2
votes
0answers
106 views

Are there public $p$ and $q$ numbers for use in DSA?

There are many RFC documents giving large primes to use in Diffie-Hellman. However, I couldn't find standards on the $p$ and $q$ large primes used in the DSA signature scheme. This is proving to be a ...
2
votes
0answers
162 views

How can I construct a distinguisher given an inverter?

Let $ PRG: \{ 0, 1\}^n \rightarrow \{ 0, 1\}^{n+s}$ be a pseudo random generator and let $A$ be an inverter that runs in polynomial time, specifically: $\large \mathbb P_{d \leftarrow PRG(U_n)}[ A(d) ...
2
votes
0answers
110 views

How does use of HMAC affect hash function combiners?

In the comments of this question, Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions: $HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus HMAC_{H1}(k_1,m)...
2
votes
0answers
72 views

Any functioning system for interactive proof?

My problem is to outsource an array of data and ask the prover to sort the data. I am wonder if there is any working system out there that support interactive proof for the above computation? Or if ...
2
votes
0answers
230 views

Diffie-Hellman exchange

So for a Diffie-Hellman problem, I am given the prime $p$ for the Diffie-Hellman exchange. I am also given $g$, secret number for machine as $A$, secret number for station as $B$, a Diffie-Hellman ...
2
votes
0answers
68 views

Protocol/algorithms based on a variable-length input PRF

Are the proofs based on a PRF assumption still valid when using a variable-length input PRF ? The answer might be obvious, but I have a doubt.
2
votes
0answers
212 views

Infinite depth BLAKE2b tree hashing

In the BLAKE2 paper, the authors define Maximal depth (1 byte): an integer in [1, 255] (set to 255 if unlimited, and to 1 only in sequential mode) Node depth (1 byte): an integer in [0, 255] ...
2
votes
0answers
158 views

How many messages needs to be send to server to get AES key in Cache-timing Attack

I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on AES,...
2
votes
0answers
589 views

Question about modifying the MD5 plain text to cause a collision

I was trying to understand MD5 and got stuck with this question, its from Michael sipser's book on Information security Principles and Practice, 2nd edition The MD5 collision in Problem 25 is said ...
2
votes
0answers
33 views

Detail about reactive simulatability framework

I'm trying to understand the framework of reactive simulatability using *"PfWa2_00AsyncModel"* from this publication which is a tech report behind the paper A model for Asynchronous Reactive Systems ...
2
votes
0answers
322 views

How to perform benchmark of block/stream ciphers?

I would like to perform some benchmarking of different block and stream ciphers for general data (lossless and lossy data) encryption and decryption (with focus on power consumption). To get general ...
2
votes
0answers
182 views

Integer factorization based password authentication

After looking at this security issue at DjangoProject, I started to think in a password-based authentication that places the burden of PBKDF2 (or whatever is the hashing function) on the client. So I ...
2
votes
0answers
93 views

partial-domain permutation and strong assumption

Quoting "Verified Security of Redundancy-Free Encryption from Rabin and RSA", Chapter 2 (on page 4): OAEP was proved IND-CCA-secure by Fujisaki et al. [28] under the assumption that the underlying ...
2
votes
0answers
86 views

Could BREACH be used to determine an HTTPS URL?

I was reading this article and had a question.... http://arstechnica.com/security/2013/08/gone-in-30-seconds-new-attack-plucks-secrets-from-https-protected-pages/ As I understand it TLS/SSL work in ...
2
votes
0answers
169 views

Security of a 3-party key exchange protocol

I am trying to find attacks on a theoretical protocol or prove its security. An initiator wants to establish a shared key with a responder with help of a trusted server. We have the following roles: $...
2
votes
0answers
115 views

Jumblar: Using map locations as passwords

I had the idea of converting map locations into passwords. Basically Jumblar takes a hash of the user's location and stores this as a comment on the PGP network. The 'stored-hash'(Vague-Hash) ...
2
votes
0answers
97 views

BLS signatures in the G-valued Random Oracle Model

This paper on semi-generic algorithms considers "non-standard properties of the employed hash function". For BLS signatures whose main group is $G$, I'm curious what can be shown when the hash ...
2
votes
0answers
139 views

Ideal system for an encryption scheme

What is the ideal system for an encryption scheme? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an ...
2
votes
0answers
149 views

Is it possible to derive the midstate of a sha256 hash?

Let's say I have an unknown string with the known sha256-hash of it. I was wondering if it was possible to now calculate the sha256 of the concatenation of the unknown string and "abc". (In PHP: <...
2
votes
0answers
169 views

Complex Numbers on Elliptic Curves & Usage in Tate Pairing

I'm working with understanding the internals of the Tate Pairing. I was going through an example of the curve $E: y^2 = x^3 + 3x$ over $\mathbb{F_{11}}$. The author is showing the computation of $e(P,...
2
votes
0answers
127 views

How well analyzed are giant block length ciphers?

I have heard about ciphers that have a block length of 256 megabytes... That is huge. How well are they understood by the encryption community? I'm referring to PMC Ciphers. Has anyone used such a ...
2
votes
0answers
180 views

How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
2
votes
0answers
96 views

Relaxed trust criterion for mental poker server?

I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a ...
2
votes
0answers
83 views

Predicate Encryption supporting disjunctions

I am not sure if I missed some subtlety in the definition of Attribute Hiding found in this paper on Predicate Encryption, but isn't it possible to construct a scheme for Predicate Encryption ...
2
votes
0answers
270 views

One-time pad and perfect secrecy properties

I have a homework problem: Explain how to find $m_{0}$ and $c$ such that $P[c=c': k \leftarrow K, c' \leftarrow E(k, m_{0})] > 0$ where P is probability and k is chosen uniformly. I do not know ...
2
votes
0answers
155 views

How hard is a known prefix hash preimage attack?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
2
votes
0answers
99 views

Prevent/minimize replay attacks in public message board

Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
2
votes
0answers
258 views

Creating colliding x509 certificates: Crafting RSA moduli step

I am trying to generate 2 x509 certificates with the same signature but different values in the common name field, based on md5 collisions, as it was specified in this paper (page 7). Now I have ...
2
votes
0answers
222 views

elgamal based decryption mixnet

Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also. ...
2
votes
0answers
683 views

Determining the algorithm used to generate a digital signature

I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature. From the signed string, is it possible to find out what ...
2
votes
0answers
220 views

Transforming simplest protocol into a Sigma-protocol

I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
2
votes
0answers
111 views

Is this a valid real-time authentication scheme?

The scenario in Alice/Bob/Cindy terms: Alice approaches someone she doesn't know, but thinks is Bob, and asks for some secret information. Bob doesn't know and doesn't trust Alice, but Alice says she ...
2
votes
0answers
127 views

Computer appliance protocol

I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
2
votes
0answers
201 views

Structure of encrypted office files

I try to find out the structure of encrypted office files (I'd like to implement something like a carving tool for finding certain encrypted file types). I try to understand the Office Document ...
2
votes
0answers
359 views

How to properly format a PGP Message Block?

As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
2
votes
0answers
196 views

Setting protocol parameters to achieve concrete security

Background One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
2
votes
0answers
171 views

Security of stream cipher based on Matrix multiplication GF(256) with randomized padding

The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components: The keyed function $F_k:\{0,1\}^{8n}\...
1
vote
0answers
42 views

Are there any digital signatures valid for multiple pieces of data?

Are there any digital signature algorithms that can be used to produce signatures valid for multiple pieces of data? For example: Pick a private key $k_{private}$, which has public key $k_{public}$. ...
1
vote
0answers
33 views

How would low-precision Gaussian sampling impact the security of BLISS?

For digital signature, I implemented BLISS in my cryptographic suite, and wrote the Gaussian sampler based on Lattice Signatures and Bimodal Gaussians. But unlike the reference implementation and ...
1
vote
0answers
15 views

Unique decentralized ID systems

We are all familiar with the standard decentralized ID system, the web of trust, e.g. for PGP keys. However, normal web of trust systems are unable to guarantee uniqueness — there's no practical limit ...
1
vote
0answers
85 views

proving indistinguishability of joint distribution using hybrid argument

Using Hybrid Argument, I want to prove following equivalence: $$\{X,Y,Z\}\equiv \{X',Y',Z'\}$$ by proving following equivalences: $\{X,Y,Z\}\equiv \{X,Y,Z'\}$(1) $\{X,Y,Z'\}\equiv \{X,Y',Z'\}$(2) $\...
1
vote
0answers
25 views

Some Question about Security Proof of authenticated identity-based encryption

In authenticated identity-based encryption by Benn Lynn, in proof of security, I have a little difficulties in understanding. In key extraction queries,if attacker request for guessed ID, then B fails....
1
vote
0answers
65 views

Why security proof uses random oracles in identity-based encryption?

In identity-based encryption, users decrypt the ciphertext by using private keys. Without private key, no one will be able to decrypt.In security proofs like here, random oracles are used with the ...
1
vote
0answers
25 views

Secure Communication Protocol Design using oblivious transfer?

I have a problem I need to solve with the following scenario and I hope someone can help me find an approach or direction to start tackling it. Consider Alice as a sender who has $n$ strings which ...
1
vote
0answers
29 views

Authenticating a range of a ciphertext

I have some data that I CTR-AES-256 encrypt already. I am aware of ways to validate the integrity of the entire file (ie: a separate MAC of the plaintext, or encrypt then MAC, etc). But none of ...
1
vote
0answers
25 views

Anonymous Identity-based broadcast encryption use single common key or different keys

In identity-based broadcast encryption, suppose the broadcast ciphertext $(r_1,r_2,\dots,r_i,U,W,V)$ is sent to the receiver. In some cases, they use some function $f(x)=k-\prod_{i=1}^{t} (x-v_{i})$ ...
1
vote
0answers
28 views

Getting a key size of DSA/Elgamal certificate

I've tried to get a public key size of DSA/Elgamal PGP certificate. Using the Cleopatra I find out that there is actually two public keys - one with DSA with key ...
1
vote
0answers
25 views

Proof that two signatures are done with the same short bases

My question is regarding lattice based signatures. Each lattice can have multiple short (secret) bases. Is it possible to proof in zero knowledge that two signatures on a fixed lattice have been ...
1
vote
0answers
23 views

What is the exact algorithm and functions of the 4 way handshake?

I have to make a detailed diagram of the 4 way handshake and formulas for its functions so I need to know the exact process behind it. Like precisely what functions are used in it? I have been trying ...
1
vote
0answers
69 views

Feasible attacks on ECRSA cryptosystem

In ECRSA cryptosystem, I want to know the feasible attacks. For illustrations we have two prime $p$ and $q$ such that $p \equiv 2 \pmod 3$, $q \equiv 2 \pmod 3$ and generate key pair as follows: $$n = ...

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