-1
votes
1answer
42 views

Question about the security of Substitution-Permutation Network

In general, we execute key-mixing, substitution and permutation sequentially in a single round in a n-round SPN, but if we execute n-round key-mixing firstly, n-round substitution secondly and n-round ...
2
votes
3answers
468 views

How do institutions like banks do RSA with big primes?

When encrypting with RSA it is often infeasible to decrypt by just doing c^d mod n, because for example when using the primes $(p,q)=(12553,1233)$, which are small ...
4
votes
3answers
1k views

What is the length of an RSA signature?

Is it the same as the bits of the key (So a 2048 bit system will yield a 2048 bit signature)? At most as the key? Or something else entirely?
0
votes
0answers
61 views

fuzzy commitment implemenation to make secure biometric template

I want implement some ideas from an article that is about making secure biometric templates using fuzzy commitment and fuzzy vault. I need to implement just the fuzzy commitment (fuzzy commitment is a ...
3
votes
0answers
68 views

Finding algorithm: desire RSA's uniqueness and ECDSA's space efficiency

I am asking for help in finding a signature algorithm with the following property: Given a message m and a private key prikey, ...
3
votes
1answer
68 views

What is the technical name for a public key container in DER format?

I have a public key in the following (format-neutral; the type is specified by the DER bytes) format: ...
2
votes
1answer
79 views

GCM: Math behind update of AAD after ciphertext has been processed

In the Bouncy Castle libraries, the GCM cipher implementation has an interesting property that does not seem described in the GCM papers (neither the NIST or the original paper): Some AAD was sent ...
1
vote
0answers
60 views

Encryption with data loss protection

Is there an existing format out there that not only encrypts data but also protects against loss of data much like the QR codes can lose up to 33% of it's bits and the message is still recoverable. I ...
1
vote
1answer
102 views

On the privacy of perfect hash functions

I'm digging into the several algorithms for building (Minimal) Perfect Hash Functions. It seems that the recent works provide quite a few very efficient algorithms. However, I'm wondering how a ...
0
votes
1answer
61 views

Pollard's Rho - Constructing the random function

Suppose we are aiming to solve the discrete logarithm problem $\alpha^x=\beta$ in some cyclic group $G=<\alpha>$. Then we are looking for a (uniformly) random sequence of elements of the form ...
-3
votes
0answers
29 views

Ciphertext-only cyptanalytic attack agianst the affine cipher? [duplicate]

Can you think of a ciphertext-only cyptanalytic attack agianst the affine cipher? Please explain step by step how it would work if possible.
3
votes
1answer
102 views

Efficient AES - Use of T-tables

I'm really in trouble! I'm trying to understand how the T-tables in AES encryption work. But I don't know if I get the point. What I understood is that they are used to reduce the whole computation of ...
0
votes
0answers
43 views

Scalar multiplication of elliptic curve point by a fraction

I'm implementing an algorithm that works on a generic finite cyclic group written in the classic multiplicative notation: (G,*) = < g > , n = |g| At a ...
5
votes
2answers
87 views

Shannon confusion and diffusion concept

I read the document(not the whole document) from Shannon where he speaks about the concepts of confusion and diffusion. I read in many places(not in the document but around the internet) that ...
4
votes
1answer
134 views

Why does a perfect secrecy can be achieved when decryption correctness is not totally required?

By Shanon theorem, a perfect secrecy encryption scheme must use a key space of equal size as the message space. But when the correctness requirement is weakened such that $Pr[Dec_k(Enc_k(m))=m]=1/2$ ...
4
votes
3answers
104 views

The difference between being not strongly collision resistant, and not weakly collision resistant?

So I understand the two concepts: (Strong) collision resistance: it is infeasible to find a pair $x \neq x'$ such that $h(x) = h(x')$ Weak collision resistance / 2nd-preimage resistance: for all $x ...
2
votes
2answers
209 views

salsa20 is invertible, useless in CTR mode?

I'm reading the salsa20 spec (sorry for the newbie question, i'm really a newbie here). Every paragraph ends with : "this operation is invertible", I suppose the whole salsa20 algorithm is. If I use ...
0
votes
0answers
36 views

ABE schemes viz., ciphertext-policy, key-policy implementation in Java [closed]

I was trying to implement simple ABE (KP-ABE and CP-ABE) schemewith search feature in java. I would like to know if there are any simple examples I can refer which are implemented in Java. I came to ...
1
vote
1answer
85 views

Is Rabin's cryptosystem secure against known-plaintext attacks?

I've bee learning about Rabin's cryptosystem, and I already know that Rabin's cryptosystem is vulnerable to a chosen-ciphertext attack, but I was wondering, is it also vulnerable against ...
0
votes
2answers
127 views

Why would an RSA library tell me that the public key must be at least 512 bits in size?

I'm trying to interoperate with a web service by reverse-engineering it. Currently, when sending a POST request, it encrypts the form data one-by-one with a 'RSA' function. But it's rather weird as ...
1
vote
2answers
45 views

Are password salts equivalent to keystream?

I am new to cryptography so my apologies for asking such a basic question. I was reading up on keystream when I came upon the definition of it: A keystream is a stream of random or pseudorandom ...
1
vote
1answer
99 views

Equal length of primes in paillier cryptosystem

In the key generation step of paillier cryptosystem , In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal length primes. Instead of taking(length as parameter to generate $p,q$) equal ...
0
votes
1answer
59 views

How to calculate kinv from the given k value

I am implementing an ECDSA NIST test vectors verification application. The test vectors are taken from http://csrc.nist.gov/groups/STM/cavp/#09. One of the test vectors is given below: ...
1
vote
1answer
52 views

Does OpenTSA support PKCS11 to talk to HSMs?

We are planning to implement the time-stamping service (RFC 3161) using OpenTSA wanted to know: Does OpenTSA support PKCS-11 (Cryptoki) to talk to HSMs? BTW: I did not find documentation or much ...
13
votes
4answers
6k views

Recommended skills for a job in cryptology [closed]

First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company ...
0
votes
0answers
29 views

Using the same IV instead of random for CTR mode? [duplicate]

Why is it a bad idea to use the same IV instead of random one for CTR mode?
2
votes
3answers
112 views

Feasibility of finding public key when private key is known

We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it. Is it the same case in reverse? Given a private key, how easy is it to compute ...
0
votes
0answers
23 views

Calculating cost of variables and equation in Groth-Sahai (DLIN) proof system

In Groth-Sahai proof system under DLIN assumption [Page 29], they have provided a few number denoting the cost of each variable and equation. Can anyone please explain how did they calculated the ...
0
votes
0answers
23 views

Discrepancy between RSA implementations [migrated]

I'm not a crypto-guy so I know close-to-zero about these things. I must interoperate with a system using RSA cryptography. When using their keys, I'm running into the problem of getting different ...
0
votes
1answer
47 views

Definition of perfect secrecy using ciphertext

This week my professor in class taught us the definition of perfect secrecy. He said that for any ciphertext the probability that it might have come from any message in the message space should be ...
0
votes
1answer
70 views

Implementing a web app where the server cannot decrypt its own data?

I'm a cryptography novice, but I think that the world needs to move towards an "encrypt everything" mentality as much as possible. As a result, I've been thinking a lot about ways to build a web app ...
2
votes
1answer
148 views

Hashing passwords

The common way to store passwords in web applications is this form: $$hash(password||salt)$$ Does it make sense to store them in the following form instead:? ...
1
vote
1answer
59 views

How hard to break a cipher if it has a different key for each word?

Recently I watched the movie 'The Prestige' again but this time the cipher diary impressed me very well. I like to create my own cipher for my diary because I have some time to kill everyday after ...
3
votes
3answers
163 views

Regarding Key Strength with DES and Blowfish

I had a small discussion with my friend on combining two encryption algorithms based on 64-bit keys. Say I have a plain text of 64 bits which I want to encrypt. My Key size is 128 bits. I will use ...
2
votes
1answer
69 views

Will I be able to (ab)use a FIDO U2F compliant hardware token to decrypt data?

I have heard good things about the emerging "FIDO U2F" standard. I am especially interested in having a JavaScript API for cryptographic functions that I can access through a plug-in in a browser. ...
1
vote
1answer
41 views

RSA-KEM construction

"Create a random key for CCPA2 scheme, encrypt m, send it along with a PK encryption of the symmetric key. " Say in the process, the KDF is HMAC, then: get a random key (128-bit) C1 = encrypt ...
0
votes
0answers
36 views

Partial Homomorphic Schemes with padding

As mentioned in wikipedia there are many Partial Homomorphic Encryption(PHE) scheme like RSA, Elgamal, Pailler etc. But out of them only unpadded RSA scheme seems to be partial(multiplicative) ...
1
vote
0answers
52 views

Engima machine decoding with PC and GPU

I saw this answer at this site about decoding a 3-rotor Engima machine's settings: How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint? And did some math for ...
4
votes
1answer
367 views

Implementations of Ntru TLS

Has anyone come across any implementations of Ntru TLS? I'm working a project for uni that does quantum secure encryption. It relies on a mix of Ntru & AES, but I can't find an implementation of ...
2
votes
1answer
66 views

Help to understand the chameleon hash function?

Recently, I'm reading Non-Interactive Key Exchange, in the section 4.2(Towards a factoring-based scheme in the standard model,Page 10), the authors uses $$t\gets ChamH_{hk}(Z||ID;r);\\ Y\gets ...
0
votes
2answers
57 views

Does NTRU provide Perfect Forward Secrecy?

Does NTRU provide Perfect Forward Secrecy if the world would use it in an HTTPS connection?
2
votes
1answer
71 views

Strong key generation using PBKDF

I know that PBKDF2 is very useful for generating strong keys. I'm trying to know is there any additional contribution of the given password to produce even stronger keys. Which key is more secure: ...
3
votes
1answer
72 views

Last Round in DES

I am studying DES for my Cryptoexam .As far as I understood , the initial plaintext is permuted and then the left half is called L0 and Right half is called R0. After that for each round the process ...
4
votes
1answer
234 views

How secure is this use of Ziv-Lempel encoding?

I'm reading patent application US 20120278897 A1 — “System and method of sort-order preserving tokenization”. Near the bottom they describe their token generation algorithm, which basically involves ...
-2
votes
1answer
71 views

Why are we advising PKI if we know that quantum computers will break them?

DNSSEC, ECDHE, RSA, even SSH and all other important specifications, protocols that we rely on and advise people to use them, they use Public key infrastructure. Question: Why do we still use, ...
1
vote
0answers
26 views

Understanding the FMS attack on WEP

I am trying to implement the Fluhrer, Mantin and Shamir attack, one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't ...
1
vote
0answers
37 views

Chi-Squared Step of Vigenere Cipher Decryption

So, I have been assigned an assignment where I had to solve a Vigenere cipher. Following along with this webpage I managed to get all the way to the chi-squared step. But, that is the problem. Upon ...
2
votes
1answer
147 views

How can AES be considered secure when encrypting large files?

Why is AES considered to be secure when encrypting large files since the algorithm is a block cipher? I mean, if the file is larger than the block size, the file will be broken down to fit the ...
4
votes
2answers
127 views

Are there cryptographic hash functions with homomorphic properties? [duplicate]

Are there cryptographic hash functions that have homomorphism-like properties? E.g. satisfying following relation $h(a || b) = h(a) · h(b)$, where $h(x)$ is hash function itself, $x || y$ is ...

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