# All Questions

27 views

### Does Kasisky test for Vigenère cyphers assumption always hold?

In the notes from which I'm studying I read about Kasisky test: "Key observation: Two identical segments of $l ≤ L$ plaintext letters, will be encrypted to the same $l ≤ L$ ciphertext letters." ...
673 views

### Creating a hash of XOR'd blocks

Suppose a message $m$ is divided into blocks of length $160$ bits: $m > = M_1 || M_2 || ... || M_l$ And define $h(m) = M_1 \oplus M_2 \oplus ... \oplus M_l$ Which of the three desirable ...
75 views

### Secret sharing scheme with ability to add or update share number

I would like to have a secret sharing scheme with the following properties: Generate secret $S$ a split it to $N$ shares $(s_1, s_2, ..., s_N)$ Require $k$ of $N$ shares in order to reconstruct ...
120 views

### Clarification on the origin of 01 in this oracle padding attack?

I have found what I believe to be a straightforward explanation of the oracle padding attack here: http://robertheaton.com/2013/07/29/padding-oracle-attack/ I am however getting confused by something ...
627 views

### length extension attack on an MD5 hash of a text file of about 10K Bytes?

How much computing time on a typical desktop computer would it take to find a new length and new data to extend a text file of about 10K Bytes with a given MD5 hash?
708 views

### Uniform distribution/randomness of characters in the sha256 hash?

I'm using the sha256 algorithm to generate a number in one of my programming projects. A sha256 hash is calculated from three strings: one the user can edit, one the user can view but not edit and one ...
44 views

### How does Ring Learning with Errors work? [closed]

I read that Google want to integrate this into HTTPS because it is safe against quantum computers. However, the Wikipedia article might as well be written in Latin because it makes very little sense ...
61 views

### HMAC vs CMAC, which is faster?

I want to know which is faster-HMAC or CMAC.I know CMAC is based on block cipher encryption,where output of each block is X-OR with the next plain text block. If security is not a concern,which will ...
315 views

### RSA and ECDSA Certificate Sizes

Is there a table (or a whitepaper from official sources) that compares the size of X509 certificates generated with RSA (starting from 1024 bits) and ECDSA (starting from 160 bits) ? Thanks for the ...
134 views

### Proof that perfect privacy implies that the number of keys is at least the number of messages

I was reading a proof to the statement: Perfect privacy implies that $|K| = |M|$ where I am pretty sure that $K$ is the set of keys and $M$ is the set of messages. The proof is the following, ...
188 views

### How to prove that a function F isn't a pseudo random function

Let $F$ be a length-preserving pseudorandom function. For the following constructions of a keyed function $F' : \{0, 1\}^n \times \{0, 1\}^{n−1} \to \{0, 1\}^{2n}$, state whether $F'$ is a ...
53 views

### How to glean info from a message that simply has the letters shuffled?

Suppose someone had published a several hundred page (sensitive) book, but had randomized all of the letters in an order known only to them (e.g. with a vector of random numbers of the same length as ...
67 views

### Plaintext for randomness evaluation of cryptographic algorithms?

I’m running an experiment to test the randomness output of many cryptographic algorithms based on INST test suite to measure the randomness of their outcome. However I’m searching to a sample data ...
125 views

### TLS RSA Certificate with Elliptic Curve Negotiation

When I look at Google's Public Key in Firefox I get PKCS #1 SHA-256 With RSA Encryption Yet according to SSL Labs Google has EC 256 bits / SHA256withRSA and supports ...
20 views

### Secure algorithm for calculating token and comparison

I am trying to define algorithm that would create a irreversible token from IDs, which are 10 digit information, and then would be compared on two different end points. Between end points, only ...
141 views

### Ciphertext with uneven letter distribution

I have a ciphertext encrypted with an unknown method. It is part of a challenge (personal quest), so I can not post it. The letter statistics is the following: ...
77 views

84 views

### Efficiency of oblivious algorithms vs non-oblivious algorithms?

Recently, plenty of researchers are looking at designing efficient data-oblivious algorithms. Roughly speaking, an algorithm is said to be data-oblivious if its data access patterns are independednt ...
73 views

### Chance of finding the right key by exhaustively searching on half of the key space

An exhaustive search of half the key space requires $2^{n-1}$ work and provides the right answer 75% of the time. If the attacker finds the key, he knows the answer. If he doesn't find the key, he ...
617 views

### Is braid-based cryptography proven insecure when looking towards post-quantum cryptography?

Braid groups has drawn the attention of cryptographers for a few years, as a promising platform for post-quantum cryptographic protocols. The security of the proposed schemes mostly relied on ...
349 views

### How were shift amount constants in MD5 found?

The md5 specification gives a series of 4 rounds to execute over a 16-word block. Each round has a repeating sequence of 4 shift amounts (s in ...
38 views

### PBKDF2 with the same salt for all IDs

I have a unique identifiers that I would like to keep secure and provide information about it through tokens. These tokens should be verifiable after using the same algorithm on other end system with ...
100 views

### How to prove a function is pseudorandom function?

I am currently enrolled in a cryptography course, which uses the book by Katz and Lindell. I am using a function having $F_{k}$ = $A_{k}(B_{k}(r,m),r)$, the random number is generated using the ...
6k views

### How was the special DES key 0E329232EA6D0D73 found?

The DES key 0E329232EA6D0D73 has the unusual property that decrypting a ciphertext block consisting entirely of zeros gives a plaintext block consisting of eight repetitions of the same byte (0x87). ...
73 views

### How to compromise the privacy of NaCl encrypted messages, when nonce is reused?

I want to know to how break NaCl encryption when a nonce is used more than once for a given key private key. According to PyNaCl docs: It is VITALLY important that the nonce is a nonce, i.e. it is ...
53 views

### What is a simple information authentication protocol for constrained devices?

Background: I have an application where devices will poll information from some source on the network. These devices are very basic and have modest processing and memory capabilities. Hashing (and ...
267 views

### AMD's implementation of RDRAND instruction

The latest AMD programmer manuals, dated June 2015, include the RDRAND instruction in the instruction set. For completeness, it lacks ...
60 views

### RSA key generation gives d=1

I was reviewing RSA by hand. I picked 53 and 59 as my primes. For e I picked 5. When I solved for d using extended euclid, I got 1 which obviously doesn't decrypt anything. I checked my answers online ...
39 views

### Cracking a PRNG by observing ranks within groups of its output

Suppose that I am generating random numbers with Python's random module, so that there is a known random number generator (Mersenne Twister in this case). I've ...
67 views

### Keyless Signature Infrastructures as a secure Post-Quantum Scheme

I came across a company that relies on hashing, similar to block chain technology. They explicitly stated in their white paper that hash based cryptographic schemes are inherently post-quantum ...
53 views

### Can we use a sort of “hash” function in CTR mode instead of a block cipher? [duplicate]

CTR mode does not use the decryption function at all, only the encryption function. This may suggest that a different primitive that has this "one-way" property could do the trick. For instance, I ...
28 views

### Authenticating a range of a ciphertext

I have some data that I CTR-AES-256 encrypt already. I am aware of ways to validate the integrity of the entire file (ie: a separate MAC of the plaintext, or encrypt then MAC, etc). But none of ...
194 views

### 2DES vs. two-key triple encryption, with no decryption step

So studying double encryption (double DES) and understanding why it is subject to a meet-in-the-middle attack, I tried to see if the same attack could be applied to a triple encryption with only two ...
15 views

### PAN authenticatable irreversible tokenization algorithm

I need to implement algorithm to create authenticatable irreversible tokens from PAN, without using any secrets. Is it possible? Is there any standards for that from associations? I was thinking ...