8
votes
1answer
965 views

Bleichenbacher 1998 “Million message attack” on RSA

I have been reading Bleichenbacher's 1998 paper on a forged message attack on RSA. The paper assumes access to an Oracle that takes a ciphertext $c$ and will check the decrypted text for valid PKCS #1 ...
6
votes
1answer
226 views

Looking For Additively Homomorphic Encryption

I have a construction that requires as primitive an Additively Homomorphic Encryption scheme that does not rely on hidden group order, meaning I can't use Paillier. I now have two different ...
5
votes
1answer
73 views

Hard-core predicates: should the adversary be given $1^n$?

In most (all?) classical sources such as the book of Goldreich (2001), hard-core predicated are defined thus: A polynomial-time computable predicate $b : \{0,1\}^* \to \{0,1\}$ is a hard-core of a ...
5
votes
1answer
246 views

Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...
4
votes
1answer
588 views

Understanding elliptic curve encryption

I'm having a hard time understanding the elliptic curve encryption. One thing thing I don't understand is listing all the points on the curve mod p. Suppose I have the following elliptic curve: $y^2 = ...
4
votes
1answer
231 views

AES-CTR with ephemeral keys vs IV

Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret $S$. Then, A and B want to use AES-CTR for the communication, which leaves us with several ...
3
votes
1answer
38 views

Source for PKCS#11 Header Files

Is there a known authoritative source for the ANSI C header files for PKCS#11 Cryptoki? Specifically, I am having trouble locating pkcs11.h, pkcs11t.h, and pkcs11f.h for v2.30 and v2.40. Are there ...
3
votes
1answer
169 views

Proving the existence of a pseudorandom function

I've been reading the Introduction to Modern Cryptography book by Katz and Lindell as part of my own learning and have come across this exercise which I am not sure how to approach. The exercise is: ...
3
votes
1answer
83 views

Build set with PKI from reliable broadcast / random beacon

I am trying to build a protocol (or find an existing one) for creating a set $S_2$ with PKI from a set of parties $S_1$ that initially does not know anything about the other parties. We assume ...
3
votes
1answer
195 views

Measure ECC key size

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
2
votes
1answer
25 views

Why should the input value on a DPA attack be non-constant?

I actually was wondering if anyone could help me out with the following problem: Let's assume we are attacking the first SubBytes() operation on AES with the help ...
2
votes
1answer
56 views

EC: Why does $h>200$ need to hold?

The class number of the principal order belonging to the endomorphism ring of E SHOULD be at least 200. From TR-03111 (pdf page 15). This value commonly is referred to as $h$. So my ...
2
votes
1answer
113 views

Is this variant of SRP useful?

I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need ...
2
votes
1answer
85 views

Image sharing without data overhead

The idea is to share n images among n persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares sent ...
2
votes
1answer
70 views

How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow ...
2
votes
1answer
175 views

Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
2
votes
1answer
401 views

AES Affine Transformation in $GF(2^4)$

in $GF(2^8)$ the AES affine transformation is defined as \begin{equation*} b( x ) = ( x^7 + x^6 + x^2 + x ) + a ( x )( x^7 + x^6 + x^5 + x^4 + 1) mod (x^8 + 1) \end{equation*} where the polynom $( x^7 ...
2
votes
1answer
86 views

Comparing n-multiple amount of merkle trees?

I would like to know what best steps are there in finding differences between a high order amount of merkle tree's or if a better associative structure should be used. I ask this questions because ...
2
votes
1answer
198 views

Is this ECC encryption key sharing method okay?

Is this encryption key sharing okay to use? Or is much better to use ECIES? $G$ = base point $a$ = Alice’s private key $b$ = Bob’s private key $A = aG$ = Alice’s public key $B = bG$ = Bob’s public ...
2
votes
1answer
186 views

Why do we need to hash both the message and the $h$ value in ElGamal signature?

The professor left us a question on ElGamal signatures: Given the hash function $H$ and message $M$, choose a random $r$ and compute $h=g^r$ and $H(M||h)$. Show that, if $H(M)$ is used instead of ...
1
vote
1answer
25 views

Pseudo Random Function

The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function. i.e. The key-ed function family $\{F_k\}$ is PRF ...
1
vote
1answer
43 views

How is wpa2 authentication structured

I would like to understand the cryptography behind Wpa2. As far as I know, there are 4 messages on the 4-way handshake and three of them are values concatenated with hashes. First, I am trying to ...
1
vote
1answer
33 views

Determine if encryption is safe against CPA

The following encryption scheme encrypts each block of length $n$ of the plaintext separately: $c_i = k_1 \oplus F(k_2 \oplus p_i)$ Where $F$ is a strong pseudo-random permutation (i.e. it is easy ...
0
votes
0answers
71 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 ...
0
votes
0answers
26 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
68 views

Self-Convergent Hashing

What is the name of an algorithm that hashes its result as an embed of larger set of data that results back to the hash? For instance where f(x) is the hashed result and x is the dataset, and ...
0
votes
0answers
46 views

Is there a practical succinct interactive argument for fortress draws in chess endgames?

(In theory, it is known that collision-resistant hashing suffices for the type of protocol that I'm asking about: page 3.) Is there a known practical candidate protocol for succinctly (and ...
0
votes
0answers
38 views

Hard problems in composite order group even when factorization is known

Composite discrete log problem has been proved to be reducible to hardness of factorization and discrete log on the prime factor groups. Are there any problems apart from that in composite order ...
0
votes
0answers
40 views

Size of Messages Exchanged by PRV and VER for Schnorr Protocol

In this file Elliptic Curve Based Zero Knowledge Proofs and Their Applicability on Resource Constrained Devices I don't understand the Table 6 (Table 6: Size of Messages Exchanged by the Prover(PRV) ...
0
votes
0answers
58 views

Advantages of using intermediate hash over full hash in digital signature application

Description of intermediate hashes Intermediate (or partial) hashes are canonical forms of digest state that can be transferred from one hash implementation to another, so that the other, limited ...
0
votes
0answers
164 views

RSA and ECDSA Certificate Sizes

Is there a table (or a whitepaper from official sources) that compares the size of X509 certificates generated with RSA (starting from 1024 bits) and ECDSA (starting from 160 bits) ? Thanks for the ...
0
votes
0answers
65 views

What is a proof of data possession that accounts for fake mirrors?

Alice pays Bob $5/month to host a gigantic file for her. She wants to occasionally verify that Bob is actually hosting the file. To do this, she selects random blocks from the file, and ...
0
votes
0answers
62 views

What are the consequences of not checking the server mac in a TLS connection?

The context for this question (it's quite involved) can be found in this document: https://docs.google.com/file/d/0B15itpMWb2ztWTJrYTgzX204OVU However, I want to make it clear that you don't have to ...
0
votes
0answers
83 views

Looking for crypto with derived keys?

I am looking for cryptographic algorithm or combination of them. Basically I need an algorithm, which can generate private key and for this key can be computed multiple keys based on some seed. So a ...
0
votes
0answers
73 views

Can you determine an unknown value when it is combined with a known value and you are given the resulting hash?

Say I have a string that I want to keep hidden. You can then enter a known string which is added to the end of the hidden string and you are given the sha256 hash of the combined string. If you were ...
0
votes
0answers
38 views

Locally Dedcodable Codes and Private Information Retrieval

Does anyone know about Locally Decodable Codes (LDCs)? It seems the private information retrieval schemes that based on LDCs are computationally efficent (answer a query without processing the whole ...
0
votes
0answers
88 views

Any field in a PKI certificate where some text info can be stored?

I want to store 5-10 lines of Text Info in a PKI Certificate. All I want is that when using common tools like openssl command line or certutil from Microsoft, this text info should be displayed as is. ...
0
votes
0answers
162 views

m ∈ Zn \Z*n, RSA works but not secure

If you happen happen to have a message m ∈ Zn \ Z*n, RSA works but not secure. How likely is it going to happen? |n|=1024 bits |p| = 512 bits |q| = 512 bits.
0
votes
0answers
134 views

Going Blind, Group or Ring?

I have several problems approaching the following problem: Let's assume that we have Alice, Bob and Cathy. Alice wants to present a message to Cathy, showing her that someone else has signed it (Bob), ...
0
votes
0answers
86 views

Question Error Correcting Codes

Let $C$ be a code over the finite field $GF(2)$ with generator matrix $G$ and parity matrix $H$. Let $e+C=C'$ be a coset of code $C$. Let $S$ be a non-singular matrix and $H'=H\times S$. Finally, let ...
0
votes
0answers
122 views

So what is quantum cryptography anyway?

I am having difficulty understanding quantum cryptography concepts. I've searched the internet and watched some videos on youtube explaining the topic, but it is still hard to understand how it works. ...
0
votes
0answers
36 views

Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
0
votes
0answers
179 views

If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
0
votes
0answers
243 views

Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
0
votes
0answers
96 views

Example of CL PKC

I am trying to solve the example of algorithms of Certificateless Signature by manually and solving the mathematics of Algorithms but not succeed while doing mathematical calculations. Please ...
0
votes
0answers
77 views

hybrid PKE scheme CCA2 insecurity

I'm reading a paper here say: As we know, in hybrid PKE schemes XOR alone cannot perfectly hide challenge bit to the CCA2 adversary The author does not define hybrid PKE schemes. What is ...
0
votes
0answers
183 views

How to safely sign a 6 characters String?

I have to decide, whether a document, which I am given, was correctly signed by a private key. my Ideas is to sign the document id using RSA with the private key and to print the following onto the ...
-1
votes
0answers
44 views

“AND” concatenation of two secure PRGs

Let $G: \ K \rightarrow \{0,1\}^n$ be a secure PRG. Define $G'(k_1,k_2)=G(k_1)\wedge G(k_2)$ where $\wedge$ is the bit-wise AND function. Consider the following ...
-1
votes
0answers
26 views

How to calculate 16x16 SBox and InvSBox in AES Encryption?

As far as I know, $GF(2^8)$ and its multiplicative inverse are used to generate the 16×16 SBox and InvSBox in AES Encryption [or maybe I am wrong]. Can anyone please explain me how to generate this? ...
-1
votes
0answers
16 views

Total Cost of 2F Authenticator

what cost is required for implementing google 2F Authentication? Is it all free or any server related cost is required. It is appreciable to provide response earlier

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