# All Questions

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### Delinearization in whitebox techniques

I'm reading through Chow et al.'s paper and Link et al.'s paper. There's a part I don't understand about Delinearization. They convert some steps of AES/DES into a Matrix, then divide the matrix in ...
69 views

### How to compare different signature scheme's performance?

I am interested in comparing the computational performance of two signature schemes. However, I am unsure how to do that. My candidates are RSA and Shamir's ID Based Signature scheme. To get a fair ...
54 views

### Expand 1-n Oblivious Transfer to retreave only an item I, for which permissions exist

To my understanding in a 1-n Oblivious Transfer the Sender has some Values $X_1...X_N$ and the receiver wants to retreave some $X_I$, with $1 \le I \le N$. Can one now somehow guarantee, that the ...
69 views

### Is Encryption without knowing the input directly possible at all?

I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of ...
110 views

### Defending hybrid encryption schemes against padding oracle attacks

I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ...
114 views

### Challenge–response authentication which can be done in head?

Say we have door where you have to say a password to pass. If theres someone standing nearby he would hear the password and could also use it. So therefore the doorman gives you a different number ...
38 views

### Distributed authentication in low trust environment

I would like to inquire if there is any Method to achieve the following: There is a list $L$ of $n$ entities that are allowed to perform a certain action. $L$ is cryptographically signed by some ...
51 views

### 1-1 trapdoor function mapping the set of $n$-bit numbers to themselves

I am looking for a trapdoor one-to-one function $f : \{0,1\}^n \rightarrow \{0,1\}^n$ (that is, mapping the set of $n$ bit numbers 1-1 onto itself [any $n$ is OK]). I was considering the use of ...
44 views

### Client puzzle using hash

When a server is under attack, it send the client the following data: Nonce - a byte array of Y length Hash - the hash digest of the puzzle solution The client has to find X such as ...
72 views

### RSA timing attack

Given an RSA implementation that uses Montgomery multiplications and CIOS exp algo, but NOT CRT. Given a decryption1 oracle that takes chosen cipher text and responds the plain text and the time it ...
33 views

### McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
77 views

### Public-key based on roots of polynomial

In general it's hard to calculate the roots of a given polynomial P(x). But the other way back calculating the coefficients is much easier (Vieta's formulas). If this is a one-way function, is it ...
122 views

### Is this a secure (and correct) sign-then-encrypt technique for transferring messages?

After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ...
69 views

### Problem implementing MixBytes functionality in Groestl

Disclaimer: School work. I am trying to implement Groestl through Java, and have got stuck on the MixBytes section which can be found here section 3.4.5 page 11. As per the description of matrix ...
71 views

### Trying to calculate the strength of a Bitcoin brain wallet created with a custom diceware password

I want to create a brain wallet using a custom diceware since I don't like the original one. Instead of 7776 words it has 46656 because I use 6 dice for each word instead of 5, and also it only has ...
114 views

### AES encryption takes more time to decrypt than encrypt

Please let me know if this is not the right place to ask this question. I will remove it. I am trying to find how much time an AES encryption and decryption takes for a given amount of data and key. ...
121 views

### Rainbow tables and blowfish

I'm thinking of implementing rainbow tables for a specific blowfish problem, but I have trouble thinking of the proper way to apply the original paper (and its application to hash functions) to ...
96 views

### Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks

Bitcoin uses SHA-256, Base58Check, ECDSA (Sep256k1) and RIPEMD-160 as the basis of its encryption (see this article for a short guide on how addresses are created). I would like to create an ...
71 views

### Parallel-resistant proof-of-work scheme without hidden knowledge

Follow-up to: Parallel-resistant proof-of-work scheme? Is there a proof-of-work scheme that: can only be solved serially; given the solution, can be verified in minimal time; deterministically ...
81 views

### Weil pairing implementation - low level programming language

I'm just started to studying elliptic curve cryptosystems. My one month-goal is to write a simple signature system based on the Weil-pairing. Some parts of it can be written without deeper ...
81 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 ...
42 views

### Random numbers for Master Key and Key_block

Exploration through RFCs concludes that random numbers used in the creation of Master Key and Key Block(Key material for Encryption Key and Mac Secret) are from ServerHello.random and ...
72 views

### Should layered use of crypto always have a cryptographic binding between the layers?

Reading the latest TLS weakness, it seems that multiple weaknesses have been found over the years caused by not ensuring that messages are sent over the same channel, and in general a lack of ...
196 views

### Using RSA key pair for file encryption

I'm looking for a way to perform encrypted nightly backups of a server I administer, without storing the decryption key on the server. A form of PK encryption seems ideal for this, as I can store the ...
68 views

### IND-CPA Security

Given a key $K$ (the key is fixed) and a nonce $N$ (changes from one message to another) Using a secure Key derivation function (KDF) such as the ANSI-X9.63-KDF with SHA-1 option to derive a key for ...
41 views

### Determine the iteration times using Pollard's rho Method for factoring

Let's say, we have a large number $n=181937053$ and $f(x)=x^2+1$. And also we know that $n=12391 \times 14683$. The problem is that ,using Pollard rho method, can we find the algorithm iteration ...
59 views

### Sextic twist of BN pairing parameters vs security

I've previously asked questions on BN pairing parameters. Here's one more. In the BN construction, one is working in a subgroup of a curve over an extension field $\mathbf{F}_{p^{12}}$ for some ...
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### Gallant-Lambert-Vanstone method

I am experimenting with the GLV method but cannot manage to get the right results according to the literature. I managed to find lambda, beta, split $K$ into $k_1$ and $k_2$ etc. for the curve I'm ...
73 views

### What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
117 views

### What RC4 key value will completely invert $S$ after initial permutation?

What RC4 key value will completely invert $S$ after the initial permutation, so that $S[0] = 255, S[1] = 254, …, S[254] = 1, S[255] = 0$?
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### Attacking hashed password by timing attack and other means

This question is inspired by this recent one, which raises a point that need to be made quantitative to be meaningfully discussed. I chose an unusual approach: a new question worded as homework that ...
70 views

### Which gives better deterministic encryption SIV or Plain ECB mode?

Lets say , if we encrypt a plain text message $msg$ with key $key$ in below two ways. Which is the below would give better deterministic encryption and why ? AES-ECB($key$ , $msg$) SIV($key$, NIL , ...
111 views

### How does converting character set affect hash entropy?

Does mapping a large character-set hash onto a small character-set hash lower entropy for a fixed size substring? I'm writing a python app that involves generating passwords for websites. During the ...
69 views

### Known vulnerabilities in (EC-)KCDSA

Does anybody know if there's known vulnerabilities in KCDSA/EC-KCDSA? I have been researching for the past few hours and I haven't found anything. Wikipedia has very limited amount of information and ...
96 views

### Safe and computationally efficient way to verify a curve25519 identity?

A client identifies itself as a curve25519 public key. The server wants to verify the client owns the associated private key. Is there a safe and computationally efficient way of doing so? Which ...
131 views

### Hash function that is efficient on GPU and poorly suited to ASIC

I have such requirements to the hash function in my project: operating on 32-bit data, not mathematically breakable (built on existing hashes known to be secure), free of branching, as much as ...
75 views

### Why do authors execute a leakage resilient election protocol inside a leak-free phase?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage", on page 1241 (that's page 7 of the PDF) under section 2.3, the authors discuss "The Election Protocol" that they use to ...
56 views

### How to specify last $t$ bits are only sent when a signature is sent?

I have read that in cases where there is a limit on the amount of data sent over the network, one idea is to sent only $t$ bits of data rather than sending all the bits. For example, in the Schnorr ...
56 views

### Is it feasible to break an encrypted and later encoded message?

A message is sent from a person to another. The plain message is first encrypted, even with a weak algorithm - say, DES. Then, the encrypted message is encoded with a simple substitution, which is ...
91 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 ...
79 views

### Factorization or discrete logarithm is difficult for an attacker?

I have read that difficulty in breaking many algorithms are based either on Factorization or discrete logarithm. I am reading about schemes that are similar to RSA which make use of integer ...
118 views

### inverse of scalar multiplier in ECC

I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers. now suppose ...
115 views

### Rabin code same message sent with different $N$

I use Rabin code with modulus $N$. Now assume that Alice sends me a message $m$ $(1\le m\le N)$ encoded by Rabin code. Unfortunately after Alice sent me the text I lose the information about the ...
58 views

### Looking for alternative key stretching

I am by no means a security expert, but I am curious whether functions that don't produce different outputs when raised to the power of N (without any psuedo-randomness) exist, that are as strong as ...
89 views

### Which is better ECDHE with TLS 1.0

I have a webserver which support only TLS 1.0 Which is the better cipher in this group for the best security? ...
89 views

### Distributed integer factorization?

I'm looking around for publicly published work on factorization of large numbers using distributed systems of any kind. So far I've come across the PDF "Mapreduce for integer factorization" by Javier ...
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### Can you show how that RSA does/doesn't provide anonymity?

Considering a CPA-secure version of RSA where the ciphertext is just a rundom element from $Z^*_N$. Does that meet the anonymity requirement in which an cpa adversary cannot distinguish between a ...
200 views

### Random Number Generation with a Entropy pool versus Seed

To give a little background I'm currently implementing a crypto library in JavaScript. I have started porting across Linux's random number generator because its both publicly scrutinized, it is ...
Let $G$ be a group of order $n$ and let $e,d$ be integers such that $ed\equiv 1 \pmod{n}$. Then the exponentiation maps $x \mapsto x^e$ and $y \mapsto y^d$ are inverse maps on $G$. These maps give us ...