0
votes
1answer
53 views

What cryptographic paradigm is appropriate for this use case?

This is a very newbie question... I have to quickly implement a solution for our application that works like this... We have a binary executable that is given a configuration file. I need to encrypt ...
0
votes
1answer
53 views

Spurious keys filter [closed]

Is there any possible way to filter a key space in a crypto-system to get a set of keys that decrypts out a valid text (text that is in same language or readable)? I tried a random approach and got ...
0
votes
1answer
237 views

Decrypting a small Message using RSA with a Private Key [closed]

If I have a private key of (43, 341). What would be the steps I need to take to decrypt a small message using RSA? I have looked ...
0
votes
2answers
56 views

Operation sequence authentication shared storage

Let's say there is a shared storage: USB flash drive, external HDD, or whatever you like. I'll refer to it as disk. Also, there are multiple parties, let's say Alice and Bob (may be thousands of them) ...
0
votes
1answer
241 views

TLS/SSL's usage of Non-Ephemeral DH vs DHE

These questions revolve around DH and ECDH vs DHE and ECDHE. Specifically within the context of TLS/SSL. There are three ...
0
votes
1answer
90 views

Is substitution with random prefix codes secure? [closed]

The following paper interests me very much: D. W. Gillman, M. Mohtashemi, R. I. Rivest, On breaking a Huffman code. IEEE Trans. Inf. Th. Vol.42 (1996), pp 972-976. However, unfortunately due to my ...
0
votes
1answer
87 views

Hash Function to get same value for different messages [duplicate]

I am studying a function where I found the some hash properties. Hash functions: Given a code c is computationally infeasible to find m such that ...
0
votes
1answer
82 views

Semantic Security Active or Passive attacks?

I'm reading A Practical Public Key Cryptosystem Provably Secure against Adaptive Chosen Ciphertext Attack and here define Semantic Security ... Semantic security, dened by Goldwasser and Micali ...
0
votes
1answer
106 views

What is the “purpose” byte in Crypto++ PBKDF2?

Does anyone know the purpose of the "purpose" byte in the PBKDF2 implementation in Crypto++? It appears that the PBKDF2 does not use this byte, but I want to make sure I am not setting the option to ...
0
votes
2answers
69 views

Finding an x such that xP = (11,44) on an elliptic curve

Given the elliptic curve $$E:y^2 = x^3+17x+5 \mod 59$$ with point $P = (4,14)$, how do I find $x$ such that compute $x\cdot P = (11,44)$ Is there a mathematical method to compute $x$, or do I ...
0
votes
1answer
96 views

Prime factors of non-random keys

I have been working on a challenge i found on the internet. It is as follows: You've stumbled onto a significant vulnerability in a commonly used cryptographic library. It turns out that the ...
0
votes
1answer
119 views

Digital signatures under plain RSA

Show that digital signatures under plain RSA are insecure (Plain RSA means that signing is done by calculating $m^d\bmod n$, with $0\le m<n$, and no padding or hashing of $m$). Write an algorithm ...
0
votes
1answer
132 views

Partially-known-plaintext attack of a stream cipher based on modular arithmetic

I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ ...
0
votes
2answers
137 views

IV/Nonce in CTR&GCM mode of operation

We know reusing IV can compromise our secrecy. I have some questions aiming to clarify the use of an IV/Nonce in CTR/GCM: Is it OK to use the same key for encrypting plain-texts in authenticated ...
0
votes
1answer
36 views

gnupg: display digest of key [closed]

How can I display what digest algorithm has a key? If I import a public key which has MD5 as digest, I get a warning about this weak algorith. But how can I check, what digest algorithms all my keys ...
0
votes
1answer
178 views

Unique, anonymous online authentication

Is there a way to authenticate users online without knowing their real identity yet preventing them from registering twice? If not, what is the least amount of information you would need? If it helps, ...
0
votes
1answer
56 views

Bicliques for permutations

So I'm trying to understand the complexity of the biclique attack on Grostl and I have some questions: 1) The paper introduces sliced bicliques where on Grostl one constructs a biclique of dimension ...
0
votes
2answers
120 views

Can you prove the existance of a PRG $G$ s.t. for each even $k$: $G(k)=G(k+1)$?

In one of the exercises in [KL] Book I need to tell whether an encryption scheme is secure under an eavesdropper of only one message. Given a PRG $G: \{0,1\}^n \rightarrow \{0,1\}^{n+1}$. The ...
0
votes
1answer
120 views

Homomorphic Encryption Notation Question

What does the following notation mean in a homomorphic encryption scheme? ENC(x;r) What does x and ...
0
votes
1answer
77 views

Efficient Robust Private Set Intersection Questions

I am trying to implement Efficient Robust Private Set Intersection using additive ElGamal. I am trying to run the full protocol mentioned in Section 3.4 on the following inputs: $p = 17$ (prime) $g ...
0
votes
1answer
87 views

ElGamal encryption with private key [closed]

Does the encryption with a private key and decryption with a public key works in ElGamal likewise what is done when we use RSA for sender authentication?
0
votes
2answers
776 views

Multiplicative inverse in $GF(2^8)$?

I know how to do multiplication over $GF(2^8)$. Logic is... ...
0
votes
2answers
147 views

Scrypt's maximum strength to increase entropy of lame passwords

The developers claim that a 6 letter long password hashed with 3.8 second's of scrypt would cost $900 to brute-force. If we use more cycles, how quickly will the brute force cost increase? What ...
0
votes
1answer
63 views

Authentication mechanism for low memory, low computing power device

I am looking for an authentication mechanism that works best with low memory, low computing power devices. I came across a paper "A Practical Zero-Knowledge Protocol Fitted to Security Microprocessor ...
0
votes
1answer
95 views

Is an elliptic curve over $\mathbb{F}_p$ order preserving for the points $(x,y) \in \mathbb{Z}_p$?

Let $E\colon y^2=x^3+ax+b$ be an elliptic curve, and consider its realisation over the finite field of prime order $p$: $E(\mathbb{F}_{p})$. Then if $0<a,b$ is the following true? $$\forall ...
0
votes
1answer
58 views

The real-life meaning of proving over a group that doesn't support the oracle?

If I proved a scheme's security under GDH assumption, in real-life, if this DDH oracle does exist, then it's good, but what about other side ? In real-life, if this DDH oracle doesn't exist, then ...
0
votes
2answers
89 views

Is the composition of collision resistant hash with non collision resistant hash a collision resistant hash?

Suppose $h_1$ is collision resistant, and $h_2$ isn't. Will $h(x)=h_2(h_1(x))$ always be collision resistant? [Edited:] the output of h2 must be uniformly distributed
0
votes
1answer
54 views

applying HKDF at both the client and the server

I have two keys (K1 and K2) at both the client and the server. I hope to use HKDF in both client and server side to concatenate the keys. I will use the same salt value at both the client ad the ...
0
votes
1answer
230 views

How to put the hash of a PDF file in the PDF file? [duplicate]

I know it sounds strange.. but, are there any ways in practice to put the hash of a PDF file in the PDF file? And after geting the hash in the PDF file - if someone would do a hash check of the PDF ...
0
votes
1answer
109 views

Hashing/encrypting an integer to produce an unique integer in the same range

I'm looking for a function or set of functions that can produce a pseudo-random permutation on an input set of arbitrary size. Given a set of $M$ values in range $0..M-1$, where $M$ is positive ...
0
votes
1answer
118 views

Is it possible to decrypt an RSA ciphertext with only $N$ and $e$?

Is it possible to perform RSA decryption if one only knows $N$ and $e$? Failing that, what is the maximum key length where brute-force is still practically feasible?
0
votes
1answer
155 views

I've got my private key compromised. How does CRL work?

How does certificate revocation list (CRL) work? How can I send a request to the CA to add my current private key to the CRL, so no one except me can add my certificate to the CRL? Related: - How can ...
0
votes
1answer
161 views

modfied man in the middle attack diffie hellman

I have been given a problem in preparation for my cryptography final that I'm not sure how to solve. It asks me to suppose a scenario where instead of where an attacker would intercept some message ...
0
votes
1answer
101 views

How to store keys for a cascading encryption?

What is the best way to implement a cascade encryption? I'm trying to figure out how to cipher a string (or message) using Serpent-Twofish-AES and then store the keys. I'll provide an explanation, ...
0
votes
1answer
85 views

What is the difference between exhaustive search and factorization in relationship to determining a key?

It seems to me an exhaustive search would simply try to use all the possible bit combinations of a key, while factorization is some mathematical formula for determining the key? When discussing the ...
0
votes
2answers
206 views

In Elgamal, the generator g is always quadratic non-residue modulo p where p is a safe prime and inverse of g can be also generator?

In Elgamal, the generator $g$ is always quadratic non-residue modulo $p$, where $p$ is a safe prime and the inverse of $g$ can also be generator? Can I prove it? I can't come up with it at all.
0
votes
1answer
248 views

openSSL ECDH private key size

When you are using a named curve like P-256 in openSSL, is there any standard key size for ECDH private key keys? If you look at the ec_key.c file in the openSSL ...
0
votes
1answer
171 views

Key space: Dense and sparse

I'm taking a cryptography class and I come across these terms dense and sparse key space allt he time. What do they mean? As far as I can I understand, dense key space means that there are more ...
0
votes
1answer
91 views

Quadratic Residues in identification setting

Suppose Alice has two primes $p$ and $q$ such that $p\equiv q \equiv 3 \pmod 4$. $n=p\cdot q$ is part of her certificate to identify her. A party say Bob, sends her a random quadratic residue ${}\bmod ...
0
votes
1answer
328 views

WIN LM Password Hashes (using John the ripper) [closed]

In a problem set, we've been asked to use John The Ripper to crack a list of Win LANMAN passwords. They are of the following form: 953A55E36AB85C0B9DA92C18555E42E1:0169295E0A6A6B35B2DD9932D10C1978 ...
0
votes
1answer
917 views

My encryption message system & question about security

I made this small tool for make & read easily an encrypted message without nothing to install, just a simple private key like a word or a couple of words to share. (Without say it directly of ...
0
votes
1answer
496 views

Attribute-based cryptography [closed]

I am trying to create a social network, in which I want to use attribute-based cryptography. One professor told me it is possible to do it only in J2EE, but he can barely code! Some friends of mine ...
0
votes
1answer
174 views

Is my understanding of CPA indistinguishability experiment correct?

Following are steps to conduct Chosen Plaintext Attack (CPA) indistinguishibility experiment $PrivK_\mathcal{A,E}^{eav}(n)$. $\mathcal{A}$ is the adversary $\mathcal{E}$ is the encryption scheme ...
0
votes
1answer
56 views

blinding a hash vs. sending the hash directly

So with blind signatures you have two parties - A and B. A has a message that they want B to sign so A creates a hash of their message, blinds it, and then sends it to B to sign. That, as I understand ...
0
votes
1answer
145 views

PKCS1 and blind RSA signatures

Wikipedia's article on RSA blind signatures says that you need to raise the message $m$ to the secret exponent $d$ modulo the public modulus $N$. Implicit within that, it seems to me, is that m needs ...
0
votes
2answers
117 views

Why do PKI schemes need security proofs? [closed]

When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed? Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol ...
0
votes
1answer
222 views

What is the relation between hash chaining and chosen prefix attack

I read that hash chaining can be used to prevent hash collisions, while the chosen prefix attack allows hash collisions for algorithms like MD5. How are they related? Does hash chaining prevent the ...
0
votes
1answer
260 views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
0
votes
1answer
127 views

Resources for basics of lattice crypto [closed]

I'm looking to fill in the gaps of my knowledge of lattices. Can anyone point me towards papers or books that introduce lattice crypto assuming a fairly solid math background? Mods: Feel free to ...
0
votes
1answer
87 views

Signature with appendix

I see sometimes signatures schemes with appendix. This is about signatures schemes in which the message is needed in the verification algorithm, that is, the ouput of the signature algorithm is of the ...

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