2
votes
1answer
58 views

How can I show RSA OAEP IND-CPA secure

How can I show, that RSA with OAEP is IND-CPA secure by using G,H one way function?
2
votes
1answer
68 views

Understanding the Hidden Subgroup Problem specific to Integer Factorization

I've been reading about the Hidden Subgroup Problem (HSP), specifically trying to understand how it is related to the integer factorization problem. I've read What exactly is the impact of the hidden ...
2
votes
1answer
33 views

Can (EC)DH keys be used as the signed content in X.509 certificates?

From Wikipedia's article on ECDH: The public keys are either static (and trusted, say via a certificate)… Also see this question on this very site. These indicate to me that a certificate (...
2
votes
1answer
47 views

reconstructing data on a noisy channel?

I have an interesting situation where I have a block cipher and a noisy channel. The interesting thing is that I happen to know much about the data. The cipher is a balanced Feistel network, and for ...
2
votes
1answer
208 views

Client Puzzles and HMAC

I'm learning about client puzzles for DoS (Denial of Services) Protection, and I came across this question. For each request, the server sends the client a freshly generated random challenge r and ...
2
votes
1answer
61 views

Is it OK to reseed a Deterministic Random Bit Generator from itself?

I want a deterministic PRNG for simulation purposes, and I don't want to have to worry about spurious correlations like those the DMCT is designed to protect the Mersenne Twister against. So even ...
2
votes
1answer
64 views

Distinguishing two sets of pseudorandom values when their keys differ by one

Suppose we use a pseudorandom function $PRF$ and a random key $k$ to generate a set of pseudorandom values: $\forall i, 1\leq i \leq n: w_i=PRF(k,i)$ Now, consider instead of picking a fresh key, ...
2
votes
1answer
33 views

Are timing attacks exploitable if each key is used only once?

Suppose that one performs (for example) AES-GCM encryption and decryption using an algorithm that is vulnerable to timing attacks, but each key is used only once. Is it still possible to perform a ...
2
votes
1answer
58 views

Practicality of codebook in current-day secret communications

Codebook appears, if I don't err, to be an antiquitated topic rarely touched upon in discussions of modern cryptography. Couldn't codebook nonetheless be of high practical utility and even be ...
2
votes
1answer
64 views

Can gnupg master key decrypt something encrypted with subkey?

When creating gpg subkeys, the master key signs and certifies that a subkey belongs to that master. That's ok, but, can master key decrypt something encrypted by a subkey? I guess no, but I want to be ...
2
votes
1answer
69 views

Understanding Diffie-Hellman - Choosing a bad g

I am taking a class on Cryptology, and I'm having a hard time understanding the potential pitfalls of Diffie-Hellman. Specifically, the professor gave the following problem: Alice and Bob want to ...
2
votes
1answer
48 views

finding the basis of a kernel in a lattice

Given a parity check matrix $A$ we define the $q$-ary lattice $$\Lambda(A) = \{x \in \mathbb Z^m\;:\;Ax\equiv0\pmod q\}$$ How to find the basis of the lattice and how to find its hermite normal form?
2
votes
1answer
37 views

I am trying to implement TLS v1.1 {3,1} but get alert 70 on hellomessage to goolge

I am trying to implement TLS on top of the winsock api's from windows. I am using port 443 and have created a socket. I have sent this message in decimal. ...
2
votes
1answer
118 views

Block cipher not resistant to collisions

If we have the following block cipher, $E(k,m)$, which is a permutation, why is $f_2 (x,y)$ not collision resistant? $$f_2(x, y) = E(x, x \oplus y)$$
2
votes
1answer
113 views

Elliptic curve ElGamal with homomorphic mapping

I am interested in ElGamal due to the fact that you can achieve some degree of homomorphic properties. I became interested in applying ElGamal to elliptic curves, and found this other question with an ...
2
votes
1answer
62 views

Proving property of Modified Rabin Signature

I'm trying to prove one of the properties of the “Modified Rabin Signature Scheme”: If $gcd(x, n) = 1$, then $x^{\frac{(p−1)(q−1)}{2}} \equiv 1 \pmod n$ This is what I’ve got so far… Proof Let ...
2
votes
1answer
77 views

Preserving Confidentiality and Integrity in a Public channel

Let's say I've got two people that are trying to talk in a public channel $A$ and $B$ and they want to preserve their confidentiality and integrity. Which cryptographic algorithm would they want to ...
2
votes
1answer
75 views

Does the time to evaluate a hash function depend on the function input size?

Suppose we have a (variable-input size) hash function modeled as a random oracle. Can it be consistent to say that the time to evaluate this function depends on the input size ?
2
votes
1answer
91 views

Can I shorten the large ECDSA public key output file from OpenSSL?

I am working in a very bandwidth restricted environment where I from time to time have the need to distribute public keys. The distribution happens in bit format, so there is no need for encoding, at ...
2
votes
1answer
60 views

How to test an implementation of a homomorphic scheme?

I want to implement the following homomorphic encryption scheme from On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption by Lopez-Alt et al. I use C++ and I want ...
2
votes
2answers
81 views

Is the security of an HMAC equally important as the security of the cipher itself?

I'm a little unclear on how hash based MAC works... So I would like to know, is the security of your hash function as important as the security of the overall cipher? Basically, if you can crack the ...
2
votes
1answer
63 views

Is (1 bit HW signal) XOR (8 bits PRNG output) sufficient for a HWRNG?

This is really a follow up question to a comment made regarding How to roll a HWRNG In the situation of whitening a hardware generated random bit stream, "XORing the two bitstreams should be fine ...
2
votes
1answer
66 views

How is the ciphertext labeled with a set of attributes in Key-Policy Attribute-based Encryption (KP-ABE)

My question is about Key-Policy ABE (KP-ABE). What does it mean when a "Ciphertext is Labeled with set of attribute"? How is it labeled?
2
votes
1answer
86 views

Attack on textbook RSA with small messages

We learned in class that if Alice wants to send a small message $m$, such that $m < N^{\frac{1}{e}}$, so we can break the system using $e$-th square of $m^e$. But what if Alice knows this flaw and ...
2
votes
1answer
60 views

NMaster key from n secret key

I have to derive master key from N secret key. With the help of master key, i can collect all the secret keys which is used to derive master key. key1, key2,..keyN ==> single master key and single ...
2
votes
1answer
111 views

Message security and also program copy detection

Imagine I have client and server running on different machines, each as a separate software. I want to ensure: message authenticity, integrity and confidentiality at least of messages coming from ...
2
votes
1answer
163 views

Modular Arithmetic in RSA

Consider the following the following RSA public key $pk = (N, e) = (1457, 1307)$. (a) Knowing that $187^2 \equiv 1 \pmod {1457}$ find the factorization of $N$. (b) Given the factorization of $N$ ...
2
votes
1answer
70 views

Implicit authentication aritcle

First, I want to know what is the logarithm used in the following system of equations (from the paper Flexible and Robust Privacy-Preserving Implicit Authentication - Domingo-Ferrer, Wu, Blanco-...
2
votes
1answer
35 views

How to force non-negative int64_t output for blowfish encryption with int32_t input?

I would like to encrypt a series of small integers one by one. The range of them is about 0~10^8. The output must be non-negative int64_t integers. Since Blowfish is 64-bit cipher, I prefer to use it ...
2
votes
1answer
81 views

Is this MAC scheme secure?

Say we have a computationally secure Message Authentication Code scheme (Gen, Tag, Ver). Let $Tag'_k(m):=$ first half bits of $Tag_k(m)$. Let's assume the range of tags is $n$bits. Is (Gen, Tag', ...
2
votes
1answer
123 views

Key Derivation Function (KDF): Can a key derived from KDF be considered as a secure key?

Consider a case where we have a master key MS that is used in pseudo-random function to generate a set of pseudo-random values. Then we use key derivation function to derive a key from each of pseudo-...
2
votes
1answer
114 views

State of the art techniques for Anonymous Authentication?

What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; ...
2
votes
1answer
43 views

Is a hash “reset sequence” possible?

Is there such thing as "hash reset sequence" that brings hash to the same known state? A hash function has a state. In MD5 and others vulnerable to the length extension attack, the attack works by ...
2
votes
1answer
131 views

Is it an overkill to add external integrity check to the AES-GCM encoding?

There is a java library for android which implements integrity checking to predefined encrypting mode(which can be found here). Short class description from author page to avoid further questions ...
2
votes
1answer
228 views

Confused with 128-bits AES round numbers

The key size used for an AES cipher specifies the number of repetitions of transformation rounds that convert the input, called the plaintext, into the final output, called the ciphertext. The number ...
2
votes
2answers
85 views

Easy hash function collision

I'm designing a cryptography-breaking assignment for a college-level introductory security course, and I'm looking for a hash function which is reasonably easy (but not too easy) to generate ...
2
votes
1answer
54 views

Are private and public key sizes of Elliptic curve related?

I'm new to elliptic curve cryptography. I just want to know in the case where I take a random number (private key) and find its associated public key, does the size of the public key depends upon ...
2
votes
1answer
42 views

Is there a single-use signature scheme, where a second use of the private key discloses it to the world?

With ECDSA (and possibly DSA too) I'm aware that if the same value for $k$ is used with the same private key $D_A$ to sign two different messages, then anyone possessing the two messages $m_0$ and $...
2
votes
2answers
116 views

How do you communicate the hash function used with RSA signing?

When it comes to RSA signing, I understand why you need to hash the data before signing it, but don't you need to communicate what hash algorithm you use to whoever will need to verify the signature? ...
2
votes
1answer
74 views

Can the salting function complexity improve the hash robustness?

I'm quite novice in security, and all examples I saw seem to salt the password by concatenating it, or by applying a simple binary OR or XOR. So the hash is based on "salt + password", "salt | ...
2
votes
1answer
71 views

Multiplication in elliptical curve cryptography

I'm practising for a cryptography test and came across this question: Let us assume that for a specific elliptic curve the formulas for the computation of $(x_3, y_3)=R+S$ are given by: $X_3=...
2
votes
1answer
50 views

Symmetric-like cyphers with several steps

Are there any good symmetric-ish cyphers that involve three or more steps with independent key material for each step? Formally, there should be a function $K(s)$ that returns a tuple $(k_1,..,k_n)$ ...
2
votes
1answer
72 views

Does Mersenne Twister generate homogeneous numbers?

I have been assigned to generate 15000+ homogeneous and uniform random numbers for a work. I have been searching if Mersenne Twister generate homogeneous distribution of numbers but I don't find ...
2
votes
1answer
41 views

Proving the security of a one-way function with partially known input

Let's say we have a construction like in this question: We have a OWF $h(.)$, a secret salt TXT, and a counter starting at 1, and we compute ...
2
votes
1answer
62 views

Weaknesses of RFC6628

In RFC6628 section 2.2, they say: w = The password remembered by the user. W = The password verifier registered in the ...
2
votes
1answer
71 views

Inverting One-Way Functions

One of the conditions that a one-way function has to satisfy is the following: $$Pr[A(f(x))\in f^{-1}(f(x))] \leq negl(n)$$ Now, suppose that we have the following function that's not one way: $$f(x)...
2
votes
1answer
77 views

Secret only known on consensus

Does a method exist where a secret is generated so that is is unknown until 3 or more people (predetermined) reach consensus that it should be revealed?
2
votes
2answers
115 views

How does perfect hash function works?

According to wikipedia, a perfect hash function is a hash function that uses algorithms that has a certain random aspect to their logic. It is suppose to be collision-free. However due to the pigeon ...
2
votes
2answers
205 views

Is my protocol that uses hybrid cryptography and AES-GCM secure?

I'm having a lot of trouble trying to understand how to implement AES-GCM. My usecase: Person A sent me a file with a gauranteed unique name. I want to be assured it was from person A, and that no ...
2
votes
1answer
111 views

Why is the tweak length 64bit in BPS FPE algorithm?

In the algorithm for BPS Format Preserving Encryption Is this tweak always the same length (64bit)? Why did they choose the length 64bit for the tweak?

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