# All Questions

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### 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 ...
1answer
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### 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 ...
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### 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....
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### 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 ...
2answers
171 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 ...
1answer
934 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 ...
2answers
374 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 ...
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 ...
1answer
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### 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 ...
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 ...
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 ...
1answer
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### 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 ...
2answers
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### 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 ...
1answer
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### 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 ...
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 ...
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 ...
2answers
245 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 ...
0answers
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### 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 ...
1answer
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### 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 ...
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 ...
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 ...
1answer
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### 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 ...
0answers
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### 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 - ...
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 ...
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 ...
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 ...
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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, ...
1answer
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### 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 ...
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### 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 ...
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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
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 ...
1answer
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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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