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Is it possible to retrieve the original hash of a digital signature using a public key?

I am running a server that is receiving packets. Each packet is signed with an RSA 512 SHA-256 digital signature. I have a public key and exponent that I use to verify the digital signatures. I'm ...
3
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1answer
31 views

Why is this signature independent of the message?

Assume that we have the following signature scheme CL Signature: Choose a cyclic group $G = \langle g \rangle$ of order $q$. Uniformly and randomly choose two elements $x,y \in \mathbb{Z}_q$, and ...
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0answers
15 views

what is the difference between RSA and DHM mathematically? And why RSA is hard to break [duplicate]

This is my assignment question and I m looking for immaculate answers from crypto experts. The aim of the assignment includes the critical analysis of both algos and answers to the given questions in ...
0
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0answers
26 views

Linkable Ring Signature

I am trying to calculate linkable ring signature taking 4 members to solve a numerical question, but there are some confusions mentioned below especially regarding hash and mod. 0: H_1 belongs to Z_q ...
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0answers
18 views

Advantage of existing Cryptosystems

I have read about the concept of perfect secrecy and statistical distance. The perfect secrecy is impossible to be implemented on real world scenario. So the cryptosystems used at various websites ...
4
votes
1answer
76 views

ECIES vs. RSA + AES

I am confused about the distinction between RSA and ECC (Elliptic curve) when it comes to encryption, and would appreciate it if someone could confirm if my understanding is correct. When encrypting a ...
4
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2answers
1k views

How are recovery keys possible if something is encrypted using a password?

I thought that encryption works as follows - it is about changing the thing we want to secure using an algorithm and using the password to mathematically change the secured content so it is unreadable....
2
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1answer
51 views

Which AES mode when using Poly1305-AES

I am reading DJ Bernstein's paper on the Poly1305-AES mac (https://cr.yp.to/mac/poly1305-20050329.pdf). I understand that AES is needed to provide the array s. In its paper on page 5 we can read: ...
2
votes
1answer
41 views

How to securely deal cards?

Thanks to a certain pandemic going around I was wondering whether there is any cryptographic way to remotely deal cards without the dealer being able to know them and without requiring to trust a ...
-1
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1answer
35 views

What factors do we take into account to compute the encryption and decryption time of an encryption/decryption algorithm?

I have been reading some papers on Image Encryption using ECC and chaotic systems such as 2D Arnold. What do they mean by 'Encryption ' and 'Decryption' time? How is it within 1 second? I tried ...
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0answers
34 views

How can we decrypt all RSA messages given a function that can efficiently decrypt a small percentage of all possible ciphertexts? [duplicate]

I saw this question in a paper and was not able to solve it. Assume that we are given an efficient algorithm called RSA_break() that can decrypt, without the ...
3
votes
1answer
66 views

Can a SHA3 engine be used to construct a Keccak implementation?

I am working on a cSHAKE-128 & cSHAKE-256 implementation that takes advantage of a number of hardware accelerators I have at my disposal, specifically for SHA-3 256/384/512 and SHAKE 128/256. ...
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0answers
35 views

Reconstruction RSA Private key from BER components [closed]

im a newbie in cryptographic. and was wondering about RSA encryption keys. all of the RSA Private keys i saw was in this format : -----BEGIN RSA PRIVATE KEY----- ...
1
vote
1answer
43 views

Examine whether a hash function is collision-resistant

Assume a collision-resistant hash function $h$ which compresses sequences of length $2n$ to length $n$. It must be examined whether the hash function which compresses seqs. length $4n$ to $n$: $$ h_1(...
3
votes
2answers
104 views

Do Korea and Japan have their own national hashing standard?

I know China has SM3 and SM4 commercial cryptographic hash and block cipher standards, and I know Japan has Camellia block cipher and Korea has SEED. Do Japan and Korea have an industry standard for ...
1
vote
1answer
30 views

mutual authentication with pre-shared key

A and B share two secrete keys: [keyA] and [keyB]. A sends this to B. AUTH_A = prf(KeyA, ID_A) B sends this to A. AUTH_B = prf(KeyB, ID_B) Does above scheme provide mutual authentication? I think so ...
0
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0answers
24 views

Decrypting iPhone Backup

Are key bag keys rotated between backups? Or if I have keys from an old backup, am I able to use then with a later backup? Short of it, have a friend w/ an incomplete backup and attempting to leverage ...
1
vote
1answer
69 views

Hashes or ciphers with all rounds executed in parallel?

Pretty much every cipher or hash I've seen has multiple rounds the are designed to be run serially one after the other. Has anyone ever designed a fully parallel cipher or hash? This would be one ...
-2
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0answers
55 views

How to unlock Shamir secret with only $2$ shares when the minimum is $3$?

From Shamir's Secret Sharing: To unlock the secret via Shamir's secret sharing, you need a minimum number of shares. This is called the threshold, and is used to denote the minimum number of shares ...
0
votes
1answer
20 views

IKEv2 mutual authentication step

I read from here that, https://tools.ietf.org/html/rfc7296 it mentioned, 2.15. Authentication of the IKE SA the initiator signs the first message (IKE_SA_INIT request), starting with the first octet ...
0
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0answers
21 views

Help identifying this message type [closed]

I'm trying to analyse some network requests and I need help identifying the type of data flowing in and out. I know it's not really a "cryptography" question but I think this community is ...
0
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0answers
28 views

Are key evolving signatures (or forward secure signatures) that secure?

Reading this paper Forward-Secure Digital Signature Scheme I discovered the notion of key evolving signatures. The intuition behind these signatures is clear: one uses different private keys to ...
0
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2answers
127 views

Does decryption with a wrong key creates a new encryption?

I'm wondering if decrypting with a wrong key is the same a encrypting in a different way. For example if I encrypt the message "hello" with Caesar cipher with key = 3 it will give the ...
3
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0answers
35 views

Does the security proof of HMAC somehow change if it's instantiated with sponge-based hash functions with small rate and large capacity?

HMAC was introduced in [1], as a MAC that has its security proof based on the properties on the underlaying hash function. The hash functions considered in that paper were ones based on the Merkle-...
1
vote
1answer
84 views

Why all multivariate schemes restrict themselves to polynomials of degree 2

If we note all multivariate schemes restrict themselves to polynomials of degree 2. I was wondering why they do it. After looking on the internet, I came to know that they do it for the efficiency. My ...
1
vote
1answer
56 views

Is a stream cipher and a (cryptographically secure) PRNG nearly the same thing?

If I let the authentification tag aside (which is important), encrypting with AES-GCM and a fixed key and nonce: ...
0
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0answers
23 views

Parallel random-access machine resistance in memory-hard functions

I'm trying to add memory-hardness to a hash function. A link to the specific line where that part of the implementation starts can be seen here. The basic approach is this: (1) Concatenate a string of ...
0
votes
1answer
49 views

byte significance with hash functions

I am using the python hmac module to generate an authentication code. Given a key, message, and hash function (I am using md5), the library returns an authentication code as a python bytes object. I ...
0
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0answers
13 views

How to restore the original mnemonics from shares? [closed]

I just read that an original mnemonic can be split into parts, I am a little confused about how the system can restore the original mnemonic from these mnemonic pieces. example i have mnemonic ...
0
votes
1answer
34 views

Can a nonce be used to steganographically hide a message?

If a standard encryption scheme involves a nonce, as most do, can the nonce be used to hide another small message? That is, the nonce (rather than being randomly generated) is a hidden message XORed ...
0
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0answers
4 views

How to create certificate signed with RSAPSS using openssl command? [migrated]

I tried https://gist.github.com/superseb/788a234647324b49ee5a56e07e3a91ac for commands, but getting following error in first command itself: ...
0
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0answers
21 views

Homomorphic encryption watermarking identity

I've been doing some research on FHE and SWHE schemes, most specifically on watermarking. As far as I've understood, you take as the merchant, take the buyer information encrypted and his public key ...
1
vote
1answer
47 views

Is is safe to use MtEtM? (MAC-then-Encrypt and Encrypt-than-MAC)

Assuming I am using different secrets/keys for each MAC pass, does running both MtE and EtM creates any vulnerability? This is what I mean about doing MtEtM: ...
-1
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0answers
28 views

How does Merkle tree Bitcoin query works?

I am trying to understand the basics of Encryption and Decryption in the Bitcoin blockchain. However there is something which is scratching my head recently? I understand how The Merkle Tree hashes ...
2
votes
1answer
149 views

Tests to distinguish between PRNG and a CSPRNG

What are the tests which a regular PRNG would fail but a CSPRNG would succeed? Is it just the next-bit test or are there multiple other tests which a PRNG which is not a CSPRNG would fail? Would a ...
0
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2answers
29 views

$\mathrm{Hash}(A\|B)$ where $B$ is known, $A$ is unknown. Would knowing $\mathrm{Hash}(A\|C)$ as well as $C$, speed up a brute force search for $A$

Let's say $\mathrm{Hash}(A\|B)$ is a hash of two concatenated strings, $A$ and $B$. Suppose I am trying to figure out $A$ from $\mathrm{Hash}(A\|B)$, I know $B$ but not $A$, I want to brute force to ...
-1
votes
0answers
31 views

Understanding Blockchain technology especially Wallet related [closed]

Hey guys I'm trying to really understand how blockchain technology works. To understand it completely I am trying to code a new coin, not sure if I'm doing it right. I came across the concept of ...
1
vote
1answer
64 views

Perfect Secrecy and Message distribution

I have been trying to come up with a proof of the following statement, Suppose a cryptosystem achieves perfect secrecy for a particular plaintext probability distribution then Prove that perfect ...
0
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0answers
28 views

Right implementation of digital signature with timestamp

The goal is to sign a file along with a timestamp using ECDSA. The signature can be later used to prove the file existed at a particular time. Signing implementation. The timestamp is appended with ...
0
votes
3answers
52 views

Is there an accepted way to cryptographically enforce tracked changes on a document?

I'm working on a document-editor project, and I would like to add a feature to lock tracked changes, similar to Microsoft Office. The goal is to allow one user to lock tracked changes with a password,...
0
votes
1answer
58 views

How many public keys and private keys are needed for RSA?

I am just learning about RSA encrytion and I am somewhat confused. First two prime numbers $p$ and $q$ must be chosen and multiplied to get $n$. Then we compute Euler function $\varphi (n) = (p-1)(q-1)...
0
votes
2answers
52 views

Encrypt a big file in blocks with AES-GCM: how many nonce do we need?

I need to encrypt big files using AES-GCM, potentially 10 GB or more. For memory (RAM) reasons, I need to processs them by blocks (let's say 16 MB), rather than doing ...
0
votes
0answers
40 views

Vulnerability in the Digital Signature Algorithm. Can I calculate k and x?

I feel DSA is vulnerable if k is randomly selected over a small set, example, {1,2,...,2^16 -1}. I am trying to come up with a program where I assume I have the public parameters (p,q,g) , public key :...
0
votes
1answer
42 views

CCA secure vs AE scheme

We already know that every authenticated encryption scheme is CCA secure, I was wondering about the converse. I believe it is not true, and I am finding trouble to construct a scheme which is only CCA ...
2
votes
1answer
36 views

Industry standard recommendations for memory usage defaults for a password hashing function?

I've been looking around for any studies done on this topic with respect to memory-hard password hashing. I'm inclined to simply impose no extra overhead by default, to be honest, but I'd really like ...
2
votes
2answers
59 views

How the coin flipping protocol prevent Alice from generating $ n $ from many primes?

This is a question from reading the paper 'Coin Flipping by Telephone - a protocol for solving impossible problems'. The fact that the coin is unbiased is based on the fact that if n is a product of ...
1
vote
1answer
69 views

Are MAC algorithms and digital signatures secure from quantum computers? If not, why?

I understand that asymmetric encryption is fundamentally deemed useless under Shor's Algorithm, and understand that symmetric encryption is somewhat quantum-resistant as long as the key-length is ...
0
votes
0answers
49 views

Encrypting a ciphertext with another cipher

Are there any disadvantages, other than performance, of using ChaCha20-Poly1305 with key K1 to encrypt a ciphertext generated by using AES-GCM with key K2? Would the answer change for combinations of ...
1
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0answers
44 views

Protecting the merkle tree from 2nd preimage attack

A 2nd preimage attack is possible on the standard Merkle tree as pictured below. I'm aware that we can add identifiers (to differentiate nodes) to the input of each hash as discussed in the link. ...
0
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0answers
22 views

Multiple Decryption Keys Where Decrypted Result Reveals Which Key Was Used

Is there an encryption scheme such that you can encrypt some data (such as an image) once, generate multiple decryption keys that can decrypt the ciphertext (so far this is just shamir's secret ...

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