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0answers
71 views

In DGHV FHE, why noise $r$ can be in $(-2^{\rho'}, 0)$?

"Fully Homomorphic Encryption over the Integer" described a simple FHE scheme based on the GACD assumption. Its encryption function (on page 6) has the form $c \leftarrow (m + 2r + 2*\sum_{i \in S} ...
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0answers
96 views

CPA-security proof of “l-padded RSA” encryption scheme

The 10.9 exercise from the Katz-Lindell textbook creates a lot of confusion, let me state it here. Consider the following experiment for an algorithm $A$ and a function $l$ with $l(n) \leq 2n-2$ for ...
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0answers
120 views

Envelope Encryption with asymmetric keys vs KMS

In Envelope encryption a symmetric secret key is used to sign the data and then another key is used to encrypt the secret to produce an encrypted secret key. The encrypted messages is packaged with ...
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0answers
93 views

Why is there no 'ECDSA' version of 'DHE-RSA-CHACHA20-POLY1305'?

So I was just checking my TLS cipherlist and noticed that there was a 'DSS' / DSA / ECDSA version of every ...
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0answers
128 views

For each of the following modifications to the Merkle-Damgard transform, determine whether the result is collision resistant or not

$(a)$ Modify the construction so that the input length is not included at all (i.e., output $z_B$ and not $z_{B+1}=h^s(z_B||L)$). $(b)$ Modify the construction so that instead of outputting $z=h^s(z_B|...
1
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0answers
62 views

Question about OR operation in fully homomorphic encryption

This page (which won't let me post a comment, sadly!) describes how the original FHE paper by Craig Gentry describes FHE. (Other references to this stuff can be found on this question.) It mentions ...
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0answers
131 views

Example describing Baek and Zheng’s threshold identity-based decryption scheme

I am trying to work through an example of Baek and Zheng’s “threshold identity-based decryption scheme” and I tried a lot to solve this, but somewhere I’m doing something wrong. I hope someone can ...
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0answers
381 views

How to calculate the avalanche effect in aes-256?

I am a beginner in cryptography. I'm testing AES-128 bit key, AES-256 bit key, and Camellia-256 bit key. I'm using AES-256, 9 character salt, CBC mode, PKCS #5 padding, and the ciphertext using ...
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0answers
67 views

Understanding a faulty Needam-Schroeder protocol

Give this mutual-authentication protocol (along with the attack) in which Alice wants to communicate with Bob, I can't understand how the attack works. A chooses $N$ (nonce) and sends to C (trusted ...
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0answers
87 views

How do we generate AES S-BOX?

I am new to AES and I am too much confused about the generation of S-box in AES. I don't have any idea of $GF(2)^8$ field and how the things are happening around. Please answer this question with a ...
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0answers
323 views

What are the problems of IKEv1 aggressive mode (compared to IKEv1 main mode or IKEv2)?

I would like to seek confirmation/clarification of the following statements about IKE: IKEv1 aggressive mode is supposed to be “insecure” if used with PSK. But as far as I can see, correct (or more ...
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0answers
58 views

FFX Encryption over alphabet of arbitrary radix

I understand how standard numeric FPE using a halved string in cycled Feistel networks is constructed and operates. I then read the paper regarding FFX encryption which should allow for any non-binary ...
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0answers
85 views

Prove that certain amount of data was stored

I'm looking for a way to prove that a certain amount of data was stored, through some easily verifiable piece of information. Similarly to how proof-of-work can prove through a hash that a certain ...
1
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0answers
54 views

What consequences do the plaintext space size has on the performances in the BGV scheme?

In the BGV paper [1], the authors say in §5.4 that you can have $\mathbb{Z}_p$ as plaintext size with a large $p$. What is the impact of the size of $p$ on the ciphertext size and computational work ...
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0answers
74 views

ElGamal signatures systems

Let $p$ prime number $q/p-1$ prime and $g\in (Z/pZ)^*$ element of order $q$.Also $a\in \{1,...,q-1\}$ the private key and $y\equiv g^a\pmod p$ the correspoding public key.For each of the following ...
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0answers
116 views

CPA-security of a pseudorandom permutation encryption scheme

Let $F$ be a pseudorandom permutation, and define a fixed-length encryption scheme $(Gen, Enc, Dec)$ as follows: on input $m \in$ $\{0,1\}^{n/2}$ and key $k \in \{0,1\}^n$, algorithm Enc chooses a ...
1
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0answers
47 views

One-Time-Signature based codes

I'm trying to understand the sentence in bold, in the follow paragraph of A new one-time signature scheme from syndrome decoding Keygen: Given a security parameter $\lambda$, choose a suitable ...
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0answers
60 views

IES: What security has the asymmetric primitive to provide?

I think most of us know the notion Shoup introduced of KEM/DEM (Key encryption material / data encryption material) which is used for example by the (famous) ECIES, where the key is the hash of some ...
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0answers
43 views

Clarify EC point addition and multiplication

Please clarify the below doubt regarding EC point addition and multiplication: $P$-Generator Point; $a$ and $b$ are integers; $X$ and $Y$ are EC points, defined as follows: $X = (a*P) + (b*P)$ $Y = ...
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0answers
92 views

Where can I find names for cryptographic notation I don't recognize?

I'm new to this space and find myself stumbling over come cryptographic/mathematical notation. Search engines are not very helpful when copying and pasting Greek letters. Is there any reference that ...
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0answers
105 views

Is this a secure method of encrypting with authentication?

My goal is to allow two clients to send files securely over an untrusted network without the need for more than one block of information to be sent. Both clients have ECDSA keys of size 256 bits. I'd ...
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0answers
73 views

RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one block,...
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0answers
31 views

Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
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0answers
47 views

Digital signature in a group chat scenario?

I understand that RSA is great for 1-to-1 digital signature. In the group chat of N people, other than storing and maintaining N public keys, is there a simpler way of authenticating each and everyone ...
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0answers
50 views

How to find an impossible differential?

Given an arbitrary SPN-based cipher with X rounds. How to find an impossible differential for this cipher? What are strategies to find one?
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0answers
133 views

Vigenère cipher frequency analysis not working

I'm writing a C++ program to use the Kasiski method to crack the Vigenère cipher. I'm testing it with a bit of Shakespeare encrypted with the key ABCDEFGHIJKL. It ...
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0answers
109 views

Unicity Distance - AES

I am quite confused calculating the unicity distance and I was hoping that someone can clarify some things for me. My main issue comes from somewhat a difference of the calculation given by our ...
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0answers
55 views

Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$. Say ...
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0answers
61 views

Elliptic curve point addition

I have this curve in E(F131) : $$Y^2 = X^3 + X + 2 $$ I want calculate the sum P + Q considering that $$P= (5,1)$$ and $$ Q = (60, 49)$$ For calculate the result i use these formulas: $$ xr = ((...
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0answers
136 views

My attempt of combining socialist millionaire and Diffie-Hellman. Is it any good?

I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so I'...
1
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0answers
47 views

Why does OMAC2 exist?

The specification for OMAC has the following to say about OMAC2: For OMAC2, we adopted u−1 instead of u2 as Cst2. It requires one right shift to compute L· u−1 instead of one left shift to compute (...
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0answers
69 views

Non-interactive zero-knowledge proof for discrete logarithm without random oracle

Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$?
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0answers
82 views

Does the encryption algorithm DES perform random permutations? If so how is information not lost?

Before round 1 begins, all 64 bits of an incoming message and all 56 bits of the secret key are separately permuted (shuffled) My question is this : Is the shuffling of the bits performed randomly? ...
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0answers
56 views

Hardening of random number generators

Boxcryptor uses various CSPRNGs and apparently hashes the output using PBKDF2 to derive the final key. Even though the choice of ...
1
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0answers
100 views

What are some hashes that do not exhibit the avalanche effect?

I do not know much about cryptography. But, I'm in a situation where I need a hashing method that does not exhibit the avalanche effect. I tried Googling but couldn't find anything.
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0answers
125 views

Which of these is a secure MAC?

Let (S,V) be a secure MAC defined over $(K,M,T)$ where $M = \{0,1\}^n$ and $T =\{0,1\}^{128}$. Which of the following is a secure MAC: $S'(k,m) = S(k,m)[0,\ldots,126]\quad and \quad V'(k,m,t) = \...
1
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0answers
94 views

How do I verify a reset token if the token is hashed in DB?

I've been searching around the web for best practice how-to on secure password reset system (email with reset url), and the idea to hash the token in the database, which I did not implement at first, ...
1
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0answers
47 views

Commitment scheme to share money

I have such problem: party $X$ has an amount of money $M$, which it needs to share with $n$ other parties. Every week the amount of money is different. Let say not, that I am a party A, which is one ...
1
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0answers
81 views

Why does the ElGamal signature have the specific form that it does?

In the original paper, ElGamal(1985) starts his discussion of signatures by saying: "The signature ..... is chosen such that the equation: $\alpha^m = y^r r^s \text{mod p}$ (equation 3 from the ...
1
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0answers
55 views

How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $ \frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
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0answers
458 views

Montgomery Reduction

I'm taking a hardware cryptography class and working on a problem that focuses on Montgomery Reduction. So by definition: Computing a x b (mod N) Pick R, s.t. R > N, gcd (R,N) = 1 Compute N^-1 (...
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0answers
53 views

Cache Attacks on Cloud Infrastructures

I read something about cache attacks like this: Enter KSM (Kernel SamePage Merging). KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory ...
1
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0answers
54 views

EC based password authenticated key exchange protocol

I would like to know: What is the currently best (efficiency and security wise) known EC based password authenticated key exchange protocol? (i.e. is there any EC based protocol may be similar to DH ...
1
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0answers
82 views

Is there any pattern in points on EC?

I read some where in crypto.stackexchange answer (related to EC-SRP protocol) that there is pattern in points on elliptic curves, i.e. if given some points containing mix of correct and wrong points ...
1
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0answers
74 views

Zero knowledge of two factor

Here I overconfident in myself state that I can show, that n has two factors. This is not completely true, can possibly show $n$ is composite - prover generates RSA key with modulo $n$, and gives $e$ ...
1
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0answers
48 views

Security of simple Skein PBKDF mentioned in the paper

From the Skein 1.3 paper section 4.8, Skein as a Password-Based Key Derivation Function (PBKDF), it mentions the following as a simple PBKDF (S = seed and P = password): An even simpler PBKDF is ...
1
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0answers
224 views

Construct rainbow table to break DES

I'm facing a project where I need to build a rainbow table to break DES. I've already collected information about Hellman, DP, rainbow table method. Finally, I chose the rainbow table approach. I've ...
1
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0answers
68 views

Resynchronizing brute-force attack against stream ciphers

There is a stream cipher without any known cryptographic weaknesses. The attacker knows parts of the key so she can reduce the key-space to a size that can be practically brute-forced. However the ...
1
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0answers
56 views

Encryption with a known plaintext

I'm building an application where users can be a part of groups, and can obtain and distribute URLs from the group page that allow anyone who clicks on them to join said group. Groups should not ...
1
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0answers
305 views

FileVault AES-XTS decryption with cipher text that's missing a part

My mac was recently upgraded to OS X Yosemite and FileVault2 full disk encryption was turned on. Encryption finished, but things went horribly wrong and key parts of the disk are filled with all 0s (...

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