Latest Crypto related questions

Score: 3
dade avatar
Difference between Non-uniformly random and Uniformly random
bt flag

I am reading up on Key Deriving Functions (KDF) and in a section of the Real-World Cryptographic book by David Wong, a comparison is being made with Pseudorandom number generator (PRNG). And one of the differences is said to be that KDF takes non-uniformly random arbitrary length input, while PRNG takes Uniformly random k-bit key. Even though both have Uniformly random arbitrary length output.

Basi ...

Score: 1
cryptobeginner avatar
Exact security requirements for extendable output functions (XOF)?
cn flag

In the FIPS202 document "SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions" an extendable-output functions is defined as:

An extendable-output function (XOF) is a function on bit strings (also called messages) in which the output can be extended to any desired length.

That is all the definition I could find on that. However, this definition does not capture the notion that the bi ...

Score: 1
Trying to understand SIV mode
jp flag

I'm trying to wrap my head around the concept of SIV in the context of encryption. I understand the aspect of nonce misuse, etc. And I understand that the key feature for SIV is that they ensure that while encrypting the same message with the same key will reveal that it is identical, it will not reveal anything else.

In particular, using the same key on different messages will not have the catas ...

Score: 0
Hern avatar
How to produce Auth Data and tag in GCM? Does MAC appended CTR mode encrypted text weaker than GCM?
is flag

In https://en.wikipedia.org/wiki/Galois/Counter_Mode, there's a diagram which tells us how GCM works in general.

I have watched computerphile video on how ECB,CBC and CTR mode works and able to implement them on my own given the block cipher (SM4) was properly implemented in library like BouncyCastle.

I have several questions on the diagram, where does the auth data comes from? If there's no auth data c ...

Score: 3
moktor avatar
Is it safe to use AES-CCM only for authentication - i.e. for sending AAD without encrypted data?
cn flag

We are employing an AES-CCM 128-bit stream-cipher with 7-Byte Nonces and 12-Byte Authentication Tags in a communication protocol. Up until this point there was no need to use Additional Authenticated Data (AAD) in this protocol, as all transmitted data - apart from the Nonce - was encrypted.

In the meantime, some new networking-related requirements came up which may require one message-field to b ...

Score: 1
Novice_researcher avatar
OWF and iO Correlation
br flag

What is the relationship between one way functions(OWF) and indistinguishable obfuscation(iO)? I know that iO exists even when P=NP and OWF don't exist. But does the existence of OWF imply iO?

Score: 5
Why Zero-Knowledge protocols are used for NP problems if IP is the class of interactive proof systems where they come from?
in flag

As stated in the title, I'm studying ZKPs and I see they are just interactive proof systems that respect the zero-knowledge property. Now, if that's true, why aren't they used for IP problems, the complexity class of interactive proof systems that was originally introduced for them? I mean, isn't the proof mechanism interactive in ZKPs between Prover and Verifier? Then why are we talking about NP proble ...

Score: 4
Novice_researcher avatar
Virtual Black Box Obfuscator
br flag

For which class of circuits does the Virtual black box(VBB) obfuscator exists? If so Why? What are the attempts/further developments made in this topic?

Score: 2
pintor avatar
What is the quadratic character of the field over which elliptic curve is defined?
ng flag

I'm trying to understand the injective encoding of a message to an elliptic curve point (from this paper).

enter image description here

However, I'm not sure what do they mean by the quadratic character of the field. Do you know what does it mean and how to compute it? Is it somewhat similar to the Jacobi symbol?

Score: 3
fonzane avatar
Encrypt/Cipher and Decrypt/Decipher a string with a secret
cn flag

In developing an app I have a simple use case in where I want to encrypt/cipher a string (it could also be a couple of bytes because it's essentially just an IP-Address). On the output I think it would be best to have a hex-string (thinking of the old md5-hashes). No one who hasn't the private key shouldn't be able to decrypt/decipher the IP-Address.

The flow is as follows: I have a string (IP-Ad ...

Score: 1
einsteinwein avatar
Discrete Logarithm in the generic group model is hard - Theorem by Shoup
st flag

In Shoups well-known paper Lower bounds for Discrete Logarithms and Related Problems he proves that the Discrete Logarithm Problem is hard in the generic group model (if group operation and inverse are the only computations that can be performed on group elements). Theorem 1 in the paper says that the probability that a generic algorithm $A$ solves this problem is bounded by $\mathcal{O}(m^2/p)$ (m is  ...

Score: 0
Dew Debra avatar
How to get a common coordinate from two different coordinates on Elliptic Curves?
br flag

I am trying to write a SageMath script that multiplies two coordinates on Elliptic Curves into one common coordinate.

SageMath Elliptic curves over finite fields documentation

p = Number

M1 = EllipticCurve (GF (p), [0,7])

C1 = M1 ([x1, y1])
C2 = M1 ([x2, y2])
C3 = C1 * C2

Somewhere they wrote that using sets of the SageMath function it is possible to do this. How to do it?

Score: 3
problem with a discrete logarithm/cyclic groups example... can anyone clarify this concept for me?
in flag

I was watching this really short video about the discrete logarithm example: https://www.youtube.com/watch?v=SL7J8hPKEWY and at 0:38 they show all the possible values that you can get if $p = 17$ and $g = 3$. At 1:00 they state that the solution is equally likely to be any integer between 1 and 17.

My questios are;

  • What about $0$? From what I learned about cyclic groups, $17 \bmod 17$ is just $0$

Score: 1
Signature of low-entropy data: can they be faked?
cn flag

I am working on an application where I have a physical product identification label containing a block of public, low-entropy data (~50 bytes) such as serial number and other info, all readily available right on the label. I would like to use a hash-based signature algorithm to provide an authenticity check that the product is valid.

  1. Is this a reasonable idea? Does the low-entropy data cause problems? ...

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