1
vote
1answer
172 views

What would the Internet be like without public-key cryptography?

The functioning of the Internet as we know it nowadays depends very heavily on public-key cryptography, including several key root systems that depend on its asymmetric properties. But what would it ...
0
votes
1answer
847 views

True 128bit secured password length?

assume we say 128bit keys are secure so a 16 character long password is safe, but if i even use lower case and upper case letters with numbers and special characters on my keyboard its about 80 ...
0
votes
1answer
115 views

AES 128bit round level recommendation

we don't want change standard just after every attack, now for AES 128bit blocks i think 16 round is secure, but what is best round amount ? we had attack for 7 round then 10 round and it going so on ...
0
votes
1answer
1k views

Why the following attack in common modulus RSA works?

Suppose that i share a common modulus $N$ with two users $u_1$ and $u_2$ with public, secret keys ($e_a,d_a$), ($e_b,d_b$). Why then $gcd(V,e_b)=1$ where $V=d_a*e_a-1/$W and $W=gcd(e_b,d_a*e_a-1)$ ...
3
votes
1answer
183 views

Does zero-padding the secret in Shamir's sharing scheme increase security?

When performed in binary Galois fields $GF_{2^n}$, Shamir's threshold secret sharing scheme produces shares that are each the same bit-size as the secret. Though the scheme is "perfectly secure" in ...
1
vote
2answers
2k views

Double Encrypting with two different keys

In terms of security, would it be MORE or LESS secure to take, say, an RC4 output (or Serpent) or other, that is encrypted with one key, and to encrypt that output with AES (using a different key)? ...
1
vote
2answers
150 views

What is an easy method of proving that a cryptographic oracle attack is possible?

Lets say an application is using CBC mode without authentication. The application is generating cipher text. This cipher text can be manipulated by the attacker and then transmitted back to the ...
-1
votes
1answer
67 views

construct an election protocol for the following election problem..? [closed]

I am something new to election protocols and I am trying to construct an election protocol for the following problem: Let $A= \lbrace a_{1} , . . . , a_{n} \rbrace $ and $B = \lbrace b_{1} , . . . , ...
2
votes
1answer
666 views

Proving that a scheme is not IND-CPA-secure

Suppose I want to prove that a given symmetric encryption scheme is not IND-CPA secure. The first thing I do is to define a specific adversary that attacks the scheme. How can I proof neatly, (using ...
1
vote
0answers
56 views

P-Complete hashes, hashing to a larger set

Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits). Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
3
votes
1answer
279 views

Is there a field guide to ECC for the IT Security layman?

I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and understand why certain features are implemented or not implemented in the ...
2
votes
1answer
9k views

AES vs Blowfish taking key-length into account

I understand that Blowfish is getting old, but is still a secure algorithm, and that AES is very popular, and is recommended by most people. My question is, how do the two compare when a 256-bit key ...
2
votes
1answer
3k views

AES key length greater than 256 bits - is it dangerous to do an implementation outside of the standard?

I'm making a digital-asset manager written in ActionScript 3, it will be used to manage highly sensitive information. I'm using the AS3Crypto library (which has quite a good reputation) to implement ...
1
vote
1answer
91 views

tower of extension field

while working on tate pairing, i have to implement towering technique. like i have point p on F(q) and point Q(F(q^k)) (here embedding degree k=12 for BN curve). instead of taking a point Q on ...
3
votes
1answer
799 views

How to generate a public key from a private ECDSA key?

Having some specific ECDSA curve and a private key, how does one calculate the public key? I am having a hard time finding the algorithm and equations for it.
1
vote
1answer
86 views

Tweaking textbook RSA to make the encryption a Pseudorandom function

Lets say I want to tweak/alter the textbook RSA encryption function to create a pseudorandom function by pre-processing the input. Suppose I do something simple like add 2 to the input before ...
4
votes
1answer
234 views

Using chi square for distinguishing between compressed and random data

I am trying to find some measurement for identifying and distinguishing between compressed and random data. I tried this first by computing the entropy of such data, the entropy value is extremely ...
1
vote
0answers
55 views

Generating Polynomials for the MPQS

I'm going to try and eventually factor RSA-100, but my current QS needs a lot of improvement, so I'm going to try and switch over to the MPQS. I'm a bit confused as to how the MPQS works, which is ...
8
votes
2answers
833 views

Why is h(m||k) insecure?

Here is the post that explains the failure for doing h(k||m) and I understand it. But I don't understand how h(m||k) is subjected to collison attack, or birthday attack. Please explain?
3
votes
2answers
221 views

Probability that an attacker wins the discrete logarithm game when exponents are drawn from a subset

Suppose $g$ is a generator of an order $p$ cyclic group in which discrete logarithm is hard and $p$ is a prime (i.e., given $g^x$ for a random $x \in \{0,1,\ldots, p-1\}$, it is hard to recover $x$ ...
2
votes
1answer
91 views

Individual bits of Textbook RSA

This question relates to the underlying RSA assumption. Forgetting about the fact that Textbook RSA is deterministic, I am curious about the assumed strength of the RSA problem. Does RSA hide all ...
3
votes
1answer
256 views

A question regarding relevance of vulnerability of MD5 when linking multiple records together

I have been studying a Supreme Court case "IMS Health vs Sorrel". In this case a Friend of Court brief filled by "Electronic Privacy Information Center" states that use of MD5 hash function to link ...
3
votes
3answers
196 views

Can the encryption exponent e be greater than ϕ(N)?

So I was just wondering in RSA, can the encryption exponent e be greater than ϕ(N)?? For an examples sake, lets just say N = 707, so p = 101 & q = 7. So, we have ϕ(707) = 600. Can I have e = ...
3
votes
2answers
2k views

AES Key Length vs Block Length

This answer points out that certain key and block lengths were a requirement for the AES submissions: The candidate algorithm shall be capable of supporting key-block combinations with sizes of ...
8
votes
4answers
621 views

Cracking WWII-era codes - code found on a pigeon's leg in Surrey

A recent BBC article entitled WWII code 'may never be cracked' posted a code: AOAKN HVPKD FNFJW YIDDC RQXSR DJHFP GOVFN MIAPX PABUZ WYYNP CMPNW HJRZH NLXKG MEMKK ONOIB AKEEQ WAOTA RBQRH DJOFM TPZEH ...
1
vote
2answers
157 views

Contruct a protocol to determine if three secret keys are different, without revealing any of them?

I am trying to find a protocol for this problem: Three persons, $A$, $B$, and $C$, know secret numbers $s_{A}, s_{B}$, and $s_{C}$, respectively. They want to know whether their numbers are all ...
3
votes
1answer
178 views

Is this attack for RSA possible?

$N=p·q$ ($p$ and $q$ are prime numbers), $m_1, ..., m_x$ are the messages, $e$ and $d$ are RSA encryption and decryption exponents, respectively. I am given $e, m_1, m_1^e, m_1^d, ..., m_x, m_x^e, ...
1
vote
1answer
86 views

Is there a big RSA Data Set

Is there a big dataset containing RSA public $(n,e)$ and private keys $d$ and primes $p,q$ where $n = p.q$ ?
10
votes
5answers
4k views

Galois fields in cryptography

I don't really understand Galois fields, but I've noticed they're used a lot in crypto. I tried to read into them, but quickly got lost in the mess of heiroglyphs and alien terms. I understand they're ...
8
votes
1answer
1k views

Necessity for finite field arithmetic and the prime number p in Shamir's Secret Sharing Scheme

Shamir's original paper (PDF, 197kb) describing a threshold secret sharing scheme states: To make this claim more precise, we use modular arithmetic instead of real arithmetic. The set of ...
1
vote
1answer
446 views

How do unkeyed hash functions (for MDCs) provide security?

Unkeyed hash functions are, by definition, hash functions computed without a key. SHA-1 is an example. MDCs (message digest codes) are a subclass of unkeyed hash functions. How are unkeyed hash ...
5
votes
1answer
2k views

A single password manager vs password generator/hash

I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise). On one hand you have ...
2
votes
2answers
120 views

Polynomials and efficient computability

In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT. It's clear that adversaries should be at ...
1
vote
1answer
163 views

inverse element in Paillier cryptosystem

As I know, in Paillier cryptosystem, the encryption $c$ of a message $m$ is calculated as $c=g^m r^n \bmod n^2$. Now, I am wondering if I can derive $g^m \bmod n^2$ given that I know $c$, $r$, and ...
8
votes
1answer
1k views

What are the benefits of lattice based cryptography?

Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ...
5
votes
2answers
1k views

RSA blind signatures in practice

Hi I have a problem with moving my blind signature implementation from educational (textbook RSA) to more practical (padded RSA) side. David Chaums paper gives a following figure: $r$ - blinding ...
2
votes
0answers
190 views

Transforming simplest protocol into a Sigma-protocol

I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...
2
votes
1answer
266 views

What is an oracle adversary?

I'm trying to figure out block ciphers and this is the first time I've encountered the term "oracle adversary". It appears in the context of defining a PRP and a PRF. Can someone please explain what ...
5
votes
1answer
263 views

Why doesn't this replay attack work on ECDSA?

I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ...
4
votes
3answers
360 views

Can I use PGP to sign a message without providing cryptographic non-repudation?

The difference between a digital signature and a MAC is non-repudiation. A message with a digital signature proves that only the sender could have signed the message, whereas a message with a MAC ...
1
vote
1answer
173 views

Need for Twin Elgamal encryption

What is the need for two private/public keys in twin elgamal? I'm relatively new and would need some help.
1
vote
3answers
306 views

Deterministic key generation

In a situation where it is required to generate n number of keys deterministically from a single piece of seed information can we assume that b breached number of keys, no matter what the quantity ...
2
votes
1answer
455 views

using Post-quantum asymmetric ciphers instead of RSA

We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
5
votes
1answer
371 views

Are there any Implementations of Secure Indexes? [closed]

There are several papers about Secure Indexes, for Example "Searchable Symmetric Encryption: Improved Definitions and Efficient Constructions" and "Secure Indexes". ...
3
votes
1answer
390 views

Why are protocols often proven secure under the random oracle model instead of a hash assumption?

Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle? I mean, is it possible to devise a protocol $P$ using a function $H$, and ...
3
votes
2answers
621 views

Public key cryptography - public key encrypts and cannot decrypt?

I understand the basics behind public key cryptography, in that each party has two keys - the public one encrypts, and the private one decrypts. What I cannot figure out is, How does the public key ...
4
votes
2answers
1k views

How can I break a Vigenère cipher with partial plain text?

I have an exercise to do regarding Vigenère encryption. I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV and a partial plain text: ...
1
vote
2answers
358 views

Are really, really long passwords any securer than short ones?

Just for fun, I want to encrypt a message that will take about 10 or so years to decrypt. My idea is to encrypt a message with AES-512 with a password one million decimal digits long. Knowing not ...
2
votes
1answer
244 views

RSA Key generation Public exponent too big

I'm currently writing a paper about RSA (a self-chosen subject). I'm writing about the key-generation in RSA, and I have problem finding the public exponent e. I have chosen p = 61 and q = 53. Then ...

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