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3
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16 views

Is it possible to construct a hash-based public key encryption scheme?

I know hashes can be used to construct symmetric encryption schemes (HMAC running in counter mode), signature schemes (SPHINCS), pseudorandom generators, etc. One thing that's missing is public key ...
2
votes
1answer
28 views

Algorithm to find primes q and p with q|p-1?

I understand that if $p$ is prime then $p-1$ must be composite (at least divisible by $2$ as it is even). But how does an algorithm find a prime $q$ such that $q \cdot r = p - 1$. I thought prime ...
0
votes
0answers
11 views

why is index “a non-negative integer less than 2^64” in the KDF for UMACs?

https://tools.ietf.org/html/rfc4418#section-3.2.1 describes the parameters for KDF as follows: ...
-1
votes
0answers
24 views

Hey, anyone know if this is a color cryptography? If yes what? [on hold]

Me and a group of friends are solving an ARG, we found some videos where every frame was an image like this one.
1
vote
0answers
25 views

Are there any symmetric Partial Homomorphic Encryption Schemes?

Note that I am asking specifically for Partial Homomorphic Encryption (PHE) schemes and not Somewhat Homomorphic Encryption (SME) schemes. I believe there are several SHE schemes that are symmetric ...
2
votes
0answers
49 views

RSA, factoring with middle known bits of one prime?

It was shown by Coppersmith, that we can factor the RSA modulus with half of the most significant bits of one of the primes. And for the lsb case, assume that we known $p_0,k$, and $p=p_12^k+p_0$. ...
0
votes
0answers
22 views

Decrypting a weak PRNG Mersenne Twister Stream Cipher

I am currently working on the crypto-challenges presented here. I created a simple stream cipher using a Mersenne Twister RNG. It basically works as follows: Seed a RNG with the key (basically up to ...
-1
votes
0answers
32 views

Can some one help and explain the approach for decryption? [on hold]

E-crime department had to decrypt the message, upon inspecting the USB Stick police found the following message: DJOCIT WWDN TYWTNAPRP BBMV SIWRVHCUTO. It is believed that before the incident, the ...
0
votes
0answers
27 views

Generating anomalous elliptic curves with given order [on hold]

First of all please see this paper, I want to fully understand the section 3 and 4 of this paper and write a script that generates an anomalous elliptic curve with given prime order. Furthermore how I ...
1
vote
0answers
23 views

General factoring and one-way functions

Let a function $f$ be one-way, if there exists a probabilistic polynomial time algorithm to find the preimage of $y = f(x)$ for uniformly chosen $x$ with non-negligible probability. Define the ...
3
votes
3answers
317 views

What security risks does exposing the size of the plaintext entail?

For this question my focus is exclusively on symmetric block ciphers (with a particular interest in AES256 in CBC mode). I have read much discussion on various ways to pad the plaintext so that the ...
10
votes
3answers
3k views

How to detect a failed AES256 decryption programmatically?

I have implemented a simple encryption/decryption program based on AES256 in CBC mode1. Actually, it is more precise to describe it as a compression+encryption / decryption+decompression program. If ...
0
votes
0answers
23 views

Security of querying multiple Merkle trees

Suppose Alice has committed to several sets of values using Merkle trees. For example, let's say there are 2 sets of values, and each set represents leaves of a separate tree like this: $a_0, a_1 ......
1
vote
1answer
30 views

How to prove an encryption scheme is not CCA secure

Given the following context below, how does one show or prove the encryption scheme is NOT IND-CCA secure The IND-CPA secure private-key encryption scheme for n-bit messages can be constructed from a ...
0
votes
0answers
18 views

Partial key reuse in hash for one time pad cipher

There are 2 computers who are going to exchange lots of small packets of data between each other. To generate a shared secret, an elliptic key exchange takes place. If this key is hashed with the ...
3
votes
2answers
109 views

Why does square root $\pmod n$ find $p$ and $q$ (as $n = p \cdot q$)?

Let $n = p*q$, with $p \neq q$ and $x^2=1 \pmod n$, $x+1 \neq 0 \pmod n, x-1 \neq 0 \pmod n$ (So x is a non-trivial square root mod n.) I don't see how $\gcd(x+1,n) \in \{p,q\}$ follows. I ...
0
votes
0answers
22 views

Could this Method be Used to Create a highly Compressed Alternative to Merkle Proofs?

See equation below as I see an easier alternative, as I'm having trouble explaining it. Is there a hash function where many hashes can be combined together in a way where any single hash can be ...
3
votes
1answer
112 views

Does knowing that the exponent is in a certain range help solving discrete log?

given: $c=g^i \bmod P$ $g$ generator for group with group size $\varphi(P)$ $g,P,\varphi(P)$,c is known by the attacker He wants to know $i$. Now the attacker also knows $j,k$ with $j<i<k$ $k-j$...
0
votes
1answer
51 views

RSA vs Elliptic Curves

I am currently reading about how more efficient and ''light'' is ECC compairing to RSA as far as key generation is concerned. My question is simple, why does RSA continue to be used today (ex.SSL) ...
1
vote
0answers
27 views

Unicity Distance of the Merkle-Hellman Knapsack Cryptosystem with Hidden Public Key

The original Merkle-Hellman scheme has undergone many successful attacks, the most famous being Shamir's from 1982. As Shamir noted about his method, "An important property of the proposed attack is ...
0
votes
0answers
21 views

What text encoding scheme is this? [on hold]

Sorry in advance; I'm not sure where to ask this. http://www.eventresourcespresents.com/artist_search If you search for any text at the above link, what you search for will be encoded in the new url....
3
votes
0answers
39 views

Hash multiset to point on elliptic curve where $A = 0$

I want to hash a multiset to a point on the elliptic curve $y^2 = x^3 + 3$ over a finite field of some 254-bit prime order, where $P = 3 \pmod 4$. Moreover, I want this hash to be incremental, in that ...
2
votes
2answers
73 views

Attack on security model for RSA-FDH

I recently read in Cryptography textbooks and online videos that compared to Textbook RSA which is insecure against Chosen Plaintext Attacks (CPA) and Chosen Ciphertext Attacks (CCA), RSA-FDH is ...
3
votes
1answer
135 views

Decrypting arbitrary numbers with RSA

I want to construct a hash-chain where I want to share millions of small AES-128 keys with Bob over a period of time. Bob should not be able to predict the future keys if he knows the past keys. I ...
2
votes
2answers
78 views

Any benefit to encrypting IV and MAC in a mode like AES-GCM or ChaChaPoly?

Would there be any benefit to symmetrically encrypting the IV and MAC in an AEAD mode of operation? More specifically would this prevent someone from exploiting the accidental use of a duplicate IV ...
0
votes
1answer
68 views

Proving the CCA-insecurity of El Gamal encryption scheme

I am trying to prove that El Gamal Encryption is not CCA-Secure. If an adversary queried the encryption oracle for the encryption of $m=1$, he'll get a pair $(c_1,c_2)=(g^y,g^{xy}\cdot m)=(g^y,g^{xy}\...
-2
votes
0answers
27 views

How to compute the number of instructions in python [on hold]

Could you please tell me how I can compute the number of instructions of a program written in python. thanks
-1
votes
1answer
61 views

How do discrete logarithm with modulo a prime and a non-prime compare?

Let $c_N = g^i \mod N$ and $N=p \cdot q$ and $c_P = f^j \mod P$ and $P$ a prime We assume $N,P$ has the same bit-length. $P$ is the best type of prime you can choose (e.g. safe prime). $N$ is a ...
0
votes
1answer
37 views

What is / How would I calculate the number of bits(?) I need to make the probability of a collision very small?

If I wanted to create a TOTP-esque algorithm that generated a string n characters long, with each character being a base64 character, generated from a user secret <...
6
votes
1answer
63 views

Limitations of boolean and arithmetic circuits

Much of modern cryptography is based around working with boolean or arithmetic circuits. For example in Multi-Party Computation the 'famous' results allow for the secure computation of any function ...
1
vote
1answer
48 views

Cipher recommendation for known-plaintext attack

I need to encrypt a 4-digit number. The cipher-text can be up to 11 digits long and there are no limits for the key size. Considering that the attacker has access to both the cipher-text and the ...
2
votes
1answer
48 views

Elliptic Curve Discrete Log in a Compsite Ring

Elliptic curves are usually defined over prime rings (fields), but what if we chose a ring of composite order? Let $n = pq$ for $p,q$ large primes. Say I have elliptic curve $y^2 = x^3 + ax + b$ over ...
1
vote
0answers
23 views

Bullteproofs with ranges not in power of two

I am new to bulletproofs,From what I understand, if i was to do a range proof using bulletproofs , both the start and end number have to be to the power of 2. is there any algorithm/approach which ...
0
votes
1answer
68 views

Learning elliptic curve cryptography for specific application

I would like to develop a protocol for specific purpose. This protocol will utilize asymmetric cryptography in which one private key can be paired with numerous public keys: messages encrypted with ...
0
votes
1answer
56 views

NaCl allows decryption with the same public key as for encryption

I followed the description here: Public-key authenticated encryption: crypto_box and created an example that encrypts a message with Bob's public key and signs it with Alice's secret key : ...
0
votes
1answer
34 views

specific scenario question relating to using NACL crypto_box in a protocol

Scenario 1: SenderA sends message1 to ReceiverB message1 is encrypted using NACL crypto_box using SenderA secret key and ReceiverB public key. we understand that the NACL crypto_box authenticator ...
-3
votes
0answers
24 views

any one can give me answer this question…it is very helpful [on hold]

The Caesar cipher shifts all the letters in a piece of text by a certain number of places. The key for this cipher is a letter which represents the number of place for the shift. So, for example, a ...
5
votes
1answer
54 views

Second preimage attack complexity when the digest is malleable

An attacker has a hash $h$ and a message $m$. He wants to find $m^\prime$ with the same length as $m$ which hashes to $h^\prime$. However, $m^\prime$ can only differ from $m$ in the 1 bits (i.e. ...
-2
votes
0answers
35 views

Which archive file format with encryption is most secure? [on hold]

If I had to bundle a bunch of files into a compressed archive file with encryption, which file format would be most secure? RAR? Zip? Other? What is recommended?
2
votes
1answer
55 views

Is there FHE (fully homomorphic encrpytion) for string/text processing?

I had a quick look at FHE libraries like SEAL, HeLib, and Palisade and they deal with addition or multiplication of encrypted data. Is there a FHE that deals with string? If no, is that because it is ...
3
votes
1answer
86 views

Is it feasible to find n hashes that sum up to a given hash?

Consider two sets $A=\{a_1,a_2,\cdots,a_n\}, B=\{b_1,b_2,\cdots,b_m\}$; We can calculate the hash sum of those sets: $$HASHSUM(𝐴)=(ℎ𝑎𝑠ℎ(a_1)+ ℎ𝑎𝑠ℎ(𝑎_2)+\cdots +ℎ𝑎𝑠ℎ(𝑎_𝑛))$$ and $$HASHSUM(𝐵...
0
votes
0answers
35 views

Constructing Differential Characteristics for Feistel Cipher

I have to construct for every i-round of Feistel cipher, for $i \in \{3,4,5,6,7,8\}$, a differential characteristic with there properties: $Pr[\Delta x = a \overset{f_i}{\rightarrow} \Delta y = b] = ...
2
votes
0answers
60 views

Is it possible to verify attributes of encrypted content?

Let's say that Alice has this information about her, { "name": "Alice", "age": 25, "eyes": "brown" } which she encrypts with a key pair so that no one access ...
1
vote
2answers
40 views

In zero knowledge proofs, would it make a difference if the prover is deterministic or probabilistic?

In zero knowledge proofs, would it make a difference if the prover is deterministic or probabilistic? As the verifier can simulate the prover's interaction with him, I assumed that the prover would ...
0
votes
1answer
40 views

Security of this PRF [on hold]

Given $F$ a secure PRF with input size $\lambda$. Define $F'$ as $F'(k,x||x') = F(k, 0||x)\oplus F(k, 1||x')$ with $x$ and $x'$ of $\lambda-1$ bits. Is $F'$ a secure PRF?
1
vote
1answer
32 views

Is PKCS#5 deterministic if both sides use an agreed salt and iteration count

In a system were both sides have access to a common secret, and publicly exchange an iteration count and salt, can a PKCS#5 (Password-based Encryption Standard) algorithm be used to generate a key ...
4
votes
1answer
56 views

secp256k1 point density

I am working on a crypto project using the secp256k1 elliptic curve. I know that I can select a random point $P = (x, y)$ from the curve by randomly selecting the first coordinate $x \in \mathbb{Z}_p$...
0
votes
0answers
18 views

Generate Private Key with AES 256 CTR [migrated]

How to generate a private key with AES 256-CTR ? I need a private key with CTR as CBC is no longer supported by my client. Please advise Details: We need to connect to an SFTP instance of client ...
0
votes
0answers
28 views

MULalpha and DIValpha operations in SNOW 3G

I'm not able to appreciate the importance of mul alpha and div alpha operations in feedback polynomial of LFSR in SNOW 3G. What problems or weakness do they help in mitigating and how ?
-2
votes
0answers
28 views

Is this encryption algorithm uncrackable he gave the key in the title but it is still not cracked [closed]

https://www.reddit.com/r/codes/comments/cq2mu6/i_made_an_encryption_method_so_secure_that_i_will/ I found this post and he seems very cocky even tho it is very likely he just can't crack his own ...

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