2
votes
2answers
212 views

How can I store a combination of multiple pass phrases?

Let's assume we have 2 phrases, one is the real password from a user, and the other is generated from the real password and almost impossible to guess. You would need both to authenticate a user. What ...
2
votes
1answer
176 views

Is there a way to provide proof of batch RSA security?

Suppose we have two encrypted messages with two different public key issued from the one server. There is a client who wants to send these to messages to the server. In the middle there is an ...
2
votes
1answer
981 views

Hash or encryption function for challenge-response protocol?

Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...
2
votes
1answer
111 views

Is it possible to spoof an identity cert modulus?

I was looking at FOAF+SSL and wondering if its possible to spoof the modulus of the browser certificate so that the FOAF and browser certificate's modulus match?
2
votes
1answer
1k views

Where can I find Secp256k1 ECDSA test vectors?

I`m currently implementing an ECDSA library based on curves like secp256k1. I would like to test it using some test vectors, like http://csrc.nist.gov/groups/STM/cavp/documents/dss/ecdsatestvectors....
2
votes
1answer
24 views

Client side encryption / hashing of “person ID's” with password?

What we're looking for A solution where data is stored and retrieved (!) from a server using a person ID that can only be known at the client (form of ...
2
votes
1answer
39 views

Finding $f^{-1}$ in the YASHE keygen algorithm

In the YASHE (Yet Another Somewhat Homomorphic Encryption) algorithm, the beggining of the key generation step specifies: Sample $\ f',g ← χ_{key}$ and let $\ f = [tf' + 1]_q$. If $\ f$ is ...
2
votes
2answers
99 views

Calculating Polynomial Inverse with extended euclid in java

I'm trying to understand the NTRU-PKCS and therefor I wanted to code a naive Version of it. Now my Problem: I tried to calculate the inverse of a Polynomial with an extended Version of euclids ...
2
votes
1answer
32 views

First preimage resistance check

So I have $H: \{0,1\}^* \rightarrow\{0,1\}^n$ a hash function resistant to the second preimage and to collisions. Let there be a function $H' : \{0,1\}^* \rightarrow \{0,1\}^{n+1}$ with the following ...
2
votes
1answer
70 views

Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
2
votes
1answer
55 views

What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a ...
2
votes
2answers
86 views

Fixed primes in discrete logarithm

The discrete logarithm problem is to find $z$ when the inputs are $g,h,p$ where $g^z\bmod p$. Supposing if you fix $p$ then does the problem become any easier to attacks and is there a $(\log p)^c$ ...
2
votes
1answer
99 views

RSA Encryption problem for Discrete Math

I am doing practice problems for my upcoming final exam, and am having trouble with this RSA encryption problem. If any one could check to see if i did these correctly, it would be greatly appreciated....
2
votes
1answer
57 views

Does revealing shares of the result reveals shares of the inputs?

Suppose Alive and Bob have shares of two polynomials $P,Q$, say, Alice knows $P_A,Q_A$, Bob knows $P_B,Q_B$ s.t. $P=P_A+P_B$ and $Q=Q_A+Q_B$. They perform some operation $f$ over the shared values, to ...
2
votes
1answer
122 views

How much weaker is AES-64 than AES-128?

It's hard to say exact QC specs, but let's assume we have decent a quantum computer using Grover's algorithm that is able to half AES-128 keyspace to that of AES-64. How long will a bruteforce attack ...
2
votes
1answer
53 views

Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
2
votes
1answer
91 views

How to detect what crypto-method is used by Filecoder.Q?

I have 2 different images, one original, and one locked by a malware detected by eset as "Win32/Filecoder.Q". How to detect the encryption method that is used and the key, that is not using any ...
2
votes
2answers
56 views

Key management and derivation - Allow changing of the passphrase

I'm working on a program, which allows encrypting files before storing it on a cloud service. Currently I'm trying to figure out how to derive and store the keys. First, I wanted to use a simple ...
2
votes
1answer
32 views

Can multi-prime RSA be used to create an abuse-resistant lawful interception mechanism?

New to site so this may have been asked before: Can multi-prime RSA, i.e. where N is product of three or more distinct primes, be used for secure communication while allowing distinct authoritative ...
2
votes
1answer
28 views

Steps to encrypt endorsements to a petition

I plan to circulate a petition, asking people to support it. This petition will reach a senior government official. In regular circumstances, people would support such petitions by writing their ...
2
votes
1answer
57 views

What would be a typical value for the security parameter of the Fully Homomorphic Encryption over the Integers scheme?

The parameters of the Fully Homomorphic Encryption scheme by Dijk et.al are chosen according to the value of the security parameter ${\lambda}$, section 3 of the aforementioned article. What is the ...
2
votes
1answer
61 views

How SAM modules secure transactions?

As you know SAM Modules are used mainly in the electronic payment industry. Due to the low security of key storing in general storage devices or MCUs, Manufacturers used SAM modules for secure storing ...
2
votes
1answer
76 views

How is it possible that $g^q \equiv 1 \pmod p$ for a generator g?

The context of this question is coming up with the parameters for the ElGamal encryption scheme. One of the requirements for the parameters for ElGamal is that we have primes $p$ and $q$ such that $p ...
2
votes
1answer
52 views

Are all self-synchronizing cryptosystems necessarily self-synchronizing stream ciphers?

I have a noisy communications link between two points that occasionally deletes a byte. By "self-synchronizing cryptosystem", I mean that the receiver attempting to recover the original plaintext ...
2
votes
1answer
69 views

Are the following schemes based on a pseudo-random permutation secure?

I am currently working on the following task: Let F be a pseudorandom permutation. Consider the encryption scheme for the message space $\{0, 1\}^n$ defined as follows: $Gen(1^n)$ chooses ...
2
votes
3answers
209 views

What is the difference between substitution cipher and block cipher?

I'm studying(and clearing my head) about block cipher. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right). And an ideal substitution ...
2
votes
1answer
151 views

Difference left-or-right CPA security, IND-CPA security

I am trying to understand the notion of left-or-right-CPA (LOR-CPA) security for private-key encryption schemes introduced in my lecture. If I understood it correctly so far, the only difference to ...
2
votes
1answer
306 views

How is a per round key generated in DES algorithm?

I am reading over a slide that I found online regarding the DES algorithm for encryption and I am a little confused about the per round key generation. From the slide below, I understand that each per ...
2
votes
2answers
74 views

Obtaining Diffie-Hellman generator

In the Wikipedia article on Diffie-Hellman, the algorithm calls for a large prime modulus, $p$, and a generator, $g$, which is a primitive root of $p$. As far as my knowledge of number theory goes, ...
2
votes
1answer
50 views

How to convert roots of Weber polynomial to Hilbert class polynomial over modulo prime?

Using any non square root discriminant $D$, we should be able to find the Weber class polynomial. How can I convert the roots of a Weber polynomial to a Hilbert class polynomial over modulo prime?
2
votes
1answer
45 views

How would you name and/or describe this algorithm?

First up: this is not a decoding request or anything. This is about terminology. Twice per year, we email another department to ask for a new licence file for their software. They are always slow to ...
2
votes
2answers
48 views

Can you update a (k,n) scheme to a (k+t, n+t) scheme (assuming old keys can be deleted)?

I know that $(k,n)$ can increased to $(k+t,n-s)$ one, by generating a random polynomial $p(x)$ of degree $k+t$ with constant term $0$, and then ordering each agent $a$ to add $p(a_x)$ (where $a_x$ is ...
2
votes
1answer
79 views

How to construct Hash function of type $H:\{0,1\}^x \times G \mapsto Z_p^*$?

In many cryptographic protocols design, I have seen the statement 'Choose a Hash function $H:\{0,1\}^x \times G \mapsto Z_p^*$ i.e a hash function which takes as input a binary string of finite ...
2
votes
1answer
146 views

Questions about a SHA3 cipher stream encryption scheme

I have written an encryption implementation using a hash as a cipherstream for demonstration purposes. I know it is slower than more sensible options such as AES but I am interested in several things, ...
2
votes
1answer
67 views

Extracting key bits from linear cryptanalysis equation for SDES

From the linear cryptanalysis of SDES, we get a linear equation consisting the K[1, 3] of the round key 1 and 2. From this how will I retrieve the key bit? How do we solve the linear equation we get ...
2
votes
2answers
95 views

Linear cryptanalysis complete key guessing

In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext. From the partial sub key, how it is possible to guess the complete ...
2
votes
1answer
69 views

Is the length limit of AES-GCM per key or per (key, nonce) pair?

AES-GCM has a limit on the length of the plaintext it encrypts: $2^{39} - 256$ bits. But is this limit per key or per (key, nonce)? That is, if I encrypt a message with the maximum length, and encrypt ...
2
votes
1answer
112 views

Is secure lattice based cryptography in future?

Lattice cryptography is a post quantum cryptography that work on two NP-hard problem in below: Find shortest nonzero vector from origin and Find minimum distance of a arbitrary point out of lattice ...
2
votes
1answer
367 views

Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
2
votes
1answer
53 views

Generalization of the DL-assumption in bilinear group pair

When thinking about a pairing-based cryptographic scheme, I encountered the following problem. Let $e \colon G_1, G_2 \to G_T$ be a Type 3 pairing. Then: Given $P, zP \in G_1$ and $Q, zQ \in G_2$, ...
2
votes
1answer
72 views

Elliptic Curve ElGamal and DSA - smooth group order and element of large prime order

In regular ElGamal and DSA, we choose large primes $p$ and $q$ such that $p\equiv 1\pmod{q}$, and a group element $g$ of order $q$ by computing $a^{(p-1)/q}$ for some random $a$. This is to prevent ...
2
votes
2answers
83 views

comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
2
votes
1answer
65 views

Which algorithm would be ideal for ephermal key generation followed by DH key exchange?

Bob and Alice, both generate a temporary public key pair each using X algorithm on their individual PC. After being authenticated by a third party, they use the DHE to come to get a common symmetric ...
2
votes
1answer
116 views

How to calculate mapping in bilinear

I am trying to read a paper in cryptography. In key generation phase, paper give a definition for bilinear like G and Gt be two cyclic groups of prime order p $e: G * G \to G_t$. be a map with the ...
2
votes
1answer
61 views

Perfect Forward Secrecy in PGP/asynchronous email

Looking at the RFC for PGP email/asynchronous chat with PFS here https://tools.ietf.org/html/draft-brown-pgp-pfs-03 can anyone tell me why the following scheme is no good? Alice and Bob retrieve each ...
2
votes
1answer
74 views

Does including the size of the hashed data improve security over just the hash

Trying to settle a discussion at work. We are mostly concerned with pre-image resistance. Suppose we have a common secure hash function $H$ (e.g. SHA-1/SHA-2) and some message $M$ we want to hash. ...
2
votes
1answer
224 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?
2
votes
1answer
39 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 ...
2
votes
1answer
68 views

Bilinear map assumpion

Is there an assumption that says from a tag $k\cdot e(g,g_1)^{rx}$ ($k,r$ are secret) it is difficult to forge it with some x': $k\cdot e(g,g_1)^{rx'}$, as long as you cannot solve DL in $\mathbb{G}_1$...
2
votes
2answers
91 views

Find plaintext of RSA by solving extended euclidean algorith for two encrptions with two different exponents for same plaintext

This is my homework question (but I am not asking the answer to it): Suppose two users Alice and Bob have the same RSA modulus n and suppose that their encryption exponents eA and eB are ...

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