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Mar
25
comment Bit commitment, two blobs with same bit, without revealing it?
The computational problem for this is the quadratic residuosity problem. Basically, this is the Goldwasser-Micali encryption scheme utilized as commitment scheme.
Mar
25
answered Does perfect secrecy imply uniform ciphertext distribution?
Mar
23
comment Should I remove these use cases of MD5/SHA1 from my program?
Honestly, I have no idea about crypto libraries in PHP. But it seems, you are using the basic commands, while (at least today) the library also supports higher level protocols, like $cipher = new Crypt_AES(CRYPT_AES_MODE_CTR);and you can use PBKDF2, etc. However, this still doesn't say anything about the quality of that library, e.g. a question on security-SE talks about this. But if you want to achieve your high security, you should invest time in researching this.
Mar
23
revised Should I remove these use cases of MD5/SHA1 from my program?
added 81 characters in body
Mar
23
answered Should I remove these use cases of MD5/SHA1 from my program?
Mar
23
answered What is the best hash for HMAC?
Mar
23
comment How many attempts does it take to crack a 32-bit password hash with this scenario?
user13741 is right for this one. The reason is simple: If you hash different inputs, you can get the same hash value on several occasions. Basically, you got a $1/2^{32}$ probability for a success on every try. This is a geometric distribution, with estimated value at $2^{32}$ (if looking for one hash value). Subtracting $1$ from the exponent is applicable, when you brute force a key for a symmetric encryption, where you directly try out every possibility. For hashes, $2^{32}$ does not give you that $100\%$ chance.
Mar
23
comment Why would using a random seed with other variables be bad for ecrypting if you can't guess the key?
Because no one said it so far: Schneier's law: "any person can invent a security system so clever that she or he can't think of how to break it.". To sum up a modern point of view: something which has security only against ciphertext only attacks is considered insecure. Arguments like "but you can't guess X from Y" are almost always neglecting actual cryptographic advances during the last 30 years.
Mar
23
comment security of pairing based cryptography
I had only a quick glance, but they present an attack on one single specific group. Advances like these are achieved now and then, but techniques like these usually can not be generalized for every group. From a theoretical point of view: If you just assume to use a pairing friendly group, this is irrelevant. From a practical point of view: Pairing friendly curves are usually not implemented outside of research, because pairings are efficient only in a theoretical sense but not a practical one.
Mar
20
comment How dangerous is it to encrypt with AES 256 if the end user knows the unencrypted value?
Security decisions should never be made without the proper knowledge. Things like that lead to all those little pieces of negative publicity, because someone botched something trivial royally.
Mar
19
comment What prime lengths are used for RSA?
A common assumption is equal length, $q<p<2q$ or at most a length difference of $1$. But that is not really a question about security, it is more about the policy for the usage of RSA. Allowing uneven factors is a potential security risk, because "small factors" can be found more easily. In general, the factoring problem scales with the smallest prime factor, not with the total length. Multiplying $2^{1000000}$ to any RSA modulus does not make it harder to factor.
Mar
19
answered Deciphering text encrypted with a changing cipher
Mar
19
comment Applying Trapdoor Function directly to plaintext
What does "secure" mean in this context? It can't be IND-CPA, because that does not work with a deterministic encryption function. It can't be in the context of signatures, because there you use $F^{-1}$ to generate the signature.
Mar
17
comment Practical strength of non-2^n RSA key lengths
The other question covers the topic nicely already. This is like asking "Why is the data type int in most common programming languages 32 bits?"
Mar
16
comment Reusing a one-time pad?
Your first idea is basically a Vigenere cipher. Its security in modern understanding: None.
Mar
13
comment Why is this a fix to Bleichenbacher's attack?
Basically, if the computation time/length/effort/energy consumption/other_sidechannel is independent of whether the PKCS format has been fulfilled or not, then there is no information to do the attack.
Mar
13
comment Why is this a fix to Bleichenbacher's attack?
In short: The entire attack is based on being able to distinguish whether the padding is correct or not, and that can be derived if the server immediately sends an error message on detecting a wrong padding.
Mar
13
answered Self verifying hash algorithm
Mar
12
comment What is the difference between a hash and a permutation?
This is completely wrong. It seems to me, that you are taking permutation as some sort of container (e.g. list, set, etc.) and think of hash only of the case of HashSets. A permutation is the process re-ordering, and does not say anything about the underlying structure. But it is also implicitly a reversible process, while hashing is not. There you just get a fancy "checksum", which can be checked for equality of objects and not much else. But ofc it is fast.
Mar
12
comment what is the current actual budget - as of 2015 - needed to build a DES breaker machine?
Check out CloudCracker. It was a cloud service to break DES in the cloud. That's roughly 2 years ago, and it seems they are not online any more. Still worth reading the news about it.