All Questions

6
votes
1answer
71 views

Why doesn't “Classic McEliece” need scrambling?

The original McEliece scheme uses two random matrices S and P to scramble the generator matrix and uses $\mathsf S·\mathsf G·\mathsf P$ as the public key. The Niederreiter variant also does about the ...
0
votes
0answers
59 views

Which functions can be used as Pseudo Random functions? Can block Ciphers be used for this purpose with our own encryption function?

Since the cloud security algorithm I am trying to implement says that for a PRF, any secure encryption algorithm or a keyed hash function can be used. The security parameter I have chosen is 15 bits ...
0
votes
0answers
41 views

Unique numbers with $P^aQ^bR^c \mod N$ for each combination of $a,b,c$ possible? Would it be safer than separate form (like $T^a \mod P$ for each)?

Main question: Is the computation of $a,b,c$ in $P^aQ^bR^c \mod N$ (much) harder than in $T_p^a \mod P$, $T_q^b \mod Q$, $T_r^c \mod R$ ? (assuming the first form exists) $P^aQ^bR^c \mod N$ With $P^...
0
votes
0answers
40 views

Brute-force threshold of Secret Sharing using XOR and checksum [on hold]

I came about a realization of how feasible and fast is this kind of secret sharing, but we can split secrets by just using XOR and random numbers. Suppose that: ...
0
votes
1answer
47 views

Comparison on Gentry's Fully homomorphic Encryption? [duplicate]

This topic is very new to me. Is it possible to do comparison on the encrypted data(data is encrypted using Gentry's FHE)? If so, how can it be done?
1
vote
1answer
72 views

Simulation based proofs, what am I missing?

In the example given by in the top answer of Simulation based proofs: Simple examples claims that this is insecure the semi-honest, and I need assistance in where I am failing to reason why that this ...
0
votes
1answer
38 views

How much more secure is $c = mg_1^r + g_2(g_1(g_1^r-1)/(g_1-1)) \mod p$ compared to just $c = mg_1^r \mod p$ (dis. log), all known but $r$?

To encode a message $m$ to a cipher $c$ you can use the only hard solvable problem of computing the discrete logarithm with a generator $g$ in base over a prime $p$. $c = mg_1^r$ mod p If an ...
0
votes
1answer
45 views

Searching for a dining cryptographers problem variant

When I frist read about the famous dining cryptographers problem, in a book years ago I remember the author made a twist on it, demonstrating the generalization of the problem. Basically the dining ...
0
votes
0answers
48 views

Perfect Secrecy for Message Subset

In "Introduction to Modern Cryptography" by Jonathan Katz exercise 2.6 goes like this: "Say encryption scheme (Gen, Enc, Dec) satisfies DEFINITION 2.1 for all distributions over ℳ that assign non-zero ...
1
vote
1answer
31 views

Can I do a forward secure half-round ephemeral-static ECDH?

In the context of the project we are working on recently, we would like to enable users to "leave a message" to someone on the Internet securely. Our setting is as below: ECC key pairs for open ID ...
0
votes
0answers
46 views

Decrypting using ECC [on hold]

Alice and Bob are again exchanging messages using ECC. I have all my curve parameters $A,B,p$ and $g$ as well as Alice's private key $k_a$ and Bob's private key $k_b$. I also have what i think is the ...
2
votes
1answer
659 views

Proof of work - 51% attack

In the 51% attack on the Proof Of Work Consensus Mechanism, it's often said that you need more hashing power than the rest of the network combined. Though I can't understand why you need that much. ...
3
votes
1answer
39 views

What is the RFC order of peer certificate verification, trust chain or expiry first?

If a certificate received from a peer: Is expired, has a valid signature, but from an untrusted root CA What error should be thrown? Untrusted certificate or expired certificate? I can't seem to ...
1
vote
1answer
29 views

ECDSA over $\mathbb{F}_{p^n}$ for $n>1$. How to calculate $r$ and $s$

I'm having some trouble understanding how to calculate $r$ and $s$ as specified in the wikipedia page for ECDSA (https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm) We can see ...
0
votes
1answer
76 views

Cryptographic equivalent of family coat of arms

As a layman when it comes to cryptography, I have recently been asking myself if there was a cryptographic equivalent of a family code of arms. I'm thinking of something asymmetric, that is future ...
-1
votes
0answers
43 views

Is there a collision free Hash Function for dynamic data that preserves already created hashes? [migrated]

I am familiar with the concept of hash functions and fingerprints but I am new to the implementation of functions and the specific characteristics of all those hash functions out there. What I need ...
0
votes
0answers
46 views

I need help understanding and answering this question about RSA Enc/Dec [closed]

Let's assume, Alice's public key is ($N = 15,\space e= 3$), private key is ($N=15, \space d=3$). Bob sends message $m = 5$ by encrypting it with Alice's public key. Attacker Eve intercepts that ...
0
votes
1answer
52 views

Euler's totient function and Carmichael's totient function in RSA [duplicate]

I'm a high school student taking IB and I'm doing my EE on Maths, more specifically on the effectiveness of Euler's totient function and Carmichael's totient function in RSA. Am I right in thinking ...
1
vote
0answers
18 views

Why does ε-differential privacy protect the subset of 1/ε edges in terms of graphs?

In the book The Algorithmic Foundations of Differential Privacy by Cynthia Dwork, Aaron Roth on page 24, databases that take the form of graphs are discussed. We could on the other hand consider ...
1
vote
1answer
51 views

Proof of correctness of an ElGamal encryption given a specific public key

Suppose Alice sends an ElGamal encryption of a value $v$ to Bob (using either the normal or exponential version of ElGamal). E.g. assuming publicly-known $pk_{BOB} = h$ and a generator $g$, Alice ...
0
votes
0answers
26 views

Need help deciphering this ciphertext which I don't know its algorithm [closed]

I got a base 32 code which I decrypted to get another ciper but don't know how to decrypt. base32 code: ...
3
votes
0answers
39 views

What is the difference between discrete-then-gaussian and gaussian-then-discrete?

In lattice cryptography, we always face the probem of discrete gaussian sampling. To the beginners, it is a bit complex. However, gaussian sampling from a continous space is much easier to understand, ...
1
vote
0answers
42 views

Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
0
votes
1answer
23 views

Is OpenSSL HMAC vulnerable to length extesion attacks when using MD5 as hash algorithm?

Given that a valid hash for a specific payload is known, would some C code like this be vulnerable to a length extension attack? ...
0
votes
0answers
43 views

Hill cipher — obtain matrix key

I have to solve Hill's cipher. I have only cipher text: CGQIYN and key: CFDG. I don't know how to decrypt it, because in all ...
2
votes
2answers
272 views

Does classifying an integer as a discrete log require it be part of a multiplicative group?

This question is not a question about the discrete log problem, the generalized discrete log problem, or an additive group. The confusion is whether any integer can be considered a discrete log or ...
0
votes
1answer
62 views

Which type of non-basic cipher works better with microcontroller which has no interface and keyboard connected to it? [closed]

Did a C++ code on Caesar Cipher to do encryption and decryption with my XMC4500 microcontroller but my lecturer said that Caesar Cipher is too simple. He wants me to use a non basic type of cipher and ...
0
votes
1answer
24 views

How many bytes of the last keystream block are used to XOR the final block of partial plaintext in CFB, OFB & CTR modes?

I apologize if this is a dumb question but I'm trying to understand how the final block of partial plaintext is XORed using only n number of bytes in the final keystream block. How do we determine ...
1
vote
0answers
39 views

How to implement correctly a “secure” authentication protocol? [closed]

Due to my lack of knowledge in this matter I am facing some problems to identify which features are sign of a bad implementation of a symmetric authorization application. As I am concerned the system ...
0
votes
0answers
36 views

Reward for anyone helping me with PHP / OpenPGP RSA implementation [closed]

I am a coder and I am currently coding my own website for practice purpose. I've learnt PHP, css, html, sql and xml... but now I'm seriously bugging on the implementation of a basic thing. I want to ...
0
votes
0answers
50 views

How to determine if a generalized $\sigma$ function (similar to what is defined in SHA-2) is invertible?

Let $ROTR^n(x)$ and $SHR^n(x)$ denote the rotate right (circular right shift) and the right shift operations, as defined in SHA-2 standard. Consider any function of the form $$f(x) = ROTR^{n_1}(x) \...
0
votes
2answers
48 views

cryptographically signed streaming data

On a high level the question is: how does one cryptographically sign streaming data? Here is the context: a number of people are continuously streaming data to me the data is public and does not ...
1
vote
1answer
59 views

Simple math ECDSA example

I'm trying to setup an ECDSA math example using just integer math and multiply (no EC). The purpose is just to help people understand why this works with out the added complication of understanding ...
2
votes
0answers
25 views

Can ideal functionalities share variables

I am trying to define an ideal world for a protocol that requires two functionalities to interact with each other. Lets call them $\mathcal{F}_1$ and $\mathcal{F}_2$. Now $\mathcal{F}_1$ maintains a ...
1
vote
0answers
56 views

If 1 can be a random number in Diffie-Hellman Algorithm

I've done some calculations and Diffie-Hellman Algorithm worked for all chosen random numbers except $1$. In the description of the algorithm, I can't find information that the random number has to be ...
1
vote
1answer
43 views

Communication cost of Oblivious Transfer and OT Extension?

Suppose there exist fixed K set of N-bit strings. Here, sender and receiver perform 1-out-of-K OT either once or many times. In the latter case, we may use OT Extension. What is the order of the ...
0
votes
0answers
19 views

Decrypt a damaged external HDD Controller with Truecrypt [closed]

I try to recover my old hdd which is really tricky. But first step by step. I am storing my private stuff on an WD external HDD which is encrypted by Truecrypt (whole HDD) From one day to another the ...
2
votes
0answers
23 views

Security strength of JPBC Type A curve compared to SecP curve

I recently encountered some problems when learning about the JPBC library. Does the curve generated by (J)PBC using the method typeAcurvegenerator(160,512) and the ...
0
votes
0answers
46 views

Is it safe to use ECB mode this way, w/o duplicate blocks?

I wanna make my own "way" of encrypting separate messages. And I want it to have the least possible size overhead while being completely encrypted (hide msg counter). Here's my current idea: we ...
0
votes
1answer
62 views

how to prove that given cryptosystem is not IND-CCA secure?

Let $m$ and $k$ be positive integers ($m$ bit plain text) ; let $Q$ be a family of trapdoor one-way permutations such that $f : \{0,1\}^k \rightarrow \{0,1\}^k$ for all $f$ in $Q$; and let $G : \{0,1\}...
1
vote
1answer
70 views

Why CBC-MAC encrypts at each step

Considering CBC-MAC as: $\qquad H_0 = IV = 0$ $\qquad H_i = E_k(P_i \oplus H_{i-1})$ $\qquad MAC = H_n$ What are the properties that makes this "safer" (less ...
-1
votes
0answers
32 views

Entropy Calculation of Affine Cipher [closed]

I'm trying to compute H(K|C) and H(K|P, C) for the Affine Cipher, assuming that keys are used equiprobably and the plaintexts are equiprobable. I know the answer of H(K|C)= $\log_2 312$ and H(K|P, C)= ...
0
votes
0answers
27 views

Difference between Sibling Intractable Function Family and Secret Sharing? [closed]

What is the difference between any Secret Sharing Scheme Link and Sibling Intractable Function Family (SIFF) Link?
-2
votes
1answer
86 views

RSA: why does $m^{ed}$ equal the original message?

Trapdoor functions are defined as that a secret key reverses the function. It seems to me more that it causes a cycle to repeat, similar to how $n^k \bmod k$, when $k$ is a prime number, equals $n$, ...
0
votes
0answers
25 views

How to 'break' a coloumnar transposiiton cipher?

First of all: sorry asking this question. I have seen that this question has been asked before, but I didn't fully understand the answers and couldn't find find anymore information through googling so ...
0
votes
0answers
27 views

Dilithium signature scheme - Public key derivation

Good day! I am very new to Cryptography but I want to make sure I understand the concept of the scheme correctly before using it to our system. So I was looking at post quantum signature schemes, and ...
1
vote
0answers
25 views

Malicious OT from 'Efficient Secure Two Party Protocols' — defining the simulators

I am looking at Protocol 7.5.1 in Hazay and Lindell's Efficient Secure Two Party Protocols, it can found here (p 201). A similar protocol is proven secure in Section 7.4 (p190) and the proof is ...
-3
votes
0answers
21 views

How to Accelerate Openssl Library using CUDA C [closed]

How to accelerate openssl library on GPU for performing faster cryptography
2
votes
0answers
32 views

Share secret non-interactively in a verifiable way

In an application, I need to share a secret (random number) with a Group of known receivers over a public channel (a Blockchain) but each receiver needs to be able to check that the others received ...
1
vote
0answers
34 views

Is there any identification for common encoding/encryption?

I come across lots of tokens which might be simply encoded and not random, but I don't know any way to identity if they are encoded or random, how to find is there any cheatsheet for the same. For ...

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