# All Questions

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### The purpose of the final xor in Davies–Meyer scheme [duplicate]

In Davies–Meyer hash construction scheme each block is xor'ed with the previous block cipher text. Why? The only obvious flaw I see in a scheme without this xor is the possibility to reconstruct a ...
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### Attacker in a key exchange

I'm having trouble with the following question: $X(A) \rightarrow B:(A,N_X)$ $B \rightarrow X(S):(B,((A,N_X,T_B),K_{BS}),N_B)$ $X(A) \rightarrow B:(((A,N_X,T_B),K_{BS}),(N_B,N_X))$ ...
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### Polynomial division hardware implementation

I am beginning the implementation of the polynomial binary division algorithm now as I understood i will be checking the MSB bit if 1 to XOR and shift the sum if 0 i will only shift. What I am not ...
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### How does Schnorr signature actually work?

I'm trying to get a grip on how Schnorr signature works. Suppose Alice sends Trent a tuple $(P, M)$, which contains a payload and a message to be signed by him. She then passes the certificate to Bob ...
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### Crack RSA with imaginary algorithm [duplicate]

I was given a cryptography question during an interview the other day and I couldn't come up with a valid answer. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is ...
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### RSA or Paillier is good? [closed]

I want to implement file storage in cloud using homomorphic encryption. I want to use paillier encryption. Can you suggest the drawback of RSA to store and retrieving the files. Then only i can use ...
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### CAST-256 (CAST6) versions or S-Boxes

Are there different versions of CAST-256 - also known as CAST6 - available? Are there different S-Boxes available for CAST-256? If there are different versions or S-Boxes what identifier should I use ...
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### Fermats Little Theorem, primitive root [closed]

So I am studying for finals and I am not able to solve the problem: Let $p = 3 * 2^{11484018}- 1$ be a prime with 3457035 digits. Find a positive integer $x$ so that $2^x\equiv 3\pmod p$ Any ...
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### CBC-R when IV unknown

I've read the CBC-R description from Rizzo & Duong but am having trouble understanding the sequence of steps that would be taken when the IV is unknown and is not included with the ciphertext. ...
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### Asymmetric encryptions' computational complexity [duplicate]

I need to know the computational complexity of the public key encryption (e.g. Paillier), please. (i.e.Paillier in his paper mentions that the computational complexity of most of public key ...
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### Modulo Square Roots [duplicate]

Here's my issue and someone can help me understand it so I can program it correctly. I have a point(X,Y) on an Elliptical Curve E(a,b) where a=-3 and B is a large number that is in hexidecimal from ...
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### FEAL-4 Wrong outputs of Round Functions

On page 2 of this article, there is example of FEAL-4. At round 2, the input to F (Round Function) is 0x80800000. As F accepts only 4 bytes I divide the input by 2 so that (As I assume the result ...
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### Which mathematical operations does secp256k1 point multiplication use?

To convert a bitcoin private key to a public key, the secp256k1 point multiplication math is used. Could I – theoretically – convert a private key to a public key just using the four arithmetic ...
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### Need to choose an ecnryption method [closed]

I've got an homework to implement an encryption algorithm (I can choose what), now we didn't learn about encryptions yet, I guess you can call it pre-class homework or something, I know what is ...
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### Are there any obvious techncial faults in F. Ruiz's 2013 URSA javascript cryptography? [closed]

The link to the cryptography is here: http://prgomez.com/ursa/ I have found the following simple javascript system of encryption/decryption portable and easy to use for emails and messaging sites, ...
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### What is the (uncompressed) x,y-representation of a curve point on the P-256 NIST elliptic curve?

I am trying to understand the FIDO U2F Raw Message Format, especially the format in which a user public key should be provided. The documentation says the following: A user public key [65 bytes]. ...
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### Forward pseudorandom permutation [closed]

Please consider the following scenario: The user A and B use their keys, K1 and K2 respectively. Each client have a vector of elements. Each client separately permutes his vector using his key and ...
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### Plaintext-aware encryption for symmetric schemes?

The notion of plaintext-awareness is well-known for asymmetric encryption, but the notion seems to make sense for symmetric encryption as well. Is this a known concept?