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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years
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Oct
9
comment what are the uses of tweaks in block ciphers?
@sashank You can encrypt each block independently, similar to ECB mode. But the tweak ensures that the same data at different positions encrypts to different values, avoiding ECB's biggest weakness.
Oct
9
comment AES file encryption with PBKDF2. Safe parameters?
@hunter Not entirely sure what you mean by "only the final round". Do you want to run PBKDF2 with 1 iteration on the output of PBKDF2 with many iterations?
Oct
9
comment post-quantum threshold secret sharing
Hashes/one-way-functions are a completely different issue. As far as we can tell they still exist, you just need to use twice the size. A 512 bit hash will offer 256 bits of security against QCs, far from any realistic attack.
Oct
9
comment post-quantum threshold secret sharing
If by threshold secret sharing, you mean something like Shamir's secret sharing, you can continue to use it. It's secure against computationally unbounded attackers i.e. it offers information theoretic security. It's essentially a system with less equations than variables, so there are many equally likely solutions.
Oct
9
comment AES file encryption with PBKDF2. Safe parameters?
@hunter one has to be careful about that. If one directly requests more than the natural size from PBKDF2 it can increase the cost for the defender but not for the attacker. Personally I like HKDF-Expand for this step.
Oct
9
comment what are the uses of tweaks in block ciphers?
I've only seen tweaks used as a block counter.
Oct
9
comment AES file encryption with PBKDF2. Safe parameters?
1024 iterations is very low. If you can afford the performance hit, use a larger value. On a desktop computer you should be able to afford a million iterations.
Oct
8
comment How do TLS 1.1 and 1.2 generate IVs (initialization vectors) for each record?
The obvious implementation is requesting 16 bytes from the PRNG.
Oct
8
comment How does redundancy in a file effects performance and security of encryption?
Proper encryption doesn't notice redundancy. You're putting in a bunch of bytes, getting out a bunch of bytes and runtime only depends on the length of the input.
Oct
8
comment Does BouncyCastle (for ECC) resist timing attacks?
I wouldn't use the ECC code in BouncyCastle C#.
Oct
8
comment How does one use AES block cipher modes of operation?
I don't get your question. You say that you have 8 bit block size, but you also mention AES. That makes no sense. Do you mean that you need to encrypt messages which aren't a multiple of 128 bits without length increase?
Oct
7
comment Does ElGamal Encryption create a different key for each block sent?
cross-posted on SO
Oct
7
comment SHA-1 colission resistance proof
Those are essentially random numbers, but created in a way that doesn't allow the algorithm designer to choose them, so called Nothing up my sleeve numbers. I don't remember what SHA-1 chose, probably the first few hex digits of square-root of a small prime.
Oct
7
comment SHA-1 colission resistance proof
1) It isn't 2) Those properties generally don't have a proof.
Oct
7
comment Why are huge prime numbers important in cryptography?
Huge primes are not important in crypto. I've never seen a prime larger than 10000 bits in crypto. Finding huge primes is just a sport.
Oct
6
comment Does BouncyCastle (for ECC) resist timing attacks?
These are large libraries, some parts my be better than others. At least the ECC part looks vulnerable to timing attacks to me.
Oct
6
comment Practical disadvantages of GCM mode encryption
That kind of bug can happen with pretty much any kind of MAC. They're the reason why I like unit tests that cover all possible message length from 0 to a few hundred.
Oct
6
comment What is adversary's advantage in cryptography and why we use it?
@LateralFractal I'd guess having a site-index (which tells google what has changed) and being popular are the most important factors.
Oct
6
comment Is this a good entropy collector and whitening technique?
A sane algorithm would be secure if the entire seed material contained enough (somewhere between 100 and 200 bits) entropy. Your algorithm is only secure if each 512 bit block contains enough entropy. So it's clearly a bad design.
Oct
6
comment Is this a good entropy collector and whitening technique?
Step 3 is silly, and step 5 shows a misunderstanding of randomness