2
votes
0answers
54 views

Cyclic group collision resistant keyed cryptographic hash function

I am self-studying cryptography from a book and have come across a really difficult question that's doing my head in. I would be very grateful if somebody can help me out here with this difficult ...
0
votes
0answers
25 views

Security of $(k, 2k)$-bit generator for small seeds

Here is the problem I am working on for context. I have $\epsilon \le 1 - 2^{-k}$ and $\epsilon$ approaches 1 as $k \to \infty$ but I'm stuck on part c). The $f$ is secure iff there does not ...
1
vote
0answers
129 views

Example describing Baek and Zheng’s threshold identity-based decryption scheme

I am trying to work through an example of Baek and Zheng’s “threshold identity-based decryption scheme” and I tried a lot to solve this, but somewhere I’m doing something wrong. I hope someone can ...
7
votes
3answers
282 views

What was the first MD5 collision ever constructed?

We all know that MD5's collision resistance is severly broken. But when thinking of "random" strings with great cryptographic importance I've come up with NIST's curve seeds and MD5 collisions. But ...
4
votes
2answers
80 views

Is there a signature scheme for the Cramer-Shoup cryptosystem?

I have a project that I have to use cryptosystem and signature scheme for it. I've read about Cramer-Shoup cryptosystem and I want to use it since it is more secure the ElGamal cryptosystem, but, I ...
4
votes
2answers
256 views

Implementing CBC Encryption Using Decryption

I've implemented this algorithm, which, working from the end of the message backwards, creates a valid CBC ciphertext from any plaintext, using the block cipher's decryption operation instead of the ...
-1
votes
1answer
120 views

Where is Signaturevalue in Certificate?

Where is the Digital Signature value in my certificate? I can find Signature Algorithm and Signature Hash algorithm. Also why there are two fields specifying the Signature's Hash? With Signature ...
2
votes
1answer
54 views

Encryption on the cloud with versioning

Can file-versioning, which is available for instance in Dropdox, weaken the security of encrypted files if someone is able to see two or more snapshots of the ciphertext at different times? To be ...
0
votes
1answer
66 views

What is the meaning of the overlapping region on OTP-perfect secrecy diagram?

I'm new to cryptography. I want to ask about OTP-perfect secrecy diagram like figure below: On the overlapping region (middle), notated by R(X;Y;Z). R can be calculated by I(X;Y) - I(X;Y|Z). ...
1
vote
0answers
54 views

2 round GOST_28147-89 cipher distinguisher

So, here is the scheme of how this will look graphically: The deal is to present distinguisher for this cipher. First of all here is my drafts: Way 1 Assume that distinguisher displays in ...
0
votes
0answers
22 views

Advantages of the general digraph trust model over the strict hierarchical model

Are there any advantages of using reverse certificates and the general digraph trust model over the strict hierarchical trust model as described here: In the digraph model each CA can generate ...
3
votes
1answer
52 views

I am trying to generate a permutation of polynomial with order m

Suppose m = 5 and N = 64. How do I choose the coefficients such that the polynomial is a permutation of nos from 0 to 63.?
3
votes
1answer
37 views

How do substution-permutation networks work?

I understand what's going on in higher level. But i don't understand what's really going on in page 3 and 4 of this slide. Specifically, How S0 and S1 is used? What goes in what goes out? How ...
2
votes
1answer
72 views

Can the key-complement property of DES be used against 3DES?

The comments in this recent question about the security of 3DES made me wonder if the key complement property of DES (which reduces its security by ~1 bit) can be used in the meet-in-the-middle attack ...
2
votes
4answers
835 views

Why is public key cryptography (RSA) used in sites like Google or Facebook?

The RSA algorithm is used for encryption (plain text to cipher text) and decryption (cipher text to plain text) of data. What is the need for using public keys in these sites; why is data is encrypted ...
1
vote
1answer
80 views

Setting up of polynomials for CP-ABE or KP-ABE Access Trees

My question I guess is how the selection is done. A brief explanation with a simple access tree will be very helpful.
1
vote
0answers
74 views

What is the 'identity function' in AES?

I'm trying to understand how AES works. I got as far as knowing how a password is converted to an unifinished key with the PBKDF2 function. After that RFC3962 says that an AES useable key most be ...
2
votes
1answer
48 views

A confusion on the proof of Yao's theorem (Yao 82)

I'm reading the proof of Yao's theorem on Boaz Barak's lecture, the main part of the proof is the following claim: My question is: How can we say "without loss of generality" here? Since ...
2
votes
1answer
91 views

Could use an explanation of the notation for an oracle adversary

In the definition below, what exactly does it mean for the adversary (not even sure that's the correct term?) to equal one? $$ \underset{K}{Pr} \left [A^{F_k(\cdot)} = 1 \right ] $$ Source (Page ...
2
votes
1answer
109 views

How to calculate mapping in bilinear

I am trying to read a paper in cryptography. In key generation phase, paper give a definition for bilinear like G and Gt be two cyclic groups of prime order p $e: G * G \to G_t$. be a map with the ...
4
votes
1answer
129 views

UKS attack on KEA protocol

I'm trying to understand the UKS attack on KEA protocol. This is described in this paper: Security Analysis of KEA Authenticated Key Exchange Protocol So to summarize: KEA protocol: UKS ...
6
votes
2answers
154 views

Is the warning given by chrome warranted?

I went to a payment page on a site recently, and chrome was warning me that the page is possibly not secure, I have a very basic understanding of crypto but not enough to fully understand why this ...
5
votes
2answers
868 views

Understanding elliptic curve encryption [closed]

I'm having a hard time understanding the elliptic curve encryption. One thing thing I don't understand is listing all the points on the curve mod p. Suppose I have the following elliptic curve: $y^2 = ...
1
vote
1answer
73 views

The example of Wikipedia on steganography doesn't work

I was reading some stuff on steganography. There is an example on the wikipedia page : However, I tried many software to get the hidden image, but no one worked. Is there anything wrong about ...
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
194 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
309 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
39 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
96 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
11 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
42 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
53 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 ...

15 30 50 per page