2,745 reputation
316
bio website
location
age
visits member for 2 years, 2 months
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
awarded  Custodian
Dec
9
reviewed Approve Generating a valid signature on El-Gamal without knowing the private key
Dec
9
awarded  Custodian
Dec
9
reviewed Leave Closed Reversing a Psuedo Crytographic Hash
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
9
reviewed Close how to represent message as an integer between $1$ and $n-1$
Dec
9
reviewed Leave Open Questions on rank-attacks in Multivariate Cryptography
Dec
9
reviewed Close CCA security in double encryption
Dec
9
reviewed Close Factoring a number who has factors with same number of digits
Dec
9
reviewed Close Stream cipher with Diffie-Hellman and Cryptographic Hash Function?