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seen Dec 18 at 22:17

Dec
18
comment Does RSA operate over a Finite Field (Galois Field)?
While the correct answer to the question is "no", the RSA definitions also can work for those elements, which are not coprime to $n$. Since they are zero divisors, they dont have inverse elements, but it can still be true that $x^{ed} = x$, with $x$ not coprime to $n$. I cant recall the exact requirement there, but there are topics on this on crypto-SE.
Dec
18
comment Attacker in a key exchange
It looks like the notation for symmetric encryption in this is: $(X,K)$ for plaintext $X$ and key $K$. It is an awful notation tho, because it should either be something like $E(X,K)$ or $(X)_K$ to be less confusing. And the same notation is used to denote tuples.. guess what is what.
Dec
18
comment What would be the best plain text Cryptography method without the use of a computer?
Let me rephrase: People call all sorts of things "OTP", which aren't OTP but streamciphers. And if you use OTP, you can just store the plaintext instead of the key, because OTP does not consider key storage. Simply put: Using OTP is almost always entirely pointless. It cant be much terrible than that, because with RC4 you have weak security, but at least you could just store the short key for a longer message. Same goes for sending messages: If you can somehow transmit a key of equal length securely, then you could just send the real message securely instead.
Dec
15
comment What are the potential (major) flaws in this security scheme?
The checksum does not serve any security purpose in this example, unless Alice and Bob also have a shared key to use a Message Authentication Code (MAC; basically a cryptographic checksum with a key). As poncho pointed out in his answer: Your problem is, that Alice and Bob don't know anything about each other, and there is no available PKI for authentication. None of them will ever know, if they are talking to someone called "Alice", "Bob" or "Eve".
Dec
15
comment Why do we have fixed output length in the algorithm SHA1
SHA1 is a standard hash function. Hash functions are defined to have a fixed size output.
Dec
15
comment What would be the best plain text Cryptography method without the use of a computer?
It is unrealistic to expect today's standards to be met while not using a computer.
Dec
15
comment What would be the best plain text Cryptography method without the use of a computer?
OTP is quite terrible from a usage point of view. Because instead of storing the key, you can just store the plaintext (key has the same length as the plaintext). And it is crucial for OTP that keys are not used more than once. Shorter keys or repeating keys are not OTP - and you can not apply OTPs security definition.
Dec
15
comment Malleability of homomorphic encryption
In one direction, there is nothing to show: Being homomorphic implies already some meaningful relation (e.g. you can always compute $2 \cdot m,3 \cdot m,...$). And for the other direction: The expression "meaningful relation" is not specific enough to achieve a homomorphic relation between ciphertexts.
Dec
15
comment Malleability of homomorphic encryption
Malleable and being (semi-)homomorphic is the almost same functionality, from a different point of view: Malleable usually is used, if that property is a security weakness (and it is more general: it is by definition not limited to the actual group structure). It is called homomorphic, if this functionality is used to achieve some more complex functionality.
Dec
15
comment How to customize a standard encryption algorithm?
"I do not want to use the standard AES because it is known to everyone." Actually, that is why you should use standard AES. Security through obscurity is one of the major pitfalls in IT security, because people don't take Kerckhoffs's principle seriously.
Dec
9
comment Can hashing become encrypting?
While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes.
Dec
2
comment practical use of homomorphic encryption
FHE currently is like using a skateboard, if you're used to drive a car. It is used for fun (well, research), but if you need to travel actually, don't use the skateboard.
Nov
27
comment What is the difference between IND-CCA2 and NM-CCA2? And how does one imply another?
What research have you done? Do you understand the difference between security notions? In its current state, the question lacks effort and information.
Nov
27
comment Elliptical curve cryptography key generation time
Concerning the naive approach: If you could do it that way, then brute forcing the key in the same manner would also be possible. Double-and-add is your only choice. (and its optimizations, especially NAF and wNAF are worth looking at)
Nov
25
comment When would one prefer a proof of knowledge instead of a zero-knowledge proof?
Proofs of knowledge are used for example to prove the knowledge of a trapdoor. If you consider discrete logarithms for an element $y$ to some base $x$, you want to prove that you know $\log_x y$. But obviously, you would also want your proof to be zero-knowledge in this case, or you could just state the solution and say "This is it, this is proof that I knew the solution".
Nov
24
comment DHE key exchange. Is it really secure?
Humans are so bad at understanding exponential growth... Best example is the question "How often can you fold a paper, and guess how thick it will be" -> typical are 6 or 7, record is at 12 atm
Oct
22
comment How Secure is a Pronounceable Password? In means of entropy
What is enough entropy for your use? How long is that pronounceable password? Entropy for passwords from language are hard to measure, because you would have to know the likelihood of each syllable, etc. Then: Do you consider saying "hash", "dot" pronounceable? Most symbols have some form to speak them out.
Oct
20
comment Database row level encryption scheme
I don't think it is a scare tactic, it is a rule of thumb for people without the necessary background and experience. What you wrote is exactly what I meant: Memory management and the other aspects you mentioned are those pitfalls, which "amateurs" overlook and thus create software with massive holes in it. Simply coding the algorithm description of AES or RSA from a textbook is not enough. And usually, cryptographers also fall in this category: Quite often the people who design a new cryptographic primitive are not the ones implementing it.
Oct
17
comment Database row level encryption scheme
"It also runs faster in software which is what I will be implementing it in" => Are you a professional developer of encryption algorithms? If not, your security just lost all those nice theoretic properties: Don't implement cryptographic algorithms yourself, unless you're an expert. This is one of the hardest lessons to learn for software developers from other fields, but it is VERY crucial.
Oct
17
comment Is it true the longer the key length is the more secure the encryption?
Longer keys mean also longer minimum sizes of the actual data: You can't encrypt "half a block". E.g. if the blocksize is 1 MB, encrypted message with a single bit of information would be 1 MB. And it applies to both symmetric and asymmetric encryption schemes (and hash functions, and so on...)