5
votes
1answer
130 views

Is it possible to fool Miller-Rabin test?

It is well known that it's possible to fool Fermat test with Carmichael numbers. But, is it possible to deliberately fool many-rounded Miller-Rabin test by constructing some special number without ...
2
votes
1answer
97 views

What kind of Quantum cryptography technology(protocols) can be used for Mobile Ad hoc networks(MANETS)?

Typically ad hoc networks do not have a proper infrastructure and the routing is done only through the base stations which are connecting a wired and wireless network. Does quantum cryptography ...
3
votes
2answers
193 views

Are there other digital certificate formats than X.509?

Hi I am a little new to security, but in researching digital certificates it seems the only format people describe is X.509. Are there other formats? If so what are they and where can I find ...
23
votes
0answers
765 views

How is the MD2 hash function S-table constructed from Pi?

For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ...
0
votes
2answers
131 views

Why use CBC-MAC? Why not just apply hash function on the whole message?

Why not just apply hash function on the whole message? Why convert that message into blocks and hash those blocks? To avoid collisions?
6
votes
1answer
301 views

Can a LFSR be cryptographically secure?

I have been looking at an embedded microcontroller which has a cryptographic hardware engine (in particular the PIC32MZ family). These devices have what they advertise as a cryptographically secure ...
-2
votes
1answer
95 views

is there an algorithm to encrypt all the datatypes?

Is there an algorithm or technique to encrypt all the datatypes such as (video , image , text , fax, audio ,file,etc...) -one algorithm encrypt every thing-? also if I try to build such this ...
10
votes
0answers
256 views

Shared secret: Generating Random Permutation

-- or: How to Play Poker Without a Dealer I know this question is long but it's a really interesting theoretical problem about shared secrets and multi-party computation. General Problem: "Shared ...
1
vote
1answer
284 views

In this example, which is a premaster secret, and which is a master secret?

In the context of this data, as shown in the image below, which one is a pre-master-secret and which one is a master-secret. It looks to me as if the final value of 2, for Alice and Bob is a ...
4
votes
1answer
1k views

What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
6
votes
2answers
374 views

How does Clifford Cocks 'Non-Secret Encryption' work?

I have read Clifford Cocks "A Note on 'Non-secret Encryption'" and thought I would try to implement this, but I don't seem to be able to get it to work. I'm obviously missing something. From the ...
6
votes
2answers
132 views

Does there exist a proof-of-retrievability scheme that is publicly-verifiable, limited-use, and does not use homomorphic encryption?

I find myself wanting to test out a practical implementation of a proof-of-retrievability scheme, simply out of curiosity. These schemes seem to be divided into two variations, publicly-verified and ...
2
votes
2answers
140 views

How can I solve congruence modulo N?

I am trying to solve congruences of the form $$J_A \cdot a^e\equiv 1 \pmod n$$ where $n=pq$ for $p,q$ prime and $\gcd(e,\varphi(n))=\gcd(J_A,n)=1$ Solve for $a\in \mathbb{Z}$, in terms of $n,J_A$ ...
14
votes
6answers
3k views

Types of Cryptography for a 4-8 bit microcontroller

This is more of a research question. I was wondering what types of crypto algorithms would work best on a small 4-8 bit micro controller. I recently read a paper called Security Considerations for ...
2
votes
3answers
460 views

How to submit a new method of encryption?

I came up with a truly new method of applying modulo-2-addition encryption function in stream ciphers which is inspired by a mechanism used to prove a mathematical theorem. How can I determine whether ...
4
votes
1answer
198 views

Keccak padding implementation, and bit ordering

I am trying to implement Keccak in Java for my school work. And I am getting stuck in two places: On the summary page the padding is shown as P = M || 0x01 || 0x00 || … || 0x00 P = P xor ...
0
votes
1answer
75 views

A replay attack question

Which of the following protocols is susceptible to replay attack :- 1) A -----> B username, password 2) A -----> B username, h(timestamp,password) 3) A -----> B username timestamp, ...
0
votes
2answers
258 views

Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precompuation of plaintext$\to$hashvalues (rainbow tables). I know from different threads, it is not necessary to keep the salt ...
8
votes
2answers
842 views

Webcam random number generator

I have a question about random number generators. I have read from a real random number generator, based on a webcam ("randcam"). My problem is, that I do not really understand how the generation of ...
2
votes
1answer
76 views

Usability of padding scheme in blinded RSA signature?

In Wikipedia's article on Blind signature, in the section Dangers of blind signing which describes RSA blinding attack one reads the following This attack works because in this blind signature ...
-3
votes
1answer
120 views

Storing the activation status of a product and expire details Android [closed]

In my Android application, it's required to store the activation status of the software and keep track of the activation expire date. What is the best way to store this information? Is it safe to ...
6
votes
2answers
621 views

Knowing pre-encryption data, can we find the private key CryptoLocker used?

One of our users seems to have been hit by CryptoLocker. As a result, he has a hard drive full of encrypted files. The ransom-ware claims to have used public key encryption on the files. If we know ...
5
votes
2answers
1k views

Replay attack in ECB mode

How do replay attacks work in ECB mode? I found this in Wikipedia: "ECB mode can also make protocols without integrity protection even more susceptible to replay attacks, since each block gets ...
7
votes
3answers
2k views

What is the most secure hand cipher?

By "hand cipher", I mean a symmetric cipher for which encryption and decryption can can both be performed with a pencil on graph paper, consuming about 10-20 seconds per character by a proficient ...
4
votes
1answer
289 views

Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5?

I've studied that the Bleichenbacher's CCA attack on PKCS#1 v1.5. is a base to many versions of attacks in the area. I'm trying to understand that attack, but every explanation I saw starts with the ...
0
votes
1answer
244 views

openSSL ECDH private key size

When you are using a named curve like P-256 in openSSL, is there any standard key size for ECDH private key keys? If you look at the ec_key.c file in the openSSL ...
3
votes
1answer
188 views

How to calculate entropy of a combined key

I know how to calculate the entropy of a key that relates to its selection process. For example if the key space is $1000$, entropy of a randomly chosen key is $1000$. Suppose now you have two keys ...
-2
votes
1answer
64 views

function of crypt called “ICE” [closed]

Using exeinfo, I have identified a function of crypt called ICE. What is it? How can I find ...
0
votes
0answers
32 views

In Merkle Damgard Constructoin, why do we add another block with value of number of blocks? [duplicate]

I'm trying to understand how can we find collisions, in simpler Merkle-Damgard constructions. consider my question as, what are the collisions for these cases of Merkle-Damgard constructions: we pad ...
6
votes
1answer
248 views

Formal definition of “explicit” algorithm?

A long time ago, I read that the definition of "cryptographic hash function" is "collision-resistant one-way function". (A similar definition shows up in the FIPS standards for SHA-1 etc.) But this ...
4
votes
1answer
260 views

How does the secret key in an HMAC prevent modification of the HMAC?

Just as a preface: I'm not implementing a HMAC - I just want to understand it, as it is part of of my Computer Science course. When using Hash-based message authentication codes, I understand that ...
3
votes
1answer
169 views

Is $q(n)=1/n$ a negligible function?

By definition - $q(n)$ is a negligible function if for every positive integer $c>0$ there exist an integer $N_c$ such that for all $x>N_c$ : $q(n)<1/x^c$ So for the function $1/x$, if we ...
1
vote
1answer
295 views

What's wrong with my security model - or how can it be attacked?

I'm working on a little personal project where security is very important, and I've thought for a while about the best way to do this. Now I am looking for a little outside help on good practices. The ...
3
votes
1answer
123 views

Is this really the correct way to do an IND-CPA test?

In a description of IND-CPA (indistinguishability under the chosen plaintext attack), I have been reading the following, simple test: The adversary can generate as many messages as he wants. Then, ...
12
votes
4answers
770 views

About Cryptography in a Character Language

Suppose I had a message in Chinese (or another non-phonetic language) and I wanted to encipher it. Some of the simplest encryptions in English are substitution ciphers, but such ciphers don't seem ...
1
vote
2answers
251 views

What are requirements for this grille?

I'm trying to program a Cardan grille, but I can't find requirements for grille. In my case, grille is square matrix A with $N$ x $N$ size, and elements are $0$ or $1$ (where $1$ means that it is ...
1
vote
1answer
240 views

What is total key space in transposition algorithms

How we can measure key space in transposition algorithms? Should we specify the method, like rail fence?
-1
votes
1answer
650 views

Is it possible to crack a blowfish 256 bits encrypted file? [closed]

I have a file of my own that I have encrypted using Coder-Abi. Now, I can just remember part of this password. So, would it be possible (much easier) for me to crack it knowing only part of it? I can ...
4
votes
2answers
479 views

A timestamping authority (digital notary)

Does there currently exist a free online service that accepts a file, hashes it, takes an authoritatively chosen timestamp (from one or more time services), signs these and sends this signed message ...
5
votes
1answer
230 views

Can you help me understand hash-preserving encryption?

I have rather simplistic understanding of cryptography, so I have to beg a pardon in advance if the question has internal contradictions. Imagine data $A$ with a hash $hashA$. This data is encrypted ...
3
votes
2answers
209 views

unique one-way hash

For a 10-digits numeric domain (swedish social security numbers), is there a hash function with the following properties? no two numbers result in the same hash it is not possible to deduce the ...
5
votes
1answer
374 views

What could “look for the constants that you might find in RC6” mean?

In this presentation at the 30c3 (long but extremely interesting and well-documented), Jacob Appelbaum gave this verbal advice (circa 43'30"): look for the constants that you might find in RC6 ...
1
vote
1answer
192 views

Verification of identity by certification authority

I have question about how a user's identity is verified by a Certification Authority. As I understand it, the process works as follows: User generates his private key and (with the help of private ...
4
votes
2answers
241 views

Hash function based on block cipher (and proof of security in the PRP model)

Do there exist proofs of security for primitives like hash functions (based on a block cipher) in the PRP model. I often see proofs in the random oracle model (for hash function based on compression ...
0
votes
2answers
116 views

Why do PKI schemes need security proofs? [closed]

When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed? Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol ...
1
vote
2answers
207 views

Why nobody considers counter re-keying as a standard Block Cipher Mode?

One of the simplest possible cipher modes is setting each successive key as a function F of the previous one. ...
2
votes
1answer
83 views

A confusion about HMQV?

As the full version of HMQV is very long, I will give a graph of it below \begin{array}{@{}l@{}c@{}l@{}} \hat{A} && \hat{B} \\ (a,A=g^a)&&(b,B=g^b) \\ x\in_R[1,q-1],\quad X=g^x ...
1
vote
1answer
108 views

Difference between implicit signature and explicit signature

In most of time, what I see is explicit signatures such as ElGamal, it's rare to see the implicit signatures. So I wonder why it's rare to be seen? what aspect is it mainly used? what's the ...
1
vote
2answers
319 views

Where is my private key stored when I communicate to a website that uses SSL/TLS?

If I communicate with a website that uses SSL/TLS, my browser will generate a private key. Would the browser store that key on the hard disk or would store just it in the RAM?
13
votes
2answers
595 views

Why xor is a linear operation but ordinary adding is not

I'm new in cryptography and try to read some articles in this field. Many of these articles talk about non-linear S-boxes, and nothing more on what they mean by their non-linearity. I have a simple ...

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