0
votes
1answer
70 views

Reducing the probability that a password will be guessed

In a file users' password hashes are stored. There are 2 approaches to reduce the probability that the password is guessed. Increase the size of the salt from 12 bits to 24 bits. Increase the length ...
0
votes
0answers
37 views

Non-repudiation in classical cryptosystem

How can we modify classical cryptography system to provide non-repudiation? I want to ensure non-repudiation in symmetric key cryptography so that we can find out who is sender of a particular ...
0
votes
0answers
31 views

Can we use more than one irreducible polynomial in AES?

I understand that the irr. poly is used to form the s-box (and inv. s-box), the key schedule and the mix columns. But could we use a different irr. poly for the mix columns and another for the key ...
0
votes
0answers
24 views

Are there any holes in my stateless encryption protocol?

I want to create a reasonably secure protocol to allow a bunch of machines within a datacenter to securely communicate to one another. Specifically as a kind of tunnel. I want to avoid building up ...
0
votes
1answer
30 views

Secret construction

Given set of random strings $w =\{s_1, s_2, s_3 ... s_n\}$ are there any algorithms to construct single master secret $S$ from them? Subsequently we should be able to deconstruct the $S$ back to ...
0
votes
0answers
38 views

ISIS as a one-way function

The usual formulation of the ISIS problem is the following: Given uniform $A$ and $u$, find a short $e$ such that $Ae = u \bmod q$. A different definition (call it ISIS-OWF) is to let $f_A(e) = Ae ...
0
votes
0answers
24 views

Composing hash functions

Suppose there is a cryptographic hash function $H : \{0,1\}^* \to \mathbb G$. Now, we want to define a hash function $H' : \{0,1\}^* \to \mathbb G \times \mathbb G $. My first idea is to define $H'$ ...
0
votes
0answers
29 views

Length extension attacks or prefix attacks on HMAC

Why HMACs are not vulnerable to length extension attacks or prefix attacks? (As commented by @codesinchaos, That's a different construction. So it's related, but no duplicate of Why is ...
0
votes
1answer
98 views

Large Volumes of Asymmetric Encryption

First of all, I apologize in advance if I use any incorrect terminology. I am just getting my feet wet when it comes to cryptography and there is a lot to learn. For the past 12 months we have been ...
0
votes
0answers
8 views

How AES/GCM deals with data smaller than block size? [migrated]

I am using bouncy castle library for encryption and decryption in c# and I was wondering how to deal with plain text smaller than block size? here is what I have done so far: ...
0
votes
0answers
17 views

Is there a German word for computationally secure? [migrated]

This is mainly intended for German cryptographers and I think since the topic is really specific it's more relevant to ask this here than in a German language section. Cryptography is mainly based ...
0
votes
0answers
18 views

McEliece variants that support signatures

Besides the Niederreiter cryptosystem, are there any other variants that support digital signatures? Can any of them sign arbitrary signatures unlike the Niederreiter cryptosystem? What are the key ...
0
votes
0answers
22 views

Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
0
votes
1answer
36 views

RC6 Key Size Understanding

I need help to understand how RC6 works. Many sites show that the maximum key size of RC6 is 2040 bits (255 Bytes). I can also have 0..255 rounds and 4 times 32bits words in the 128bit block variant ...
0
votes
0answers
36 views

Is pseudo-random letter insertion secure?

Is pseudo-random letter insertion a secure mechanism? I mean by expanding the key or taking two parameters in the encryption function, you select positions in the text at which to insert random ...
0
votes
0answers
6 views

the code generate error while using bouncycastleprovider [migrated]

I am trying to generate signature using ECDSA with binary curve (B163) . Also i am using Bouncy Castle libraries. but it generate error like this- Exception in thread "main" ...
0
votes
0answers
25 views

generate unpredictable value with a shared key

Is there any function that taek a key to generate (un)predictable value ? I hope you will more understand more what I mean with this example f take in input an array, a key and a round number ...
0
votes
0answers
30 views

Key size limitations due to software compatibility?

At the moment, much popular encryption-based software routinely handles up to 4096 bit keys and standard usage is broadly migrating from 1024 to 2048 bit keys. Hashes widely used are MD5/SHA1/SHA256 ...
0
votes
0answers
10 views

warning: 'gcry_ac_key_t' is deprecated [migrated]

I am implementing gcrypt library and I face some issues with data types. I want to instantiated data types for private key and public key. What I found is that I can do like this: extern ...
0
votes
2answers
26 views

What info should be signed with a digital signature to provide entity authenticaton for DH?

$i \to r\colon\; g^x\bmod p$ $r \to i\colon\; g^y, \langle g^y,g^x\rangle_r$ $i \to r\colon\; \langle g^x,g^y\rangle_i$ Looking at run 2, I am trying to work out why it is necessary to include ...
0
votes
0answers
18 views

Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
0
votes
0answers
14 views

Can XTS + checksum be used for authenticated encryption?

Is it possible to use XTS+a checksum for authenticated encryption? Specifically, it seems like a good $n$ bit checksum applied before encryption should ensure that any change to the ciphertext ...
0
votes
0answers
18 views

Is it okay to use Threefish-512 in ECB mode with Poly1305 MAC to protect some AES keys?

A person has some independent AES-GCM-SIV keys they need to protect as part of a hypothetical protocol or product, where it is publically known that it is in fact AES-GCM-SIV keys that are being ...
0
votes
2answers
100 views

How does SSL work on the browser

I recently bought an SSL certificate from a website and was able to make it work on my Apache server. As far as I know, it uses asymmetric keys and the private key is stored on the server while the ...
0
votes
0answers
10 views

What does prevent MITM in quantum cryptography? [duplicate]

One thing I really doesn't have understand, is how MITM is prevented in quantum cryptography. Lets say Alice sends to Bob a random sequence of photons organized in a specific way (vertical, ...
0
votes
0answers
21 views

If you receive a message with a digital signature, how do you know what verification key to use and the verification algorithm?

Really, I'm asking how do you know who sent it? My confusion has arisen from the following scenario... Problems with Signing-then-encrypting. If Alice digitally signed some data and then encrypted ...
0
votes
0answers
29 views

Is original DSA a TEGTSS-I scheme?

Brickell et al. define TEGTSS-I scheme in paper "Design validations for discrete logarithm based signature schemes" In this paper original DSA is generalized as DSA-I variant where $r = g^k \bmod p ...
0
votes
0answers
16 views

Security Level Same or not in key extraction of identity-based encryption

In identity-based encryption, key generation is performed using ($s$) as a secret key for identity a as in (eq.1) $\bullet$ $Priv_{a}=s.H(ID_{a})$(eq.1) If key is generated as follows, $\bullet$ ...
0
votes
0answers
27 views

Security for this scheme or not in pairing

Let be $G_{1}$and $G_{2}$ cyclic groups of prime order $q$ and $g =<G1>$ and $h=<G2>$ the generators of these groups. Let's consider the following protocol: Select $s \leftarrow ...
0
votes
0answers
14 views

Does the user need to know how the decryption scheme works in identity-based broadcast encryption [duplicate]

For example, in Delerablee's identity-based broadcast encryption scheme, decryption scheme is defined as $E(C_1,h^P)$ $E(\mathcal{SK}_{id},C_2)$. Are the users allowed to know how decryption works? ...
0
votes
0answers
18 views

Do users need to know decryption scheme in Identity-based broadcast encryption?

I have a question related to identity-based broadcast encryption: For decryption, there are different decryption schemes. Does the user need to know that scheme, or does the system firmly define the ...
0
votes
1answer
34 views

ElGamal scheme signature: if private key a mod p is equal to private sig. key k mod p-1, can an attacker notice and determine the value of a?

If someone is signing a document using the ElGamal signature scheme, and if the random involved in the signature $k \mod (p-1)$ is equal to $a$ (the private key), can an attacker notice? If so can he ...
0
votes
0answers
51 views

Lightest symmetric, fixed key, “Format preserving Encryption” algorithm?

message m = 49 bit string key k = any format but fixed Ciphertexts should be 49 bits long. Are there several "Format Preserving Encryption" algorithms? I want an algorithm that is as light as ...
0
votes
0answers
21 views

Value of security through amiguity?

Let's say that you have a symmetric cipher which takes in an 8 bit plain text value and a key, and generates cipher text which can be decoded using the key to get the original plain text value. Since ...
0
votes
0answers
32 views

autocorrelation and entropy of historical ciphers

I'm learning cryptography and come across historical ciphers such as vigenere cipher,hill cipher,random substitution and etc.I'm using cryptool for learning purposes and I have a question in mind.I've ...
0
votes
0answers
36 views

ECIES is must with Symmetric?(ECIES-AES or ECIES-TDES)

I can't understand the ECIES algorithm. I saw two different ECIES algorithms: Using only Public key Key generation: $A_{pri} : n_A$ $A_{pub} : n_A G$ $B_{pri} : n_B$ $B_{pub} : n_B G$ ...
0
votes
0answers
7 views

calculating n-gram lists and spaces in ciphertext

I'm doing an analysis on a block of ciphertext message with 27 characters(including spaces).Now do the spaces need to be taken into account when performing the digram and trigram analysis?because the ...
0
votes
0answers
38 views

If I send a signed email, how does the end user get the public key?

I am sending a signed email using Python and smtplib. I have successfully signed the email using this example: ...
0
votes
0answers
28 views

Recryption of ciphertext with a different key

Let's have $P$ some sensitive piece of data and $K_1$a secret value, both known to Alice, but not to Bob. $K_1(P)$ means $P$ encrypted using $K_1$. Alice sends $K_1(P)$ to Bob. Bob keeps the value of ...
0
votes
0answers
28 views

Encoding issue - PKCS#11 CKM_RSA_PKCS wrapping unwrapping EME-PKCS1-v1_5

I am trying to figure out why I am not able to get compatible format of EME-PKCS1-v1_5 3DES key encrypted by public RSA key. I need to send to a third party 3DES key encrypted using their public RSA ...
0
votes
0answers
19 views

What is the benefit of artificially padding messages?

For ECB, CBC, and CFB, padding is required when the plaintext does not fill out a complete multiple of the block size. However, I have heard that is good practice to pad all messages, even if the ...
0
votes
0answers
27 views

how MitM compute server secret number in logjam

I would like to know how man in the middle can compute the server secret number if the prime is 512 bit in length and if knowing ($g$) parameter as in the following figure help him or not? is the man ...
0
votes
1answer
41 views

How to calculate the probability to get two random numbers equal from the same generator

I have deterministic random bit generator (DRBG) to generate a random numbers in which it is 10 byte value and I want to turn this algorithm twice, what is the probability to get the two random equal ...
0
votes
0answers
58 views

Why is it so hard to make a good KDF?

Why are we stuck with only 2-3 KDF functions since KDFs don't imply mathematically conceiving a cryptographic primitive like the inner workings of AES or SHA but instead build a system out of existing ...
0
votes
0answers
27 views

Decrypting a file encrypted with AESCRYPT using key instead of password

i have encrypted a file using aescrypt and took memory image while the file was being encrypted and hence have the key that was used for encryption in the image but not the password, can i decrypt the ...
0
votes
0answers
50 views

I am trying to understand how AES works

I am trying to understand how AES encryption operates. I am trying to run through the steps on paper to understand. So far, I am creating a simple example. I have the plain text "MESSAGE TESTTEXT" ...
0
votes
0answers
33 views

Using quadratic residue to learn the sign of a field element

Given $x' \in \{-x, x\} \bmod q$ (where $q$ could be any prime of my choice), $s$ is a random element in the field, $y = x'\cdot s$ and $y' = \pm\sqrt{(x\cdot s)^2}\bmod q$ (i.e., both solutions to ...
0
votes
1answer
50 views

Proper forward secrecy [closed]

Currently I have a protocol using a simple RSA to AES handshake. I have been reading more and more and would like to implement proper forward secrecy, but at the same time I'd like to improve the ...
0
votes
0answers
23 views

MISTY1 encryption/ extension tricks

I'm trying to understand MISTY1 encryption algorithm but i faced some problems in key scheduling part : Key scheduling part consists of the following operations. for i = 0, ..., 7 do EK[i] = ...
0
votes
0answers
16 views

Implications of pattern in finial digit of prime numbers [duplicate]

http://qz.com/639452/mathematicians-are-geeking-out-about-a-bizarre-discovery-in-prime-numbers/ What are the implications of this (very) new research on crytopgraphy? I would have thought this would ...

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