0
votes
1answer
39 views

Value of S and r in Fiat-Shamir Protocol

In the book Cryptography and Network Security by Forouzan,in chapter 14, Fiat-Shamir protocol, its mentioned that two large prime numbers p and q are chosen and kept secret. However n=p*q is made ...
2
votes
1answer
76 views

RFID Protocol Cryptanalysis

Assume we have the following scheme for RFID: TAG & READER both have initially k keys. Every session the TAG computes $k_i$=F($k_{i-1})$ where F is a function which computes XOR of previous key ...
1
vote
1answer
40 views

Errata for NIST SP 800-63

I'm looking through the latest version of NIST SP 800-63, and there is a table (Table A.1) in the Appendix that supposed give the "entropy" of a password for a 94 character alphabet for various ...
1
vote
1answer
72 views

Benefit of using random key in Shamir's Secret Sharing

I am implementing Shamir's Secret Sharing, and I find that in (t,n)-threshold scheme, the shares are just using 1,2,3...,n as the key to form the shares ...
0
votes
1answer
80 views

SSL / TLS digital signature exchange

If server is sending its digital signature, in which message / where does the digitally signature is provided to the client. Is it after the server_hello message because there the public key of the ...
1
vote
1answer
38 views

Meaning of Signature hash algorithm field in certificate

I'd like to understand what is the meaning of this field, especially considering that when calling a crypto library to sign data the digest method is specified by the caller. For example, this simple ...
0
votes
1answer
43 views

Rationale of “r” AES key use in OTR version 3 AKE protocol?

I just tried to review & understand AKE (Authenticated Key Exchange) protocol as defined in OTR secure messaging protocol version 3 here , and aiming to achieve Perfect Forward Secrecy I am a ...
-1
votes
0answers
64 views

What are the difference between cryptographic primitives and encryption primitives?

For example, from reading I found that the cryptographic primitives of both AES and DES are Confusion and Diffusion. However the encryption primitive for DES was Substitution and Permutation while ...
-4
votes
0answers
46 views

Why is plain ElGamal not secure?

Why is plain ElGamal not secure? What is the proof behind it?
1
vote
1answer
86 views

How does the Blowfish algorithm key initialization work

I'm having some trouble understanding the Blowfish encryption algorithm. From the Wikipedia article... The secret key is then, byte by byte, cycling the key if necessary, XORed with all the ...
1
vote
0answers
58 views

Standards/RFCs for non-Diffie-Hellman perfect forward secrecy?

Some time has passed since PFS introduction and we now have secure&proven asymmetric ciphers that can generate strong keys very efficiently (elliptic RSA variants and/or QD-Mceliece can generate ...
2
votes
1answer
57 views

Secure ElGamal with OAEP

Is it possible to make ElGamal IND-CCA2 using OAEP or OAEP+? The reason I ask is that I recently answered this question and it came to my mind that OAEP or OAEP+ might be possible solutions. Note ...
0
votes
0answers
25 views

AES-XTS: find key from ciphertext and plaintext [duplicate]

Let's say I have a plaintext, the corresponding ciphertext encrypted using AES-XTS, and the initialization vectors. Is there any way - not brute force, of course - to compute the key? Even if there's ...
1
vote
1answer
66 views

Prove there is PRG that is not necessarily one-to-one

We assume that there is at least one PRG .Now prove there is a PRG like $G:\{0,1\}^{n} \rightarrow \{0,1\}^{l(n)} $ such that it is not necessarily one-to-one.
1
vote
1answer
34 views

CTR_DRBG versus OFB_DRBG

As far as I know, in the development of ANSI X9.82, there was consideration of OFB_DRBG, a pseudorandom number generator based on block ciphers like CTR_DRBG, but it appears to have been rejected of ...
2
votes
0answers
70 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 ...
3
votes
0answers
62 views

How to recover $e$ from $f_A(e) = Ae \mod q$ when knowing trapdoor

I have a silly question, but I don't know a solution, so I need to question. Assume, with a algorithm $TrapGen(1^\lambda)$, it generates $A\in\mathbb{Z}_q^{n\times m}$ with a basis $B ...
0
votes
0answers
44 views

GPG: What public key do I have to publish? [migrated]

I just created a master key and two subkeys. The first subkey is used for encryption, the second one for signing. Now i am wondering what public key do I have to publish on my website. Does is ...
0
votes
1answer
55 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?
1
vote
3answers
70 views

Why do we get the following equation in case of a One Time Pad?

If m: message, M: message space, k: key, K: keyspace, c: cipher, C: cipher space and $E_k$: encryption function, such that $E_k(m) = c,\ m,m^* \in M,\ k\in K,\ c\in C.$ My first question is, is the ...
-6
votes
2answers
88 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 ...
1
vote
1answer
48 views

Zero knowledge proof relation + number is binary

I want to develop a ZKPK for the following problem: $$Y=g_0^{r_Y} \prod_{i=1}^n g_i^{s_i}$$ and $$Z=h_0^{r_Z} \prod_{i=1}^n h_i^{s_i}$$ I want to proof knowledge of $r_Y,r_Z$ and $s_i$ which I have ...
1
vote
1answer
41 views

Using similar passwords and salts for PBKDF2

I'm trying to generate a bunch of pseudo-random keys for AES using PBKDF2, where the AES ciphers will be used in CTR mode as pseudo-random number generators. My goal is to create a 2-dimensional ...
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
2answers
83 views

What do these notations mean in the definition of Perfect Secrecy, if we read those in English?

If m: message, M: message space, k: key, K: keyspace, c: cipher, C: cipher space and $E_k$: encryption function, such that $E_k(m) = c,\ m,m^* \in M,\ k\in K,\ c\in C.$ Then, what do the following ...
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? $$f(x)=g((x+1)\bmod2^l)$$
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
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 ...
1
vote
1answer
60 views

(Simple) Tool for analysing performance (speed in particular) of cryptographic hash function?

I am doing some research for which I intend to insert some (external) function in different cryptographic hash functions and I would like to analyse how the insertion of this extra code in the hash ...
-1
votes
1answer
54 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 ...
-2
votes
1answer
82 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 ...
0
votes
1answer
60 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 ...
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 ...
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
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 ...
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, ...
2
votes
1answer
92 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 ...
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 ...
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 ...
1
vote
1answer
43 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 ...
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 ...
1
vote
1answer
50 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
1answer
54 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
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
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 ...
0
votes
1answer
77 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 ...
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 ...

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