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Sep
26
comment Define “cryptographer”
People who state "I am not a cryptographer" in a question here, probably don't imply anything, but that they would appreciate an answer that only requires basic prior knowledge of the subject. Possibly, it might also be an appeal to the ego of any expert prepared to answer. Flattery is the simplest form of manipulation.
Sep
11
comment Encrypt with one cipher and decrypt with a different cipher?
Storing the algorithm in the ciphertext does not compromise security provided that the algorithm identifier is treated as additional authenticated data when the message authentication code is calculated.
Sep
7
comment What are the strenghts and weaknesses of Whirlpool Hashing Algorithm
This is not a weakness. It is a theoretical result that demonstrates that the number of rounds in the full algorithm can't be significantly reduced.
Sep
5
comment Is it possible to have E=D and Ke <> Kd?
Text book RSA fits the description: $E((N,x),t) = D((N,x),t) = t^x \bmod N$
Sep
2
comment Confusion regarding computing Multiplicative Inverse Modulo P?
$6 \times 2 = 2 \mod \phi(11)$.
Sep
1
comment POODLE attack on TLS 1.2
Technically, the Netscape formal specification of SSL 3.0 didn't specify how the padding should be generated. The SSL 3.0 specification is consistent with deterministic TLS 1.0 padding. A SSL 3.0 implementation that checks the padding is consequently consistent with the specification, but incompatible with a lot of implementations.
Aug
28
comment Key Size for Symmetric Homomorphic Encryption Over the Integers
You find the formula for the value of $\eta = \Theta \lambda log^2 \lambda$ later in the paper. $\lambda$ is the security parameter and $\Theta$ depends on the depth of operations to be supported.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
@mikeazo You forgot about the highest order coefficient. $k(x-2)(x-1)(x+1)$ has the same roots for any value of $k$. And if you don't know $k$, you can't calculate the constant term.
Aug
26
comment Shamir Secret Sharing: Why cannot we recover polynomial's root if we have $t-1$ shares?
Knowing all $t-1$ roots of polynomial of degree $t-1$, would still not be sufficient to deduce the constant term. The coefficient of degree $t-1$ will not show up knowing nothing but the roots, and this coefficient might have as many values as there are non-zero elements in the field.
Aug
21
comment Combine two sha512 hashes to a single hash
en.wikipedia.org/wiki/Length_extension_attack
Aug
18
comment Is calculating HMAC from hashed input a good idea?
Doesn't the fact that breaking HMAC generally requires a greater effort than finding a collision in the underlying hash algorithm, mean the answer is "yes"?
Aug
15
comment Anonymous offline digital cash scheme
The answer to the question, as currently worded, ought to be "no". Blind signatures are online by definition, so a digital cash system based on blind signatures can't be (completely) offline.
Aug
10
comment Order of MACing and Encrypting in TLS
Some servers are updated. Technically, a modern browser and a modern server might still negotiate an older version of TLS. Since there are still a lot of buggy TLS 1.0 servers out there that will choke on TLS 1.1 and later, some generic TLS clients solve that by only enabling TLS 1.0 by default, unless they know for sure the server supports later versions.
Aug
10
comment Order of MACing and Encrypting in TLS
RFC 7366 is widely implemented, e.g. by Chrome, Mozilla, OpenSSL etc.
Jul
3
comment Working on subgroup of $\mathbb{Z}^*_p$ in practice
It is important to know in exactly what sense you "need to work on some elements not in the subgroup". Your question does not include any reference to any cryptographic scheme or algorithm.
Jul
3
comment Working on subgroup of $\mathbb{Z}^*_p$ in practice
It is unclear what you are asking. Are you asking what role large multiplicative subgroups play in cryptography, or do you simply want to know more about the algebraic properties of the fields and groups involved?
Jul
3
comment Easy explanation of “IND-” security notions?
No, I don't think it is a duplicate. You will not necessarily understand the precise meaning of IND-CPA just because you know what is meant by a Chosen Plaintext Attack, etc
Jul
1
comment Deriving HMAC key and cipher key from passphrase?
@mistika: It depends on which algorithms you use for the generic EtA composite scheme. In some cases your scheme will break down completely if you use the same key for both (e.g. if you combine AES-CBC for confidentiality with AES-CBC-MAC for authentication). In other cases the algorithms are likely different enough for there not to be any practical attacks, should you use the same key for both components. However, you can't prove that the generic composition by itself is as secure as the least secure component, unless your premise is that the components use independent keys.
May
9
comment Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509
RSASSA-PSS is a completely different beast altogether. A correct representation would require not only Signature Algorithm and Signature Hash Algorithm, but also identifiers for MGF Algorithm and P Source. This is however beside the point.
Mar
9
comment Will SHA1 or Other Hash Functions Ever Contain Quotes
I'm voting to close this question as off-topic because this is an apples and oranges kind of question. SHA-1 will output a string of 160 bits. A quote character is a character and not a bit. Your question will only make sense, if there is an implied conversion algorithm from the bit string output of SHA-1, to the character string you store in your database. This conversion algorithm might be chosen independently of the hash algorithm. Hence, your question is off-topic.