2
votes
2answers
85 views

What is the purpose of Pseudorandom Function Families (PRFs)?

I'm currently in a course in Cryptography, and was wondering why pseudorandom function families exist at all. If there existed one pseudorandom function f(x), based on its definition, could that not ...
0
votes
1answer
121 views

Combining a block cipher with a (pseudo) OTP

One of the drawbacks of OTP is that it can require an inconveniently long key. Besides that, it doesn’t provide data authentication. Therefore, I have been working on an algorithm idea, which I hope ...
8
votes
0answers
968 views

Elliptic curve cryptography related key attacks

This question is an extension of Families of public/private keys in elliptic curve cryptography As described above, bitcoin "type 2" deterministic wallets use a root private/public key pair, where ...
2
votes
4answers
597 views

Does it make sense to have a 4000 bit long key?

My question is about the key length of a asymetric algorithm. How is it possible to memorize or remember a key that is about 4000 bits long?
2
votes
1answer
3k views

When NIST disallows the use of 1024-bit keys, what effect will that have on SHA-3 (with max. 512 bits)?

Quoting the article Gone in 60 Months or Less: The National Institute of Standards and Technology (NIST) has disallowed the use of 1024-bit keys after 31 December 2013 because they are insecure. ...
2
votes
1answer
103 views

Would SHA-1 be safe for certificates with short validity?

There are articles floating around the topic of SHA-1 deprecation. The gist of it is that in (mostly) developing countries, people are still using mobile/computing devices that are 5 years old (or ...
0
votes
1answer
70 views

How can I study the math behind cryptography? [closed]

I am a junior in high school and I am currently studying algebra 2. Where can I go to learn about the mathematics behind cryptography? I have a very basic knowledge of cryptography, but I am really ...
0
votes
0answers
51 views

Translation of Schorr Ring Signature to ECSchnorr Ring Signature

I have to write an EC version of Schnorr Ring Signature Scheme. I've already wrote regular ECSchnorr Signature Scheme using this (page 128). I've found a scheme of Schnorr Ring Signature Scheme (page ...
3
votes
2answers
142 views

Best modern cipher for morse code?

I am looking for a modern cipher to encode morse code, ie. input is [A-Z 0-9] (base36 as I learned in the comments below) and output is the same, one character at a ...
3
votes
2answers
102 views

Implementation of ECC over binary field

I am supposed to implement ECC over binary field (in C++) for equations of the type - $y^2 + xy = x^3 + ax + b$, as my project. I wish to include the following features : The user will enter a prime ...
2
votes
1answer
66 views

Elliptic Curve ElGamal and DSA - smooth group order and element of large prime order

In regular ElGamal and DSA, we choose large primes $p$ and $q$ such that $p\equiv 1\pmod{q}$, and a group element $g$ of order $q$ by computing $a^{(p-1)/q}$ for some random $a$. This is to prevent ...
6
votes
1answer
110 views

Non-deniability of data sent over TLS

Andy is going to connect to a server Selma over TLS. Later, Andy would like to be able to publish everything (the ciphertexts, the plaintexts, all his keys) and prove to a mediator what data he sent ...
2
votes
2answers
174 views

Given a pseudorandom function F, is $(F_k(r) \; | \; F_k(r + 1))$ also a PRF?

Given: F is a pseudorandom function, G is a pseudorandom generator with $l(n) = n+1$. The following schemes should be classified as being insecure, IND-COA secure, IND-CPA secure. To encrypt $m \in ...
2
votes
1answer
48 views

Generalization of the DL-assumption in bilinear group pair

When thinking about a pairing-based cryptographic scheme, I encountered the following problem. Let $e \colon G_1, G_2 \to G_T$ be a Type 3 pairing. Then: Given $P, zP \in G_1$ and $Q, zQ \in G_2$, ...
2
votes
2answers
98 views

RSA and difference between factors

As I understand, for RSA $n = p \cdot q$. For the key to be safe enough from getting factored, $p$ and $q$ have to be far from each other. How far do they have to be? For example, if I have two ...
1
vote
1answer
67 views

Username and Password: How does it work?

Suppose a client (Alice) goes to an HTTPS website (Bob) over TLS 1.2. Alice sends Client Hello with some random number $r_a$. Bob sends Server Hello with another random number $r_b$. Suppose they ...
1
vote
1answer
144 views

AES-256 add round key how

Can anyone explain to me (or send a link to somewhere) how round keys are added in AES-256? I understand that the round keys is added to the state matrix for each round and how XOR works. But since ...
1
vote
4answers
3k views

Is a Mersenne-twister cryptographically secure if I truncate the output?

I want to create an online roulette game. Is it OK if the PRNG is seeded only once, when the user starts the game, or is it recommended to re-seed sometimes during game? Maybe just seeded once a day ...
18
votes
1answer
34k views

How is SHA1 different from MD5?

On the surface, SHA1 and MD5 look pretty similar. Their diagrams include chunks of bits, bit rotation, xor and special functions. Their implementations are roughly the same length (at least the ones ...
2
votes
1answer
108 views

textbook RSA signature scheme security

Are textbook RSA signatures secure if an Adversary does not have access to ask signing oracle queries?
3
votes
2answers
138 views

Security analysis of this one time password based scheme for copy protection

Imagine such protocol. Client and server initially share secret K[0]. When client wants to contact server she sends server K[0] and her ID. Server accepts request, and generated new random K[1] and ...
2
votes
1answer
180 views

How broken is a xor of two multiply with carry generators?

How broken is a xor of two LCGs? How Brittle Are LCG-Cracking Techniques? Based on the above two questions, I have simply one additional question: how broken is a XOR of two 64-bit multiply with ...
4
votes
2answers
525 views

Is Chaocipher a secure cipher under ciphertext-only attack?

Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ...
4
votes
3answers
850 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 ?
4
votes
2answers
114 views

Hash functions vs Stream Ciphers in terms of Speed

We know that it's possible to create a hash using a stream cipher (for instance, RC4 or AES in Counter Mode). As stated here: "A Pseudo Random Generator (PRG) and a hash function are both Pseudo ...
3
votes
1answer
109 views

DES: How to find the Inverse of the Initial Permutation?

I am doing a DES problem by hand and I want to know how you calculate the inverse of the initial permutation. I know what the permutation is, but how do you find it based off the given initial ...
1
vote
0answers
17 views

RSA incorrectly translates for small keys [duplicate]

I've been learning about RSA and wrote my own implementation. I don't pretend to have intuitive understanding of RSA or that I understand why it works, but I believe to have some basic understanding ...
6
votes
2answers
721 views

On AES, is a true random string enough for a key?

The string (32 ASCII characters) is entered by a human, and considered truly random. Should a key derive from this string, or it is secure to use this string as a key directly? In other words, does ...
5
votes
2answers
124 views

Data Leakage and Data Switching

I have two secret values $a$ and $b$ (i.e. they are arbitrary values). I mask them as follow: $v_1=r_1a+r_2$ $v_2=r_1(b-a)$ where $r_1$ and $r_2$ are uniformly random values. I send $v_1$ and $v_2$ ...
1
vote
4answers
308 views

Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula: $$ M = C^d \bmod n = 2^{17} \bmod ...
4
votes
3answers
642 views

What is the appropriate public key encryption for secure coin flipping?

I quote Bobby's question here since I encountered the same one... Random Coin Flip using ElGamal and a Trusted Party Consider the following protocol for two parties to flip a fair coin. Trusted ...
3
votes
0answers
35 views

Seeking an implementation of the Satoh algorithm for elliptical curve point counting

I would be very grateful if someone has an implementation of the Satoh algorithm (Fast Elliptic Curve Point Counting). Can someone point me to practical algorithm implementations or provide some ...
6
votes
1answer
307 views

Difference between actual attacks and theoretical attacks on SHA cryptographic series

Could anyone tell me what the difference is between a theoretical attack (Like the one done on SHA-1) and an actual, practical attack (Like the one done on SHA-0)? Is a theoretical attack a proposed ...
1
vote
0answers
33 views

How to apply linear cryptanalysis to PRESENT?

Can someone help me implement linear cryptanalysis of the PRESENT block cipher? How should I start with 64 bits of plaintext and 80 bits of key?
15
votes
1answer
764 views

Is it possible to actually verify a “sponge function” security claim?

When using a “sponge function” to create a cryptographic hash, we can look at the flat sponge claim, which flattens the claimed success probabilities of all attacks using a single parameter: the ...
21
votes
2answers
1k views

Selective format-compliant JPEG encryption?

I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
19
votes
3answers
1k views

Cryptographic Challenge: How to Say Something Confidentially to Snowden?

The Snowden situation raises an intereting cryptograpic problem. At present, how can something be sent confidentially to Snowden? Claim: I have no particular political orientation. The above ...
1
vote
0answers
24 views

Generating keys in RSA [duplicate]

I'm trying to learn how RSA works. From what I found online, I'm supposed to generate private key using Extended Euclidean algorithm. I've managed to generate the public key, but don't know how to ...
18
votes
1answer
663 views

How to provide secure “vanity” bitcoin address service?

Bitcoin addresses are RIPEMD-160 hashes of the public portion of a public/private ECDSA keypair (along with an abbreviated hash of the hash to provide a check code, as @pulpspy notes in a comment). ...
24
votes
2answers
2k views

How do I apply differential cryptanalysis to a block cipher?

I have read a lot of summaries of block ciphers particularly with regards to the NIST competitions stating that reduced-round block ciphers are – for example – vulnerable to differential ...
0
votes
1answer
94 views

How much stronger is RC4 if it is keyed with an RSA private key?

My idea is to generate a RSA 2048 bit key and use RC4 with the private RSA key to encrypt a stream of data. RC4 is weak because RC4 keys are small, 256-bit. But when we use RC4 with private RSA 2048 ...
3
votes
1answer
158 views

Concrete example of Weil Pairing

I am trying to find a concrete example of the Weil Pairing. What I have done until now is that I took $E=(x-1)(x-2)(x-3)$ over $F_5$. I took $E[2]=\{\infty,(1,0),(2,0),(3,0)\}$. I know that there ...
11
votes
1answer
82 views

How to tell if a hardware RNG is rigged?

On a related note of building my own RNG, as someone suggested to use several commericial solutions how can I check if it is rigged against me? (although I am still strongly biased to a homebrew ...
-1
votes
1answer
33 views

Execution time for HMAC-MD5 on a 160 bit data using 128 bit key on a 3GHz CPU [closed]

I need to know the execution time for HMAC -MD5 for a 160 bit data using 128 bit key on a 3 Ghz CPU, kindly specify other parameters of the machine like RAM, operating system used etc
8
votes
2answers
105 views

Historic Authentication Schemes Before Computers

The Bulletin of the Atomic Scientists recently ran an article about an alleged near miss with rockets in 1962, which raises some interesting cryptographic questions: ...
4
votes
1answer
75 views

Is my pin algorithm secure?

I'm a hobby programmer and very new to this field. I opened a bank account recently and got two pins. One for the girocard and the other for a creditcard. And I needed two more pins for the online ...
3
votes
0answers
73 views

Lattice attacks against Multilinear Maps [CLT13]

I am currently studying an article on a construction of Multilinear maps. There are some attacks on the scheme presented by the authors and I got stuck at the one in section 5.1. I will try to ...
3
votes
0answers
44 views

Cost of attack on DSA with attack on DLP

Are there any (recent) estimates of cost of attack on DSA by solving the discrete logarithm? I'm especially interested in attacks that use Pollard's rho algorithm. Are there any optimized ...
6
votes
2answers
163 views

How much entropy is generated by 'random' human keystrokes?

I'm wondering about using human input as an entropy generator. We all know humans are terrible at making up random numbers or keys or passwords. But what if we let a user 'randomly' type in some ...
1
vote
0answers
23 views

802.1X Radius WLAN protected by certificate 1024-bit key

I want to ask you a question. I have WPA-2 (enterprise) network. Also called as 802.1x. I use the Linux Zeroshell distribution, which is optimized for these services. Linux Zeroshell is provides a ...

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