2
votes
1answer
67 views

How is it possible that $g^q \equiv 1 \pmod p$ for a generator g?

The context of this question is coming up with the parameters for the ElGamal encryption scheme. One of the requirements for the parameters for ElGamal is that we have primes $p$ and $q$ such that $p ...
2
votes
2answers
65 views

Exploiting XOR one-time-pads with dictionary length that isn't a power of 2

I realized that if the key is chosen randomly from a range that isn't a power of 2, the one-time-pad leaks information about the plaintext. For example, if the alphabet was the first 20 naturals, ...
2
votes
3answers
95 views

What is the difference between substitution cipher and block cipher?

I'm studying(and clearing my head) about block cipher. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right). And an ideal substitution ...
2
votes
1answer
120 views

How is a per round key generated in DES algorithm?

I am reading over a slide that I found online regarding the DES algorithm for encryption and I am a little confused about the per round key generation. From the slide below, I understand that each per ...
2
votes
2answers
61 views

Obtaining Diffie-Hellman generator

In the Wikipedia article on Diffie-Hellman, the algorithm calls for a large prime modulus, $p$, and a generator, $g$, which is a primitive root of $p$. As far as my knowledge of number theory goes, ...
2
votes
2answers
42 views

Can you update a (k,n) scheme to a (k+t, n+t) scheme (assuming old keys can be deleted)?

I know that $(k,n)$ can increased to $(k+t,n-s)$ one, by generating a random polynomial $p(x)$ of degree $k+t$ with constant term $0$, and then ordering each agent $a$ to add $p(a_x)$ (where $a_x$ is ...
2
votes
1answer
125 views

Questions about a SHA3 cipher stream encryption scheme

I have written an encryption implementation using a hash as a cipherstream for demonstration purposes. I know it is slower than more sensible options such as AES but I am interested in several things, ...
2
votes
2answers
89 views

Linear cryptanalysis complete key guessing

In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext. From the partial sub key, how it is possible to guess the complete ...
2
votes
1answer
50 views

Is the length limit of AES-GCM per key or per (key, nonce) pair?

AES-GCM has a limit on the length of the plaintext it encrypts: $2^{39} - 256$ bits. But is this limit per key or per (key, nonce)? That is, if I encrypt a message with the maximum length, and encrypt ...
2
votes
1answer
103 views

Is secure lattice based cryptography in future?

Lattice cryptography is a post quantum cryptography that work on two NP-hard problem in below: Find shortest nonzero vector from origin and Find minimum distance of a arbitrary point out of lattice ...
2
votes
1answer
56 views

Data Encryption Standard (DES) S-Boxes

I read that the S-boxes introduce the much needed nonlinear behavior to DES. Can someone give me a lay mans explanation of why the effect of the S-boxes is said to be non-linear?
2
votes
1answer
230 views

Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
2
votes
1answer
48 views

Generalization of the DL-assumption in bilinear group pair

When thinking about a pairing-based cryptographic scheme, I encountered the following problem. Let $e \colon G_1, G_2 \to G_T$ be a Type 3 pairing. Then: Given $P, zP \in G_1$ and $Q, zQ \in G_2$, ...
2
votes
1answer
66 views

Elliptic Curve ElGamal and DSA - smooth group order and element of large prime order

In regular ElGamal and DSA, we choose large primes $p$ and $q$ such that $p\equiv 1\pmod{q}$, and a group element $g$ of order $q$ by computing $a^{(p-1)/q}$ for some random $a$. This is to prevent ...
2
votes
1answer
57 views

Which algorithm would be ideal for ephermal key generation followed by DH key exchange?

Bob and Alice, both generate a temporary public key pair each using X algorithm on their individual PC. After being authenticated by a third party, they use the DHE to come to get a common symmetric ...
2
votes
1answer
109 views

How to calculate mapping in bilinear

I am trying to read a paper in cryptography. In key generation phase, paper give a definition for bilinear like G and Gt be two cyclic groups of prime order p $e: G * G \to G_t$. be a map with the ...
2
votes
1answer
47 views

Perfect Forward Secrecy in PGP/asynchronous email

Looking at the RFC for PGP email/asynchronous chat with PFS here https://tools.ietf.org/html/draft-brown-pgp-pfs-03 can anyone tell me why the following scheme is no good? Alice and Bob retrieve each ...
2
votes
1answer
74 views

Does including the size of the hashed data improve security over just the hash

Trying to settle a discussion at work. We are mostly concerned with pre-image resistance. Suppose we have a common secure hash function $H$ (e.g. SHA-1/SHA-2) and some message $M$ we want to hash. ...
2
votes
1answer
106 views

How to prove secret value in Pedersen commitment is equal to secret value in Fujisaki commitment?

We have Pedersen commitment C to the secret value x, and Fujisake commitment C' to the secret value x. How can we make a zero-knowledge proof of equality for x value in the commitments?
2
votes
1answer
64 views

Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
2
votes
1answer
36 views

Should I authenticate memory data which was loaded from authenticated disk file?

Encrypted fields are loaded from disk file to process memory only after file's HMAC validation is successful. Data is still encrypted in memory and will be decrypted later, on demand, when it needs to ...
2
votes
2answers
75 views

Find plaintext of RSA by solving extended euclidean algorith for two encrptions with two different exponents for same plaintext

This is my homework question (but I am not asking the answer to it): Suppose two users Alice and Bob have the same RSA modulus n and suppose that their encryption exponents eA and eB are ...
2
votes
1answer
109 views

Breaking a Modified Caesar Cipher

Does anyone know of an efficient way of breaking a modified Caesar cipher (where the key is a set of numbers (the amount of shift) that is repeated throughout the plaintext, e.g. {1,2,3,4,5}) via ...
2
votes
1answer
78 views

IV larger than block size of cipher?

Is there any advantage to using an IV larger than a cipher's block size? Say I'm using AES-256 in Galois Counter Mode (GCM). My file format looks like this: ...
2
votes
1answer
147 views

Encryption that can only be decrypted once?

I want to encrypt a message so that it can only be decrypted once. I know that we can use nonces to do this when we exchange data over a communication channel, but in my case the cipher text will be ...
2
votes
1answer
155 views

For a given PlainText-CipherText pair how many valid keys are there in AES?

For $PT\in \mathbb{M}$ and $CT\in \mathbb{C}$, let $\mathbb{F}=\{f|f:\mathbb{M}\rightarrow\mathbb{C}\}$ be the collection of all functions from $\mathbb{M}$ to $\mathbb{C}$. Then AES encryption under ...
2
votes
1answer
51 views

PublicKey Unknown Encoding

I have a public key: ...
2
votes
1answer
212 views

Public Key Encryption using ECDHE and AES-GCM

Using a text book example, Alice and Bob want to communicate securely using encrypted messages over an insecure channel (the Internet). Alice and Bob have decided to use ECDH (using ephemeral keys ...
2
votes
1answer
50 views

What is the most an adversary can do in the context of public key masquerading?

Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair: $$ A: (P_A, S_A), B: (P_B, S_B)$$ and A already ...
2
votes
1answer
81 views

Collision likelihood from /dev/urandom for VMs using the same underlying hardware

We have multiple virtual machines sharing the same physical hardware. We use /dev/urandom for session key generation. But a question comes up: if ...
2
votes
1answer
55 views

Design for file transfers to a new party

I'm pondering a problem of how to enable transfers of files from clients to people that does not yet have an application/account/keys yet. Here's my current thought for Alice wanting to send Bob ...
2
votes
1answer
49 views

How to detect changes in data while preserving confidentiality (under constraints)?

Suppose party $A$ has two pieces of data, $X$ and $Y$, either of which may change separately, or they may change together. Given the following constraints: $A$ knows its current $X$ and $Y$ but has ...
2
votes
1answer
242 views

Given a linear block-cipher,how can an attacker decrypt any plaintext value encrypted,using 128 chosen ciphertexts

Given the linear block cipher $\operatorname{LinearCipher}(k, p) = c$ $$\operatorname{LinearCipher}(k, p_1 \oplus p_2) = \operatorname{LinearCipher}(k, p_1) \oplus \operatorname{LinearCipher}(k, ...
2
votes
1answer
133 views

Very short signatures? (eg: 48bits?)

Our application requires some 'mild' form of 'proof of origin' for the tokens we issue (~200 bytes), however, the value of each is trivial. The requirement is to provide 'tamper resistance' rather ...
2
votes
1answer
54 views

What is the notion of an interactive assumption?

In this paper: Sequential Aggregate Signatures with Short Public Keys: Design, Analysis and Implementation Studies the authors sell the paper as the first who propose Aggregate signatures without ...
2
votes
1answer
132 views

Wanted: Simple ring signature example

I spent all day trying to figure ring signature schemes out but apparently I wasted time. I read the original ring signature paper (Rivest's How to leak a secret). I'm having numerous problems. Let's ...
2
votes
2answers
69 views

Profile Complexity LFSR

I try to understand how Complexity of an LSFR calculated. For example I have a bit sequence 110101 and it's profile 1 1 2 2 3 3. Is there any easy way in order to produce the profile?
2
votes
2answers
48 views

Is it secure to use TOTP with same key and different time-counters?

If I use TOTP to generate codes with different "expiration" time, using the same key for HMAC, will I create some kind of weakness?
2
votes
1answer
60 views

Is it possible to add error propagation to OTP?

What would be the recipe to add error propagation to a one time pad? I.e. if I change a single letter in the clear text message, I want the encrypted message to change starting from that letter and up ...
2
votes
1answer
118 views

Is succinct verification of an arbitrary data transformation theoretically possible? Is it feasible? How?

Given input string S, and transformation (i.e. computer program) T, is it possible to provide a succinct proof that another binary string S' is identical to the output T(S)? By "succinct", I ...
2
votes
1answer
146 views

CPA and pseudorandom generator

Just started learning about Cryptography and Network Security in general, and I can't seem to grasp the understanding of the following question. Please correct me if I am misunderstanding anything. ...
2
votes
1answer
98 views

Reverse output of general Fibonacci LFSR

Suppose we have some Fibonacci LFSR, and it outputs some sequence. How to change starting LFSR so, that it outputs exactly same sequence, but in reverse order?
2
votes
1answer
85 views

Is Shoup's Practical Threshold Signatures considered secure?

I am planning to use threshold cryptography in a Java application. So far, I have only found ThresSig and a ECDSA implementation used in TwoFactorBtcWallet. However, ThresSig is based on a 15-years ...
2
votes
1answer
154 views

OpenSSL ECDH key exchange mechanism

I am using FIPS based OpenSSL module for encryption of sensitive data for my desktop socket server and client applications. I am using ECDH for key agreement.The keys public and private pair is ...
2
votes
1answer
66 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
2
votes
1answer
58 views

Is there an existing AE protocol with forward secrecy for embedded devices?

I'm working on an embedded device that is connected to a computer over an untrusted channel. According to my threat model I need authentication and encryption on the wire with perfect forward secrecy. ...
2
votes
3answers
73 views

Digital signature algorithms within the European Union

I've just noticed that US NIST has accepted DSA as a digital signature standard. Does the European Union have a similar standard, specifying an algorithm to use when digitally signing messages? I ...
2
votes
1answer
95 views

Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?

Using a truncated hash of a key seems to be a safe way to identify the key (i.e. key fingerprint), but what about truncating a key itself in the case of HMAC-SHA256? Example: ...
2
votes
2answers
89 views

What kind of operations are involved in NTRU?

I've read that lattice based algorithms involve matrix-vector products. Is this the case of the NTRU algorithm? When I've read the details of the NTRU algorithm, I've seen products of polynoms. Where ...
2
votes
1answer
149 views

How AES treat string input to encrypt data and what will happen if the cipher key is less than that expected?

The official docs of AES have several example of how hexadecimal or byte input can be encrypted. I have some problem about the input text and cipher key. My question is: How can encrypt string input ...

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