3
votes
0answers
222 views

Secure Secret sharing

I'm trying to come up with a new way to do oblivious transfer that is faster and requires less computation than existing methods. The basis of my method is shamir secret sharing. Below is an example ...
3
votes
0answers
47 views

Can anyone explain how the modified r-adding walk works?

I was going through a paper titled “Accelerating Pollard's Rho Algorithm on Finite Fields” by Jung Hee Cheon et al. I understand the table(Ml) creation part of it, but after that I somehow fail to ...
3
votes
0answers
287 views

Pseudo-Hadamard transform, most significant bit

For clarification: The Pseudo-Hadamard transformation is a reversible transformation of a bit string that provides cryptographic diffusion. Splitting a bit string (with bit length of $2n$) into two ...
3
votes
0answers
64 views

space complexity of quantum collision search

Is there a known way to reduce the space complexity of quantum collision search beyond what is offered by the built-in time-space tradeoff, while keeping the time complexity significantly below what ...
3
votes
0answers
136 views

FHE over the integers - Is that paper's scheme known to be insecure against quantum adversaries?

I was reading the paper Fully Homomorphic Encryption over the Integers, and started wondering if there is a known quantum attack on their main scheme, because There is an efficient quantum attack ...
3
votes
0answers
135 views

Paper about this secure P2P idea?

Two or three years ago, I was reading something interesting, but then I lost the paper. The paper described building secure and fast P2P networks (not like tor or I2P). Unfortunately, I only remember ...
3
votes
0answers
183 views

Why does HMAC use two different keys?

Suppose $H$ is a hash function; why is $H(k||H(k||m))$ not secure? See this HMAC definition. In there, indeed two keys are used and the mac algorithm is $H(k_1 ||H(k_2 ||m))$ . Why don't we use $H(k||...
3
votes
0answers
127 views

What might be assumed about a PRF if the key has been chosen?

The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function $g:\{0,1\}^s\mapsto\{0,...
3
votes
0answers
154 views

Looking for a detailed example of proof by reduction

I'm looking for a very detailed example of proof by reduction. Say we have two or three protocols (that have been proven secure) and we construct a new protocol. We want to provide a proof of security ...
3
votes
0answers
336 views

Key expiration policy for 3DES / TDES / Triple DES

I have a system that signs plain text messages using a message authentication code (MAC) encrypted with 3-key Triple DES. The short message is used on connection to establish a session key, so it ...
3
votes
0answers
112 views

Is MITM possible after key exchange phase done successfully in RSA?

Is MITM attack theoretically possible after public/private key pair exchange is done successfully. Say Alice and Bob have genuine public keys of each other. Is MITM possible further during ...
3
votes
0answers
232 views

File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kind of keys: RSA public/private, AES ...
3
votes
0answers
72 views

How to generate initial vectors during DPA attack on stream cipher in real life?

I was trying to understand the procedure of the DPA attack on Stream cipher (like Mickey-128). I learned that, the attacker need to build hypothetical power consumption matrix with different initial ...
3
votes
0answers
119 views

How much plainext could be known without reducting security of RSA?

It is known, for example, that exposing 50% of most significant bits of RSA private exponent does not provide security risk (when a small public exponent it used). So how to qualify security ...
3
votes
0answers
229 views

Prove preimage resistance property

Let $ f : \{0,1\}^* \rightarrow \{0,1\}^n$ and $ g : \{0,1\}^* \rightarrow \{0,1\}^m$. $h$ is created by concatenate f and g: $ h : \{0,1\}^* \to \{0,1\}^{n+m}$ with $h(x) = f(x) || g(x)$. How do I ...
3
votes
0answers
171 views

On the Definition of a PRG and a CSPRG

I've been looking at the definition of a PRG, here. This is a broader notion than a cryptographically secure PRG ("CSPRG"), which is described here. I am realizing that I am very confused by this ...
3
votes
0answers
206 views

Secret sharing - no dealer, modifiable, verifiable

I need to find a secret sharing scheme with these properties: The scheme is set up by all participants, ie no single entity called the dealer The parameters of secret sharing need to be modifiable,...
3
votes
0answers
276 views

One-Time-Pad with key-reuse: Faster way of decrypting?

I know there are already of few questions about this and I'm working with the advices that were given but I still doubt my approach is the fastest, so I'd really appreciate if you helped me find a ...
3
votes
0answers
79 views

How do you distribute secret shares without knowing who to first distribute them to?

Figure 1 on page 1249 of the “Multiparty Computation Secure Against Continual Memory Leakage” paper shows $m$ committees are elected in step 1 and then later in step 3 are each given a secret share. ...
3
votes
0answers
143 views

When do I need to renew keys for Salsa20 or HMAC?

I currently have a system which uses two keys sourced from a single key subjected to HKDF. One key is used in the Salsa20 stream ...
3
votes
0answers
91 views

Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key?

In this paper, the authors construct an encryption scheme that is supposed to be resilient to tampering and leaking (as opposed to just leaking). Specifically this scheme: If you look at the ...
3
votes
0answers
118 views

What role plays Quantum Fourier Transformation in Shor's integer factorization algorithm?

I cannot seem to understand the role or goal of Quantum Fourier Transformation in Shor's integer factorization algorithm. Is it used to collapse all quantum states into one, in which it has a factor ...
3
votes
0answers
144 views

Designing a protocol to record attendance to lectures

Scenario: a class that is not mandatory. The teacher wants a protocol that will satisfy the following requirements: It must record each student's attendance. A student X should not be able to say ...
3
votes
0answers
129 views

Question about proof of knowledge defintion?

I am just reading the "soundness"-definition for proofs of knowledge by Bellare / Goldreich. A proof of knowledge is a proof between a prover $P$ and a verifier $V$. $P$ convinces $V$ to know a secret ...
3
votes
0answers
70 views

P-Complete hashes, hashing to a larger set

Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits). Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
3
votes
0answers
181 views

Does Keccak have an eTCR mode?

On page 7 of NIST's views on SHA-3's security requirements and Evaluation of attacks, I see that, at least at this point, NIST planned on offering SHA-3 having eTCR security (defined on page 3): ...
3
votes
0answers
430 views

RSA reencryption scheme

Is there such an algorithm that would allow to upgrade the encryption of a RSA-encrypted message without revealing the plaintext to the untrusted user? Basically, such an algorithm would probably be ...
2
votes
0answers
29 views

FIPS 186-4 seems to have an excessively complex q generation

So in DSA you have two primes - p and q. q is N bits long (let's assume 160 bits) and p is L bits long (let's assume 1024 bits). Here's what FIPS 186-4 says about generating the q parameter for DSA: ...
2
votes
0answers
40 views

How does Bluetooth pairing (SSP with numeric comparison) work?

I have a question concerning the pairing of two Bluetooth devices using Simple Secure Pairing with numeric comparison. The NIST document I am looking at states on page 14: Numeric Comparison was ...
2
votes
0answers
48 views

Avoiding doubled letters in encrypted text

I have an encrypted string based on an "alphabet" of 29 runes and access to successfully decrypted (runes->English) plaintext. Testing for a Vigenere cipher, I tried a Friedman attack (aka Kappa test, ...
2
votes
0answers
39 views

Why is a LCG not suitable for use in a cryptographic primitive?

Two's complement addition (and multiplication) are non-linear with respect to XOR and AND. This means that for bit vectors over $\mathbb{Z}_2$, the operation $a + x$ cannot be expressed as the matrix ...
2
votes
0answers
65 views

How do they avoid Zero Knowledge Proofs in the paper Priced Oblivious Transfer: How to sell Digital Goods?

I don't understand a part of the paper Priced Oblivious Transfer - How to Sell Digital Goods. Particularly, the authors avoid using zero knowledge proofs and in section 3.3 they explain how they do ...
2
votes
0answers
47 views

Proof of IND-q-CCA security

I have some questions about the paper Bounded CCA2-Secure Encryption (pdf). On page eight "3.2 Construction", the authors have done a black-box construction of an IND-q-CCA security schema and then ...
2
votes
0answers
24 views

What is bounded-retrieval model?

What is bounded-retrieval model in cryptography? How is it related (or apply) to leakage-resilient cryptography?
2
votes
0answers
60 views

Are analog quantum computers a threat to RSA and DLP?

We already know that D-WAVE's "quantum computers" can't really run the Shor's algorithm, because the way they're built doesn't qualify them as universal quantum computers. Now researchers actually ...
2
votes
0answers
52 views

Is the ring learning with errors problem still hard if the errors are drawn from some subspace?

Let $R=\mathbb{Z}_p[x]/x^n+1$ be the ring used in normal RLWE, which is linear space over $\mathbb{Z}_p$ with dimension of $n$, let $S$ be a linear subspace of $R$ which described by linear ...
2
votes
0answers
30 views

Boneh/Franklin Identity based encryption with Tate pairing

Boneh/Franklin developed an identity based encryption scheme based on the Weil Pairing. This algorithm has also been standardised in IEEE P1363.3 . I know that this algorithm can also be implemented ...
2
votes
0answers
82 views

Designing a secure protocol to avoid MITM?

Imagine that you are designing an online game, the framework consists of a player A, a game host H and a trusted central server S. The player A has a symmetric key KAS and id A that is known to ...
2
votes
0answers
208 views

The knife paradox?

In one of the hot forums of today on how to convince friends cryptography is good one of the arguments stated is the knife paradox, I was unable to find the answer on Google and my question is what is ...
2
votes
0answers
25 views

Security of randomized data dependant key schedules?

An example to demonstrate the point with two Feistel networks: Cipher A: \begin{align} roundkey = hash(key || counter)\\ roundkey = hash(key || roundkey)\\ left = left\oplus hash(roundkey || right)\\...
2
votes
0answers
37 views

Can I serve data for user without the ability to access them? Which functions for the user remain?

My Problem I want to serve sesible data for users as a webservice that is accessed by the user via the browser. Restrictions: I may not be able to technically acces the data of the user Data is ...
2
votes
0answers
48 views

Is this PRG secure?

$G$ is a safe PRG in range $\{0,1\}^n\rightarrow\{0,1\}^{n+1}$. Let us define $G'(S)=G(S\oplus G(S)_{1,...,n})$, s.t. $G(S)_{1,...,n}$ is the first n bits of $G(S)$. Is $G'(S)$ a secure PRG? ...
2
votes
0answers
30 views

Proving CCA security for scheme constructed from secure PRP

We have a $PRP : \{0,1\}^{3n} \rightarrow \{0,1\}^{3n}$ and encryption scheme constructed from this $PRP$. $E_k(x\|r\|0^n)$, where $r$ is randomly chosen from $\{0,1\}^n$ and $0^n$ is a block of ...
2
votes
0answers
54 views

Is there any symmetric key cipher (block or stream cipher) providing partial decryption?

symmetric key cipher (block or stream cipher) providing partial decryption of data at some points. Although the entire data has not been decrypted, the data decrypted to that specific point should be ...
2
votes
0answers
24 views

Creating an SPN cipher from ChaCha20 or Salsa20's double round function

Given that ChaCha20's building blocks have been also used to construct a hash function, can the double round function from either ChaCha20 or Salsa20 be used to construct a secure SP-network cipher? ...
2
votes
0answers
34 views

Some confusions about Repeated Doubling Algorithm?

The following repeated point doubling algorithm is taken from the book Guide to Elliptic Curve Cryptography by D. Hankerson, A. Menezes, and S. Vanstone on page#93. Clearly, this algorithm is ...
2
votes
0answers
53 views

CryptDB data re-encryption and onion layers

From the CryptDB paper , I understoond that the onion layers once decrypted are not re-encrypted. Only columns which are queried infrequently will be re-encrypted to higher onion layers. But if we ...
2
votes
0answers
44 views

Unpredictable value rotation

I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once ...
2
votes
0answers
79 views

Bitwise method of generating r for RSA-KEM

It seems that RSA-KEM has a very troublesome method of generating the secret $r$. It seems that the random value needs to be in the range $0 \le r \le {n - 1}$. Now most cryptographic environments ...
2
votes
0answers
38 views

RC6-like key schedule with 16-bit S-boxes

I am trying to figure out an encryption algorithm whose key schedule function seems to be similar to RC6. However, it seems to be creating S-Boxes using 16-bit integers instead of 32-bit ones. I have ...

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