-1
votes
3answers
67 views

Some doubts about GnuPG

I've reading on GPG since yesterday and I have a doubt: the whole system of double key encryption does make sense but it looks to me like either way you are compromising something in terms of ...
0
votes
1answer
36 views

Physical entropy source: How many bits entropy per byte is sufficent?

8 bit / byte would be perfect obviously. head -c 1M /dev/urandom | ent gives ~ 7.9998 bits per byte. Now, if I have a physical entropy source, how much entropy ...
3
votes
0answers
51 views

How to generate new LWE samples

Assume we are given a small fixed number of LWE samples with secret $s$ and error $e$, where the error distribution is taken so that the LWE problem is hard. My question: How can one further ...
0
votes
1answer
126 views

Is it OK to encode data using key equal to data

For some project, I need to store some short string in encrypted form. It would be ideal for the current purposes to encrypt it using itself. ...
2
votes
2answers
162 views

Is it possible to choose which point will have the public key of a given Elliptic Curve?

I am wondering if there is a feasible way that, given a specific elliptic curve (such as secp256r1), I could create a keypair where the public key has a given $x$-coordinate. If it is not possible, is ...
0
votes
0answers
23 views

Creating a LCG with m = 32767 [migrated]

I hope this question is not too simple for you: I want to create a PRNG for an integer only (with a max of 32767) system and tried to use an LCG. So I've chosen as m = 32767 and c = 3 and I tried to ...
0
votes
2answers
39 views

PQ Key Exchange based on Elliptic Curve Isogenies

I was reading the Wikipedia article on Post Quantum Cryptography and was interested in opinions as to whether the Supersingular Elliptic Curve Isogeny Diffie-Hellman listed there would be a good Post ...
0
votes
1answer
35 views

Is randomsound for increasing entropy pool not doing what it is supposed to do?

I am using randomsound because I thought it would be a good idea to inject some additional entropy into the entropy pools of my linux machines (clearly those machines have a corresponding sound card). ...
0
votes
0answers
48 views

Unicity Distance - AES

I am quite confused calculating the unicity distance and I was hoping that someone can clarify some things for me. My main issue comes from somewhat a difference of the calculation given by our ...
0
votes
1answer
43 views

computational complexity class of decryption of AES

I haven't really seen what computational complexity class of decryption of AES is. Can anyone provide reference papers or answers here?
0
votes
0answers
42 views

AM protocol for 2 distinct objects

Prover is going to convince verifier that 2 objects are distinct, do you know any Arthur-Merlin protocol for this problem?
1
vote
0answers
24 views

Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$. Say ...
0
votes
1answer
46 views

Key exchange using ECDH vs ECIES

I'm a beginner to ECC crypto programming. Does any one explain to me the difference with using ECDH for shared key exchange and use of ECIES by encrypting shared key with the public key of the ...
5
votes
1answer
198 views

Why does anyone use elliptic curves for a CSPRNG?

I saw Martijn Grooten's talk on elliptic curves at BSides London this year, and it helped me understand how elliptic curve crypto works, especially in the case of Diffie-Hellman (ECDH). He also ...
1
vote
1answer
52 views

What is meant by - computational complexity $2^x$?

Recently Bi-clique Cryptanalysis allowed to obtain following results on full AES ES that claim to have The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$ The ...
-3
votes
1answer
57 views

SHA-256 hash of null input?

What is the SHA-256 hash if the input is null, i.e. an empty bitstring? (Not the hash of 0 or "0".)
1
vote
2answers
50 views

Distinguishing attack on stream cipher created from a block cipher in counter mode

A block cipher in counter mode creates a key stream by: $$z_i = E_K(IV || i)$$ Where $IV$ is some chosen initialisation vector (with some length $l$ less that $n$ bits) and $i$ is the binary ...
1
vote
1answer
61 views

Will adding space to the Vigenère block make it truly unbreakable?

I just have gotten into cryptography and learned about the Vigenère block. I think it's a very good idea because, if used correctly, it is unbreakable. But the only downsite is, the key must be the ...
0
votes
1answer
49 views

Cryptanalysis of Marvin32

So I am curious about the security analysis of Marvin32, the randomized hash algorithm used in .NET (to prevent hash-table DoS). I found the source code here: ...
9
votes
4answers
2k views

Is the one-time-pad a secure system according to modern definitions?

Occasionally I hear people say that one-time pads are "useless" or even "broken". "modern cryptography knows more security definitions, under some of which the one-time pad is completely ...
0
votes
1answer
173 views
0
votes
1answer
58 views

Why is a Feistel network bijective?

EDIT: Fixed for clarity of intention I was reading "The FFX Mode of Operation for Format-Preserving Encryption" when I came across Figure 1 (see below). It's obvious why it's reversible (top-down ...
0
votes
2answers
43 views

Are there security issues with adding plaintext length to TLS packets?

I have quite a big problem, because of a software implementation of TLS I had to adapt I had to create something which is now biting me. It all comes down to this: I need to know the length of the ...
2
votes
2answers
102 views

What makes SHA-2 and SHA-3 have security levels half their output hash length?

The tag wiki for sha-256 says, in part: SHA-256 ... processes the input in 512-bit block and has a 256-bit output, for a 128-bit security level. I'm not a cryptographer, just an interested ...
1
vote
1answer
48 views

Is it right about an example of bilinear map $e$?

The equation for the elliptic curve is $y^{2} = x^{3} + x$ and is defined over the field $F_{q}$ for some prime $q\equiv 3 \pmod 4$, and set $q=307$. Choose random generator $g=[182, 240]$. My ...
0
votes
0answers
38 views

Solving discrete logarithm when p is not a safe prime

If you have the cyclic group of integers modulo $p$, where $p$ is not a safe prime, as well as a generator $g$ with which for all factors $q$ of $(p-1)$, $g^{(p-1)/q} \ne 1$, This answer says that ...
0
votes
0answers
20 views

Generating whitening keys through encryption

Question, if I generated whitening keys by encrypting the plaintexts of 0000... and 0A0A... would this reduce vulnerability to meet in the middle and related key attacks? If so, any rough idea of how ...
1
vote
3answers
80 views

Is it possible to encrypt a message's destination as well as its content?

I have imagined a way to break through any kind of censorship but since I don't have enough professional knowledge of cryptography I don't know whether it is feasible or not. If there is a method ...
0
votes
1answer
50 views

Share two secrets between two parties

Alice has a secret A, Bob has a secret B. They have a secure channel and a MAC. They each want to know the other's secret, but don't particularly want to give up their own. However, neither will not ...
16
votes
4answers
4k views

How do we know a cryptographic primitive won't fail suddenly?

It took more than a decade from when MD5 looked like it was going to break to the point when it was actually broken. That's more than a decade of warning. How can we be sure that when our ...
0
votes
1answer
136 views

Trying to understand the use of ECC in TLS certificates

I was looking the certificate of this website: https://www.cloudflare.com that has an ECC based certification. I'm just curious to know if is possible to understand which elliptic curve is used and ...
2
votes
1answer
57 views

Is it OK to substitute a PRF for a random oracle?

Random oracles don't exist, but aren't PRFs essentially indistinguishable from them? So why can't we substitute pseudorandom functions wherever we use random oracles? And if we can do this, why is ...
0
votes
2answers
66 views

Brute Force on Key

If you are brute forcing a key and trying trillions of combos, how will you know when you accidentally hit the right answer? Clearly you can't look at each decoded answer to see which "looks right".
3
votes
2answers
115 views

Is it OK to use a hash of the key as nonce for AES GCM?

I don't see an immediate risk of using the hash of the key as the nonce for AES GCM. Is there something I could be overlooking?
3
votes
1answer
238 views

How is information disclosed by modular multiplication?

Consider the case that $c = a \cdot b \mod p$ where $p$ is a known prime and $0 < a < p$ and $0 < b < p$ are unknown integers numbers. Furthermore, some bits on the value of $c$ are ...
0
votes
2answers
66 views

Sending the next one-time pad key in this one-time pad message? [duplicate]

I am doing a research project on cryptography next year, and I'm really new to cryptography. This isn't some really advanced thing or anything, and I'm just trying to come up with something basic. ...
1
vote
0answers
46 views

Secure content-defined chunking

I am writing an app that needs to split a stream of plaintext bytes into variable-sized chunks (for deduplication). The way this is traditionally done is using a rolling hash function defined over ...
0
votes
0answers
35 views

Anyone familiar with domain of hash functions in bilinear pairing based system?

I need a clarification regarding domain of hash functions. I have defined a bilinear pairing based system as follows: Let G1 and G2 be cyclic multiplicative groups of prime order p generated by g1 ...
2
votes
0answers
59 views

Which attacks are possible against raw/textbook elliptic curve?

A quick question, we know that raw RSA is a no go. To solve this we have different PKCS standards forcing structure on the input messages. For EC the story is something else. For signatures we have ...
0
votes
2answers
108 views

AES-CTR in BouncyCastle with string key, without IV or salt [closed]

Our team is encrypting data using a javascript snippet. My problem is I'm supposed to parse them back in my Java code. I am having troubles identifying parts of the algorithm. The code says it's CTR ...
0
votes
1answer
49 views

Advantages/Disadvantages of Bcrypt vs. hash/salt

I have an application that I use sha3-512 to hash my password with a randomly generated 64 characters salt for each password. Is it bad to use this method to store passwords? I know many people ...
0
votes
0answers
43 views

Property of Multiplicative group of integers mod n

While practising on paper I've realized of a property of multiplicative group of integers mod $n$. First, let's define $G$ being $p$ a prime and $g$ a primitive root mod n or a generator of a ...
0
votes
0answers
53 views

Is it possible to make an encrypted text look like a sentence consists of random words?

Without having any knowledge of common encryption methods, I wonder if an encrypted text can look like random valid words as if it is a sentence. Is it possible? If so, what methods should I use?
0
votes
1answer
64 views

Correctness in Multi-party Computation: Real/Ideal Paradigm in Malicious case

I need to know: 1- What does exactly correctness mean in this context? 2- How is correctness implied in malicious model? 3- If the correctness means " the adversary cannot cause the output to be ...
0
votes
1answer
36 views

Can Hill Chipher be considered as Asymmetric?

I know hill chipher is a block chipher ,We produce decryption key by inverse of key matirx but we still use different key for decryption. Therefore Can we say that Hill chipher is asymmetric chipher? ...
1
vote
1answer
88 views

Is $(a,g^{ab})$ computationally indistinguishable from $(a, g^c)$?

From wikipedia, the DDH assumption says,given a cyclic group $G$ of order $q$ with generator $g$, $(g^a, g^b, g^{ab})$ looks like $(g^a, g^b, g^c)$ where $a,b,c$ are randomly and independently chosen ...
0
votes
1answer
55 views

Euler's Totient function for semiprime numbers

I have noticed, during the period I spent studying RSA, that Euler's Totient function can be calculated in another way than $ϕ(N) =(p-1).(q-1)$ Let me explain myself by pointing to a brief example: ...
0
votes
0answers
30 views

verify fails on 3rd party after signing with BouncyCastle

I am using BouncyCastle to perform ECDH and then encrypt the data between the mobile (Android) and my hardware with ECIES. It all works fine. When I try to sign a byte array and send it to the ...
1
vote
1answer
57 views

Encryption through multiplication of encoded key [closed]

Yesterday I finished programming my own encryption program. It is using an input and a key. Here are all the steps it is going through. For an example, let say the ...
0
votes
1answer
51 views

Shamir secret sharing with field 2^8

I want to split a message using Shamir's Secret Sharing by splitting each byte of it so the field I'm using is $2^8$. Assume $(2,2)$ scheme, i.e., splitting it into $2$ shares and both of them are ...

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