2
votes
1answer
284 views

Public Key Encryption with forward secrecy

Is there a known non-trivial system with plausibly secure public key encryption where: 1. $\;\;$ the $\:$ time $\:$ function is efficiently computable 2. $\;\;$ [pubkey,privkey] $\:$ pairs are ...
2
votes
1answer
83 views

Distributed knowledge problem

I need a way to distribute knowledge among multiple parties - lets start with two. The idea is while the knowledge is originally created by one party I need to transform it into a situation where no ...
2
votes
1answer
561 views

How are the primes used to generate RSA keys?

I am confused about how keys in RSA asymmetric encryption are generated and what the implications for open communications are. Textbooks say the one-way function is merely two primes (with some ...
2
votes
1answer
113 views

Secure Remote Protocol - Are these 2 equations equivalent?

I'm implementing the Secure Remote Protocol that is specified to have this equation for the parameter S, the premaster secret. ...
2
votes
1answer
224 views

Shannon entropy calculation: is $H(A|R·A) = H(A)$?

Suppose I generate a random $m×m$ matrix $R$, where each of its elements belongs to $\mathbb Z_n$. I ensure that $R$ is invertible in $\mathbb Z_n^{m×m}$. Now I take a non-random $m×m$ ...
2
votes
1answer
252 views

synchronization of counters in HOTP

How is synchronization of counter values achieved in the HOTP protocol? As I understand it, the server increments its counter value only if a match (of the OTP value) is found. What happens at ...
2
votes
2answers
575 views

DES Crack simulation

I wish to simulate an implementation of a DES Cracker using verilog. But every paper I read give only abstract hints but no concrete steps or how really to go about it. How is it usually done? For ...
2
votes
2answers
244 views

AESManaged Trade Compliance Issue in United States

I am currently using AESManaged encryption for my silverlight application. Does AESManaged encryption have a severe trade compliance issue in Bureau of Industry and Security in terms of shipping the ...
2
votes
1answer
1k views

Cryptanalysis Affine Cipher: Brute-Force Search Vs. Meet-in-the-middle

Affine Cipher: $Enc(x) = (ax + b) \mod m$ $Dec(x) = a^{-1}(x-b) \mod m$ For a brute-force key search, we need to do $a \cdot b$ encryptions in the worst case. For a meet-in-the-middle attack, how ...
2
votes
2answers
599 views

Is there an effective way for public key generation in homomorphic encryption schemes?

Is there any way to effectively generate valid distributed public key in schemes like ElGamal or Benaloh for a number of participants? There's no need in private keys since there's no intent to ...
2
votes
2answers
47 views

Research for video game: Novice cryptography concepts

I'm making a video game which has some basic cryptography as a main base for puzzle design. I'm hoping players will get great puzzle challenge and learn a few cryptography concepts through playing the ...
2
votes
1answer
53 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
67 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
51 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
39 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
1answer
21 views

What does CMS standard mean by “initial input to the message digest”

I'm really grinding my teeth against digest calculation explanation in the CMS standard. Let's consider the case when the signedAttrs are present. The first ...
2
votes
1answer
41 views

What is the viability of a hybrid vigenere cipher?

So a vigenere cipher's main weakness is that you can use frequency analysis on each alternated alphabet, and thus crack the cipher with relative ease... But that implies that you know what the ...
2
votes
1answer
57 views

AES-256 add round key how

Can anyone explain to me (or send a link to somewhere) how round keys are added in AES-256? I understand that the round keys is added to the state matrix for each round and how XOR works. But since ...
2
votes
1answer
125 views

MiTM on RSA public key encryption

a) Alice just generated a new pair of public and private RSA keys (pkA , skA ) = ((N, e), d) and would like to start a private conversation with Bob. How can Alice interact with Bob and exchange a ...
2
votes
1answer
77 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
106 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
59 views

Is there short period in AES 128 key schedule?

I am wondering if for some particular keys the AES 128 key schedule lead to a periodic pattern for the round keys. The key schedule is only 10 rounds, but I am also wondering in the general case where ...
2
votes
1answer
28 views

NORX duplex padding

MonkeyDuplex constructions defined by Keccak authors has padding in every duplex block. Why only last duplex block is padded in NORX? Is it because NORX has domain separation, or simply because ...
2
votes
1answer
49 views

RSA Optimal Asymmetric Encryption Padding Beginner

I'm new to the OAEP scheme. I learn it from the Wikipedia page. Link The page does not explain a proper setup for of the system. So I'm not sure if the output of the padding scheme which contains ...
2
votes
1answer
38 views

Probabilistic RSA, IND CPA

Suppose we have classic RSA scheme. Let $n=pq$, $e$ public, $d$ secret. Then message(M), not empty(not 0), is encrypted by choosing random $r$ and computing $A=(r^e)^e$ and $B=(Mr)^e$ $(A,B)$ is ...
2
votes
1answer
30 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
63 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
74 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 ...
2
votes
3answers
127 views

Memory hard key derivation (password hash) using AES encryption

I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt (and I am not trying to compete with the likes of scrypt). My ...
2
votes
1answer
110 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
41 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
94 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
43 views

Is it secure to use ciphertext feedback with RC4?

Consider the following modification of RC4 to give some "ciphertext feedback" ...
2
votes
2answers
59 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
33 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
65 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
79 views

How to build a difference distribution table?

i am studying about differential cryptanalysis, and found one metric to measure the resistance of a sbox to it, but to use it, it is necessary to build a difference distribution table, like the one in ...
2
votes
1answer
60 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
52 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: ...
2
votes
1answer
47 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
39 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
60 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
72 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
1answer
160 views

RSA 1024 bit forge a new matching signature from a chosen message

I have an RSA signature scheme with 1024-bit key where I know the following: Public modulus $N$ Public exponent $e=3$ A lot of signatures Summary: To compute a signature, an MD5 hash is ...
2
votes
1answer
74 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?
2
votes
1answer
30 views

What are the number of output bits of the internal function F used in BPS algorithm?

In the BPS specification document it says We denote by f the number of output bits of the internal function F What is this if the internal function is AES? Would it be the block size (e.g. 128)? ...
2
votes
1answer
154 views

Forward-secure static-ephemeral ECDH key agreement protocol

The question is whether the following simple key agreement protocol design has good security properties, and how it can or should be improved. Assumptions Alice is a persistent entity with a static ...
2
votes
1answer
32 views

Is it not secure if we use weak passwords to protect exported PKCS #12 files with private keys?

Consider a practical scenario as described in Microsoft's Expand Export a Certificate with the Private Key. We can see a certificate with private key can be exported as a PKCS #12 file, where the ...
2
votes
1answer
50 views

Encryption on the cloud with versioning

Can file-versioning, which is available for instance in Dropdox, weaken the security of encrypted files if someone is able to see two or more snapshots of the ciphertext at different times? To be ...

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