1
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1answer
41 views

Elliptic ElGamal Public Key Cryptosystem doubt

I need an example of Elliptic ElGamal Public Key Cryptosystem. I have been trying with some values but I don't get the right solution. I have $p=13$, the elliptic curve $E:y^2=x^3+11x+7$ and a point ...
1
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1answer
56 views

What is the viability of a hybrid vigenere cipher?

So a vigenere cipher's main weakness is that you can use frequency analysis on each alternated alphabet, and thus crack the cipher with relative ease... But that implies that you know what the ...
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1answer
34 views

Multi Party System with n-1 adversaries

Novice here. Is there a MPC function where no information is leaked even if all parties are not trustworthy ?
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1answer
124 views

Encrypting passwords

I am using Android's keystore to generate a key which is protected by fingerprint authentication. This key can be used to encrypt any secrets. In my case, I want to encrypt a user password (which is ...
1
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1answer
98 views

Would it be better to use HKDF or SCrypt for deriving a child key?

Okay so I'm trying to derive a child public key from an EC public key. I've come up with a couple ideas and now I'd like to know which is more secure. Mp: The master key pair, this includes a ...
1
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2answers
44 views

How to check the integrity of a key received through mail using symmetric encryption?

I would like to provide access to encrypted data through a cloud service provider, using a pay-as-you-go model. This means that we will sometimes need to revoke a user's access to the data. To ...
1
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1answer
53 views

Can the original message be retrieved from a public/private key signature?

When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)? I want to prove – ...
1
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1answer
72 views

Username and Password: How does it work?

Suppose a client (Alice) goes to an HTTPS website (Bob) over TLS 1.2. Alice sends Client Hello with some random number $r_a$. Bob sends Server Hello with another random number $r_b$. Suppose they ...
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1answer
63 views

What is a good algorithm to scramble data in a 2-D grid

I want to know if there exists an algorithm i can use where the input is a string of data and the output is a scrambled version of the same but in a 2 D array ie given something like: |1 2 3 4 5 6 ...
1
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1answer
58 views

bcrypt collision probabilities assuming same password and work factor?

What is the likelihood of 2 bcrypt hashes colliding if they use the same work-factor and input? Are bcrypt's salts large enough to prevent this from happening?
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1answer
49 views

How to store keypair generated by RSA in a textfile?

I'm trying to write an encryption decryption program using Openssl-RSA. There are only two operations. User stores the data and retrieves it whenever he needs. To decrypt something, we need the ...
1
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1answer
38 views

Deletion complexity in a RSA accumulator

My question is about the existence of a dynamic RSA accumulator with deletion of an element in O(1) time. Do you know some practical implementation?
1
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1answer
82 views

Is there short period in AES 128 key schedule?

I am wondering if for some particular keys the AES 128 key schedule lead to a periodic pattern for the round keys. The key schedule is only 10 rounds, but I am also wondering in the general case where ...
1
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1answer
131 views

Cryptography of numbers

Is there any algorithm capable of encrypt securely (symmetric) N numeric digits in a numeric message of M digits (N < M)? I am especially interested in a specific case in which N = 10 and M = N + 3....
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1answer
81 views

Few questions about CBC MAC

I want to use CBC MAC. First I hope to find some implementation of block cipher which I will use in CBC mode, which I understand is CBC MAC. But I have two questions: 1) If the length of the message ...
1
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1answer
42 views

Probabilistic RSA, IND CPA

Suppose we have classic RSA scheme. Let $n=pq$, $e$ public, $d$ secret. Then message(M), not empty(not 0), is encrypted by choosing random $r$ and computing $A=(r^e)^e$ and $B=(Mr)^e$ $(A,B)$ is ...
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2answers
82 views

Continuous stream of strong randomness from limited entropy?

I need a continuous (infinite) strong random generator, but I've only got limited entropy as seed. I know there's already a contradiction there, but I'm looking for a practical approach. Suppose I ...
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1answer
52 views

Finding collisions for the DES F-function

It's known that for a given subkey, the F-function of the DES is not injective (see Is the DES F-function injective for a given subkey?). I am interested in efficiently finding collisions for this ...
1
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1answer
132 views

S boxes in Blowfish

I know how the s-boxes in blowfish are initialized, but how is the output sorted, I mean which bit from the input goes where in the box ? and what do mean they have 256 entries if they are 32-bit S-...
1
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1answer
103 views

RSA: must $d$ be an integer?

I am only taking baby steps in RSA. If $p=11$, $q=7$ and $e=3$, $$\phi(n) = 10*6 = 60$$ Then: $$d = (2 (\phi(n)) + 1 ) / 3 = 121/3$$ Should $d$ be kept as a non-integer or is such a $d$ invalid?
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1answer
63 views

Rogue CA Certificate MD5 Collision Control

Papers from Marc Stevens et al show that X509 certificates that rely on MD5 signatures can break the assumed security model, that is, it allows for a forged certificate to have the same signature as a ...
1
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1answer
72 views

Fully homomorphic encryption arbitrary functions formulation

I am currently studying the interesting field of homomorphic encryption. I read that from a fully homomorphic encryption function that supports both addition and multiplication you can perform any ...
1
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1answer
65 views

how to calculate maximum data size of an RSA signature

I am reading a content, and am not sure if I follow how they come up with the maximum data size which can be signed by an RSA key. The author states: "...if you are trying to sign a message using a ...
1
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1answer
111 views

How to prove that a SKE scheme is IND-CPA secure

There's an IND-CPA SKE scheme 1 $(\mathsf{Gen}, \mathsf{Enc}, \mathsf{Dec})$. Scheme 2 is defined as $(\mathsf{Gen}', \mathsf{Enc}', \mathsf{Dec}')$, where $\mathsf{Gen}' = \mathsf{Gen}$, $\mathsf{Enc}...
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1answer
155 views

Cracking simple RSA when just the ciphertext and one public key is known

Can someone explain to me (Or better yet, point me to a tool that does the brute forcing) how to crack a standard, simple RSA cipher (So don't bother with padding) if I know just one public key, the ...
1
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1answer
166 views

Proving collision resistance of a hash function?

Let $f$, $g$, and $h$ be hash functions that each map binary strings of length $2n$ to binary strings of length $n$. Suppose that $h(x) = f(g(x)||g(x))$. Prove that if $f$ and $g$ are collision ...
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1answer
47 views

Key material leak from initialized cipher?

Let's imagine that cipher (say AES256 in CBC mode) is initialized when application starts: ...
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1answer
90 views

Time complexity of trial division

Suppose $n=pq$, where p,q are prime numbers. let $p ( \le q)$ be the smallest prime, then we know that $p \le \sqrt{n}$. In trail division, we check $n \mod i$ for the values of $i$ from 2 to $\...
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1answer
54 views

Help with pseudorandom functions

I started a new lecture this year about crypto and I've had a few problems in the first few weeks with the exercises we got. I would appreciate a "guide" on how to solve problems like the following ...
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1answer
53 views

How many Hashes to find a digest of 2^{n−k}?

Given an n-bit cryptographic hash function $H$, how many messages should we expect to hash before finding a message $x$ such that $H(x) < 2^{n−k}$ for some integer k? My take: Shouldn't it simply ...
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1answer
79 views

Alter plaintext in block cipher AES in CBC mode

How can I alter the plaintext before decryption by changing the IV? I know what the value of the plaintext should be. I also know the value of the IV (initial vector). The IV and the AES block are ...
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2answers
108 views

Homomorphic Encryption with Addition and Exponentiation

Is there any homomorphic encryption scheme which supports addition and power over cipher text ? Paillier is close but it supports addition and multiplication with a constant. I am getting an output ...
1
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1answer
144 views

With ECDSA is there a way for the verifier to calculate any properties of $k$?

With ECDSA, given $(r,s)$ and $m$, is there a way for a verifier to calculate any (boolean) properties of $k$, without knowing $k$ or the private key $D_A$? (I understand that $k$ should be random, ...
1
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2answers
211 views

Is there an algorithm to hide text in another text, while preserving the meaning of the latter?

Is there a way to hide a text message $A$ inside another text $B$ using a cryptographic cipher/algorithm, while preserving the sense/meaning of $B$ and without anybody being able to notice there is a ...
1
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1answer
121 views

Storing a secure key in an embedded device's memory

I am working on an embedded device which send/receive data and stored them in ciphertext mode (encrypted mode ). Now what's best approach for storing Keys (I used ARM CORTEX M series MCU) ? Storing ...
1
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1answer
39 views

How to use a secret to allow the generation of public keys, where the private keys can be calculated later

Alice has a secret S and publishes some public information P, about S which is insufficient ...
1
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1answer
54 views

PRF that can be distinguished after $k$ queries?

In adaptive attacks, if we design poorly, adversary can modify his queries and break the given pseudo random function (that is being able to distinguish it from uniform randomness). Is there a poor ...
1
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1answer
87 views

Degree of M and Max Sequence Length for LFSR

For the LFSR mod 2, determine the degree of m and maximum sequence length s_(i+3)≡ s_i+s_(i-2)+s_(i-4) mod 2 determine the degree of m and the maximum ...
1
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1answer
37 views

Deriving a Set of Seeds from a Seed

I need a set of seeds $S=\{s_1,..., s_n\}$, for pseudo-random function where seed $s_i$ is used to generate a set of pseudo-random values. Obviously I need to be able to regenerate the sets of pseudo-...
1
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1answer
243 views

Encrypt large data with RSA through blocks in java

I'm working on a communication protocol where a client sends encrypted data to a server. What happens is that in some point, the client creates a symmetric key used to create data digests through the ...
1
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1answer
74 views

Properly storing an E-mail Password

I'm creating a messaging application that will use an outlook account to send an email. However, I'm unsure about the proper steps to store the e-mail password on the user's computer. Suppose I had ...
1
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1answer
44 views

Security of SRP-6a against impersonating server choosing small/wrong N

I'm looking at an implementation of SRP (Secure Remote Password) that essentially follows the Stanford documentation (http://srp.stanford.edu/design.html). I'm worried about one aspect though: In the ...
1
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1answer
65 views

Byte size of Diffie-Hellman public values

I have a scenario that uses RFC-3526's Diffie-Hellman Group 14 for 2048 bit key exchanges. From the document, it specifies the P (prime) value in hexadecimal value as: ...
1
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1answer
92 views

How can IND-CPA encryption be identity revealing?

This is problem 10 of Chapter 4 "Symmetric Encryption" (pdf) from Lecture notes by Bellare and Rogaway: An IND-CPA secure encryption scheme might not conceal identities, in the following sense: ...
1
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1answer
129 views

DES and using the S-Box 1

Can someone please check my work and correct me if I am wrong, I am just starting to learn about DES. I am trying to solve the following problem: Show that ...
1
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1answer
84 views

Which ECB ciphertext stealing scheme is this?

I am stuck with identifying ciphertext stealing method with the following properties: mode of operation is ECB; recommended padding scheme for this application is PKCS#7, but apparently it is not ...
1
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2answers
122 views

PKCS#7 message content

I am using a vendor library that signs a text producing a PKCS#7 message. I'm not sure of the content of this message. Does a pkcs#7 message have to contain the signed message, the certificate, the ...
1
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1answer
194 views

How does the Efficient Fully Homomorphic Encryption from (Standard) LWE work?

I am interesting to learn the low level implementation of Efficient Fully Homomorphic Encryption from (Standard) LWE and I am wondering if anyone can answer the following questions: Does the BV ...
1
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2answers
56 views

Are Anonymity and Authentication possible together?

Anonymity and authentication look to be seemingly contradictory but are both possible together ? I tried reading couple of papers but could not get the big picture. So what are the major approaches ...
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1answer
89 views

Is this scheme to derive multiple keys secure?

I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also: Neither private ...

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