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1d
comment Can AES be considered as Perfectly Secure?
More concretely, "perfectly secure" means that mathematically, the ciphertext contains no information about the message unless you have the key (except for a maximum possible length). That said, it's a poor choice of terminology, because one-time pads are susceptible to some forms of attack (for instance, they are malleable).
2d
comment Is it practical to use a stream cipher in a block cipher mode?
Cryptography is not an subject where you should endeavor to be creative. What do you hope to accomplish with such a construct? What shortcoming of a stream cipher are you aiming to overcome?
May
26
comment One time pad in CBC mode?
The point @mikeazo is trying to make is that your question is nonsensical. It's like asking whether or not it's safer to have anti-lock brakes on a jet-ski. Just as anti-lock brakes only apply to wheeled vehicles, CBC mode only applies to block ciphers — but one-time pads are a form of stream cipher. The property you want to avoid is malleability, but this is not something CBC defends against as it is trivially malleable. You are looking for cryptographic authenticity.
May
26
comment HKDF entropy extraction
Both any new cryptographic concept added to a system and any line of cryptographic code written brings non-negligible risk of messing it up. Cryptographers strive to use the absolute minimum necessary to provide the required security to a system.
May
24
comment Can you find the search space?
When asking homework questions, it is typically considered good form to give some indication that you have attempted to answer (or at least research) the question. What progress have you made? What is your intuition?
May
24
comment HKDF entropy extraction
Again, if you are trying to defend against an operating system that is actively working against you, you have already lost. CryptGenRandom may very well be backdoored. If it is, you have no reasonable expectation that any other function of the operating system is acting faithfully.
May
22
comment HKDF entropy extraction
This is security theater. First, CryptGenRandom already collects entropy from mouse movements, keystroke timings, etc — and using a much more well-tuned algorithm than you are likely to. Second, if Microsoft is untrustworthy and CryptGenRandom is backdoored, you're already screwed. Just use the output of CryptGenRandom and spend your leftover time addressing attack scenarios with a higher ratio of risk vs mitigation effort.
May
21
comment one-way deterministic hash for low entropy input?
The best you can do in this case is something like an HMAC with a secret key. If an attacker doesn't have the key (or an oracle), they won't be able to enumerate the hashes.
May
20
comment Can i get a list of over hard and long RSA keys? i think i have found a vulnerability in RSA Algorithm
Sorry, but unless you have discovered a new branch of mathematics, it is overwhelmingly likely that you have not found a way to quickly factor large primes.
May
18
comment Building a combined encryption scheme from two encryption schemes that's secure if at least on of them is secure
What directions have you tried? The hint in the question, plus @MaartenBodewes's answer is 98% of the solution.
May
15
comment Authenticate a short message with redundant encryption instead of using a MAC?
If you are validating tens of thousands of these per second, are you certain your assumption holds that sub-millisecond resolution is good enough to guarantee uniqueness?
May
15
comment Authenticate a short message with redundant encryption instead of using a MAC?
Yes, this would absolutely not work with a stream cipher, as flipping the same bit in both halves would result in the same plaintext output.
May
11
comment AES_GMAC implementation
To elaborate on @SOJPM's comment, it seems suspicious that you would have any need to implement AES-GCM as a person with a non-cryptographic background. If this is for a class, it's curious that there would be an expectation of implementing such an algorithm without having previously analyzed the construction. So it, frighteningly, looks like you might actually be trying to implement this for a real-world use.
May
1
comment Block cipher does not provide security by itself
Put succinctly by Bruce Schneier, cryptography is not magic dust you can sprinkle on your software to confer the property of "security".
May
1
comment PGP digital signature vs SHA256 HMAC Comparison
To be honest, regardless of which one you choose, it will likely be the strongest component of your security architecture. If it were considered feasible to recover the key or plaintext in either solution, it would be treated as a complete break of the system. The decision between symmetric/asymmetric crypto should be based upon the types of attack you want to defend against, not based on which is "stronger" by some benchmark.
May
1
comment Alice and Bob's crush
That approach does. Other similar approaches don't necessarily have to.
May
1
comment Alice and Bob's crush
I suspect, actually, you could achieve some uncertainty in the yes/no case if you tolerated a 50% chance that the protocol outputs "no" even in the event of a mutual crush. Consider the case where you included a random coin flip, and required that all three results be "yes". In the event that one party says "yes" and the other says "no", for the party who said yes, there's now only a 66% chance that the other party said no (instead of 100%, as in the original problem).
Apr
30
comment Why aren't zero-knowledge proofs used for authentication in practice?
How do you change a password later? What happens when the password requirements of a site conflict with the way you generate your passwords? Now you have to store information to regenerate the password correctly. And go through several time-consuming steps to actually log in. Or, you could just generate completely random throwaway passwords in a password manager and log in anywhere with essentially a single button press.
Apr
30
comment Why aren't zero-knowledge proofs used for authentication in practice?
Just use a password manager like LastPass, KeePass, or 1Password. You can synchronize the encrypted vault between laptops, phones, or whatever. Many have browser plugins that will automagically log you into websites at the push of a button.
Apr
30
comment Why aren't zero-knowledge proofs used for authentication in practice?
Don't reuse a password if you think there's a possibility any server that sees it might be compromised. Which boils down to, don't reuse a password.