0
votes
0answers
6 views

How do Raptor (Fountain codes) encoding and decoding work?

As described in this article, a Raptor code is a fountain code that encodes a message of $k$ symbols into a limitless sequence of encoding symbols, such that knowledge of any $k$ or more encoding ...
0
votes
1answer
28 views

Decomposing an ideal in intersections

Let $R$ be an ring, and let $(a),(b)$ be the ideals generated by $a,b\in R^\times$ respectively. Let $c=a\cdot b$ and $(c)$ the ideal generated by $c$. I am supposing that, given $c$, it is ...
4
votes
1answer
34 views

RSA: revealing the modulus factorization by choosing a bad message

I started reading the book Cryptanalysis of RSA and its variants by M. Jason Hinek and I stumbled upon a phrase that intrigued me: plaintext messages that are relatively prime to the modulus (i....
0
votes
0answers
5 views

Secure logical AND using Ishai-Sahai-Wagner Scheme

I want to try to implement a secure AND the way it was described here: https://eprint.iacr.org/2010/441.pdf It says that there are two bits a and b and that they have been split into d+1 shares. How ...
8
votes
2answers
169 views

Security of a self-decrypting block-cipher?

If I have a block-cipher like for example AES, a plaintext $x$, we use different function to encrypt and decrypt : $\text{encrypt}(x) = y$ , $\text{decrypt}(y)=x$. Now, if we build a function with a ...
7
votes
1answer
931 views

Why is it OK for secretbox to leak the message length?

Most block cipher implementations expect users to pad so that the message matches the cipher block size. I understand the purpose of the padding is to make the input match the cipher block size. It ...
3
votes
2answers
372 views

How to measure ECC key size?

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
1
vote
2answers
68 views

How to design a balanced LFSR with period 1023 and linear span 55?

I am trying various combination of LFSR's to try to design sequence of period 1023. The linear span should be 55 and the output 1023 bits has to be balanced. I have tried with five LFSR's with degree ...
1
vote
1answer
38 views

Given $ g^s, g^y , g^r, g^t, g^{st-rs}, g^{(yr+d)/t}$ , is it hard to distinguish $e(g,g)^{syr}$ from a random value?

Where $g$ is a group element in bilinear group $G$, $e(g,g)∈GT$ and $s, y, r, t, d$ are randomly chosen. I understand it is very similar to the conventional DBDH problem, but $g^t, g^{st-rs}, g^{(yr+...
2
votes
3answers
2k views

Can a shift cipher attain perfect secrecy?

On a practice question for my intro cryptography exam, it asks the following: Assuming that keys are chosen with equal likelihood, the shift cipher provides:    A) computational security ...
2
votes
1answer
30 views

Given $g^a, Y$, is it hard to distinguish $e(g,g)^{ab}$ from a random value?

where $g$ is a group element in bilinear group $G$ $Y = M.e(g,g)^{ab}$ $M$ is a message Does anyone know the answer or suggest some material for reference? Many Thanks
2
votes
2answers
169 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… ...
6
votes
2answers
89 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 ...
0
votes
1answer
24 views

How secure is encrypting with self-hash [duplicate]

I don't have much knowledge about cryptography beyond using libraries for it. So just wanted to understand if the following two cases differ sufficiently in security or is it just psychological: Say ...
2
votes
1answer
28 views

Using the Unix epoch as nonce

Since a nonce must be unique and that time only goes forward, is it safe to use the Unix epoch as nonce ? My use case is be AES w/ GCM which recommends a nonce length of 12B. Current Unix time can be ...
0
votes
0answers
29 views

Is it possible to turn an image (e.g. a photo) into a cryptographic hash? [on hold]

I am looking for a way to turn an image (e.g. a photo captured on a phone) into a cryptographic hash (e.g. SHA256). Is this possible? If so, how?
0
votes
1answer
24 views

In NTRU digital envelope, do everyone know the hash function $H$ used?

I have a simple question about the NTRU original cryptosystem using a digital envelope. The article can be found here: http://grouper.ieee.org/groups/1363/lattPK/submissions/ntru.pdf It is said that ...
1
vote
1answer
39 views

Is security against semi honest adversary inheritable?

I have a two party protocol, let's call it $M$. At some point, there are $k$ steps, each one involving an oblivious transfer protocol, which is known to be secure against semi honest adversaries. ...
1
vote
0answers
17 views

How long is the tag T in AES-GCM(Or: Can implementations freely choose t = len(T)?) [duplicate]

I've started to learn about GCM. In the paper I read on page 4 there is the equation: $$ T = \text{MSB}_t(\text{GHASH}(H, A, C) \oplus E(K, Y_0)) $$ It's clear to me that the function $\text{MSB}_t(S)...
1
vote
0answers
93 views

Are Diffie-Hellman, RSA and other types of public key cryptography different? [duplicate]

Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different ...
6
votes
2answers
934 views

Do I really need to use the same private/public key pair in RSA?

So I'm making an Android application, I need my application to be only able to scan my own generated QR codes, and I want to make sure that nobody else can generate fake ones. The data isn't ...
5
votes
0answers
32 views

Using a single Ed25519 key for encryption and signature

The libsodium documentation contains a function crypto_sign_ed25519_pk_to_curve25519 that converts an Ed25519 key into a Curve25519 one, so it can be used for both ...
2
votes
1answer
44 views

When is AES chosen instead of a stream Cipher (e.g., RC4) during an SSL connection?

During an SSL handshake, the browser sends a list of cipher suites to the server, from which the server selects one option. For data encryption, two of the several possibilities for the ciphers in ...
2
votes
2answers
25 views

Homomorphic Encryption operation for regression

I must be missing something, and I am sorry if this is a novice question... I have seen in places (eg. https://crypto.stanford.edu/~dwu4/talks/SecurityLunch0214.pdf page 13) that linear regression is ...
1
vote
1answer
30 views

Acceptable condition for dictionary search

I am trying to write a program to break transposition cipher using dictionary search. But I cannot understand the finishing condition of the search. Is there any theory that the maximum number of ...
4
votes
2answers
75 views

On the security definition of password-authenticated key exchange

I found in all PAKE papers, the security is defined as something like this: Let $Succ(A)$ be the probability that an attacker $A$ successfully distinguished the session key from a random string. Then ...
4
votes
0answers
56 views

Replacing signer with simulator

Assume we can prove security of digital signature scheme against key-only (no message) attacks. Now we want to prove security against adaptive chosen message attack. We use random oracle model. The ...
1
vote
2answers
244 views

Verifying Without Knowing Key

Say user Bob sends an encrypted message to a server. People can download the message from this server and later get the key directly from Bob. Is it possible for the server to somehow verify that ...
3
votes
0answers
34 views

ED25519 and hierarchical deterministic wallet

I'm building a solution based on the stellar codebase and using the ED25519 curve for the signatures. One of the features I've been adding to the system is a support for hierarchical deterministic ...
3
votes
1answer
59 views

PRNG output with truly random noise

I am considering a situation where an adversary does not have access to the $n$-bit output string of a PRNG, but instead receives a noisy version of it, where each bit of the string is flipped with ...
6
votes
1answer
72 views

How to forge signatures in the Schnorr scheme if $r=g^k$ is eliminated?

I need some help to demonstrate how to forge signatures in the Schnorr scheme if I eliminate the random string $r=g^k$ used in the hash – using $H(M)$ instead of $H(M||r)$. How would one be able to ...
8
votes
1answer
298 views

Salary Negotiation Problem

Imagine Alice is applying for a new job. Alice has an idea of the minimum salary that she is willing to accept—let's call this value A. Bob, the hiring manager for ...
1
vote
1answer
30 views

Generating passwords using Password-Based Key Derivation Function

I was thinking of using different and independent password for different websites, but not storing them in some password manager so I don't need to backup the passwords. I thought I could use some ...
1
vote
0answers
21 views

Is manually 'salting' my passwords a safe alternative to having a different password for each site? [duplicate]

It is highly recommended to use a different password for each site to prevent the breach of security of one site from compromising the user accounts on all other websites that have the same username - ...
2
votes
0answers
35 views

How does Bluetooth pairing (SSP with numeric comparison) work?

I have a question concerning the pairing of two Bluetooth devices using Simple Secure Pairing with numeric comparison. The NIST document I am looking at states on page 14: Numeric Comparison was ...
3
votes
1answer
121 views

What do they mean when saying that a certain value should be “super-logarithmic”?

What do they mean when saying that a certain value should be “super-logarithmic”? I've found the Wikipedia definition of a “super-logarithm”, but I'm having trouble understanding how a given value ...
6
votes
5answers
5k views

How do ciphers change plaintext into numeric digits for computing?

For example, in RSA, we use this for encryption: $ciphertext = (m^e \mod n)$ and for decryption. If our message is "hello world", then what number do we have to ...
0
votes
0answers
277 views

Changing plaintext for encryption in RSA [duplicate]

In the RSA crypto scheme, the message $x$ (plaintext), is encrypted to produce ciphertext ($y$), by computing $x^e \bmod n$. Of course, that means that $x$ has to be a numeric value for this to work, ...
-1
votes
1answer
63 views

How to calculate this binary operation? [on hold]

I found this binary operation, however It is the first time that I found this operator '.' : That is the equation: 02 • 63 = 00000010 • 01100011 = 11000110 I don't understand how 0 • 0=1 I ...
0
votes
0answers
4 views

OpenSSL: Generate ECDSA key and CSR [migrated]

I know how to generate an RSA Private Key and CSR: openssl genrsa -out my.key.pem 2048 openssl req -new -sha256 -key my.key.pem -out my.csr But, How do I do the ...
-1
votes
0answers
27 views

Anyone know of a portion of the Enigma Code? [on hold]

I was reading about it today and it sounds like it would be a fun thing to try to decode. Problem is that I can't find a portion anywhere. Is it classified or am I not looking in the right spots
3
votes
2answers
184 views

Is the security of MAC function is based on HASH function

It is widely known, generally, that a MAC is a HASH with key. I just want to ensure that my understanding is correct to avoid base further assumptions on wrong conception. So, if I used MAC that uses ...
1
vote
1answer
33 views

Randomized functions cannot increase statistical distance

In these lecture notes instructor Chris Peikert states the following lemma without a proof Let $f$ be a (randomized) function on the domain of $X$, $Y$. We have $\triangle (f(X), f(Y)) \leq \...
5
votes
1answer
74 views

Problem with LLL reduction on truncated LCG schemes

I am struggling to apply Freize et al. paper to break a truncated LCG. A truncated LCG is a pseudo random generator that outputs the $n$ leading bits $y_i$ of $x_i$, where $(x_i)$ is such that $x_{...
0
votes
1answer
31 views

Easily reversible hash functions as a method of data transmission [duplicate]

I've been looking through the literature because I want to see if anyone has implemented this idea I have. I know data compression algorithms work by removing redundancy in data. I was wondering ...
6
votes
1answer
565 views

Is unusual (non power-of-two) RSA key size more secure?

On this blog https://blog.josefsson.org/2014/06/23/offline-gnupg-master-key-and-subkeys-on-yubikey-neo-smartcard/ there is a following sentence Generate master key Below I will use a 3744 bit ...
2
votes
1answer
473 views

DES S-Box properties

Two of the properties that lead to the design of DES S-Boxes are: For any non-zero 6-bit difference between inputs, no more than 8 of the 32 pairs of inputs exhibiting that difference may result in ...
3
votes
1answer
63 views

How to create reduction functions in rainbow tables?

I have been trying to understand rainbow tables lately and one part is giving me trouble to understand here. Let's say I want to generate a table where the chains are 100 000 hash/plaintext long. I ...
10
votes
4answers
2k views

Desirable S-box properties

What desirable properties should an S-box have? My current standard selection process is to just pick them at random and verify that they fit the following criteria: The probability that any random ...
5
votes
2answers
89 views

Is the difference distribution table of AES S-box uniform?

I am studying about various block ciphers and their weaknesses, so I have a doubt about AES S-boxes, Is the difference distribution table of AES uniform ?

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