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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 ...
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0answers
16 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 ...
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0answers
13 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 ...
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1answer
22 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)...
3
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1answer
34 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 ...
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0answers
23 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.
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3answers
48 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. ...
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1answer
57 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 ...
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0answers
16 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 ...
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0answers
42 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 ...
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2answers
85 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 ...
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0answers
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 ...
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3answers
659 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 ...
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1answer
35 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: ...
2
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1answer
130 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 ...
2
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0answers
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. $ \ '' $...
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0answers
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 ...
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0answers
28 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 ...
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0answers
30 views

The following exercise is given in our book and I don't know how to solve it. Could somebody show me how to do it?

$\textbf{13.10 (Probabilistic full domain hash).}$ Consider the following signature scheme $\mathcal{S} = (G,S,V)$ with the message space $\mathcal{M}$, and using a hash function $H: \mathcal{M} \...
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1answer
48 views

How can I show RSA-OAEP is not IND-CCA secure if G always outputs 0 (i.e. there is no hash function)?

Here is what I understand the algorithm to be: Let $G, H$ be one-way functions, where G outputs the 0 string. 𝐸𝑛𝑐𝑜𝑑𝑒 Select a random $𝑘$-bit integer $𝑟$. Pad out $𝑚$ with $0$s to length $𝑙...
0
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0answers
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 ...
0
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1answer
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, ...
1
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1answer
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 ...
1
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0answers
22 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.
2
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2answers
49 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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1answer
27 views

Is Type I lattice trapdoor hard to find even given oracle access to compute inverse of trapdoor function?

Consider the Type I lattice trapdoor in [GPV08]: https://eprint.iacr.org/2007/432.pdf Suppose a PPT adversary is given the LWE trapdoor function in the picture: $g_{A^\top} (s,e) = A^\top s + e = b (...
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1answer
33 views

Why is the server's public key always used in SSL encryption and never the client's public key?

I spent a lot of time looking for an answer to this question, but the majority of answers never explicitly explain why the client's public key is never used; it's always the server's public key that's ...
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0answers
94 views

Cryptography Puzzle! [closed]

I'm new to this forum, and I'm certainly not a cryptography expert. I have to decrypt a message and I have NO IDEA what algorithm I can use. In the same context, I solved another encrypted text using ...
2
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1answer
47 views

Why is the function $f$ one of the inputs of the verification algorithm in homomorphic signature?

As we known, a homomorphic signature scheme consists of the usual algorithms $(\text{KeyGen} , \text{Sign} , \text{Verify})$ as well as an additional algorithm $\text{Evaluate}$ that “translates” ...
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0answers
33 views

key exchange: diffie-hellman with addition

Why we can't use simple additions to exchange keys in the diffie-hellman protocol? Example: Alice needs to send a secret "abc". Alice encrypts the key using a secret key "121". Alice sends "bdd" to ...
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0answers
17 views

Downloading videos from cloudfront? [closed]

is there anyway to download videos from cloudfront ? I got a paid subscription but i cant download
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0answers
12 views

using TAILS OS to secure my password in veracrypt [closed]

thanks for taking a look at my post, i did a search and i couldn't find any information about this topic, so i thought i would post my question here. my question is this, i have recently learned that ...
0
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0answers
18 views

Why doesn't my hash function work? [migrated]

I'm a newbie in this field and am trying to learn a bit about how to write cryptographic hash functions. To get some hands-on, I tried updating the PySHA2 algorithm for Python 3.6 and up (the original ...
2
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0answers
25 views

Use Signal protocol without server

I'm trying to establish E2E secured channel with nearby devices (using WiFi direct). Obviously, I wouldn't like to rely on internet connection. Can I use the signal protocol without a server? 1)Will ...
2
votes
1answer
136 views

Is it safe to reuse the same nonce for decryption an indefinite amount of times in this context?

I'm creating a password management application and I'm considering using the following procedure to keep passwords safe: Asking the user for raw_password, for ...
0
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0answers
33 views

Unable to determine plaintext from ciphertext

Given the letter-number cipher: a=00, b=01, c=02, etc., encrypt the word 'hi' and decrypt its ciphertext using RSA. The public key is (5,35) and the private key is (29,35). I know that 'hi' is ...
1
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2answers
46 views

How to properly sign and verify using DSA? Can anyone spot my mistake?

The question that I am trying to answer is as follows: 10.14. The parameters of DSA are given by p = 59,q = 29,α = 3, and Bob’s private key is d = 23. Show the process of signing (Bob) and ...
0
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1answer
49 views

Diffie–Hellman key exchange, why it's hard to break it?

I'm a bit confused why it's hard to break Diffie–Hellman Let's take the example ALICE has G, a, and n BOB had G, b and n Eve ...
0
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0answers
19 views

Related-key impossible differential search on SIMECK via MILP?

What should be the objective function , constraints and bounds for the model for Related-key impossible differential search on simeck cipher using mixed integer linear programming (MILP)?
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0answers
66 views

Partially Repeated Roots of Classical Modular Polynomial

So I was trying to compute a normalized model of elliptic curve as described here. Consider $p$= ...
0
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0answers
26 views

does increasing the number of rounds in feistel increase the security [duplicate]

In feistel cipher , does it matter that number of rounds ? is using more rounds will give the best result? or it's all about the key size ?
-4
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0answers
51 views

get q from p in rsa [closed]

i want to get q, but i dont know how. Informations: N = ...
1
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1answer
42 views

Proof by reduction definition in “Serious Cryptography”: Cipher reduced to hardness problem or other way around?

In Serious Cryptography by Jean-Philippe Aumasson on p. 46, paragraph "Provable Security", it says: Provable security is about proving that breaking your crypto scheme is at least as hard as ...
2
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1answer
39 views

Which is the irreducible polynomial in GF(2^256) used in AES256-GCM?

I was able to find the irreducible polynomial used in AES128-GCM: $x^8+x^4+x^3+x+1$. But I cant' find the one for AES256, I'm searching in OpenSSL implementation of AES256 but with no luck so far.
0
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0answers
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<ܵ»...
0
votes
1answer
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 ...
1
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1answer
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 ...
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0answers
14 views

Is there any software available online for checking the properties of substitution boxes for block ciphers?

I have designed a s-box and now i want to find out its properties i.e. what are the values of non linearity, SAC, BIC etc?
1
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1answer
29 views

Why do SignTool/Authenticode Message Digests not match the direct hash of the file?

I'm attempting to validate an Authenticode signature (generated by signtool /fd SHA256 /f <code signing PFX> /p <PFX password> test.exe), and I've run ...
2
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0answers
17 views

Groth-Sahai Proof of multi-exponentiation

I want to create a NIZK proof of a multi-exponentiation via Groth-Sahai proofs. In the lectures of Jens Groth in a winter school of Bar-Ilan University, he shows a way to transform multi-...

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