2
votes
0answers
66 views

Looking for C++/Python Open Source code library for cryptanalysis of classical ciphers

I've done a significant amount of coding over the years working on classical ciphers (e.g., Chaocipher, D'Agapeyeff). My main programming languages today are C++ and Python, although there was a time ...
0
votes
0answers
37 views

Is the key schedule of Serpent a circle?

The creation of the prekeys for Serpent works by XORing some previous values with a counter and a fixed value. Every word is 32 bits big and 4 words form a round key (after applying a S-Box, but this ...
1
vote
2answers
80 views

Generate secure password hashes without access to PBKDF2 or bcrypt

Given is a system, which does provide only implementations of fast hash algorithms (MD5, SHA1, SHA-256, SHA-512). There is no implementation of PBKDF2, bcrypt or scrypt available. The system does ...
0
votes
1answer
64 views

How to compute accumulated values in bilinear map accumulators

How to compute $ g^{1/(e_1+s)}$, where $g$ is the generator of group $\mathbb G$, and $e_1$ and $s$ are keys? I know only $s$ and $g^{e_1}$, not $e_1$. $\mathbb G$ has prime order for some prime $p$ ...
0
votes
1answer
53 views

AES Mix Columns and Shift Rows

Why we use Mix Columns and Shift Rows in AES? FOr example, if i want implement an AES algorithm without Mix Columns and Shift Rows what is the difference in the ciphertext?
-6
votes
2answers
84 views

OTP - Reusing key IS SECURE! PROVED! [duplicate]

EDIT: This is not a duplicate, in this I have explained WHY this should be secure and not if it is secure, so please stop down-vote if you haven't read everything. I have questioned before about my ...
8
votes
1answer
4k views

How do I store encrypted files on a web server and decrypt them locally?

I want to store files (images) on a public webserver and let users see them if they know a password. The server shouldn't have the unecrypted files and the server can only serve files, not perform ...
-2
votes
1answer
81 views

OTP - Why not reuse key? EDITED! [duplicate]

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! This might sound really dumb but why is it bad/insecure too use the same key twice on One-time-pad? Question: Why and how does using ...
-1
votes
1answer
53 views

OTP - Reuse key BUT add IV, is it secure enough?

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
0
votes
1answer
48 views

Is $f\colon x\mapsto g(x+1)$ necessarily a pseudorandom function?

Let $l\in\mathbb N$ and suppose $$g\colon\;\{0,1\}^l\to\{0,1\}^l$$ is a pseudorandom function. Is $f$, defined as below, necessarily a pseudorandom function as well? $$f(x)=g((x+1)\bmod2^l)$$
0
votes
0answers
30 views

Would a pictographic, phoneme-based, hand cipher be difficult to crack with computer crypt-analysis?

What I'm talking about is a hand cipher which uses phonemes instead of individual characters and pictograms instead of the usual shuffling/substitution methods (e.g Caesar, Solitare, Vignere). The ...
1
vote
0answers
32 views

Generate hash value using public key along with message

I was trying to understand one way signature chaining on message by saxena and soh. As the message is passed from one user to other, every user can combine their signature to create one single ...
0
votes
1answer
61 views

How to encrypt a vector $e\in Z^{m}$ using LWE

I have a vector $e \in Z^{m}$, now I want to encrypt it by using LWE (Learning With Errors). Because in LWE, we have to encrypt of a bit $\{0,1\}$. How can I encrypt a vector $e \in Z^{m}$? Thank you ...
0
votes
0answers
31 views

Using a Secure RNG in Probabilistic Fair Exchange

I am attempting to implement probabilistic fair exchange described in Probabilistic Non-Repudiation without Trusted Third Party. A secures a message using AES with 512 bit keys (in my ...
5
votes
2answers
1k views

Why is this the inverse of a Enigma Machine rotor?

I am learning about how the Enigma Machine works and I found this example of one letter being encrypted by an Enigma Machine. It shows the letter "G" going through three rotors and then it goes into ...
0
votes
1answer
58 views

What is the proper way to generate a fixed length key from a variable length password?

The password is entered by the user and the key is processed locally. Neither the password nor the key will be stored, only used and forgotten (but hopefully not by the user). Is SHA256 by itself ...
0
votes
1answer
64 views

How much of Probability do I need to know to study Cryptography?

I have just started MSc in Computer Security. I didn't study probability before. Now, I have some short time to complete my MSc semester. What are the minimum topics from 'Probability' do I need to ...
1
vote
2answers
125 views

Prove that if we redefine the key space, we can assume Gen chooses a key uniformly

I am working on problem 2.1 in Introduction to Modern Cryptography 2nd edition by Katz and Lindell. 2.1) Prove that by redefining the key space, we may assume that the key generation algorithm ...
9
votes
3answers
7k views

How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?

If cryptanalysts today were to crack the original Enigma machine, how fast/ how easily could they do it? What methods would they use? The original cracking was significantly helped by operator ...
6
votes
4answers
657 views

Is the logic for how the enigma machine worked documented somewhere?

I know that there is a formula to calculate the result of any input but is the logic of how the machine actually worked documented? I have seen schematics for the circuitry and even a how to make ...
1
vote
1answer
49 views

algebraic attacks for mixed operations (mod 2 and mod 256) [closed]

If a cipher has mixed operations, e.g $\oplus$ (addition mod $2$), and addition modulo $2^8$. How we we going to express them mathematically? Thanks in advance!
0
votes
0answers
18 views

Substitution Permutation Network (SPN) - Decryption In Mathematica

I am working with a Substitution Permutation Function, SPN, in Mathematica. I have an encryption function for an SPN. By changing the parameters that go into the spn function, and not the function ...
2
votes
1answer
101 views

Encrypt entire payload or only confidential parts of payload?

In cases where a large complex data structure contains elements that are a mix of confidential and not-so-confidential data, what would be the pros & cons of: encrypting the entire structure ...
0
votes
1answer
41 views

Randomness in generation of Virtual Machines from pre-built Image [closed]

I am studying Multi-Tenancy vs. Virtualization, and I got thinking about randomness, true randomness, virtualization etc, and I couldn't find anything on it. From what I gather, ...
0
votes
0answers
23 views

Why the Symmetric Key algorithm requires small key compared to Asymmetric algorithm? [duplicate]

According to a book I am studying: The key lengths for symmetric and asymmetric algorithms are dramatically different. For instance, an 80-bit symmetric key provides roughly the same security as a ...
1
vote
3answers
101 views

Salsa20-GCM composition secure?

AES-GCM seems to be used by everyone but I never seen even one post about Salsa20-GCM. Is it secure? Wikipedia mentions that GCM ...
3
votes
1answer
65 views

Is it possible to combine true streaming with AEAD?

It seems there is a difference between "streaming" in cryptographic sense (as in CTR) and "streaming" in general programming sense (as in "accept a file larger than RAM from socket and save it on ...
2
votes
1answer
90 views

How multiplicative property of RSA can be exploited

It is known that RSA has the multiplicative property $E(m_1) \cdot E(m_2) = E(m_1 \cdot m_2)$ because $m_1^e \cdot m_2^e = (m_1 \cdot m_2)^e \pmod n$ But how can this property be used to break ...
2
votes
1answer
52 views

Algebraic cryptanalysis on public-key schemes

The book Algebraic Cryptanalysis (Bard, G.V.; Springer, 2009) speaks about transforming a symmetric scheme into a system of polynomial equations and solving these equations to break the scheme. But ...
1
vote
1answer
42 views

KDFs for symmetric encryption master key & serial number

Let's assume that I generate a high entropy AES master key (through /dev/random for example) and I want to derive it with a fixed-length serial number (12345 for instance). The derived key is used to ...
6
votes
1answer
179 views

Looking For Additively Homomorphic Encryption

I have a construction that requires as primitive an Additively Homomorphic Encryption scheme that does not rely on hidden group order, meaning I can't use Paillier. I now have two different ...
0
votes
2answers
109 views

CTR HMAC SHA256 implementation

After trying to invent my own AES mode, I decided to just implement something that's known to work, namely CTR with HMAC SHA256. From what I understand, I can use the IV as a counter, and the IV ...
2
votes
1answer
101 views

What use is the signature without the message under RSA?

Using RSA for signing & verification, is there a way to take a valid signature for an unknown message, and for someone else to generate a valid signature using a different key against the valid ...
3
votes
2answers
255 views

Is it possible to tweak AES-GCM so that it is satisfactory for whole-disk encryption (like XTS mode)?

Is it possible to leverage a preexisting implementation of AES-GCM to provide the key security benefits essential for full-disk encryption (similar to AES-XTS)? GCM is a popular encryption mode ...
14
votes
2answers
5k views

Differences Between White-Box Cryptography and Code Obfuscation

I have been reading the question "What is a white-box implementation of a cryptographic algorithm?" and it led to this short article / Q&A which states in question 2: Q2: What is the ...
0
votes
1answer
52 views

Cipher text only attacks on deterministic fully homomorphic encryption schemes

If we have encryptions of additive and multiplicative identities in the corpus of cipher text of a deterministic fully homomorphic encryption (FHE) scheme, I guess we can break it. If the FHE scheme ...
1
vote
1answer
74 views

Creating a random password based off of a prime number

So I am making an application that basically creates strings that must be encrypted before they are stored on a user's device. If the user blindly starts running the application without creating a ...
6
votes
6answers
1k views

Any efficient text-based steganographic schemes?

While there are sophisticated and efficient steganographic schemes with images as cover available, I am yet ignorant of the existence of any fairly efficient and secure schemes with texts as cover. ...
1
vote
0answers
36 views

BER or DER X9.62 ECDSA signature

The signature format for ECDSA signatures can be encoded using ASN.1 integers according to X9.62 or it can comprise of two integers with the same size as the key size. In case the X9.62 format is ...
1
vote
1answer
99 views

Creating unique keys with md5

The project I'm working on requires me to find a way to create a unique key based on data stored in a table. The table in question consists of x columns and y rows. In order to create the key I want ...
0
votes
1answer
55 views

How does the certificate authority generate a signature F?

E=encrypt(K,M) - is message M encrypted with key K gives encrypted text E M=decrypt(K,E) - is encrypted text E decrypted with key K gives message M KCA−pub,KCA−priv - is the private-public key pair ...
0
votes
1answer
74 views

What do I use as the encryption key and initialization vector in AES cfb128

I'm writing a program that can encrypt a file using AES cfb128 (using Openssl and C++). The scenario of the program is this: Person A visits computer, encrypts a file they make, takes away a key ...
32
votes
5answers
27k views

Should I use ECB or CBC encryption mode for my block cipher?

Can someone tell me which mode out of ECB and CBC is better, and how to decide which mode to use? Are there any other modes which are better?
0
votes
1answer
48 views

Altering the message space of Paillier

Is there any obstacle if we restrict in Paillier the plaintext values to be drawn from $\mathbb{Z}_N^*$ instead of $\mathbb{Z}_N$ as the original scheme indicates.
1
vote
1answer
31 views

difference between soundness in ZKPoK and special soundness for sigma proofs

What is the difference between soundness in ZKPoK and special soundness for sigma proofs?
1
vote
1answer
61 views

Why is a Feistel network not a type of substitution-permutation network?

I understand what substitution-permutation networks look like. I understand what Feistel networks and Feistel-like networks look like. A Feistel network or a Feistel-like network features substitution ...
2
votes
1answer
203 views

How can I map arbitrary group elements to unique integers without using Hash functions?

Let's say, I have a group $G$ of large prime order $p$. A set $S$ consists of $n$ random elements chosen from $G$. Without using a collision resistant hash function $H$, how can I map elements of $G$ ...
0
votes
0answers
43 views

Are there any noisy homomorphic encryption schemes?

Are there any Homomorphic Encryption(HE) schemes that result in noisy answers ? By noisy i mean , the answers could be approximately near the actual answers by noise factor $\epsilon$. For example , ...
0
votes
2answers
105 views

Removing “security by obscurity” from port knocking

Every article about port knocking, for instance https://wiki.archlinux.org/index.php/Port_Knocking , declares this method as security by obscurity. Is the following enough to remove that title; a ...
3
votes
2answers
186 views

Why would an Initialization Vector be supplied externally?

My software uses a 3rd party encryption appliance. One of the capabilities they allow is for the client software to supply an IV while doing CBC encryption. Why would they not generate a random ...

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