker can replace it with an RSA key $(N,e)$ and plaintext/ciphertext pairs $(P,eC)$; any attack on this system would immediately imply an attack on the RSA system. We believe the RSA system to be secure (because, while $e$ was chosen so that $e^{-1}$ is small, there's no known weakness there), and hence this system is secure.
Apr
1
comment What is h in this RSA variant?
Actually, these authors just copied the 2KGEA algorithm from their reference [3]: iasir.net/IJSWSpapers/IJSWS13-272.pdf - however, that paper doesn't answer any of the above questions.
Apr
1
revised What is h in this RSA variant?
deleted 5 characters in body
Apr
1
answered What is h in this RSA variant?
Apr
1
comment Demonstrating Diffie-Hellman key exchange using only p, A, B;
There are 50976 generators for $Z/104933$, and that's assuming that, by generator, the question meant a generator for the entire group, and not the generator for the subgroup we'll be doing DH in. So, 5 is a generator; how do we know that that's the generator that's meant, and not any of the 50975 other generators that exist?
Apr
1
comment Demonstrating Diffie-Hellman key exchange using only p, A, B;
No, there is not enough information given to let you derive $g$. Now, if they said "use the smallest value that generates the group for $g$", then you could find that, and then use that. However, remember that any value of $g$ will work within the protocol (although some choices, such as $g=1$, do have some security issues, of course, in this toy example, there aren't any secure choices). Also, in practice, we generally don't use values of $g$ which generate the entire group, and so you are told to use such a value, that's something contrary to common practice.
Apr
1
comment Demonstrating Diffie-Hellman key exchange using only p, A, B;
I believe you'll also need the value of $g$; you cannot derive it with the information you have
Mar
31
comment Can a commutative block cipher be indistinguishable from a random permutation, for fixed key?
@fgrieu: actually, it sounds like what you really ask about are known plaintext attacks; given a random set of $(x, P(x))$ pairs, can we distinguish a random $P$ from $E(k)$? Given the Pohlig-Hellman cipher, we can distinguish it in this model; is that a fundamental property of all commutative ciphers, or is that just a side effect of how Pohlig-Hellman achieves commutativity and another commutative cipher might be secure in this model?
Mar
31
answered Can a commutative block cipher be indistinguishable from a random permutation, for fixed key?
Mar
29
awarded  rsa
Mar
27
answered Is it secure to choose d in a RSA key pair?
Mar
26
comment m ∈ Zn \Z*n, RSA works but not secure
You still have the wrong value for $\phi(p)$. $\phi(p)$ is defined to be the number of values between 1 and $p-1$ which is relatively prime to $p$. If $p$ is prime, how many of the values between 1 and $p-1$ are relatively prime to $p$?
Mar
26
reviewed Approve suggested edit on Encryption of numeric value using playfair
Mar
26
answered Is there a time-space tradeoff attack for breaking symmetrical cryptos?
Mar
24
comment How secure is the AES master key if Round Keys are found
I believe that's assuming the key scheduling for AES128. Yes, for AES128, learning any one round key gives you everything. However, the original question specified AES256; AES uses a different key expansion process when it is given 256 bit keys. If, with AES256, you can determine the entire transform with just one 128 bit round key, that would mean that AES256 encrypts in at most $2^{128}$ different ways, and hence it would effectively have a 128 bit key.
Mar
24
answered How secure is the AES master key if Round Keys are found
Mar
22
comment No of keys used in Triple DES Algorithm
@user2966119: actually, if we look at how 3DES is used in standard protocols (TLS, IPsec), we see that it is treated as if it were a block cipher that takes a single 192 bit key (192, not 168, because standard DES keys are 64 bits, and it doesn't matter to the protocol that some of those key bits are ignored).