3
votes
3answers
562 views

What is the difference between online and offline brute force attacks?

I read some papers saying a certain scheme is secure for offline brute force attacks, but vulnerable to online brute force attacks. I wonder the difference between the online and offline brute force ...
2
votes
2answers
67 views

Mutual verification of shared secret

Is it possible to develop a scheme where two parties, unsure if they have the same secret, can verify that the other does or does not share the same secret, without one party being able to cheat and ...
1
vote
0answers
37 views

Commitment scheme to share money

I have such problem: party $X$ has an amount of money $M$, which it needs to share with $n$ other parties. Every week the amount of money is different. Let say not, that I am a party A, which is one ...
0
votes
1answer
22 views

Encryting data with password for local storage using libsodium

I want to encrypt data that is stored on the hard disk using a user-entered password. For this I look into the sodium docs and all I can find for symmetric encryption is authenticated encryption. ...
0
votes
0answers
22 views

Encrypting a file so that it can be decrypted everywhere out of the box [closed]

I would like to encrypt a file and be confident that: I can open it on any platform with just a password. I can do this even on computers where I have restricted access, such as on computers in a ...
1
vote
2answers
94 views

How does SafeNet MobilePASS generate passwords? (TOTP Variant)

This question is similar to How does SafeNet MobilePASS generate passwords? The question and answer there is related to the HMAC Variant of SafeNet Mobilepass. I'm looking for details on the TOTP ...
1
vote
1answer
30 views

Does failure of indistinguishability of encryptions imply lack of CPA-security?

Suppose we have an encryption scheme that fails the indistinguishability of encryptions test. That is, given messages $m_0, m_1$ and a ciphertext $c_b = Enc_k(m_b)$, where $b \in \{0, 1\}$, the ...
0
votes
0answers
32 views

Encryption on mobile devices? [closed]

I have studied the basics of cryptography, so it would be okay to say that I am familiar with the concepts of Cryptography (Theoretical). I have surfed the net for days to implement my theoretical ...
2
votes
1answer
39 views

On composition of encryption schemes

If we composed (as in function composition) multiple CPA-secure encryption schemes would the result also be CPA-secure?
0
votes
1answer
48 views

Is there an asymmetric One-Time-Pad? [duplicate]

Is there something like a perfect asymmetric crypto-algo? Is there proof that there must be one or not. From a logical point of view it seems to be possible to design such algorithm if your keysize is ...
0
votes
1answer
57 views

Computational indistinguishability with Example

Based on computational indistinguishability definition no PPT algorithm can distinguish $X$ from $Y$, where $X=\{X_n\}_{n \in N}$ and $Y=\{Y_n\}_{n \in N}$ are ensembles of probability ...
0
votes
0answers
24 views

Finding patterns in a gambling game [closed]

I'm working on a program that I hope it will help me to get better chances on a gambling game. I have a very large database of numbers how occur in this game and my program pass through those numbers ...
0
votes
0answers
76 views

Which of these is a secure MAC?

Let (S,V) be a secure MAC defined over $(K,M,T)$ where $M = \{0,1\}^n$ and $T =\{0,1\}^{128}$. Which of the following is a secure MAC: $S'(k,m) = S(k,m)[0,\ldots,126]\quad and \quad V'(k,m,t) = ...
0
votes
1answer
34 views

Which of the following hash functions is collision resistant?

Let $H: M \to T\ $ be a collision resistant hash function. Which of the following is collision resistant: $ 1.H'(m) = H(m \big\| m)$ $2.H'(m) = H(m) \big\| H(0)$ $3.H'(m) = H(m) \oplus H(m)$ ...
0
votes
0answers
25 views

Signing a pdf document [closed]

I want to read a pdf document through an android application developed my me .Then i want to sign it through an certficate recorded in the smartphone.There is someone who know how to do it and thanks ...
-1
votes
2answers
92 views

Meet-in-the-Middle attack on 3DES [duplicate]

How can I apply the Meet-in-the-Middle attack to the 3DES algorithm, and why does the literature say that 3DES is more secure than DES?
0
votes
0answers
23 views

Why does self-signed HTTPS show an error page, but self-“signed”/made HTTP does not? [closed]

Is there any reason, why browser show a huge warning message when a website uses self-signed HTTPS, but do not show a warning when the website is using HTTP? As far as I know using HTTPS - no matter ...
0
votes
1answer
48 views

Paper from NSA sponsored conference? [closed]

I'm interested to read paper presented on this conference: https://www.nsa.gov/about/_files/cryptologic_heritage/2011_SYMP_Package_25_July.pdf Dr. Jerca Vodusek Staric, University of Maribor ...
3
votes
1answer
82 views

Build set with PKI from reliable broadcast / random beacon

I am trying to build a protocol (or find an existing one) for creating a set $S_2$ with PKI from a set of parties $S_1$ that initially does not know anything about the other parties. We assume ...
0
votes
0answers
37 views

Enigma algorithm Question about the Ringstellung

This might be a stupid question but I need to implement the Enigma algorithm and I don't fully understand how it works. I've googled the subject and I am confused about what the Ringstellung is and ...
1
vote
0answers
23 views

How do I verify a reset token if the token is hashed in DB?

I've been searching around the web for best practice how-to on secure password reset system (email with reset url), and the idea to hash the token in the database, which I did not implement at first, ...
-2
votes
1answer
75 views

SAT as a basis for a PKCS - Effective? [closed]

I recently read this paper on a public key cryptosystem based on the SAT-problem.(SAT=boolean satisfiability problem, NP-complete) The speed of this system looks quite promising as extreme ...
1
vote
3answers
121 views

Is what i'm trying to do safe?

What both parties have: Server Master Secret (MS) Server supported versions (Svers) Agreed upon version (ver) Client Master Secret (MS) Client supported versions (Cvers) Agreed upon version (Ver) ...
0
votes
1answer
59 views

AES process candidates implementations and usages

There were fifteen candidates in the AES selection and I suppose that Rijndael wasn't the single good algorithm. I know that Camellia is an evolution of E2 candidate and can be used as symetric ...
0
votes
1answer
30 views

CCA secure or not?

Let $F : \{0,1\}^n \times \{0,1\}^n \rightarrow \{0,1\}^n $ be a PRF. And let the encryption function be $Enc{_k}(m) = r || (F{_k}(m) \bigoplus r \bigoplus 0^n)$ , where r's value is random. Is this ...
0
votes
2answers
59 views

Fortuna: why are source ID and data length added together with entropy data into the pools

Section 9.5.6 of Cryptography Engineering states that The concatenation [of source number, length of data, and data itself] is then appended to the pool. Why are we including source number and ...
1
vote
2answers
68 views

Negilible Function $\frac{1}{n!}$

Is $\frac{1}{n!}$ a negligible function where $n$ is a security parameter? Application: I have a vector of n>100 elements. I permute it and give it to an adversary. The adversary can break it if it ...
-1
votes
0answers
107 views

Is Information Loss in Crystalline Cipher a Good Approach to Anti-Cryptanalysis? [closed]

Crystalline Cipher is a new cipher released under the MIT license. The approach employed manipulates the locations of bits and bytes to effectively scramble the plaintext, erase information from ...
1
vote
1answer
111 views

Generate a list of valid ASCII codes

I have read many pages about encryption but I am really stuck on this. For access control to a building I want to print a 10 character ASCII code on a ticket (as a barcode). The barcode reader ...
2
votes
1answer
59 views

Authenticate a short message with redundant encryption instead of using a MAC?

I have a short message that’s exactly 128 bits of length. The message serves as a time-limited authorization token for a database. It contains a permission profile ID (64 bits) and an issue timestamp ...
2
votes
0answers
23 views

Proposed unidirectional authentication scheme

I've been looking around for a way to authenticate a client to the server and deliver a message, but in a unidirectional fashion - that is, the client sends messages to the server, but the server ...
0
votes
2answers
60 views

Modifying a [CRC32] checksum protected file [closed]

I dont want to ask for help without showing how far I came by myself, so this is what I have so far: The file of interest is an encrypted/obfuscated .bin script, which cotains information on certain ...
0
votes
1answer
40 views

Why perfect secrecy can be ensured when a plain message and a cipher-text based on one-time pad are correlated?

First, some well-known results are as follows. For random variables $X$ and $Y$, we have $$H(X,Y) \leq H(X) + H(Y).$$ The equality is achieved when $X$ and $Y$ are independent. Second, in one-time ...
2
votes
1answer
38 views

Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher

In polyalphabetic substitution cipher, if we have a key $k$ (a string of letters) of length $n$ does the plaintext $m$ (also a string of letters) have to satisfy $|m| \geq n$? Also, side question, ...
0
votes
1answer
39 views

what is legend of h(r) in this protocol?

can you help me what is legend of h(r) in below protocol? ‎‎$A‎\leftarrow‎{B}\quad:{h(r)‎‎}{,B}{,P{_A(r,B)}}‎\\A‎\rightarrow‎{B}\quad:r$
6
votes
3answers
2k 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 ...
-2
votes
0answers
31 views

How to implement H1(x) [closed]

I want to implement H1(M,S1) in python for my project.Where , H1 :{0,1}* × Zp->Zq. M is the message and s1 is the key.
1
vote
1answer
106 views

Inserting a backdoor into a cryptographic hash function

I'm curious as to how a backdoor can be built into a hash function. What might it take the form of? What's probability of getting one that can be backdoored in a way that can actually undermine its ...
-1
votes
0answers
22 views

How can one improve Rijndael's with more efficient SBoxes?

Knowing that the Rijndael's SBox is a pre-calculation from a composition of two operations (an inversion in a polynomial field, and an affine transformation that can be saw as a product and an ...
0
votes
1answer
17 views

Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
0
votes
2answers
34 views

what is recommended x length in Diffie Hellman algorithm

According to rfc documents http://tools.ietf.org/html/rfc2412#appendix-E.2 & http://tools.ietf.org/html/rfc3526#section-3, it has defined the prime and the ...
0
votes
0answers
12 views

AES GCM Mode Client Side [closed]

I am implementing browser side cryptography in my project. I want to implement the AES-GCM in both client side and server side. I am using nodejs for that. I have researched on the net but I found ...
2
votes
1answer
61 views

How do we guarantee plaintext is coprime in RSA?

The specifications for RSA state: $P^{\phi(N)} \equiv 1 ~mod~N$ if and only if $P$ and $N$ are coprime. Here $P$ is the plaintext and $N$ is the product of two suitable primes $x_1, x_2$. My question ...
0
votes
0answers
46 views

Calculating XOR Key Sizes

I've been playing around with the Matasano crypto challenges (cryptopals.com). I had a couple false-starts on the challenge that has you creating a program to calculate the key size of a XOR encrypted ...
11
votes
1answer
1k views

Duration for attacking Two-Key Triple-DES Encryption using all RAM ever built?

I am considering attacks on Two-Key Triple-DES Encryption assuming $2^{32}$ known plaintext/ciphertext pairs (that's a mere 32MiB of ciphertext) by the method devised by Paul C. van Oorschot and ...
1
vote
1answer
92 views

Why doesn't this defeat RSA?

Apologies for the obviously ridiculous question but I need to know where I'm going wrong here. For RSA, we compute $n=pq$ for primes $p$ and $q$. We then choose an $e$ such that $gcd(e, ...
0
votes
1answer
49 views

Value of S and r in Fiat-Shamir Protocol

In the book Cryptography and Network Security by Forouzan,in chapter 14, Fiat-Shamir protocol, its mentioned that two large prime numbers p and q are chosen and kept secret. However n=p*q is made ...
1
vote
1answer
52 views

How to exchange authentication keys

I am trying to create a secure Bluetooth Low Energy connection. The peripheral server (the main device other people would connect to) would need to service many clients (users) and due to hardware ...
3
votes
2answers
1k views

ASCII to same-length ASCII encryption?

I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight. The ...

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