# All Questions

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### AES and Known-plaintext attack [duplicate]

Can you help me to finding some papers that shows AES is secure against known-plaintext attack?
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In this paper on pg. 1241 the authors discuss bullet point on Adaptive Zero-Knowledge : I am new to Zero-Knowledge and I am having trouble understanding what they are saying. I think they are ...
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### Why use a timestamp and how can someone know it's the correct one?

Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message : ...
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### applying HKDF at both the client and the server

I have two keys (K1 and K2) at both the client and the server. I hope to use HKDF in both client and server side to concatenate the keys. I will use the same salt value at both the client ad the ...
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### Flaw in the security definition of Stateful Length-Hiding Authenticated Encryption (sLHAE)?

In the paper On the Security of the TLS Protocol: A Systematic Analysis, the authors define the notion of a stateful length-hiding authenticated encryption scheme (sLHAE). For the purpose of this ...
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### Example of CL PKC

I am trying to solve the example of algorithms of Certificateless Signature by manually and solving the mathematics of Algorithms but not succeed while doing mathematical calculations. Please ...
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### Asymptotic Hash Function and Concrete Hash Function

I'm reading Collision-Resistant Hashing: Towards Making UOWHFs Practical, and they say that its formalization is non-asymptotic. Why is the formalization non-asymptotic? What is an example of hash ...
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### What is the difference between a bijective random oracle and a random permutation?

Assume $S$ be a finite set $O$ be a random oracle from $S$ to $S$, such that $O$ is bijective $f$ be a random permutation of $S$ Is there any difference between $O$ and $f$? Does it makes any ...
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### Bit commitment with 1-out-of-2 oblivious transfer

I know a protocol for bit commitment using regular OT (Bob has 1/2 chance of learning the bit Alice transferred to him) which goes like this: COMMITMENT PHASE Alice chooses a bit $b$ For ...
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### Can you help me understand the Common Modulus Attack in a Lucas Group?

I'm trying to decrypt a message that is encrypted using a LUC encryption scheme and running into roadblocks. I know that with RSA if Alice and Bob use the same public modulus but different encryption ...
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### KCV and compatibility with block cipher modes of operation

There has been lately a question on KCV (key check value), value provided by many CRYPTOKI (PKCS#11) implementations. I don't particularly like KCV, but I decided to ask about proper use of KCV. ...
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### OpenPGP Brainwallet

This question is an intersection of two pieces of technology. The first is on Hierarchical Deterministic Wallets from the Bitcoin Space. The second is on OpenPGP key generation. Has anyone created a ...
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### hill cipher encryption way 1x3 plaintext matrix

Can someone help me with a Hill cipher? When do I have to use: 1x3 plain text matrix (p1, p2, p3) * 3x3 key matrix 3x3 key matrix * 3x1 plain text matrix Or they are both correct? I tried to ...
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### how to truncate a PRF on n bits to PRF on t bits where t < n?

Dan Boneh's courersa lecture on format preserving encryption at 5.50 mins , talks about truncating a PRF on n bits to PRF on t bits. The approach is by appending (n-t) zeros to input t bits then ...
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### Are hash trees an alternative, quantum-resistant signature scheme which can replace RSA?

Can hash trees can provide quantum resistant signatures to replace RSA for signing securely? What is the key size and how many times can we use same key?
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### Is it possible to decrypt an RSA ciphertext with only $N$ and $e$?

Is it possible to perform RSA decryption if one only knows $N$ and $e$? Failing that, what is the maximum key length where brute-force is still practically feasible?
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### ElGamal signature: Forging a signature of a specific form

I have a question I can't solve from one of the courses I'm currently taking: Show that given a legitimate ElGamal signature $(S,R)$ on a given message $m$, an attacker can compute a signature ...
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### Replacing 8 sBoxes in DES with just 1 sBox, expected result?

Ok, i am trying to modify DES by my own way. There will be just one sBox and it will also contain all values from other 7 sBoxes. How it affects DES in this case? [? more secure/less ...
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### Merkle Tree High Tree

I'm reading Merkle tree signatures and I like know if the security of the that scheme depends, also, of the high of the tree or only depends that hash function is resistant to collision?
### Why can we always assume that $Gen$ algorithm choose key uniformly?
Talking about a (symmetric) encryption scheme $\Pi=(Gen,Enc,Dec)$ where $Gen$ take the security parameter $n$ as input and generates a key $k$ of length $n$. Generally speaking we say that $Gen$ ...