CodesInChaos

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680 Comments

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May
22
 comment Is modern encryption needlessly complicated?
Quantum crypto does not solve the key exchange problem. It just solves the problem of securely stretching a short symmetric key into a one time pad i.e. at best it's a secure stream cipher with additional limitations. Pretty much everything interesting is outside its abilities. So IMO quantum crypto is one of the most useless things ever.
May
22
 comment Encrypting documents through a proxy key
With KDF I mean something like PBKDF2, scrypt or bcrypt. i.e. a deliberately slow, salted hash function.
May
22
 comment Encrypting documents through a proxy key
I hope you did design your system carefully, choosing an appropriate mode(probably using authenticated encryption of some form), deriving the key from the password using a fitting KDF, using salt and IVs correctly,...
May
22
 comment Is my pseudo-random initialization vector secure?
This is a programming problem, and not a crypto problem. So it fits SO rather than crypto.SE. But of course you need to specify your programming language/platform to get a meaningful answer.
May
22
 comment Is my pseudo-random initialization vector secure?
@infact In CBC more IVs must be unpredictable, and it many other modes it must at least be unique/not reused.
May
20
 comment Lamport signature: How many signatures are need to forge a signature?
You'd need to find a pre-image for $m_3$ and $m_4$, and that's hard, assuming the function used to hash the message is a good one.
May
12
 comment Is using slow password hashing on the client side easier attackable than on the server side?
Is there a reason why you salt the second cheap hash?
May
11
 comment How were the AES key and block length subsets of Rijndael selected?
I guess 128 because it's the standard level of what's considered secure, and the other two because it's more than that, at reasonable steps.
May
11
 comment Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings
2^51 sounds computationally feasible. Why haven't we seen any collisions yet?
May
11
 comment Why DSA cannot be used for encryption?
@jug That scheme is certainly not asymmetric encryption. It's not even real encryption, it's just a way to transmit secret information without using "real" encryption.
May
11
 comment Does NTRU decrypt correctly now?
A failure rate of 2^-256 is small enough, since hardware failures are certainly more likely than that. But I imagine convincing people that it doesn't matter isn't easy. In my experience many programmers have an irrational fear of probabilistic algorithms.
May
11
 comment Why DSA cannot be used for encryption?
@LunarMushrooms That's a nonsensical question. It's a signature algorithm. You can't use RSA signature algorithms for encryptions either. You'd need to ask if the mathematical structure underlying DSA can be used for encryption. AFAIK it can't, but it can be used for key-exchange, which is very similar to encryption.
May
11
 comment Why DSA cannot be used for encryption?
You can sue Diffie-Hellman keyexchange to achieve something similar to encryption.
May
9
 comment Encryption with “constant” initialization vector considered harmful
"you are not supposed to change your secret (the key) often, because this needs to be shared with the other party" Many protocols, including TLS, use a new symmetric key for each connection. Only the asymmetric keys used for authentication need to be fixed.
May
9
 comment How can we find Public key have only 8 or 16bits? How many messages does Eve need to know the Public key in RSA?
RSA below 512 bits is ridiculously broken, and RSA below 1024 bits is still pretty weak. If you want small keys/blocks, go with elliptic curves, but even they become weak below 160 bits.
May
9
 comment How can we find Public key have only 8 or 16bits? How many messages does Eve need to know the Public key in RSA?
One can't even apply padding to 16 bit RSA. So do you want to use textbook RSA?
May
8
 comment How can disk encryption systems (like Truecrypt) resist frequency analysis when they allow random access?
"However, things change when an attacker can take multiple looks at the volume at different points in time." That's why the TrueCrypt authors discourage backing up a volume by copying the container.
May
5
 comment Order of hashing concatenation
Probably HMAC is a better choice
May
5
 comment Order of hashing concatenation
Not sure what exactly you're trying to protect against. Could you clarify that?
May
4
 comment Do public/private pairs work both ways?
It's possible in principle, but useless in practice.
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