0
votes
1answer
18 views

Any weakness when sha256'ing output of sha256, repeatedly?

Is it significantly easier to reverse a sha256 hash if you know that the input was a 32 byte output of sha256? I assume for most outputs of sha256 there will be zero, one or two possible 32 byte ...
2
votes
1answer
161 views

Hierarchical Encryption

Is there a way to setup a hierarchical encryption using public key encryption? Let's say a higher level user can decrypt messages encrypted by lower level users. Is that possible? I guess it is only ...
0
votes
1answer
36 views

Homomorphic encryption based on XOR

Consider the values a and b are encrypted as c1=(a XOR D )and c2=(b XOR D), my question is that can we derive b+a from any combination of c1 and c2 ? Note: (1) I admit that the D should have not been ...
1
vote
1answer
63 views

In HMQV, can one use multiple identities with one public key?

The HMQV protocol has 2 "identity" fields $\hat{A}, \hat{B}$ that are used in the dual signature - and it tries to guarantee that any properly-generated session key is only shared by a single $(A, B, ...
-1
votes
1answer
58 views

Is One Time Pad something like this? [on hold]

Alphabet: [A-Z] = [0-25] Plaintext = HELLO = 7 4 11 11 14 // QUESTION: do this key must be as long as plaintext? KEY: [QWERT] KEY = 16 23 4 17 19 Plaintext + Key = 23 27 15 28 33 Plaintext + Key ...
10
votes
1answer
3k views

Compare Blockmode CBC (with diffuser) against XTS

I have some problems in understanding the "advantage" of AES-XTS compared to CBC with diffuser. I read something about FileVault, in this paper they mention the two modes of operations XTS and CBC ...
4
votes
1answer
215 views

reducing false positives in searchable encryption

Practical techniques for searchable encryption proposed by Song et al. [1] have a false positive rate of $l/2^m$ where $l$ is left half of encrypted bits and $m$ is right half and $l+m=n$ where $n$ is ...
3
votes
1answer
74 views

PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
7
votes
1answer
582 views

Why should CAST5 and 3DES not be used for encrypting files over 4GB?

On https://www.gnupg.org/faq/gnupg-faq.html#define_cast, it says that Like 3DES, its 64-bit block size means it should not be used to encrypt files larger than 4Gb in size… How and why does the ...
0
votes
0answers
14 views

how to convert DSA private key to byte[] ? [migrated]

Is there any way to convert DSA private key as string or byte[] in java?
0
votes
0answers
25 views

Possible Digital Signature Hack?

I am starting to learn more about cryptography and I just read more about how asymmetric keys can make a digital certificate, and I would like if someone could explain me why the following case can't ...
2
votes
1answer
95 views

Message encrypted with a LFSR based stream cipher

I am learning about LFSR sequence and I came across this question: A 16-bit message consists of two ASCII characters. This message was encrypted with a one-time pad, and the key for the one-time pad ...
0
votes
0answers
73 views

Slow perfect hashing scheme from length N to length 2N? [on hold]

How can one reversibly hash a $n$-bit message (plaintext) to a $2n$-bit message (ciphertext) without collisions, and s.t. each $2n$-bit message is meaningful, i.e. can be uniquely traced back, in the ...
0
votes
0answers
14 views

Known-plaintext attack on two-dimensional affine cipher

Problem: We have a two-dimensional affine cipher with $n = 2,\,\,\,\mathcal{P} = \mathcal{C} = {\mathbb{F}_{16}^2}$, where $\mathcal{K} = \{ A,\,\,b\} $ and $b = (0,0)$. The encryption and decryption ...
2
votes
0answers
32 views

Bridging the gap between security proofs and “real-world” security

I've been studying cryptography for a little while. I understand fairly well the nuts and bolts of security proofs, but I'm having trouble reconciling the formal statements of security in these proofs ...
1
vote
1answer
31 views

How can I extract a X.509 DER certificate from a byte[]?

I have a byte array beginning with a (variable length) DER formatted X.509 certificate. After the certificate there are more bytes containing irrelevant data. How can I extract only the bytes ...
2
votes
3answers
127 views
+50

cryptographic data structure wanted: sparse array without membership test

I would like a data structure supporting two operations: set(k,v), and get(k), with the following properties: k can be any number between 0 and something impressively large, like 2^256-1. If there ...
1
vote
1answer
71 views

INT_32_BE in PBKDF2

Trying to understand PBKDF2 in detail. It is clear that the password and the salt is given to the PRF (which is HMAC-SHA-1 in the specification). But what is the role of the INT_32_BE(i)? What does it ...
3
votes
3answers
274 views

Is there any area where AES-CBC cannot be used ? If so, why ?

I would like to know the domains or specific applications where using AES-CBC is not advised due to any drawbacks like sequential encryption of AES-CBC ?
1
vote
0answers
45 views

Are there any obvious techncial faults in F. Ruiz's 2013 URSA javascript cryptography? [on hold]

The link to the cryptography is here: http://prgomez.com/ursa/ I have found the following simple javascript system of encryption/decryption portable and easy to use for emails and messaging sites, ...
2
votes
0answers
99 views

Cipher built from GPU primitives [on hold]

Is it feasible to build a cipher (or hash) out of GPU or DSP primitives (e.g. big matrix multiplication, Fast Fourier Transform, big block SIMD, or hardware H.264/AVC codec)? Preferably those are slow ...
0
votes
0answers
93 views

Simpler proof of RSA's correctness

Working out the details of RSA, I've seen many proofs of correctness. While none were really difficult, and I think I may have come up with one that's simpler. Since this is not really my area of ...
1
vote
1answer
58 views

Question about second preimage resistance of hash function combiner [on hold]

Construct a hash function as follows: Two schemes $\Pi=(Gen_1,H_1)$ and $\Pi=(Gen_2,H_2)$. Compute $s_1 \gets Gen_1$ and $s_2 \gets Gen_2$. Let $H^{s_1,s_2}(x)=H^{s_1}(x)\|H^{s_2}(x)$, is it second ...
0
votes
2answers
51 views

Does brute force attack use the program that created the ciphertext?

I've read several articles about brute force cryptanalytic attacks, but none explicitly say what algorithm is being run for each attempt, nor what criteria is used to declare an attempt a success or a ...
6
votes
2answers
2k views

Encrypting and obscuring data between site/user without SSL

Im trying to figure out what the best way to encrypt data sent between a webpage and the user(both ways) is, when hosted in an environment that doesn't support SSL. The purpose of encryption would be ...
3
votes
1answer
36 views

NIZK Proof of knowledge N of M discrete logarithms (threshold)

It is well known how to produce a NIZK that curvepoints $aG$ and $aP$ have the same discrete logarithm $a$ with respect to the curvepoints they are multiplied by. There is also a way to prove that a ...
1
vote
1answer
59 views

Strength and weaknesses of this JavaScript charCodeAt based login script

I know of a company on their website who are using this very basic password login page written in JavaScript. This doesn't seem very secure at all, because in the html source code it shows where the ...
0
votes
2answers
48 views

Brute Force Attack Strategies

A Brute Force Attack obviously involves attempting to decrypt ciphertext (with the associated plaintext being known) using all possible encryption keys. Aside from attempting all possible ...
2
votes
0answers
64 views

Encrypted database: how to deal with general queries?

My question is quite related to the concept of homomorphic encryption, which is not practical at all nowadays. In short, I would like to know how to query encrypted databases. Simple queries which ...
7
votes
2answers
86 views

Is deniable error-correction possible?

This question came up as I tried to answer an earlier question I asked: cryptographic data structure wanted: sparse array without membership test. I still have not resolved that question to my ...
-1
votes
1answer
24 views

Use encrypted private keys for login operation? [on hold]

I am trying to develop an application in which I want to do the following things: First I want to generate private keys using DSA algorithm and stored in a file in encrypted form using some key. To ...
6
votes
3answers
748 views

Is there benefit to signing unencrypted emails?

I came to this article from another comment on Crypto StackExchange. After reading it, I am wondering if there is any benefit to using a digital signature on unencrypted S/MIME emails?
-1
votes
2answers
44 views

Vigenere ciphertext encrypted with another vigenere cipher

I have been learning about Vigenere ciphers and then thought of this scenario: if a cryptographer encrypts a plaintext English message with a Vigenere cipher and then another cryptographer, who wants ...
-1
votes
1answer
37 views

Hash function and indifferentiability [on hold]

What are the properties derived from the fact that a hash function is indifferentiable from a random oracle?
1
vote
0answers
39 views

See any problems with this search-specific homomorphic encoding strategy?

I'm imagining this for use in the scenario of cloud-stored client-encrypted email, where, when seeking to do a string search across messages, you don't want to have to download every stored message in ...
-1
votes
1answer
50 views

Keccak and compression functions

Keccak follows a sponge construction. Can we say that Keccak employs a compression function? Generally speaking, for sponge constructions, can we say that there is an underlying compression function? ...
1
vote
1answer
110 views

Equal length of primes in paillier cryptosystem

In the key generation step of paillier cryptosystem , In order to satisfy $\gcd(pq,(p-1)(q-1))=1$ , we can take equal length primes. Instead of taking(length as parameter to generate $p,q$) equal ...
-1
votes
0answers
41 views

SSL heartbeat design [migrated]

So, about Heartbleed again, why does SSL/TLS allow the client to specify the message and its length in the heartbeat requests, rather than sending a simple ping?
-1
votes
1answer
50 views

Calculate the avalanche effect

I need to solve this problem, however, I didn't get the concept right. Is it I need to sum up all bits to get the total avalanche effect? eg. (1x8bits) + (5x8bits)... until I get the total for its ...
1
vote
2answers
80 views

Determining average number of hash calls to get a hash that begins with X

I have been attempting to find an answer to a self-study question: If I have a hash algorithm that outputs 256 binary bits, on average, how many times would I have to call the hash function so ...
-1
votes
0answers
26 views

Bitlocker suspension mode explanation [on hold]

I know when Bitlocker is suspended it publish the cryptography key,if i change SO in while how can he keep the key? Is stored in TPM? I don't think so... Can i install a new OS while Bitlocker is ...
2
votes
2answers
187 views

Reusing message in One Time Pad

One of the main rules of the OTP is, that a key should never ever be reused. But if we use some commutative operation (XOR for example) for generating the cipher text, then I don't see any difference ...
0
votes
1answer
87 views

Roots of polynomial in Shamir secret sharing

I need to know whether one can obtain any roots of the polynomial in Shamir secret sharing if he possesses less than threshold shares. For instance in (t,n) if he has t-1 shares can he obtain any ...
0
votes
0answers
23 views

EC Public Key length in ASN.1 DER

I have two X.509 certificates in DER format. A: ...
1
vote
0answers
98 views

Is it feasible to use combination of ABE schemes for encrypting the data?

I have a peculiar requirement for preserving the shared log files. For example I have 1000 records which belong to different organizations as listed below and all the logs are present in a single CSV ...
0
votes
1answer
69 views

stream cipher computation cost [on hold]

With AES-CTR the computation time to encrypt a message of lengh $n$ blocks is $n$ computations of the block cipher. What is the running time to encrypt a message of $n$ bits using a stream cipher, ...
0
votes
1answer
40 views

Group Dependent Language

The text below has been taken from the below paper Groth-Sahai Paper. The relevant part is highlighted in red. What does this group-dependent language mean in this context? From the definition of a ...
0
votes
0answers
42 views

Fully Homomorphic Encryption over the Integers [on hold]

In the scheme described in "Fully Homomorphic Encryption over the Integers" (van Dijk et al., 2010), how can I calculate the keys?

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