Latest Crypto related questions

Score: 2
Random avatar
Prevent Bleichenbacher by adjusting Padding
ve flag

I got the following question and I really don‘t know how to answer them. My I ask you for your input?

Do you think, that the following adjusted Padding will prevent the classic Bleichenbacher attack

2Byte Random prefix | Random padding bytes unequal 0xff | 0xff | PremasterSecret

In theory I would agree (at least for the classic Bleichenbacher), but wouldn‘t that be to easy? And what other proble ...

Score: 1
Symmetric key generation for ECDH
st flag

Trying to implement a mechanism for one way transmission of encrypted string values using ECC.

  • Assume there is a fixed secret unavailable private key FPK, and public key FP for it is available to the application.
  • As user enters a value, a new private key is generated, then shared key is produced from exchanging it from FP. Resulting sharing key is different every time.
  • Symmetric encryption key DSK is d ...
Score: 14
Cryptographically safe lookup of value in a set
cn flag
vnd

I'm looking for an elegant solution to the might-seem-trivial problem of looking up for specific value in a known set of values without disclosing what value we look for. Let me describe it in a classical way:

Alice will soon celebrate her birthday and she wants to know if anyone in her class has the birthday on the same day as her. Unfortunately, the only person who knows the dates of birth of all the ...

Score: 1
karim abousselham avatar
What does a uniform n-bit string mean?
ht flag

I am a total newbie to cryptography and I would like to know the meaning of a "uniform n-bit string". Also, why keys of that type are commonly used in private-key encryption?

Thanks!

Score: 3
Jake avatar
Impersonation attack on Lamport's one time password
in flag

So here I am, googling my brain on the possibilities of impersonation attempts by a MITM attacker on Lamport's one-time password scheme.

Here's my scenario:

Say we have a client and server setup. Given a nonce $n$, and a hash function $h()$, a client computes the hash of $n$ several times (say $100$) and sends at first instance $H^{(100)}$ where $H^{(100)}=h^{(100)}(n)$. First, how does the serve ...

Score: 1
Soteri avatar
Performance of AES CTR + HMAC SHA1
cn flag

I'm doing a performance test on AES with CTR mode and HMAC SHA1 for message authentication and found the openssl speed tool for that.

I run multiple tests with openssl speed -evp sha1 aes-128-ctr aes-128-gcm because I want to compare it to the GCM mode which do encryption and message authentication in a single mode.

Now my question: how can I compare these values? Is the value of the sha1 result the "sp ...

Score: 2
miky avatar
Question about malicious security in protocol using OT
cn flag

I was studying a protocol that used an OT and suddenly and suddenly I realize that I fail to imagine how a protocol using an OT could be malicious secure.

Suppose we have a protocol P that use an OT as subrotocol. Suppose that the OT is used $N$ times. Each OT has input $x_{0,i}$, $x_{1,i}$, where $i$ denotes the $i-$th istance of the OT, from 1 to $N$. It is reasonable to suppose that, for every ist ...

Score: 3
What exactly does "Extension of a polynomial" mean?
et flag

This from the manuscript of a book on Zero Knowledge Proofs - https://people.cs.georgetown.edu/jthaler/ProofsArgsAndZK.pdf

3.5 Low Degree and Multilinear Extensions Let $\mathbb F$ be any finite field, and let $f : \{0, 1\}^v \rightarrow \mathbb F$ be any function mapping the v-dimensional Boolean hypercube to $\mathbb F$. A $v$-variate polynomial $g$ over $\mathbb F$ is said to be an extension of  ...

Score: 2
Nick Fleetwood avatar
I don't quite understand hashing
id flag

I don't quite understand hashing, for encryption or otherwise.

So, if you have a website, and a user signs up, you store his password as a hash. When they log in, your website takes the submitted password, hashes it, and compares hashed submission to the stored hash, right?

Say you are hashing a sentence using SHA-256, do you EVER decrypt such a hash, or even have the ability to?

One last followup: Wha ...

Score: 2
peanutButter avatar
What are the first bits of a bitstring, for instance generated using SHA-256?
ve flag

I have a string that generates from SHA-256

x = fea5f97f9ca1e1a0a2ae344f4e12a3ab0c4d9221e6bb5d70bc567e39f8fbc3d5

What's are the first 10 bits are of the value of x?

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