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Apr
15
comment Rijndael vs. Serpent vs. Twofish: General comparison
The link in the answer belongs to an archived part of the nist web site that is supposed to remain the same for the overseeable future. It is up now, and it is a static page so it rarely goes down. If you have trouble connecting the problem is more likely closer to your end.
Apr
14
comment What is the strength and attack vectors of this simple scheme?
If you reveal something by sending a cipher text list $L$ that the attacker didn't already know, your scheme isn't secure. OTOH, if you manage to only reveal as much as the attacker already knows and secrecy is preserved, it would be a lot more efficient, and exactly as secure, to use some form of OTP. And an OTP is already considered impractical.
Apr
12
comment Comparison of RSA and DRSA scheme using SageMath
Is this ccis2k.org/iajit/PDF/vol.3,no.4/9-Padhey.pdf the DRSA scheme you are referring to?
Mar
23
comment TLS padding format
This is for historical reasons. TLS uses the same formats as SSL 3.0, which was designed by Netscape back in the mid 1990's.
Mar
12
comment How is injective, inverse, surjective & oneway related to cryptography?
Regarding the last paragraph, a function will by definition return a single unequivocal output for each input; otherwise it is not a well-defined function, but a relation. However, a function might have a power set as codomain, meaning that the output could be interpreted as a "set of possible outputs".
Mar
10
comment What is the intuition for ECDSA?
Asking for "intuition" makes it hard to know in advance exactly what kind of answer you are hoping for. Could you perhaps relate your question to exactly what you find unclear e.g. in the Wikipedia article en.wikipedia.org/wiki/Digital_Signature_Algorithm?
Mar
9
comment Using One Time Pad with a block cypher
@ratchetfreak: You are correct, but the question stipulates that no key reuse cannot be assumed.
Mar
3
comment Does RSA have two trapdoors?
Do you have a link to the media from Khan University you reference?
Feb
23
comment Public key crypto without modular arithmetic?
@mikemaccana: No, it doesn't matter. It doesn't matter if the numbers are primes, smooth or products of large primes - either way the number will be a large integer, and Eves attack works for any large integer, as long as it is not so large it will be infeasible to carry out any arithmetic operation at all on it. But if Alice and Bob are able to multiply and divide the numbers, so will Eve.
Feb
20
comment Public key crypto without modular arithmetic?
@CodesInChaos: Well, the difference is that with Shamir three-pass, the multiplication operations wouldn't be performed in the same group that the cipher text messages belong to. If the Diffie-Hellman assumption applies to the group, the "multiplication" would be impossible to compute.
Feb
18
comment Is it ok to store the plaintext hash of encrypted data
What is it used for? What are your security requirements, i.e. why are you using encryption in the first place? Are you planning on storing the digest and the cipher text in the same location or in different locations?
Feb
17
comment To understand Feistel permutations in md5
It is the four-word state vector.
Feb
17
comment How to encode a message to MD5?
It might be noted that the Bit String to Octet String conversion in MD5 uses Big Endian bit order, despite the Octet String to Word conversion within MD5 uses a Little Endian byte order. The RFC is a cautionary example of an under-specified algorithm specification.
Feb
9
comment Is reusing keys for CBC and CBC-MAC secure when using encrypt-then-MAC?
CCM mode (counter mode with CBC MAC) uses the same keys for CTR mode encryption and for the CBC MAC.
Feb
3
comment Determining Involutary Keys in Substitution Ciphers
The symmetric group $S_n$ is defined as the set of all permutations over the elements of $\mathbb{Z}_n$ with composition of permutations being the group operation. If and only if an element in such a group is of order 2, then it meets the condition in your question, yes.
Jan
30
comment Side channel security of HMAC in software
True, if the hardware leaks the number of bits affected by instructions that would otherwise be assumed to be atomic, all bets are off. This obviously begs the question exactly what might be assumed about the hardware?
Jan
30
comment Side channel security of HMAC in software
Are you aware of any kind of side channel attacks against SHA-1 or SHA-2? There are no data dependent table look-ups like in AES and the algorithms appear to have a completely input independent operation flow.
Jan
28
comment Can I use a one time pad key twice with random plaintext?
Let us continue this discussion in chat.
Jan
28
comment Can I use a one time pad key twice with random plaintext?
I understand your point from a purely semantic point of view, but in practice, as the example in my answer is written, there is no practical meaning to the notion of guessing the message with probability $2^{-n}$. There will still be no way to test which guess is correct, all alternatives will be equally probable, exactly because the message was random, secret and has been discarded, as stipulated.
Jan
27
comment Can I use a one time pad key twice with random plaintext?
Isn't your point covered by the second paragraph in my answer? You will preserve the entropy of the message if you discard it immediately after transmission, but only then, and that's typically not what you want to do with messages.