-1
votes
2answers
307 views

Why this k parameter is in unary in adversary PPT algorithm? [duplicate]

While reading some text on cryptography, I found that algorithm $A$, that the adversary (called Eve by convention) runs to break the cipher message, needs two parameters, candidate message ($y$) and ...
3
votes
1answer
250 views

Alternatives to HMAC + CBC?

I'm looking at using HMAC + CBC. The combination looks like this: ciphertext = AES256(text, k1) data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext Where: ...
2
votes
2answers
641 views

Is Base64(SHA1(GUID)) still unique like the original GUID?

Basically what the title is; GUIDs are unique by design. If you run the GUID through SHA1 and then Base64 the hash, will the resulting string have the same guaranteed uniqueness as the GUID, or not?
2
votes
2answers
358 views

What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?

Background: My current server-provider tells me it's no problem to store the passwords in plain-text in the database, saying he has to do so because they use CRAM-MD5 for email authentication. But ...
3
votes
1answer
135 views

When truncating an AES MAC value by “w” , how do I justify that “w” is still negligible?

I'm taking an online class on cryptography at corsera.org / Stanford, and the professor is explaining that it's OK to truncate an AES MAC to $w$ bits as long as $1/2^w$ is still negligible (say $w ...
1
vote
1answer
254 views

Polynomial multiplication and division in2^128

I want to multiply and divide polynomials, and implement the extended Euclidean algorithm for polynomial greatest common divisors, over a Galois Field of size $2^{128}$. Moreover, I want to use the ...
2
votes
1answer
377 views

How does OAEP improve the security of RSA?

The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions $H$ and $G$. Does everybody (so also an adversary) know these functions? If YES: How does it help the ...
1
vote
1answer
144 views

Is this a sensible cryptographic protocol intending to reduce the impact of compromised security?

I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data. The basic crux of it is that keys ...
1
vote
2answers
492 views

Generate fixed length cipher text from arbitrary length plaintext

Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
3
votes
1answer
447 views

Hill-cipher, disordered alphabet

I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model? In other words, instead of the ...
1
vote
2answers
270 views

Help me describe/identify this challenge-response protocol/algorithm?

My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation. I was asked to ...
2
votes
2answers
169 views

Is Functional Encryption about Access Control over encrypted data alone?

Informally, In functional encryption system , a decryption key allows a user to learn a function of the encrypted data. But all i see is that the function acts as an access control over the data. ...
1
vote
0answers
41 views

calculating beta for elgamal elliptic curves [duplicate]

Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime $p$, an elliptic curve $E$, a point $\alpha$ on $E \pmod p$, and a secret integer $f$. Suppose that Bob has ...
2
votes
2answers
341 views

SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?

Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
2
votes
2answers
743 views

True random numbers generated by sensors

Is using sensor raw data a good way of generating true random numbers? I mean using an IPhone's gyro/accelerometer raw output as a base for generating an array of true random numbers.
2
votes
2answers
279 views

Generating IV in TLS 1.2

I'm writing a TLS 1.2 implementation (in C#) using a custom protocol. My question is how to generate the IV attached to each message, I don't want to use RandonNumberGenerator because I've heard it ...
0
votes
1answer
54 views

PKCS#11: Which CKK_types are supported by CKM_PKCS5_PBKD2?

On Solaris there's a function pkcs11_PasswdToKey() which is a wrapper of C_GenerateKey(). I made a simple test and it turned out ...
2
votes
1answer
195 views

What is a fair exchange scheme?

The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated. Is this a new field in cryptology or can someone give an ...
0
votes
1answer
73 views

Encrypting a broadcast channel

We're building a data service that is expected to go out through a single "fat pipe" channel. The design requirement says that the data in the channel must be protected by authentication and ...
6
votes
1answer
725 views

Using an MD5 hash as a password

Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password. Memorization of long strings of random characters is not one of Alice's strengths, so she ...
2
votes
2answers
283 views

CSPRNG in JavaScript using Audio and Video

I ported GnuPG to Javascript using Emscripten (not released yet). Now I need a good replacement for /dev/random//dev/urandom. ...
3
votes
1answer
227 views

Why is the discrete log problem easy when the exponent comes from a binomial distribution?

I read in http://epubs.surrey.ac.uk/7219/2/esorics06.pdf that in exponential El Gamal the discrete log problem for recovering $m$ from $g^m$ can be made tractable when $m$ is drawn from a binomial ...
1
vote
2answers
255 views

Why is the following RSA PRNG cryptographically secure?

One requirement states that the generator has to withstand the next-bit test. Consider the following PRNG, where we calculate next output $x_i$ via the formula $x_i = x_{i-1}^ e\mod n$. I can see ...
3
votes
2answers
319 views

Is there a way to do fair exchange between two parties who don't trust each other?

Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts $m_A$, Bob encrypts $m_B$) with their own key, and ...
1
vote
1answer
243 views

Designing a security system from scratch with a custom protocol, suggestions needed

For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ...
2
votes
2answers
352 views

Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?

Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
6
votes
2answers
244 views

How to do a literature search

How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
2
votes
1answer
174 views

Does SRP reduce to DH key echange when shared password is not secret?

I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ...
2
votes
4answers
612 views

random number generator 10-side dice alternative

A lot of sites (e.g. Dirk Rijmenants') refer to 10-side dice to generate random number for one-time-pad. I was thinking about new ways to generate random numbers, letters and passwords. here what I ...
2
votes
1answer
229 views

Is the DES algorithm in OPENSSL random?

Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext ...
7
votes
2answers
280 views

Finding hash almost-collisions

A few months ago, XKCD posted a challenge to find a plaintext which hashed (using Skein 1024 1024) to a specified value. Inputs were scored based on the hamming distance between the hash of the ...
-2
votes
1answer
200 views

Cryptography based upon neural networks [closed]

I would like learn about use neural networks in cryptography. Is there any research literature on this subject? What should I do to learn about the subject? I am taking short course in neural ...
1
vote
1answer
231 views

Security of Salsa20 with some known plaintext?

Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known? Assume that a different IV and Key are generated before each file is ...
4
votes
1answer
347 views

Trying to better understand the failure of the Index Calculus for ECDLP

So I'm going to give you guys my understanding and then if you would be so kind as to tell me where I'm off the mark (hopefully I'm not completely wrong). So basically the index calculus for the ...
2
votes
2answers
128 views

Does knowledge of original file size provide a cryptographic weakness?

I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ...
6
votes
3answers
336 views

What kind of adversary is the cloud?

I just started some work on computation over encrypted data in the cloud. We're still in the early planning stages, and to really understand the kind of security we can offer I need to determine what ...
3
votes
1answer
770 views

Winzip AES256 vs PGP

If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption?
3
votes
1answer
432 views

Recommended way of adding a pepper/secret key to password before hashing?

There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
3
votes
4answers
705 views

Increased CRC collision probability when adding bits to input message

The Scenario I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ...
2
votes
1answer
125 views

How to derive formulas for addition and multiplication in Jacobian coordinates

Is there a way to derive the formulas for point addition and multiplication on elliptic curves in Jacobian format by yourself? How could I have derived these formulas by myself?
2
votes
2answers
206 views

Many consecutive hashes to slow down brute force attack?

I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ...
0
votes
1answer
135 views

Weak One Way Function

Show The function $mult(a,b)$ is weak one way if the Integer Factorization Assumption is true. I am read the proof of this enunciated but I want know if I understand this in my way. The proof use the ...
1
vote
1answer
300 views

What does $(\mathbb{Z}_n^*)^2$ mean?

In a paper they write once, $(\mathbb{Z}_n^*)^2$. Is this the group of quadratic residues or is it something else? Here the theorem: Under the strong RSA assumption, given a modulus $n$, along with ...
0
votes
1answer
74 views

How to hash a structure that needs to include that hash's outcome?

so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
4
votes
1answer
229 views

Injecting salt into PyCrypto KDF - useful?

I have noted some sources indicate that when using a KDF like PBKDF2 (alternatively) some advocate injecting the salt at the time of execution - like this: ...
2
votes
1answer
174 views

Attacking AES/CCM with random IV

A cryptosystem is using AES-128 in CCM mode with random IV. Suppose an attacker capable of: asking the cryptosystem to encrypt a single plaintext as many times as he wants; and asking the ...
4
votes
1answer
173 views

Are digital signatures secure for signing lots of small messages?

I need to sign the numbers from 1 to 1 billion (literally this, it's not an analogy) using a digital signature and then send these numbers in a particular order to someone. The message is not private ...
1
vote
1answer
249 views

Solving a discrete logarithm using GDlog

I am trying to calculate an $x$, such that $t = g^x \pmod p$ in order to crack a weak ElGamal encryption for university. I found GDlog, but I cant figure out how I can use the input to calculate my ...
8
votes
5answers
435 views

RSA leak bits to factor N

Suppose you randomly generate large primes p and q as in RSA, and then tell me N=pq but not p or q. Then, you would like to actually let me factor N, except you should tell me as few bits of ...
4
votes
2answers
657 views

Why is SRP not widely used?

SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations? I tried to ...

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