4
votes
1answer
100 views

Distribution based integer factorization

The past week I've been looking into - and playing with - algorithms for factoring RSA moduli. From what I understand, it's important that the primes p and q are of the same magnitude as the square ...
39
votes
6answers
195 views

How to check that you got the right key when brute forcing an encryption?

How do you know when you have the right key when brute-forcing? Let's say that they test the right key. They then have to check that the decrypted text makes sense. To do so, they can test whether ...
37
votes
1answer
3k views

What is a “freestart collision”?

In their work on SHA-1 collisions (cf. the currently unpublished paper “Freestart collision on full SHA-1” by Stevens, Karpman, and Peyrin) Stevens et al show that they are able to generate "freestart ...
1
vote
2answers
69 views

Does a stream cipher provide perfect secrecy?

From WAR10CK here: If I actually do create a machine using RC4 or AES-CTR and have a TRNG continually feed it a constant steady stream of random bits. Provided that the stream of bits is purged ...
5
votes
0answers
139 views

help with cryptanalysis of a sponge permutation

I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less ...
1
vote
2answers
81 views

What does the comma mean in m, c := E(K, m)

Disclaimer: I'm a beginner to cryptography. Background: I'm reading Cryptography Engineering by Ferguson, Schneier, and Kohno, where the authors use this image: Question: What do the commas mean ...
3
votes
0answers
72 views

How to overcome issues with big ciphers? E.g. with small vs. big Vigenére Ciphers

I understand that bigger ciphers show more recurring patterns and therefore should be easier (or at least faster) to decrypt as you'll have a better statistical analysis, being However if we use a ...
5
votes
1answer
310 views

Small subgroup confinement attack on Diffie-Hellman

I am trying to understand the small subgroup confinement attack on the Diffie-Hellman algorithm. I will present the attack and try to explain why it works. Small subgroup confinement attack on the ...
1
vote
1answer
71 views

For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at ...
2
votes
1answer
69 views

Implicit authentication aritcle

First, I want to know what is the logarithm used in the following system of equations (from the paper Flexible and Robust Privacy-Preserving Implicit Authentication - Domingo-Ferrer, Wu, ...
5
votes
2answers
78 views

Would adding daily changing nulls in front of their messages have made the Engima harder to crack?

The British decrypted the German enigma because they knew that they would repeat the message key twice at the start of every message. Of course, technology to encrypt enigma without the repetition ...
1
vote
1answer
71 views

the decryptNode function for leaf nodes in CP-ABE

can someone please explain to me why decryptNode gives as result e(g,g)^rq(0) for leaf nodes, i don't understand how they went from the sconde step to the third ...
1
vote
1answer
95 views

Exponent operation over element of G

I found a definition of an exponent operation over the element of $\mathbb{G}$ in this paper (page 4): $$ (g^a)^{\% b} = g ^{a \text{ mod } b}$$ I couldn't understand the rest of the paper (Decrypt ...
-1
votes
0answers
40 views

Question about "toy: streamcipher

May I know what method should I use to solve question #3? I totally don’t understand it and I can not find any things about the clocking pattern on the internet. Is it still using LSFR to ...
1
vote
0answers
20 views

TPM specification physical presence requirements

I am looking at TPM Main-Part 1 Design Principles_v1.2_rev116_01032011 and on page 69 of pdf, equivalent to page 57 of the document itself,there is comment on physical presence as follows: "Observe, ...
0
votes
1answer
97 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...
0
votes
1answer
29 views

SSL Traffic Inspection

Is the firewall decrypted my session? There is an error "Certificate Not Trusted" (Server Certificate changed to Firewall Cyberoam Certificate). Which public Key I got? Is Main server Public Key or ...
4
votes
1answer
163 views

How to generate a bilinear group of prime order p for key generation

I am trying to implement an IEEE Paper In Cryptography. I read many reference regarding an RSA key generation. But i am confused with above statement. Please someone explain me What it says with ...
0
votes
1answer
59 views

RSA-OAEP: How does it work?

I was looking at this image about OAEP: ..and was wondering what was happening here. We have a data block DB which consists of: ...
2
votes
0answers
34 views

Hiding the identity of a party within the Kerberos authentication scheme

In the Kerberos authentication protocol, as described here: would it be safer to replace step (1) with: $$ A \rightarrow T : A, E_{K_A{_{T}}}(B, N_A) $$ so that a passive adversary does not know ...
3
votes
1answer
122 views

How to enforce data privacy, integrity and authenticity of distributed firmware images for an embedded device?

I'm developing a bootloader for an embedded device, with which it should be possible for customers (i.e. device owners) to update the device's firmware. It is required that: the firmware is ...
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 ...
-4
votes
0answers
12 views

Breaking El Gamal defined over Sn

How can we break EL-GAMAL Encryption defined over Sn the permutation group ? Kindly give the efficient algorithm for it.
0
votes
2answers
43 views

Length of encryption password aes-256-cbc

I'm encrypting a file with sensitive information with cat secret | openssl aes-256-cbc -a -salt > secret.enc I am choosing a random encryption password with ...
0
votes
0answers
54 views

Smart Card choice for PKI implementation

I'm seeking to implement a national digital signature standard on a smart card. I feel like this is a good place to ask if anybody is acquainted with a hardware supplier offering smart cards that ...
3
votes
1answer
55 views

Do you need a HMAC if decryption attempts are severely limited?

I am considering an application where data bandwidth is extremely limited, and considering removing message authentication codes from encrypted transmissions. The encryption method is currently ...
0
votes
0answers
12 views

Two nodes in p2p network exchange data and read data in same time [on hold]

I want to finde paper about exchange data between two nodes in p2p network. They must read each other's data in same time. In example two player a,b play rock scissors paper. A must read b's data ...
1
vote
1answer
43 views

Tackling encryption problems with “Zipf's law”?

I am new to cryptography and was wondering if it would be possible to semi-reliably "decrypt" an encrypted message by using the statistical distribution of symbols (/letters/numbers) in the encrypted ...
-4
votes
0answers
13 views

Autokey Cipher Question [on hold]

you receive the message DQIXFQETXPPZZR Given that the ciphertext has been encrypted using an Autokey cipher with key k in the range 16 to 18, decipher the meassage. Thanks,
0
votes
0answers
18 views

Why does DSA require that a new $k$ be chosen and the algorithm restarted if $s=0$?

DSA is an algorithm used to generate a digital signature, which consists of a pair of values $(r,s)$. The algorithm computes $r$ first and then $s$. However, if we calculate $s=0$, it says to restart ...
1
vote
1answer
32 views

how to prove sequence y uphold golomb's third axiom

given $\{ x_k \}$ is a m-seq of order $n$, we define $\{ y_k \}$ to be a $m$ digits number: $$ y_i=x_ix_{i+1}...x_{i+m-1} $$ for every integer $n \ge m \ge 1$ how can I show that $\{ y_k \}$ upholds ...
1
vote
0answers
31 views

How to use OpenSSL command line utility to encrypt data with encrypted key from public key?

I may not be asking the right question. I am fairly new to data encryption. I am currently being sent encrypted data that's stored as follows: [ [keysize] [key encrypted with public key] [ivsize] ...
5
votes
1answer
90 views

Key size for HMAC-SHA256 [duplicate]

After reading a bunch of past stack exchange posts like this one and RFCs 5869, 2104, and 4868 I felt comfortable that a 32-byte key was sufficient for HMAC-SHA256. However, I am implementing my code ...
3
votes
0answers
30 views

EC Schnorr signature: multiple standard?

I 'm working on some EC-Schnorr signature code. Reading various papers on that, it's seems EC-Schnorr is not standardized as well as ECDSA. For example, I found two main differences in two main ...
1
vote
1answer
2k views

Traditional DES scheme in Unix crypt function

In a security context course, we need to reproduce the old DES hashing scheme in the crypt program, on an old unix system. I am actually reading the crypt page on wikipedia: The traditional ...
-1
votes
0answers
64 views

How to prove that twice the application of a secure PRF stays secure? [closed]

Problem 4.6*: Let $E: \{0,1\}^k \times \{0,1\}^l \rightarrow \{0,1\}^l$ be a block cipher. The two-fold cascade of $E$ is the blockcipher $E^{(2)}: \{0,1\}^{2k} \times \{0,1\}^l \rightarrow ...
5
votes
3answers
125 views

Searchable Encryption with Substring Search

I want to search substrings in encrypted string. To do that I have read “Implement Rabin-Karp Algorithm” and “Substring-Searchable Symmetric Encryption”. After that, I completed the Rabin-Karp ...
1
vote
3answers
107 views

with RSA encryption, how do I find the md5sum of the private key from the public key?

This is a purely mathematical question on RSA encryption. Having $e$ as the public key exponent and $n$ the modulus of a public key. Can I recover the md5sum of the private key $d$ (inverse of $d$ ...
0
votes
1answer
52 views

Give a simple hash chain example in Java [closed]

I am looking for a very simple example of cryptography hash chain source code. Could you forward me some examples or link, guys? For example, https://en.wikipedia.org/wiki/Hash_chain [1]. ...
3
votes
2answers
340 views

Why is “multiplying” $g^x$ and $g^y$ not possible?

The computational Diffie-Hellman problem states that for a cyclic group $G$ of order $p$ and a generator $g$, it is hard to find the value $g^{xy}$ given only $g^x$ and $g^y$ (but easy if either $x$ ...
1
vote
0answers
32 views

Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
0
votes
1answer
146 views

In RSA. Why is $\phi(n)$ kept secret and $n$ is public?

I mean, $n$ can also be easily used to find the factors $p$ and $q$ right?
-1
votes
0answers
24 views

Denial of service using Merkel tree proof

If suppose client and server using Merkel tree and some how Server got compromised, what he can do is always send wrong proof therefore denial of service. Is it as simple?
5
votes
1answer
191 views

Authentication by hardcoding public key in client software

It would seem to me that mobile applications could reduce network traffic by hardcoding the server's public key into the app. The idea being that they could then encipher a secret to share with the ...
0
votes
0answers
24 views

Using a straight password for encryption and authentication

Assume we have a password like 3buNCh_7kaRmencrEst3. Now suppose we have two parties who know this password. We a have communication scheme that uses the password ...
0
votes
0answers
23 views

Is there a function that can be used to satisfy collision resistant property in MAC? [on hold]

I am doing a project in cryptography where i need to satisfy collision resistant property in my MAC algorithm, is there any function that can be used in MAC that already satisfies collision resistance ...
3
votes
1answer
76 views

Is there any function that does not suffers birthday problem?

I am eager to know that if there is any function that does not suffer birthday problem and how to prove it formally that the function is not suffering the birthday problem.
3
votes
1answer
32 views

Can one extend the nonce of ChaCha20 by using XORing the extra bits with the key?

Can one extend the ChaCha and Sslsa nonces by XORing the extra nonce bits with the key? Both functions are considered secure against related-key attacks.
0
votes
0answers
24 views

MAC is constructed by hashing and then encrypting

Suppose the MAC is constructed by hashing and then encrypting, that is $MAC(m, k2)=E_{k2}(H(m))$ where H is a public hash function. There can be several alternatives in how the transmitted message is ...
3
votes
0answers
20 views

About BGV Scheme Batching Technique

I am reading BGV12 about BGV homomorphic scheme right now.But I am being stuck to understand Batching technique in this paper. In Pack function (page 32),this paper feeds ciphertext $c_i$ and sk ...

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