# All Questions

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### Implementing AES-CBC (Matasano Crypto Challenge 10)

I am currently doing the Matasano Crypto Challenge to learn a bit about cryptography. In that specific challenge one had to implement AES in CBC mode. I did that and verified that encryption and ...
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### Continuous stream of strong randomness from limited entropy?

I need a continuous (infinite) strong random generator, but I've only got limited entropy as seed. I know there's already a contradiction there, but I'm looking for a practical approach. Suppose I ...
65 views

### programming a sniffer for AES GCM with gcrypt

I want to write a sniffer that can read AES-GCM communication using the gcrypt lib I can see in the manual that for encryption there is an additional 2 methods (for AEAD) but what about decryption ? ...
52 views

### Finding collisions for the DES F-function

It's known that for a given subkey, the F-function of the DES is not injective (see Is the DES F-function injective for a given subkey?). I am interested in efficiently finding collisions for this ...
176 views

### How much entropy is generated by 'random' human keystrokes?

I'm wondering about using human input as an entropy generator. We all know humans are terrible at making up random numbers or keys or passwords. But what if we let a user 'randomly' type in some ...
23 views

### gpg 2048R - why encryption data length is different if text data 36 bytes

We are using gpg2 and base64 commands with 2048R algorithm Input: encrypted 36 bytes input text data with fixed length(36 bytes) current problem: if I run gpg command continuously, some times ...
151 views

### Why does GPG ciphertext length differ with fixed plaintext length?

Thank you for your reply. Based on your inputs. I was investigated further, find details below Step 1) Input string for encryption is UUID format Input data = c0c6f311-a793-4d65-9374-1c0e45f5382c ...
187 views

### How to prove secret value in Pedersen commitment is equal to secret value in Fujisaki commitment?

We have Pedersen commitment C to the secret value x, and Fujisake commitment C' to the secret value x. How can we make a zero-knowledge proof of equality for x value in the commitments?
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### What Does This Symbol Mean? (Hardcore Predicates for One-Way Functions)

I am studying Pseudorandom Number Generators and when reading the discussion on One-Way Functions and Hardcore Predicates, I came upon this equation. $$b(x,r)=\displaystyle \bigoplus_jx_jr_j$$ I ...
124 views

### Are there comprehensive alternatives to RSA?

If we wished to, is there a comprehensive alternative to RSA? I say comprehensive as I wonder if there is one which does both encryption and digital signature like RSA? If not, simply what ...
61 views

### How does a user register his verifier at host in SRP (Secure Remote Password) protocol?

I read RFC 2945 and 5054 describing SRP, but there was no mention of registration. How should user registration happen in SRP? Is there a standard or paper describing it?
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### How to force an adversary to call a certain oracle?

Consider there is a protocol in real world, which uses a random oracle $\mathcal{H}$. In the ideal world, after the calling of $\mathcal{H}$ by some parties, intuitively I want the simulator gets some ...
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### Cryptographic operations for NISTP256 can be implemented using montgomery method?

I need to implement cryptographic operations starting with the curve NISTP256. I have been told to implement it using Montgomery method. I read a pfd from http://saluc.engr.uconn.edu/refs/sidechannel/...
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### May I use Random Oracle for Inversed Look-up?

Consider there is a protocol in real world calling a random oracle $\mathcal{H}$ for a priavte input $k$. Then in the ideal world, after the calling of $r \leftarrow \mathcal{H}(k)$ by a honest party, ...
1k views

### RSA & DH at risk due to math advances, will this eventually affect elliptic curves too?

I was looking into the predictions by some researchers that RSA and Diffie-Hellman may not be secure in the next few years due to advances in math and being able to calculate the discrete logarithm ...
127 views

### Why does the time complexity of RSA encryption and decryption depend on the size of the modulus?

I would think that the time complexity would depend on the exponent, not the number of bits in the modulus. For example, if the exponent were 5, using the "naive" method, we would perform 5 ...
107 views

### Is the RC4 keystream random or not?

I have cause to use the PRNG half of RC4, but am seriously confused as to the randomness of its output. (Only the PRNG half.) On the one hand, there is a large body of literature finding ever ...
68 views

### What is the difference between LCG and Affine cipher?

What is the difference between LCG and Affine cipher? More specific: What are they used for, and what are the structural differences between them?
129 views

### More rounds after AES related key attack?

In his blog Schneier discusses that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of ...
97 views

### Implementation specific differences between RDRAND and RDSEED

I've read Intel's The Difference Between RDRAND and RDSEED and Intel Digital Random Number Generator (DRNG) Software Implementation Guide, but I have some open questions that are specific to usage in ...
132 views

### S boxes in Blowfish

I know how the s-boxes in blowfish are initialized, but how is the output sorted, I mean which bit from the input goes where in the box ? and what do mean they have 256 entries if they are 32-bit S-...
116 views

### Big block cipher as memory-hard function

I'm wondering, if something like block cipher with big block size is a good memory-hard function? All memory-hard key derivation functions I've seen look more complex than that, which made me ...
529 views

### bank websites using AES_256_CBC vs AES_128_GCM/CBC [duplicate]

Hello i have just recently started learning about cryptography, so i was doing some little research on what kind of encryption techniques and modes that were used in bank web pages. I have noticed ...
116 views

### Muchomor cipher

I've been given a task to research and possibly implement so called 'Muchomor' cipher. Has anybody ever heard of this cipher? I've found only one article about it and it was in Russian. I'm quite ...
103 views

### RSA: must $d$ be an integer?

I am only taking baby steps in RSA. If $p=11$, $q=7$ and $e=3$, $$\phi(n) = 10*6 = 60$$ Then: $$d = (2 (\phi(n)) + 1 ) / 3 = 121/3$$ Should $d$ be kept as a non-integer or is such a $d$ invalid?
50 views

### Reusing same source for single-source randomness extractor

Let $ext$ be a single-source randomness extractor which takes a $d$-bit seed and a $n$-bit source as input and produces a $m$-bit output. Suppose we have a source $X$ with min-entropy $k$. Is it ...
63 views

### Rogue CA Certificate MD5 Collision Control

Papers from Marc Stevens et al show that X509 certificates that rely on MD5 signatures can break the assumed security model, that is, it allows for a forged certificate to have the same signature as a ...
207 views

### paradox on fully homomorphic equality checking

Imagine, a client encrypts a corpus of data (say documents of text) with the public key of a Fully Homomorphic Encryption scheme (FHE) and outsources the data to an untrusted server.Now the client ...
90 views

### Problem reproducing AES results

First of all, I just implemented AES because I wanted to understand how it works and as a challenge to see if I could do it and I won't use to encrypt anything important, ever. The (German) Wikipedia ...
104 views

### Using HMAC as a nonce with AES-CTR encrypt-and-MAC

Suppose I use the following encrypt-and-MAC construction: $E(k_1, k_2, n, m) = E_\text{AES256-CTR}(k_1, n, m) \| \text{HMAC-SHA256}(k_2, m)$, where: $k_1$ and $k_2$ are 256-bit keys $n$ ...
194 views

### RSA: Most significant key bit always 1?

Is it possible to say that the most significant bit of an RSA private exponent is always 1? Wouldn't that weaken the key strength by exactly that one bit? I refer to the paper "Timing Attack: What ...
96 views

### How can there be AES-256-GCM, when GCM is defined for 128-sized blocks?

In both node.js and OpenSSL, I am seeing cipher "aes-256-gcm". However, in NIST Special Publication 800-38D, that defines GCM, I am reading: The underlying block cipher shall be approved, the ...
72 views

### Fully homomorphic encryption arbitrary functions formulation

I am currently studying the interesting field of homomorphic encryption. I read that from a fully homomorphic encryption function that supports both addition and multiplication you can perform any ...
42 views

### Unbreakable encryption [duplicate]

I am a newbie, I know that I must be wrong, but I need a good explanation. How is it possible to break a cryptographic algorithm created by me, when only I know the algorithm and the key for ...
79 views

### Which hash function is usually used in RSA?

I know there are several available, however I can't seem to find whether there is one standard one or not. I think I understand the process of digital signatures, just wondering which has function is ...
64 views

### Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
109 views

### Multiple NTRU public keys for the same private key?

An NTRU public key is generated essentially by multiplying the inverse of a polynomial $f$ by a polynomial $g$. The polynomial $f$ is the private key; $g$ is discarded. My question is: Is it insecure ...
53 views

### StoredKey in Salted Challenge Response Mechanism (SCRAM)

In SCRAM (RFC5802, page 8) the client generates ClientKey to server, which is a derivation of the original password. This is communicated to the server in a secure ...
58 views

### User revocation in Identity Based Encryption

I read several papers about user revocation in IBE recently. A common point is that when a user is revoked, some other valid users should also update their private keys. Does this mean that one ...
152 views

### Help understanding basic Franklin-Reiter related message attack

I am trying to understand this attack at the most basic level. I set up the following basic scenario: Let the public encryption exponent, e = 3. Let p, be some arbitrary but known (to the ...
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### Edwards / Montgomery ECC over binary extension fields

I recentely had a discussion about the redesign of our ECC code for the library I'm collaborating on and the person I was discussing with came up with Edwards and Montgomery curves over binary ...
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### Multi-Party Encryption for a Shared Document

Is there an encryption algorithm/protocol where any of a pre-defined set of keys/passwords will succeed in decrypting a document? The number of keys can be fixed, say, 10 or 20 possible passwords. ...
82 views

### Lattice attacks against Multilinear Maps [CLT13]

I am currently studying an article on a construction of Multilinear maps. There are some attacks on the scheme presented by the authors and I got stuck at the one in section 5.1. I will try to ...
175 views

### Backdoorable hash function in password database

I want to use a (preferably established) hash function that is backdoorable in a password database. I want to do so because I need password escrow (being able to get the cleartext back. I want to ...
86 views

### Deletion in RSA Accumulator

I am studying RSA Dynamic Accumulator and I have a question: why is simpler to calculate the new accumulator value after a deletion if is known the secret ϕ(n)? Is possible to calculate the deletion ...
190 views

### How can I use the whole potential of DES?

I have recently programmed the DES algorithm. Right now it works just with integers (or better to say chars) in the range <0;255>. How can I use its whole potential - using just ASCII would be a ...
38 views

### Should I authenticate memory data which was loaded from authenticated disk file?

Encrypted fields are loaded from disk file to process memory only after file's HMAC validation is successful. Data is still encrypted in memory and will be decrypted later, on demand, when it needs to ...
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### Reversible hash function

I met the following 'reversible hash' function applied on a data $d$ consisting of $d_1, \ldots, d_n$ words: $h_0(d) = 0, h_i(d) = c ∗ (d_i + h_{i−1}(d))$, for $0 < i \leq n$. $c$ is a small, odd ...