3
votes
2answers
94 views

Long passwords and Bcrypt

I need to store passwords for a web application, and was looking at Bcrypt for a possible solution. After some research, it appears only the first 72 bytes influence the final hash output. While it is ...
0
votes
2answers
98 views

RSA algorithm private key extraction

Decrypting messages can be done by using the following formula: $$M = C^d \mod n$$ Where $M$ is the decrypted message, $C$ is the encrypted message and $d$ is the private key Theoretically ...
4
votes
1answer
98 views

Exactly how bad is using 'mod' to clamp reduce numbers to a given range?

Let's say I'm naive and want to generate a random integer in the range [0, m), so I do the following: ...
0
votes
2answers
65 views

RSA numerical questions

Let $n$ be the modular arithmetic, $p$ and $q$ the two large primes such that $n=p*q$ and $e$ the public exponent. Here they are two "simple" numerical questions: If $p = 13$ and $q = 17$, what is ...
0
votes
3answers
97 views

How to calculate plaintext from modpower cipher

Let $a$ be the plaintext message, $e$ be a small prime exponent (such as 11, 13, 17 etc.), $b$ be cipher text and $n$ be a large modulo (non-prime). Suppose that: $b \equiv a^e \space mod ...
0
votes
0answers
11 views

A standard for multi-key provider encrypted data?

I'm looking for a standard that standardizes data encryption with multiple and diverse key sources to represent a heterogene access structure and culture. The standard must offer the following ...
3
votes
1answer
48 views

What information should I send along with an AES ciphertext and is there any standard to do that?

While using some crypto implementations I got to see that many times a comment is added to the ciphertext. For example: ...
8
votes
1answer
113 views

Side channel security of HMAC in software

Assume we have a processor with a symmetric co-processor that supports AES. This processor does however not provide co-processor support for hash algorithms such as SHA-1 or SHA-256. I've got the ...
6
votes
4answers
784 views

Are there any practical ways to transfer random data securely?

The owner of the random.org service recommends that you do not use randomly generated numbers from their website in cryptographic keys. This makes sense, but it got me wondering. Is it possible to ...
1
vote
2answers
69 views

Theoretical security of bit rotation for encyption

This is a theoretical question. I have a idea, encryption by bit rotation in byte. Do not know if something like this already exists. General concept is: First n bytes is rotated to left or right ...
3
votes
1answer
41 views

Generating passwords from a master password using rules

I realize it's generally considered bad idea to use the same password everywhere. I can use icloud / lastpass to generate my passwords for me, but that leaves me clueless when I don't have access to ...
2
votes
0answers
32 views

Are collisions in AES-128 theoretically possible when the plaintext is the same? [duplicate]

Is it theoretically possible to find $P$, $K$, and $K^\prime$ such that $E_K(P) = E_{K^\prime}(P)$ where $E$ is AES-128 and $K \ne K^\prime$? I'd imagine this would be infeasible, but is it actually ...
0
votes
0answers
39 views

When we use permutation and random long sting to hide a message

This question is modified version of this: Can we use merely permutation to hide a message? I have an English name $m=m_1 || m_2 ||..||m_{30}$. I pick a random string $d=d_1 ||..||d_{70}$ I mix ...
3
votes
1answer
75 views

How exactly does certificate based authentication work?

I know the concept of key generation, as well as encryption and decryption using public and private keys. When it comes to authenticating a user by a server, in general there are three types: ...
3
votes
1answer
733 views

Is this DIY remote lock protocol secure?

I need your advice on following scheme of exchange protocol between remote lock and key. I'm planning to use following algorithm: Key generates unique value that never repeats (in reality it's just ...
-1
votes
1answer
45 views

Security for secret key of server in Identity-based Encryption

In the key set up phase, server generates Pub=s.P, where s is the secret key.Then , it gives clients Pub,P as public parameters and pairing descriptions. Is it possible for clients to pre-compute r.P ...
3
votes
1answer
62 views

Does key renewal increase complexity of MAC forgery?

Suppose I have encrypted messages sent to a device authenticated with a MAC keyed with a strong shared cryptographic key. This device can only process so many messages per unit of time. This ...
1
vote
0answers
41 views

Vulnerabilities in SHA-1 [duplicate]

Are there any known vulnerabilities in SHA-1 that can be exploited? Certain patterns that it shows? I recently performed a frequency analysis using 20,000 common words, and found nothing exploitable. ...
3
votes
2answers
59 views

Should the most significant byte of a cryptograhic key be nonzero?

Is it safer to give a non zero value to the most significant byte (MSB) of a cryptographic key to ensure its length (not 31 instead of 32 for an EC private key on a 256-bit curve for example)? Or is ...
2
votes
1answer
166 views

Is $H'(M) = 5M + 9H(M) \pmod{2^n}$ a secure hash function?

theorem: For arbitrary $i≥0$ there exists $m,n≥0$ such that $35+i=5m+9n$. We can use this theorem for constructing simple hash function. Let $M$ be message and $H(M)$ be its hashed value with ...
-1
votes
1answer
81 views

Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
0
votes
1answer
66 views

RSA-OAEP: How does it work?

I was looking at this image about OAEP: ..and was wondering what was happening here. We have a data block DB which consists of: ...
4
votes
1answer
187 views

When all shares of a secret are given to adversary as a permuted matrix

Suppose we have a secret $\sigma$. The secret comes from a universe in which the elements are not necessarily distributed uniformly. We split $\sigma$ into $n$ shares $[\sigma_1,...,\sigma_n]$ ...
0
votes
0answers
29 views

Subset sum hardness

Hardness of a subset sum probleme depends on it's density. Is it possible for a subset sum problem to be intractable even if it's density is less than 0.9408 ?
1
vote
0answers
40 views

Compressing AES [duplicate]

I have this program which encrypts multiple files using AES then compress it using LZO into one single file. The problem is that the final file is almost equal in size than all the files which means ...
0
votes
2answers
84 views

Understanding the distinguisher for a PRG

Given the following definition of a psuedorandom generator, I'm having trouble understanding what exactly the "distinguisher" D is outputting, and when?
1
vote
0answers
19 views

Security issues with self encryption? [duplicate]

I'm thinking about the scenario of using a set of (potentially untrusted) hosts to store (potentially private) files. Think something like distributed backup where you contribute some disk space and ...
0
votes
0answers
71 views

Degrade in performance with SSL_OP_SINGLE_ECDH_USE?

We have used SSL_OP_SINGLE_ECDH_USE when setting up our SSL_CTX . This seems to be causing a degrade in performance. I'm not able to find proper documentation for it except that it generates new ...
1
vote
2answers
64 views

Single-algorithm authenticated encryption

Are there any authenticated encryption methods that combine encryption and authentication, rather than useing a separate cipher and MAC?
0
votes
1answer
105 views

Is this a good communication scheme?

I'm writing a wrapper for a chat program to allow for end-to-end encryption. I'm using Python and PyCrypto to accomplish this. I'd like to use a well known library to do this, but to my knowledge, ...
0
votes
1answer
55 views

Proof of Knowledge/Data Integrity using Hash Function

Objective: A verifier wants to ensure that a block of data M is also known to a prover. The protocol should exchange little information and should not leak information about the value of M. Proposed ...
3
votes
3answers
145 views

In interactive proofs, do we assume that the prover can always solve the problem?

I'm having a difficult time understanding a concept from interactive proofs: A trivial interactive proof for the graph isomorphism problem is having the prover just send a permutation that shows an ...
2
votes
2answers
86 views

How can a message encrypted with the public key be decrypted with the private key? [duplicate]

I've been reading about encryption and have a basic understanding of the concept. What I don't understand, however, is how a calculation with one key can result in a number that, through calculation ...
-1
votes
0answers
58 views

How much information is revealed?

Let Alice pick $v_{1}$,$m_{1}$$\in \mathbb{P}$ and Bob $v_{2}$,$m_{2}$$\in \mathbb{P}$. Now Alice computes $v_{1}$$^{m_{1}}$ and so Bob does $v_{2}$$^{m_{2}}$ Then Alice exchanges $v_{1}$$^{m_{1}}$ ...
0
votes
0answers
47 views

Show that the shift, substitution, and Vigenere ciphers are all trivial to break using a known-plaintext attack

i think that we can use the notion of knwn plan text that we could have pairs of both cipher and plantext msg and try to find way from one to another to recover the key i dont knw how to make it with ...
0
votes
1answer
61 views

Function with no fast path and with fast proof

When a function is iterated and each time a previous result is used as input to the next iteration (feedback), so that there is a limited benefit from parallel computing, is there such function that: ...
0
votes
0answers
142 views

history of non secret cryptograph

Prior to the discovery of any specific public-key schemes, such as RSA, an existence proof was developed whose purpose was to demonstrate that public-key encryption is possible in theory. Consider ...
7
votes
2answers
559 views

What is an example of a secure sigma proof?

I want to implement Threshold Elgamal as described in section 6.3.1 and in the decryption phase each party must broadcast a sigma proof to show that it actually has a valid secret share of the secret ...
4
votes
1answer
110 views

How to attack RSA-CRT with large public exponent?

Suppose we have $(n,e)$ and the ciphertext $c$ where the public exponent $e$ is of the same length, 1023-bit, as the modulus $n$. It is also assumed that the factors of $n$ are balanced. The message ...
3
votes
0answers
33 views

no speedup from preprocessing in blynn's PBC library

I am implementing some pairing-based cryptography protocol using blynn's PBC library. I am only at the beginning and I wanted to confirm that preprocessing does increase the speed. However I seem to ...
1
vote
1answer
131 views

AES key and block size

I am trying to understand $AES$ and I wondered what happens in the case of a $128$ bit block size and a $256$ bit key. All documents I read about $AES$ told me the key expansions algorithm for $128$ ...
3
votes
1answer
383 views

Is XOR adequate for encrypting truly random data? [duplicate]

It is well-known that the two-time pad is very insecure. However, it seems unexploitable in the case where the plaintext is indistinguishable from random (ex. symmetric keys). Is this property ...
3
votes
1answer
183 views

Difference between Pseudo Mersenne primes and Generalized Mersenne primes

The field prime numbers $p$ proposed by the NIST standards are referred to as Generalized Mersenne prime numbers [1] and as Pseudo Mersenne prime numbers [2]. Is there a difference between Pseudo ...
1
vote
1answer
49 views

Why Boneh-Franklin BasicIdent IBE is not chosen-ciphertext secure? Why use random oracle?

I don't know why BasicIdent is not chosen-ciphertext secure. If there are anybody who knows well, please explain it to me with example. Moreover, I don't know random oracle and its usage for security ...
3
votes
1answer
47 views

Is it okay to send an encrypted key using XSalsa20-Poly1305, and send subsequent messages using ChaCha20-Poly1305?

I am looking at a cryptographic protocol in a somewhat unusual environment: the communicating parties can share arbitrarily long secret keys over a secure channel. If forward secrecy is not required, ...
5
votes
1answer
89 views

Do Carter–Wegman MACs allow key reuse if the MAC tag is kept secret?

Poly1305 (and GHASH) are secure authenticators, but only for one use. Thus, nonce reuse in Poly1305-AES, ChaCha20-Poly1305, and AES-GCM all reveal the authentication key. However, my understanding ...
1
vote
0answers
18 views

Are there known practical attacks on RC4-dropN? [duplicate]

RC4 is known to leak information about the first few bytes of the ciphertext due to keystream biases. However, are there known attacks on RC4-drop[N] where N is large enough, that leak information ...
0
votes
0answers
26 views

Implementing cryptosystems with various programming langauges

I know that most cryptosystems are currently implemented in C/C++. Has there been any effort to implement cryptosystems in programming languages such as Agda where proofs can be written about ...
7
votes
2answers
151 views

Is TLS secure against VM reset attacks?

Is the TLS protocol secure against VM reset attacks? Background: Imagine running cryptographic software inside a virtual machine (VM). A VM reset attack is one where the the state of the software is ...
10
votes
3answers
201 views

Are there reasonably secure online voting implementations e.g. for student council elections?

Assume a university want to elect the student council. This was done via paper ballot and there is a need to reach more students for voting, so electronic voting is on the table. While researching ...

15 30 50 per page