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1answer
2k views

How can I implement the “Multiplication Modulo” and “Addition Modulo” operations in IDEA?

I am currently working on IDEA (International Data Encryption Algorithm), and I don't know how to perform Multiplication Modulo and Addition Modulo. This is how IDEA operates: IDEA operates on ...
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1answer
346 views

password entropy calculation

I have the following password with a prescribed format: it starts with a fixed value of 111, followed by 2 random lower case letters and then lastly a random digit: "111""2 Random lowercase ...
1
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1answer
115 views

Using pairings to verify an extended euclidean relation without leaking the values?

Let $P_i(x)$ be polynomials $i=1,...,n$, $s$ some value, and $g$ a generator of a group $G$ where the discrete logarithm is hard. Assume a prover wants to convince a verifier having access to the ...
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1answer
227 views

Tree hash and multithreading for parallelism

I am using tree hash mode of Skein on a 16 core processor. Will it automatically employ parallelism using more than one cores or do I have to use multi-threading within the tree hash for parallel ...
1
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1answer
416 views

Is there a method to break an EC curve for all key-pairs (Q,d) such that (Q=d*G) faster than breaking every single key-pair?

Related to this question: Is there any memory trade-off that helps such attack? Obviously if the field size is very small (say 40 bits) it´s possible, but what if the field size is 160 bits long? or ...
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2answers
462 views

which of these is more secure (bcrypt vs srp)

OK, here's the two different ways I was thinking about making the authentication for the login thing to store the passwords securely. The first is the following. Client hashes password ...
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3answers
183 views

verify contents, but not order

Is there an algorithm that can be used to verify the contents of a cyphertext, but not the order of the elements? I am thinking that a deck of cards could be shuffled, and it must be verifiable that ...
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1answer
1k views

How can the Diffie-Hellman key exchange be extended to three parties? [duplicate]

Possible Duplicate: Can one generalize the Diffie-Hellman key exchange to three or more parties? How can Alice, Bob, and Charlie share a common secret key using an extended version of the ...
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1answer
312 views

Blowfish Encryptions in Bcrypt hashing algorithm

I am trying to understand the ExpandKey function used in the bcrypt hashing algorithm. As per the documentation of bcrypt hashing algorithm on USENIX here: ...
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1answer
476 views

Recommended Books for Cryptography : Theory and Implementation [closed]

It is a great idea if experts in Cryptography from mathematicians to security engineers introduce books and textbooks which they think is helpful or instructive for all people interested in the ...
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1answer
305 views

Digital Certificate Chain Verification

Does a certificate contain the complete chain of all certificates up to the trusted root certificate, or does the program that verifies certificates have to fetch each parent certificate individually ...
1
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1answer
62 views

Design question for a service that signs messages on behalf of a user

I'm working on a messaging service that lets users author messages and have them signed with an RSA key. The key is used for identity purposes only and can be revoked, so compromising the private key ...
1
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1answer
528 views

Deniability of OTR messaging

I've been looking at the off-the-record messaging protocol, and there is something about its deniability property that seems strange to me. Consider the following scenario: In the course of an ...
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1answer
187 views

Do Quantum Key Distribution and Physical Unclonable Functions combine, and how?

I see there's a project to combine Quantum Key Distribution, Physical Unclonable Functions, and classical crypto, in order to secure a high speed (100Gb/s) optical link. While there does not seem to ...
1
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1answer
2k views

Deciphering a key from XOR encrypted cypher using boolean logic

Assume there's an unencrypted message A, and an encrypted message B. You know that message B was encrypted using a simple XOR method of A with a private key K, resulting in message B. Thus, B = A ⊕ K ...
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1answer
581 views

Expectation Value of the Index of Coincidence

Can Anybody tell me why the expectation value of the Index of Coincidence is the following? For a cipher text string of length $L$, where $n$ is the number of alphabet characters, $k_r = 1/n$, and ...
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1answer
2k views

Use of nonces in Kerberos and Needham–Schroeder protocols

Can you please explain me what is the reason of using nonces in the Needham-Schroeder and in the Kerberos protocols for Key Transport. In particular : Can you explain me the use of $N_A$? And ...
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1answer
82 views

Incorporating known ciphertext into new message

Which ciphers $c_k$ enable one to define a joining function $f_{c,k}$ such that: $$ f_{c,k}(c_k(p_1), p_2) = c_k(p_1 + p_2) $$ That is, the result of joining some known ciphertext $c_k(p_1)$ with a ...
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1answer
545 views

How to represent a 32-byte SHA2 hash in the shortest possible string?

I'm calculating a SHA2 hash of a certain sensitive key value. I need to store files on disk using this hash a directory path prefix. So lets say I hash the key value 150023, I get a 32-byte value ...
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1answer
123 views

Tips on conceiving safe software messaging platform

I have a personal project in mind in which I plan to use cryptography in order to let the users be confident in the fact that, even if all data get's stolen, it would be virtually impossible to crack ...
1
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1answer
481 views

Brute forcing Cardan grille

Having a "rotating" square Cardan Grill with sides long n cells, how could i determinate the cost of a brute-force attack? How many configurations should be considered to perform an exhaustive ...
1
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1answer
294 views

Twofish key length

I'm using twofish. Say you have a 120 bit key, is there any difference in using a 128 bit bit keylength or a 256 bit one? Since the most significant digits of the key will be allo zero in both cases, ...
1
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1answer
583 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
1
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1answer
140 views

How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
1
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1answer
684 views

iSeries (AS/400) Database File: password encryption

I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except... In order to allow users to login and maintain ...
1
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3answers
31 views

Is this client-side password hash scheme secure?

I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of ...
1
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1answer
53 views

RSA function over $Z_t^{*}$ where $t$ is prime

RSA function is defined over $Z_N^{*}$ where $N=pq$ with $p,q$ primes. A public key is a pair $(N,e)$ and a private key is $(N,d)$ where $d=e^{-1} \mod \phi(N)$. Assume that RSA function is defined ...
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1answer
28 views

Forgery attack on OCB

When using same nonce in OCB mode of authenticated encryption, how forgery attack can be done?
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1answer
27 views

Can I use HKDF to improve security of HMAC used with weak hash function?

I am writing a framework which encrypts/decrypts files (or streams, in general) with symmetric key using block cipher (for example, AES). To authenticate encrypted file, I use HMAC, which is ...
1
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1answer
37 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
1
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1answer
59 views

Generating PGP key *without* random generator? (using fixed input only)

I understand why in general, a strong random generator or source of entropy is used when generating PGP keys. However, I have a use case where I want to generate PGP keys deterministically, i.e. ...
1
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1answer
60 views

How to generate own secure elliptic curves?

I know that the algorithm used to generate the Brainpool curves and the NIST curves is published. The algorithm should be this one. From what it looks like it's rather slow to find secure parameters. ...
1
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1answer
48 views

Period of pseudo random sequence generated from (5, 2, 0) LFSR

I was reading about the Linear Feedback Shift Registers and I am confused about the technique to find the period of a primitive polynomial. Consider the polynomial $x^5 + x^2 + 1$. As this is a ...
1
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1answer
65 views

What's the principle to design the functionality under UC framework?

Though I can get the basic idea of UC Framework, namely let the environment cannot distinguish the real protocol with the real adversary and the functionality with the simulator, I am still puzzled in ...
1
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1answer
67 views

Why isn't Rabin-Williams cryptosystem widely used?

I think we all know RSA. And of course we also know DJB (a.k.a. Daniel J. Bernstein). Now some already have noticed that he has an opinion towards cryptographic questions. In his 2008 paper on ...
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1answer
23 views

Why does P1363 require RW signature with $0 ≤ s < n/2$?

I'm using an older copy of P1363 Public Key Cryptography was used below. It may (or may not) reflect the current state of affairs. P1363 has the following requirement in section 8.2.8 IFSP-RW, p. 45: ...
1
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1answer
42 views

Tweaked Square Roots and Rabin-Williams

I'm reading Bernstein's RSA signatures and Rabin–Williams signatures: the state of the art. In section 6, Bernstein states: Recall that Rabin’s system needed to try several values of r, on ...
1
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1answer
52 views

What is meant by - computational complexity $2^x$?

Recently Bi-clique Cryptanalysis allowed to obtain following results on full AES ES that claim to have The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$ The ...
1
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1answer
57 views

LED cryptography algorithm

I would like to better understand the operation of the LED algorithm, especially the process of substitution and permutation of the blocks and especially the use of the keys in each round. The keys ...
1
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1answer
36 views

Differences between HMAC and HKDF in a specific case

I want to use a key derivation function to derive a key to another one. I think HKDF is the easiest solution in my case. The following picture gives a clear definition of it : ...
1
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1answer
105 views

About Primitive roots mod n in Diffie-Hellman [duplicate]

I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$). In some crypto papers and documents I've read that $g$ needs to be a primitive root mod $n$ ($g$ ...
1
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1answer
21 views

Why do we truncate the hash when using DSA?

All the articles I read on the web about DSA keep telling me that the size of the hash needs to be truncated so that the bit length is equal to or lesser than the bit length of the prime number of the ...
1
vote
2answers
88 views

Does the One Time Pad rely on confusion or diffusion?

From what I could research, XORing a random key adds confusion. But I do not undertand the rationale for that classification. Shannon's confusion is supposed to obscure the relationship between the ...
1
vote
1answer
50 views

HKDF entropy extraction

I collect entropy from the following sources: system_entropy = System provided crypto entropy stream (CryptGenRandom on Windows) user_entropy = User-provided entropy - in a form of a byte stream of ...
1
vote
2answers
31 views

Can a TLS client perform any DH regeneration?

I have only the barest understanding of cryptography, but I've been following the Logjam issue; some posts and articles (elsewhere) imply that a client can regenerate DH keys. Is Logjam solely a ...
1
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1answer
61 views

one-way deterministic hash for low entropy input?

My problem is the following: we have a low entropy data called ID. (personal id number of 10 decimal digits plus a sum, and it contains a date) We want to create a data (H) which is the same for the ...
1
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1answer
34 views

Could this alternative hash based MAC construction be as, or even more secure than an HMAC?

Begin hashing (Key||Message) Encrypt the hash state (or some part of it, such as the first 128 or 256 bits), with the key. Add the encrypted hash state to the ...
1
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1answer
60 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 ...
1
vote
2answers
56 views

Reciprocal block ciphers

I'm interested in the property of involution in block ciphers and how one would go about constructing one. Creating a cipher where $E_K(E_K(M))=M$ for any $M$ and $K$ isn't an obvious task and the use ...
1
vote
1answer
53 views

Turning data into seemingly random noise

I am currently working on a python script that does image steganography, altering the least significant bit on each channel of the image. Now imagine encrypting a file with a bunch of null bytes, or ...

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