2
votes
1answer
169 views

Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
2
votes
1answer
154 views

Extension of a password hashing algorithm using Fibonacci

I am right now taking a class named Applied Cryptography and our final project is to create a password hashing method using at least one existing algorithm and then add additional steps to make it ...
2
votes
1answer
156 views

Is there a secure source of entropy on a typical microcontroller?

On a device that does not have a hardware RNG, what is the best source for entropy? Some options and pitfalls floating around: Use the ADC to read something analog: can become deterministic if ...
2
votes
2answers
214 views

Is Checksum to file back decoding possible?

So, I was having this weird thought. If the checksums(MD5 or SHA...) are unique to any file and are modified if any part of the file is edited, why cant the checksums be decoded back to get the ...
2
votes
1answer
75 views

Permuting Small Sized Set in Practice

Imagine we have a set $S$ of $m$ elements and we wants to permutes the set elements. Thus the original position of each element should be unknown after permuting. If we define a permutation function ...
2
votes
2answers
175 views

Transforming Gaussian random $[0,1] $ numbers to uniform $[0,255] $

I am not exactly sure if this is for math stackexchange or crypto: A TRNG outputs numbers in $[0,1]$ in a Gaussian distribution. I would like to convert them into uniform random bytes ($[0,255] $) to ...
2
votes
2answers
48 views

Correctness of ideal protocol of MPC in presence of malicious adversary

In presence of malicious adversaries in ideal protocol of Multi Party Computation, how can honest parties get the correct output? i.e., corrupted parties modify their inputs and give to the trusted ...
2
votes
1answer
133 views

Is ElGamal IND-CCA1?

We all know that textbook ElGamal falls due to chosen ciphertext attacks, because of its multiplicative homomorphic property ($E(A)*E(B)=E(AB)$). However these attacks require the ciphertext ($E(A)$ ...
2
votes
2answers
124 views

Inner product with homomorphic encryption

I want to do a very simple thing: Given two vectors, I want to encrypt them and do some calculation, then decrypt the result and get the inner product between both vectors. I want to do this as fast ...
2
votes
1answer
127 views

Proving membership of a group without revealing identity

I have an interesting problem for which I've failed, so far, to find an elegant solution. Imagine that a user needs to repeatedly prove to public observers that they are a member of a trusted set ...
2
votes
1answer
316 views

Attack for RSA 1024 bit with Low Public Exponent

I am facing a challenge at university. Our teacher give us the challenge to try to break an RSA 1024 bit. We have public modulus N and public exponent e (0x03), we don't know the padding. We have a ...
2
votes
2answers
197 views

RSA private key d knowing e,n

I need to find RSA private key $(d, N)$ knowing $(e, N)$. It's "own" RSA implementation. As i know $p$ is random 70 bit number, then $q$ is $p-2^{10} < q < p+2^{10}$ $d$ is max 16 bit long with ...
2
votes
1answer
78 views

Is “Bit Independence” of SHA-2 hashes secure?

I know bit independence is good in SHA2 function output, but is it truly 100% secure? For example: Y = SHA512(secretKeyNonce256bit) A = first 32ytes / 256bits of Y, used as message encryption key B ...
2
votes
1answer
88 views

Is randomsound for increasing entropy pool not doing what it is supposed to do?

I am using randomsound because I thought it would be a good idea to inject some additional entropy into the entropy pools of my linux machines (clearly those machines have a corresponding sound card). ...
2
votes
1answer
149 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 ...
2
votes
2answers
364 views

Elliptic curve brute forcing

I have elliptic curve of equation $y^2 \equiv x^3 -x $. And the coordinate of points $Q$ and $P$. I want to solve $Q=[k]P$ (where $k$ is the unknown) by testing all possible $k$. Is this the right ...
2
votes
1answer
155 views

What's the differences among Blind Computation, Secure Multi-Party Computation, Secure Circuit Evaluation and Homomorphic Encryption

We know that Blind Computation, Secure Multi-Party Computation, Secure Circuit Evaluation and Homomorphic Encryption all can process the encrypted data, but I am puzzled by them. What are their ...
2
votes
1answer
446 views

Why is diffie-hellmangroup1-sha1 used instead of diffie-hellman?

For SSH why is diffie-hellmangroup1-sha1 used instead of just diffie-hellman? In other words, why is the hash function used?
2
votes
1answer
277 views

Concatenation of two strong hashes may have striking weakness

For any hash functions $H_0$ and $H_1$, it is easily proved that their concatenation $H_0\|H_1$, defined by $(H_0\|H_1)(X)=H_0(X)\|H_1(X)$, is at least as resistant as the strongest of $H_0$ and $H_1$ ...
2
votes
1answer
208 views

Differential Fault Analysis of AES

Let's say: an error is induced into an implementation of the AES-128 to produce a faulty ciphertext. The error is a one-byte eror and is always induced on the last state byte, during round9, before ...
2
votes
2answers
143 views

How obvious is it to decrypt numerics encrypted with a reused one time pad?

For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could ...
2
votes
1answer
102 views

Hash “Preimage by product” resistance

Let H() be a hash function that achieves collision resistance as well as first and second preimage resistance. Let's equip the output set of H of a multiplicative group structure, more precisely a ...
2
votes
1answer
618 views

How to accurately calculate Unicity Distance for English?

The Unicity Distance for the DES cipher is around $8.6$ characters, and can be calculated using the $U=H(k)/D$ formula, where $D = R - r$, and where $R = 8$ is the number of bits in a byte (ASCII is 7 ...
2
votes
2answers
356 views

Explanation of each of the parameters used in ECC

I'm having a very difficult time finding a clear explanation of the parameters used elliptic curve cryptography. I know for certain that $p$ is the number or order or whatever of the given field that ...
2
votes
1answer
250 views

Why are there no MACs inspired by block cipher modes other than CBC and CFB?

I've been studying message authentication codes and I was wondering why a MAC can only be produced with AES in CBC and CFB mode and why not the other modes such as ECB, OFB and counter. Why are CBC ...
2
votes
2answers
751 views

Proving the semantic security of the One Time pad

Currently hearing a lecture on cryptography, and the professor gave us the definition of semantic security, which is roughly the following (formally not quite complete, but you get the idea): ...
2
votes
2answers
152 views

I don't care about replay attacks. What should I do with the nonce in nacl?

My system forwards encrypted and/or signed messages on a gossip network. Replay is part of the design. What should I do with the nonce? I'm tempted to just set it to the same number always. Is this a ...
2
votes
1answer
129 views

what are multi-primes and how are they different from semiprimes?

I came to know of semiprimes recently. The simplest explanation of semiprimes is you take any two prime numbers and you multiply them, say 3*11 = 33 in which case 33 would be a semiprime. The numbers ...
2
votes
1answer
144 views

Private Information Retrieval--Is it still theoretical?

Are there any real world products in which private information retrieval techniques are used?(a data hosting server oblivious of which data item was fetched from it?)If not what are the major barriers ...
2
votes
1answer
168 views

What is the difference between order of base point and curve order in EC? [duplicate]

When I was read about the elliptic curve cryptography I found some definition about domain parameter of elliptic curve like the follow. But I did not understand something $p$: prime number. $a, b$: ...
2
votes
1answer
206 views

What is the use of segments in Cipher Feedback Mode (CFB)

In NIST SP800-38A: Recommendation for Block Cipher Modes of Operation CFB can be used with a parameter s - the size of a data segment in bits - which determines the ...
2
votes
1answer
245 views

Why is this cryptosystem insecure?

Can someone help me see the flaw in this cryptosystem? Note: This is homework and it is due today at 1:30pm. An answer before that is not expected; I'd just like to understand what the flaw is. ...
2
votes
1answer
107 views

Is XCBC where k2 and k3 might be the identical, secure?

XCBC paper says all three keys should be independent. It doesn't say they must always be different. However it seems this is necessary to differentiate padded message and message without padding. ...
2
votes
1answer
457 views

The Boneh-DeMillo-Lipton fault attack (RSA CRT)

I am trying to understand the Boneh-DeMillo-Lipton fault attack on RSA CRT signature. Suppose that we sign a message $m$ with RSA-CRT : $d_p = d \bmod (p-1)$ and $d_q = d \bmod (q-1)$ $s_p = ...
2
votes
2answers
134 views

Is it safe to salt a MAC?

Say that I define a scheme where the salt is public and is MAC-ed with the message: $k = KDF(password, salt)$ $tag = MAC_k(salt || message)$ Is it safe to salt the MAC this way? Assume that the salt ...
2
votes
1answer
310 views

Do Export Restrictions Still Apply To The Key Length of RC4?

I've just read a paper from 2004 which stated that the RC4 encryption algorithm was restricted to a 40 bit key size when exported from the USA; however the reference for this information (Applied ...
2
votes
3answers
297 views

If a cipher has key length shorter than plaintext, then it is not perfectly secure

I am trying to verify the statement above. So far I only know that a One-Time-Pad is the only “perfectly secure” cipher. It has a key length which is exactly the same as the plaintext. I think the ...
2
votes
1answer
207 views

RC4 key schedule and algorithm design

I've looked up RC4 algorithm and it's seems easy enough but some parts of it seem random to me. In the key schedule part take for example the following part : ...
2
votes
1answer
635 views

Why is 224 bit ecdsa faster than 192 bit ecdsa?

I ran several benchmarks using openssl on 2 different computers and I got a surprising result. for the Nist 192 bit curve the benchmark result is ...
2
votes
3answers
185 views

Feasibility of finding public key when private key is known

We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it. Is it the same case in reverse? Given a private key, how easy is it to compute ...
2
votes
1answer
421 views

Will I be able to (ab)use a FIDO U2F compliant hardware token to decrypt data?

I have heard good things about the emerging "FIDO U2F" standard. I am especially interested in having a JavaScript API for cryptographic functions that I can access through a plug-in in a browser. ...
2
votes
1answer
307 views

Perfectly secure shift cipher

Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. I want to show that $P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone ...
2
votes
1answer
853 views

Entropy of the key

Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated. Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and ...
2
votes
1answer
352 views

Why are some key stretching methods better than others?

I'm trying to understand why some key stretching methods are better than others. The wikipedia article presents 3 different key stretching methods: A collision prone simple key stretching ...
2
votes
1answer
114 views

How to only encrypt a subset of the plaintext

I was wondering if there is a smart way for a user to only encrypt a subset of a plaintext. I'll try to be more specific. Let's suppose the user U wants to use a special cipher such that given a ...
2
votes
3answers
490 views

Can a EC private key be derived from a public key?

I understand that the public key does not expose the private key. That is not the question. The question is: Given a EC public key, can a different, but plausible and functional private key be ...
2
votes
1answer
299 views

How to calculate complexity of ElGamal cryptosystem?

How to calculate time and space complexity of ElGamal encryption and decryption as there are two exponentiation operation during encryption and one during decryption? Here is my code for encryption: ...
2
votes
2answers
248 views

What is the entropy per Diceware word if a random symbol is inserted into a random position in the word?

On the Diceware page is this little gem: For extra security without adding another word, insert one special character or digit chosen at random into your passphrase... Inserting a letter at ...
2
votes
1answer
208 views

Is either brainpoolP320r1 or brainpoolP320t1 a SafeCurve?

Not all elliptic curves are safe to use for cryptography, especially from an ECC safety perspective. The site http://safecurves.cr.yp.to/index.html shows that two tested Brainpool curves, ...
2
votes
1answer
152 views

Pick faster private exponent

I recently tried to send 1536-bit modulus CSR to COMODO. They refused to sign the certificate. I later found out that it's because NIST mandated 2048-bit modulus on the SSL certificate. I think it's ...

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