5
votes
2answers
695 views

Are there any signature schemes for underpowered devices (8-bit microcontroller)?

I am currently researching into a small scale home automation system, aiming for cost. The system architecture is basically one master and several slaves which are connected in parallel. Recently ...
0
votes
1answer
57 views

Derive $x$ when given $g,g^x$ and $g^{(1/x)}$?

If an adversary has access to the generator g of a group G and is given access to $g^{x}$ and $g^{(1/x)}$, will it make it any easier to derive the value of $x$ compared to when he had access to only ...
-1
votes
0answers
7 views

Is this a good choice of a digitial signature scheme?

This is a concrete instantiation of Rabin-Williams signatures. Specifically: The private key is 2 primes $p, q$. The public key is their product $N = pq$ and is approximately 3072 bits long. the ...
1
vote
1answer
11 views

Is this hash function almost XOR universal?

Consider this hash function: The key $K$ is $2^n$ bits. The message $M$ is divided into $2^n$ bit blocks. Arithmetic is performed modulo $2^{n+1}$. The hash is defined by: $ H_0 = 1 $. $H_{i+1} = ...
0
votes
0answers
9 views

Combining Elgamal encryption with the Elgamal signature scheme - Security issues?

For didactic (not real-world) purposes, I would like to teach other students the Elgamal encryption system and the Elgamal signature scheme. Are there known security issues when combining them? (i.e. ...
3
votes
1answer
7 views

Encrypt-then-MAC when encrypting data in multiple blocks

Given a stream cipher such as ChaCha20 and a MAC such as Poly1305, how do we handle data that comes in chunks in the encrypt-then-MAC scheme ? For example, the plaintext is 530 bytes long. We read ...
1
vote
2answers
45 views

CBC mode with same plaintext

I'm working on a file encryption system where multiple versions of the same file might exist. The filenames are encrypted using AES in CBC mode with a random IV and stored in metadata. Since versions ...
0
votes
0answers
6 views

Montgomery multiplication without final subtraction

I am looking for methods to avoid the final subtraction in Montgomery multiplication. I found this paper "A Cryptographic Library for the Motorola DSP56000 " (http://goo.gl/DHePEx) In this paper they ...
2
votes
1answer
24 views

DTLS 1.2 Key Expansion

I am using DTLS 1.2 and my cipher is TLS_ECDHE_WITH_AES_128_GCM_SHA256 According to RFC 5246(RFC 5246 key calculation) i am calculating keys but i can not find the size of these keys in this RFC. ...
1
vote
2answers
68 views

Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
1
vote
1answer
55 views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
4
votes
2answers
266 views

How can a poor RNG impact security?

I have read this article and I do somehow "understand" that the reduction of entropy makes it easier to guess. But how exactly can the security be reduced by that? Can you give a concrete scenario, ...
4
votes
1answer
38 views

How to distributively compute a secret of that form $\mathsf{s=sk\cdot g^a}$?

Is there a standard way to distributively compute secrets shares such that any $t+1$ combination out of $n$ of them constructs the secret $\mathsf{s=sk\cdot g^a}$, for a generator $\mathsf{g} \in ...
0
votes
0answers
20 views

OpenSSL ECDSA verification [migrated]

Using ECDSA, how do you verify integrity of Data (D), Given the value for the following: Random number (r) Signature (s) ECpublic Key (K) In other words, Using OpenSSL command line, can I decrypt ...
2
votes
1answer
80 views

How to detect what crypto-method is used by Filecoder.Q?

I have 2 different images, one original, and one locked by a malware detected by eset as "Win32/Filecoder.Q". How to detect the encryption method that is used and the key, that is not using any ...
1
vote
2answers
40 views

Why is padding the plaintext with a random string before encryption worse than OAEP / PKCS#7?

I'm reading about OAEP / PKCS padding used for PGP to turn deterministic algorithms like RSA from deterministic encryption to probabilistic encryption (randomness in the resulting output). That way ...
6
votes
2answers
89 views

What use cases would benefit from a faster RNG?

The paper “Explicit Two-Source Extractors and Resilient Functions” (PDF) by Eshan Chattopadhyay and David Zuckerman is described by some as being a technological leap in RNG – opposed to slow and ...
7
votes
2answers
398 views

The effect of truncated hash on entropy

Suppose I have a 128-bit random binary string (128 bits of entropy), then I hash it using SHA-256, then I take the first 128 bits of the output hash. Does the taken bit string still have (almost) 128 ...
11
votes
1answer
1k views

Why can an elliptic curve private key be 1?

I often see in papers (e.g. this one) that for an elliptic curve with generator point $G$ and order $n$ the private key $d$ can take on any integer value in the range $[1, n)$. When $d = 1$ the ...
1
vote
1answer
706 views

How to multiply a matrix of bits with another?

For example, assume I have two 4x4 matrices of bits: 1 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 1 0 1 1 1 1 0 1 0 I want to apply ...
2
votes
1answer
32 views

Master keys' strengh

If I am going to use a master key to generate a session key, why the master key must be "stronger" than the session key? Like should not be distributing 128-bit AES keys derived from a 56-bit DES ...
0
votes
0answers
12 views

Use MDC to provide origin authentication for public key encryption?

Why can't we use an MDC to provide origin authentication when using public-key encryption?
4
votes
1answer
66 views

Differential & linear characteristics for integer multiplication

What are the probabilities of differential & linear characteristics for the function that XORs the high and low bits from a $n \times n \rightarrow 2n$ bit multiplication? I remember reading ...
4
votes
1answer
45 views

Padding schemes for asymmetric encryption with provable security in the standard model

Most padding schemes for asymmetric encryption (OAEP, OAEP+) are only proven secure in the random oracle model. Although no attacks are known, it would be nice to find a padding scheme with provable ...
3
votes
2answers
169 views

Should I use XTS or GCM to encrypt my hard drives?

I want to start encrypting all of my hard drives, but I don't know whether to choose XTS or GCM mode. Why is it that XTS is recommended (since the most websites I visit use GCM in their HTTPS ...
5
votes
1answer
221 views

Do key-dependent S-boxes make efficient constant-time software implementations almost impossible?

It seems to me that algorithms like Blowfish and Twofish with key-dependent S-boxes are almost impossible to implement without table lookups, and thus are almost impossible to implement in software ...
8
votes
1answer
57 views

About random self-reducibility of DDH

In Section 8 of this, Lindell presents a construction of an oblivious transfer protocol which is secure in the malicious model under the following variant of the DDH assumption (page 53): [F]or ...
6
votes
0answers
41 views

Collisions in the cyclotomic knapsack function

I've been working my way through the paper “Efficient Collision-Resistant Hashing from Worst-Case Assumptions on Cyclic Lattices” by Peikert and Rosen, and I've come across something that doesn't seem ...
1
vote
3answers
128 views

Is Threefish the only cipher with 1024 bits of security?

Threefish has up to a massive 1024 bits of security. Is it the only cipher with such overkill security?
7
votes
1answer
55 views

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys?

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys? This is a common operation (ex. PEM keys) and is variable time in typical implementations.
1
vote
1answer
18 views

How do two parties put together the AUTH data in the SKEME protocol?

SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ...
5
votes
1answer
179 views

Full encryption of IDs, partial decryption with customer specific key

I am looking for a "partial" encryption/decryption algorithm. Let's say I am encrypting the following List of IDs (long values) $[1,2,3,4]$ (with a secret key) to an encrypted string $e$, I would ...
2
votes
2answers
145 views

System parameters in identity-based encryption

In IBE schemes, the system parameters are $(q, \mathbb{G}, F, \hat{e}, P, Q, T, H_1)$. I don't know $\hat{e}$. For example, in type A pairing… ...
5
votes
1answer
174 views
+150

Secure content-defined chunking

Intro For deduplication purposes, I need to split a stream of plaintext bytes into variable-sized chunks. The way this is traditionally done is using a rolling hash function defined over some window ...
2
votes
0answers
73 views

Designing a secure protocol to avoid MITM?

Imagine that you are designing an online game, the framework consists of a player A, a game host H and a trusted central server S. The player A has a symmetric key KAS and id A that is known ...
4
votes
1answer
63 views

ORAM over Third Party DB

Oblivious Ram (ORAM) is a cryptographic technique that is used for secure DB querying without leakage on the access patterns. There are several schemes for ORAM, amongst the most popular ones, there ...
4
votes
1answer
47 views

Can you still decrypt XTS if half of the cipher text is deleted?

If a part of my data is damaged, corrupted, or deleted, is it then still possible to decrypt the rest of the data if you still have the key? The situation: a piece of data (something like a document ...
5
votes
1answer
306 views

Decrypting an encrypted text out of order

Does there exist a cipher that can be encrypted twice with two different keys and then decrypted twice using either key first? For example: ...
1
vote
1answer
20 views

Use $e$ in GGH as shared secret?

I was wondering if we could construct a symmetric encryption scheme by assuming that the secret key itself in GGH is public and the shared "key" is the error vector $e$. To encrypt we would take the ...
2
votes
2answers
524 views

Using bcrypt for MAC - is it correct and secure?

Suppose there is a hashing function: $$ph = bcrypt(sha256(m + k), salt)$$ Here $ph$ is a password hash obtaining by applying $bcrypt$ on $sha256$ result of concatenating a message $m$ with a secret ...
3
votes
0answers
41 views

Election communication protocol

I'm not a cryptography expert, but this seems like it falls into this area. Imagine I want to design an election system (senate race for example) where I send the exact same ballot of 100 candidates ...
4
votes
1answer
421 views

How to sign a large file for random-access reading?

I need to write an "Authoring" application which produces large files. These files must be signed so that the "Consuming" application knows that it was authored with a matching key. The consuming ...
-3
votes
0answers
27 views

What is this encryption type? [on hold]

I just get the encryption from some website. Here the encryption output: 1) ZFRSA00013GDU and this is the key before encrypted PKR003 2) YHZSA00100PE9 and this is the key before encrypted PJR011 ...
0
votes
0answers
14 views

NORX parallel speedup?

How much of a speedup can be expected going from serial NORX (6441) to 4-way parallel NORX (6444) assuming the latter is implemented as 4 word-sliced instances of the former?
1
vote
1answer
130 views

AES implementation to encrypt files

I'm making a small python program to encrypt an arbitrary text file. Currently I have a file to store passwords (hashed values), so nothing stored in plaintext. The user enters the command line ...
1
vote
1answer
46 views

How to convert roots of Weber polynomial to Hilbert class polynomial over modulo prime?

Using any non square root discriminant $D$, we should be able to find the Weber class polynomial. How can I convert the roots of a Weber polynomial to a Hilbert class polynomial over modulo prime?
6
votes
1answer
79 views

Is a composition of clocked entities a clocked entity in the UC model?

In the book titled "Secure Multiparty Computation and Secret Sharing" the authors define an interactive agent and an interactive system. Further, the author defines a clocked entity for considering ...
4
votes
1answer
83 views

How to prove that an integer is hard to factorize when sampled from a known distribution

Suppose that an $n$-bit integer $c$ has been randomly drawn from a distribution $\chi$, whose description is known. Is there a general method to check if this particular sampling helps factorize $n$? ...
16
votes
9answers
5k views

RSA with small exponents?

Just to establish notation with respect to the RSA protocol, let $n = pq$ be the product of two large primes and let $e$ and $d$ be the public and private exponents, respectively ($e$ is the inverse ...
3
votes
2answers
220 views

Background for modular arithmetic function

I'm investigating this function: $a := ((b\cdot c) \bmod k) - (b \cdot c)/k$ where $/$ indicates integer division. Two things I've noticed: It's equivalent to multiplying a·b, and then ...

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