# All Questions

122 views

### Signing MD5 hashes with RSA? [duplicate]

Lets say I need to update a project and allow anyone to distribute the updates, however I need it to be secure, so I hash the data and sign the hash, this project uses MD5. How likely would it be ...
52 views

### I am trying to understand how AES works

I am trying to understand how AES encryption operates. I am trying to run through the steps on paper to understand. So far, I am creating a simple example. I have the plain text "MESSAGE TESTTEXT" ...
19 views

### security of Even-Mansour scheme with keyed shuffle

I was researching the Even-Mansour scheme and had a question that wasn't addressed in the paper that I saw, and google was minimally helpful. What if a permutation that uses secret data like the ...
327 views

### How secure is a client-side javascript encrypter?

A friend of mine needed help with her website and asked how to send me her login information securely. I've never known how to do this, so I figured now was the time to learn. After some googling, I ...
34 views

### Using quadratic residue to learn the sign of a field element

Given $x' \in \{-x, x\} \bmod q$ (where $q$ could be any prime of my choice), $s$ is a random element in the field, $y = x'\cdot s$ and $y' = \pm\sqrt{(x\cdot s)^2}\bmod q$ (i.e., both solutions to ...
57 views

### Padding password before SHA-512 hashing to avoid info leak via timing

I've noticed that SHA-512 password hashing leaks some information about the password length. There's a weak correlation between password length and time to hash. It's roughly linear, but in steps of ...
50 views

### How to deal with collisions in Bitcoin addresses?

When creating a Bitcoin account, you need to issue a couple of private/public ECDSA-keys. Then, you derive your account address by taking a 160-bit hash (through sha-256 and ripemd) of the public key ...
84 views

### Exploiting XOR one-time-pads with alphabet size 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, ...
52 views

### Proper forward secrecy [closed]

Currently I have a protocol using a simple RSA to AES handshake. I have been reading more and more and would like to implement proper forward secrecy, but at the same time I'd like to improve the ...
36 views

### homomorpic encryption [closed]

I am doing project k-nearest neighbor classification over semantically secure encrypted relational data I have doubt for in smin algorithm in 1)Li ← Wi ∗ Φir′; ri′ ∈R ZN this line it the out put is ...
83 views

### Is it acceptable to write the nonce to the encrypted file during AES-256 GCM? [duplicate]

I've used AES-128 in CTR mode in the past and using the same key but different IVs for each file, I wrote the IV to the first 16 bytes. Is it safe to do so with the nonces used in AES-256 GCM? I'm ...
58 views

### Is WPA2(PKS) AES vulnerable to 4 way hand shake and brute force attack?

I can easily crack a WPA TKIP using a dictionary/brute force method, provided that I collect the four way handshake. Is the same method possible on WPA2 AES? I cannot find any articles about '4 way ...
281 views

### Finding Private key in RSA with public key, cipher text and plain text

Is there a known 'non-brute force' method of determining a private key in an RSA system when all other parameters are know? I found the values of a ciphertext ($C$), its corresponding plaintext ($P$) ...
33 views

### Breaking linear blockcipher - expanding recursive formula

I am trying to break a block cipher that can be defined as follows: We have 12 rounds and at each round we perform the following operation. We split 64 bit data into 2 parts each 32-bits, $\ x_r$ ...
60 views

### Selective and existential unforgability of signature schemes

I understand that one can define EUF-CMA of a signature scheme is terms of a game where the adversary is allowed to query signatures on messages of his choosing, and at the end of the game he must ...
151 views

### What are the minimum constraints on RSA parameters and why?

The RSA cryptosystem only works if certain constraints are applied to its input parameters. Some of those constraints are made to make it "hard" to determine the private key whereas other constraints ...
29 views

### Publishing only items your subscriber previously subscribed to, without you knowing which those items are

Let's say you were given a dump from a security breach. You want to share the email addresses affected by the breach with a separate company who pays you for this service so that they can protect ...
376 views

### Can double-encrypting be easier to break then either algorithm on its own?

As was pointed out in Martin Bonner's comment I cannot prove this, but it seems intuitively impossible. An encryption function is supposed to obscure the plaintext to the point where no information ...
69 views

### Unicity-distance of Playfair

Given the classical scheme Playfair, say, for 5*5 matrices, I am interested to determine its unicity-distance. How should one proceed to properly do that? I should appreciate it, if I could obtain a ...
26 views

### MISTY1 encryption/ extension tricks

I'm trying to understand MISTY1 encryption algorithm but i faced some problems in key scheduling part : Key scheduling part consists of the following operations. for i = 0, ..., 7 do EK[i] = ...
27 views

### Uniqueness of checksums using DES-MAC encryption?

I'm in an Intro to Computer Security class, and one concept I'm having trouble understanding is how two different files could produce the same checksum. How would you produce the same checksum given ...
36 views

### Simple application of verifiable random function?

I have been reading a little bit about verifiable random functions (e.g.). In the literature, these are described as "pseudo-random functions that provide a non-interactively verifiable proof for the ...
20 views

### Which protocols / file formats use CBC with a random IV and without a MAC?

Disclaimer: I am a noob so this may well be a stupid question or one that's been asked before. I didn't see it come up after searching, though, so I'm going to assume it hasn't been asked here. The ...
62 views

### PyCrypto and AES: can i use a longer key than the block size (16byte)?

I see that in many scripts are used keys of 16 characters for a block of 16 byte, but can I use key of 40 (for example)? And then why in some scripts with aes module the block size is set to 32 byte ...
61 views

### Testing implementation of cryptography algorithms: Brainstorm

I wonder what kind of techniques can be used to validate implementation of cryptography algorithms? The obvious one is to run specific algorithms against publically known test vectors (i.e. from ...
104 views

### Anonymity problem after voting with blind signatures

In a distributed voting system (all the messages are public, but signed and maybe encrypted/blinded), having: $d$, $e$, $N$ — registrar key params $m$ — msg $r$ — random blinding factor $m'$ —...
44 views

### Three-Pass Protocol number theory

I've got a homework problem that I'm having a hard time understanding. It's for the Three-Pass Protocol, and we are given p, the three messages, and are told that the original plain text is one of two ...
82 views

### DGHV Bootstrap - How can I recrypt my cipherbit [closed]

I'm implementing this homomorphic crypto-system : http://eprint.iacr.org/2011/440 I'm using SAGE math. I don't get how the bootstrap is done in this scheme, in the appendix A, they say ...
75 views

### Which encryption is recommended for own messenger [closed]

I wrote my own messaging-app and now I would like to encrypt the data transfer between my client (app) and my server. What kind of encryption is easy to implement and can be recommended? I am very ...
16 views

### Implications of pattern in finial digit of prime numbers [duplicate]

http://qz.com/639452/mathematicians-are-geeking-out-about-a-bizarre-discovery-in-prime-numbers/ What are the implications of this (very) new research on crytopgraphy? I would have thought this would ...
117 views

### Which attacks are possible against raw/textbook NTRU encryption?

In the same fashion that these questions about attacks to textbook RSA and ECC, I was wondering what are the immediate drawbacks of applying NTRU Encryption directly, without any padding scheme, such ...
930 views

### AES key reuse and guessing the key

Bit of a noob question and a fair bit of Googling didn't help. I understand that the current encryption standard is AES256. A few questions Is the point of this (and other encryption techniques) to ...
33 views

### Playfair Cipher Confusion with one column encryption

Recently I decided to learn "Playfair Cipher", and I have hit a road block. what do i substitute the letters for if they are on the same column? Here is an example: ...
249 views

### Is it better to encrypt before compression or vice versa?

Is it better to encrypt a plain text file before compression, or vice versa?
102 views

### Why does AES ciphertext entropy always close to 8?

I have three binary files: 31744 byte length (1), 5712980 byte length (2) and 10806008 byte length (3). The alphabet is all 256 symbols from 00 to ff. I compute the shannon entropy, replacing ...
77 views

### Best differential characteristic for this PRF

Consider the following construction of a PRF $F: \{0,1\}^{128} \times \{0,1\}^{64} \to \{0,1\}^{64}$ on 64-bit messages and 128-bit keys. Define $f:\{0,1\}^3 \to \{0,1\}$ by f(c,x,y) = \begin{...
72 views

### “Prime conspiracy”'s effect on cryptography [duplicate]

Recent news reported about the discovery of a "Prime Conspiracy" which can be read about here. In summary, researchers have discovered that the last digit of prime numbers have a greater ...
48 views

### Encryption using two keys

Suppose we have two secret keys K1 and K2, I'd like to ask if there is any encryption scheme that allows us to derive another key K12 from K1, and K2 and for a message x, EK12(x) = EK1(EK2(x)). EK(x) ...
2k views

### Why is Pearson hash not used as a cryptographic hash?

The original algorithm produces 1 byte long hash and is (of course) not suitable for cryptography use. But according to wikipedia, it is possible and easy to produce Pearson hash of any length, ...
98 views

### Is there an asymmetric algorithm that can perform double encryption?

I'm looking for any asymmetric algorithm can perform the serial encryption, by serial I mean double or more encryption with different key(same key size). RSA can not do it since the cipher of the ...
81 views

### Asmuth-Bloom's threshold secret sharing scheme

I was learning Asmuth-Bloom's threshold secret sharing scheme. I was working out an example as given in this Wikipedia article. As per the example, the secret,d is 2, the number of shares, n is 4 and ...
56 views

### Sum of digits flaw name request

Let's say I am making an encryption algorithm, and in the algorithm in have the following step: "multiply the integer from the previous step by 9 and take the sum of the digits of the resulting number....
128 views

### What is Deterministic Authenticated Encryption?

I came across something known as deterministic authenticated encryption in my studies and a lot of people were associating it with Synthetic IV mode. I am having trouble what exactly DAE is because I ...
48 views

### Key diversification is a good alternative?

This is just a concept question that I need to clarify, I know that you can use key diversification as an alternative to store different symmetric keys in a database. Key diversification uses a "...
831 views

### Do these new insights into prime numbers affect encryption security?

Quanta Magazine reports: Two mathematicians have uncovered a simple, previously unnoticed property of prime numbers [...]. Prime numbers, it seems, have decided preferences about the final digits ...
101 views

### Whether this PRG is secure or not

This is the question. Suppose $G$ is a secure PRG with expansion factor $\ell(n) = 2n$ such that $n$ is a security parameter. Is it always the case that, \$G'\colon \lbrace 0,1 \rbrace^n \to \lbrace ...
58 views

### Format preserving encryption

Can format preserving encryption be used for any other applications than Credit card, pan card or social security numbers? If, could you provide a few examples for my further research on the topic?
97 views

### Difference between MAC and Authenticated Encryption?

I am currently studying authenticated encryption and I was wondering if there was a difference between using a MAC and authenticated encryption. It seemed like authenticated encryption schemes use ...