# All Questions

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### Fooling Proof-of-Storage Protocols. What's the difference with Length-Extension attack?

I've searched a bit for this question, but I haven't found anything, so I've decided to post it here. Lately I've been reading "Serious Cryptography: A Practical Introduction to Modern Encryption" by ...
17 views

### In ElGamal, how does knowing the secret number used for a signature reveal the signer's private key?

In ElGamal, how does knowing the secret number used for a signature reveal the signer's private key? How do two signatures using the same secret number reveal the signer's private key? [Hint: p-1 is ...
22 views

### How to compute an identity function on encrypted vector by using a third party?

I want to compute an identity function over encrypted vector on a third party. For example, F(x) = [a1,a2,..,an] where x is a tag. However, i do not want the third ...
18 views

### Why can a symmetric encryption algorithm be considered a pseudo-random number generation algorithm?

I have a question from my teacher: "Why can a symmetric encryption algorithm be considered a pseudo-random number generation algorithm? Can anyone explain it to me? And sorry if my english is not ...
25 views

### random mask reversible after homomorphic encryption

I would like to know if this process is feasible under homomorphic encryption, ideally under paillier or any other additive scheme Apply a mask X to obfuscate a message A ie. Am = A (op) X where (op)...
41 views

### Random permutation

I wrote a toy pseudo-random permutation out of a Feistel network using blake2b. However, looking at the distribution of permutations for small n = 6, it's clearly not uniform unless many rounds are ...
26 views

### Good Books for self learning crpytography basics

What are some good books to learn basics of crpytography? Maybe with some coding examples? And what are must read cryptography articles? I am a beginner and i have got a few knowledge on crpytography.
49 views

### Curve25519 Specification

The Curve25519 is defined over the prime $2^{255}-19$ with $A = 486662$, so that the curve equation is: $y^2 = x^3 + 486662x^2 + x$ I'm trying to understand, why the parameters are what they are. ...
60 views

### Algorithm for factoring a 30 decimal digit number

My professor has given me an RSA factoring problem as an assignment. The given modulus is 30 decimal digits long. I have been searching a lot about factoring algorithms. But it has been quite a ...
18 views

### Is security of zk-SNARKS related to the size of the arithmetic circuit they evaluate?

In the context of zk-SNARKS, we are given an arithmetic circuit $C$, public outputs $y_1, \ldots, y_n = \mathbf{y}$ and some public inputs $x_1, \ldots, x_ℓ$. The prover wants to prove knowledge of ...
44 views

### Cryptanalysis of a Feistel network

I'm having some issues finding keys to a Feistel network. The function is unknown but we can have as many plaintexts and their given ciphertexts as we want. I'm trying to generalize the cryptanalysis ...
87 views

### How to pad a 448 bit message for SHA256?

I recently implemented a very simple SHA256 hashing program in C++, since the SHA256 hash function's block size is 512 bits or 64 bytes, and messages less than that size have to be padded as per the ...
24 views

### How do the signatures or message authentication codes achieve the authenticity, integrality or non-repudiation？

Actually, I want to know whether there are explicit and formal definitions of the properties which are authenticity, integrality or non-repudiation. It seems that the signatures and MACs can achieve ...
664 views

### Is there a maximum number of encryptions I should make with the same RSA key?

From an answer to the question RSA maximum bytes to encrypt, comparison to AES in terms of security? I learned that there is a theoretical limit of how much data can be safely encrypted with symmetric ...
36 views

### What is wrong with this CMAC computation?

I have an example of a CMAC computation, which I want to reproduce in Python, however I am failing. The example looks like this: ...
133 views

### Why can you use shorter keys with elliptic curve Diffie Hellman key exchange?

I am a layperson interested in how cryptography works. I would like to know why you can use shorter keys with elliptic curve Diffie-Hellman (ECDH) than with the discrete log DH key exchange. Both have ...
149 views

### Using digital signature to reduce storage requirement

Below question is a part of my assignment and I was completely clueless about where to start from. So, I am posting it here for the purpose of getting hints/resources to help me get started. $\ ''$...
23 views

### What is the exact algorithm for encryption and decryption with hummingbird-1 cryptography?

I have really googled the entire internet but could not find a clear algorithm for hummingbird-1 cryptography.The problem emerges in the decryption module: What is the initial value of state register ...
29 views

### Signal Key Stretching Regarding Their Blog Post

I just read this blog post (Signal - Technology Preview for secure value recovery) by Signal and something is not quite clear to me. In section "Stretching beyond a KDF" they generate a ...
30 views

11 views

### how can i encrypt webm files using clearkey encryption and obtain both key and keyid to play it using on the web dash [closed]

hi I can't seem to be able to encrypt WEBM files and get back any valuable information like key value or key id so i can use them with EME API and create a dash media player so i can protect my media ...
26 views

### Disk storage of RSA and DSA keys

I have generated one RSA-2048 signing key and one DSA-2048 signing key, using gpg command gpg --full-generate-keys I would expect the key to have size 2048 bits, ...
27 views

### Small complex multiplication field discriminant for solving ECDLP

I've seen from the SafeCurve criteria that one should try to avoid small complex multiplication field discriminant as it can speedup the discret log computation via the Polard Rho method. However, I ...
24 views

### Compared with plain RSA , what is the advantage of randomised public key encryption scheme such as EIGamal encryption?

I am new to cryptography, I am very interested in cryptography, thank you for your answer.
50 views

### How to require two PRIVATE keyholders to decrypt a document?

Consider 3 entities A,B and C. I want A to be able to encrypt a document that can be decrypted only when keys of both B and C are combined. This question talks about a similar problem, but it uses AES....
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32 views

### How to decode this Base64 message? [closed]

The code is ovTSeyGlJoIrvjLvvoLtM0NMsqbs7INB2zzciLW7Nek= Which is I believe is encoded in Base64. However, decoding it through ASCII results in a garbled message of ¢ôÒ{!¥&+¾2ï¾í3CL²¦ììAÛ<Üµ»...
28 views

### How to apply a block cipher to (large) packetized communication when packets can get lost/erased?

In light of current events (Zoom getting strong headwinds for using AES-128 in ECB mode), I was wondering what the general approach is to packetized data encryption, where the packet length (UDP for ...
45 views

### On what basis is padding chosen in OpenSSL?

I am using CAPI Engine in OpenSSL and I did some test. When I use TLS 1.0 or 1.1, during handshake and RSA signing, PKCS padding is chosen. When I use TLS 1.2, RSA signing uses PSS padding. What ...