0
votes
1answer
72 views

Are these hash function compositions collision resistant?

If a hash function $H$ is collision resistant, are the following two hash functions collision resistant or not? ($||$ is concatenation) $H'(m) = H(H(m)) || H(m)$ $H''(m) = H(m) || H(m)$ My first ...
1
vote
3answers
48 views

Possible to generate a one time secret which all nodes on the distributed network can know but cannot pre compute

I have a distributed P2P network. Everyday, I want each node to have a secret which is only valid for that day, while each of the other remaining nodes on the network will be able to calculate the ...
2
votes
4answers
648 views

PRNG taking advantage of very large seed

Can anyone suggest a good (CS)PRNG algorithm that takes advantage of having a very large (ideally arbitrarily large) seed? I'd like to use several kilobytes, perhaps several hundred kilobytes, of ...
2
votes
1answer
58 views

Why is AES-128 considered secure while RSA needs a 1024-bit size to be considered secure [duplicate]

I got asked this question today and I didn't know the answer, AES-128 is considered secure, the key size is 2^128, so you would need in average 2^127 tries to break the key. Why does RSA need at least ...
0
votes
2answers
395 views

Why does WPA2-PSK use 4-way handshake instead of 2-way handshake

I don't seem to grasp why is the handshake for PTK in WPA2-PSK 4-way and not 2-way. Isn't it enough to just have these two steps: First party sends Nonce1 to the other party Second party sends to ...
1
vote
1answer
79 views

What effect does a salt have on attacks against hashes's fundamental properties?

I am interested in analyzing how adding a salt to our hashed passwords affects the three types of attacks we can use. The three types of attacks against hashes are as follows: We have the hashed ...
0
votes
0answers
25 views

Do most TLS 1.2 implementations express curves in a canonical form when performing EC arithmetic?

Sorry if this is a silly question, but does anyone know if the cryptographic libraries which implement TLS 1.2 for Firefox, Chrome, etc. express a given curve in a canonical form (i.e. one of ...
1
vote
0answers
44 views

Caculated time One Point Multiplication with double and method

I am using double and add method for point multiplication in affine coordinates. How we compute 1PM in double and method? Di Wang said one point multiplication consists of repeated addition and ...
4
votes
1answer
82 views

How to design a deliberately weak PRNG for experimentation?

I'm looking for a PRNG that is deliberately weak, that is, follows a set of rules stochasticly. For example: Encounters a set of bits that is a multiple of X, starts exhibiting bias, or starts to ...
3
votes
2answers
95 views

How can we define division operation by using Fully homomorphic encryption

Last fews months, I'm working with homomorphic encryption. Now I am dealing with some computational problems with integers or real-numbers (like arithmetic mean, standard deviation) where division is ...
0
votes
1answer
27 views

Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
0
votes
0answers
49 views

Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
0
votes
0answers
29 views

How are the attributes of a user authenticated in attribute-based encryption?

It seems that the papers I am reading do not talk much about this point. That is how the attributes of a user are authenticated in ABE system. To my understanding, there is an attribute authority ...
0
votes
1answer
32 views

How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
1
vote
2answers
64 views

Single-algorithm authenticated encryption

Are there any authenticated encryption methods that combine encryption and authentication, rather than useing a separate cipher and MAC?
0
votes
1answer
64 views

How Diffie-Hellman authentication works? [duplicate]

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
1
vote
0answers
68 views

Data integrity using steganographic methods

I am looking for a lightweight and fast (almost real time) data integrity checker for a very time critical application. Is it possible to provide data integrity using a steganographic method, lets say ...
1
vote
0answers
18 views

Attribute based access control and role based, online bookstore example

I am asked to answer a question that says: One online book-store wants to grand access to clients regarding their subscription. There are 3 types of subscriptions A , B and C. Customers get access ...
1
vote
3answers
137 views

Security of a parallelizable block cipher mode

This is the scheme of a parallelizable block cipher mode of operation: $IV$ is the initialization vector. $BN$ is the zero-based index number of a block in a stream of data. $BT$ is the tweak that ...
9
votes
1answer
4k views

Why do we need Diffie Hellman?

Diffie–Hellman offers secure key exchange only if sides are authenticated. For authentication, sides are using public/private key. So if side A knows the public key of the side B, then A can simply ...
0
votes
1answer
32 views

Determining collision resistance of a function?

I am having trouble trying to understand if the function is collision resistant. As I understand it, preimage resistance means that it is hard for an adversary to find two messages that produce the ...
0
votes
1answer
47 views

Multi Authority Attribute Based Encryption Library

Anyone aware of a library that has MA-ABE implemented in any language preferably python? P/S - I hope this is the right place to ask this. Apologies if not, then a redirect will be appreciated
0
votes
1answer
63 views

Steganographic embedding of an RSA-encrypted message into an image

The goal is to combine the RSA encryption system with the LSB steganography system in a BMP image. Since every pixel of the image is an integer between 0 and 255, if we choose $p$ and $q$ such that $N ...
5
votes
2answers
99 views

Is reusing keys for CBC and CBC-MAC secure when using encrypt-then-MAC?

I know reusing keys is a bad idea, especially for CBC and CBC-MAC, but the example for why on Wikipedia seemed to use encrypt-and-MAC. It seems obvious that the last block of encryption will be equal ...
0
votes
0answers
39 views

Have ciphertext and key but need to figure out encryption method

So I have a block cipher (I think) that I need to break. I have the ciphertext and the key, but not the method of encryption, and was wondering if anyone could help me figure that out? The key is a 9 ...
-1
votes
1answer
71 views

Need CryptDeriveKey AES implementation in C#

I am integrating with 3rd party software that uses AES 128 encryption. I know this is not ideal, but the choice of encryption is up to the 3rd party software. I am using C#. My problem is in deriving ...
0
votes
0answers
30 views

AES Twofish Serpent [duplicate]

AES-Twofish-Serpent how to create this combo encryption? I am using Linux Mint and i want to encrypt few big folders in one folder, but to be hiden.
1
vote
1answer
38 views

OpenSSL & TLS1.2 with aes-cbc and initialization vector

I'm trying to manually decrypt DTLS traffic using OpenSSL and TLS 1.2. The cipher suite im using is AES256-SHA256 as listed here. Im able to decrypt the packets with the key that the server and the ...
0
votes
0answers
43 views

What are the pre-requisites I need to be able to code Salsa20 in C#?

I've taken a basic course in Cryptography and we've learnt various algorithms and their usage. I've implemented RC4 and Triple DES in C# with ASP.NET. For a project that I am a part of, I need to ...
108
votes
19answers
15k views

Time Capsule cryptography?

Does there exist any cryptographic algorithm which encrypts data in such a way that it can only be decrypted after a certain period of time? The only idea that I can think of, is something like this: ...
1
vote
1answer
114 views

RSA PKCS#1, v1.5 padding output

If I make use of RSA PKCS#1 in v1.5 what padding length is used. Basically, it is not allowed that the plaintext is bigger than the modulus. But what if the length in bits is the same (padding to ...
1
vote
0answers
100 views

Breaking Vigenere via Kasiski/Babbage method? (non-programmatic)

I'm really hoping someone can explain to me what is going on in the second major component of this form of analysis. If you wish, for convenience, here's a page that already has some ciphered text ...
1
vote
1answer
95 views

Why does a fixed key not make MACs like CBC-MAC or GMAC into secure hash functions? [duplicate]

Why does setting the secret key to a fixed, public value not make MACs like CBC-MAC or EMAC into secure unkeyed cryptographic hash functions? In other words, why is the resulting hash function not ...
0
votes
0answers
23 views

How do you apply bilinear mapping to attribute based encryption?

I'm new to both bilinear mapping and ABE. I have a vague idea of how bilinear mapping works now, but I don't understand how it applies to ABE. Can someone give me an example?
2
votes
1answer
116 views

Block cipher not resistant to collisions

If we have the following block cipher, $E(k,m)$, which is a permutation, why is $f_2 (x,y)$ not collision resistant? $$f_2(x, y) = E(x, x \oplus y)$$
10
votes
2answers
11k views

What is the difference between MAC and HMAC?

In reference to this question, what are the "stronger security properties" that HMAC provides over MAC. I got that MAC requires an IV whereas HMAC doesn't. I also understood that MAC may reveal ...
3
votes
3answers
35 views

What are possible caveats when generating a group for use as parameters for Diffie-Hellman key exchange?

As reusing a widely used group for Diffie-Hellman key exchanges might lead to far easier third-party key discovery through precomputation for that specific group, I would like to know what can ...
11
votes
3answers
2k views

McEliece Cryptosystem Implementations

Are there any current implementations (language irrelevant) of the McEliece Cryptosystem? I have been hunting around all day, and yet, have only found a few mathematical equations pertaining to the ...
5
votes
4answers
350 views

Get permutations from password

Are there any "good" ways to get a permutation from a password/pass-phrase? If one, for example, wanted to get a permutation of letters from a password, how might one do that in a smart way? I would ...
0
votes
0answers
29 views

Permuted Hash Table

Suppose we have a hash table, $HT$, consisting of $100$ bins.The hash table uses a hash function $H$ that is public. We all know that given value $a$ we can compute the address in the hash by ...
0
votes
2answers
38 views

OpenSSL Signature different each time

I have a file that I am generating a signature for using OpenSSL, and each time I generate the signature, it is different to the last time. ...
2
votes
2answers
247 views

Simulation based proofs: Simple examples

I am aware that,(in theory) in order to proof that a scheme is secure using simulation based proof we replace an adversary in real world with a simulator in ideal world. Then we try to show that their ...
0
votes
0answers
36 views

Poly1305 vs VMAC: is VMAC much better for long messages?

VMAC seems to me much more secure than Poly1305 on long messages (the security of the latter decreases linearly with increasing message length). Is this of practical relevance?
-1
votes
1answer
103 views

How to find roots of equation $f(x)=0 \pmod p $, where $p$ is prime number?

$f(x)$is any nth degree equation $n>0$, how to find roots of $f(x)$ over prime modulo.
3
votes
1answer
39 views

Updating values authenticated by Merkle Tree

Assume we have 4 values: $v_1,v_2,v_3$ and $v_4$. We construct a Merkle tree on top of them such that the values are leaves of the tree. I send the values and the tree to an untrusted server. But I ...
3
votes
1answer
81 views

What is wrong with simple concatenation in salted password hashes?

I once heard that if implementing a password hashing scheme, simply concatenating the password and salt together before hashing could lead to some subtle vulnerabilities, and I'm trying to figure out ...
7
votes
2answers
838 views

Is there a null HMAC?

I came up with this question while unit testing a function that includes an HMAC. What is the expected behavior of an HMAC with a well-defined key and a set of data with no elements in it? Is there ...
4
votes
3answers
117 views

Common Modulus Attack not reproducible

I want to calculate a simple example of the RSA common modulus attack. However, the result is not correct and I do not find my mistake. p=$29, q=37, n=p*q = 1073, \phi(n) = 1008, e1 = 5, e2 = 11$ ...
1
vote
1answer
29 views

Cardholder to Merchant SET Protocol

I have some doubts regarding the SET protocol. Let say the Alice payment information runs through a sha-1 hash function which is a one-way algorithm, irreversible to create a message digest. How do ...
2
votes
1answer
68 views

Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...

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