# All Questions

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### Multi-round Transposition/Playfair as a secure hand cipher in the computer age

Given that computers can be easily compromised, there is a need for a hand cipher that can withstand computer attack. Clearly the traditional hand ciphers fail. One time pads work. They also have ...
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### Is $(f(X), G(X))$ pseudorandom?

If $f:\{0,1\}^n \to \{0, 1\}^n$ is a one-way function, $G:\{0, 1\}^n \to \{0, 1\}^m$ is a pseudorandom generator, and $U_m$ is the uniform distribution over $m$-bit strings. Is the joint distribution ...
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### Using same key for encryption and ECBC-MAC k2

ECBC-MAC: $E_{k_2}(CBC-MAC_{k_1}(m))$ If we use same key for encryption (CTR or CFB) and k2 (end tag encryption) in ECBC-MAC in encrypt-than-MAC sheme, is it secure?
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### How good is middle cube method with jumbled digits?

I had to make my own prng for a stream cipher for an inter school science project (I am mentioning that a lot). So I thought of cubing the seed instead of squaring it (like in the middle square ...
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### Is XCBC where k2 and k3 might be the identical, secure?

XCBC paper says all three keys should be independent. It doesn't say they must always be different. However it seems this is necessary to differentiate padded message and message without padding. ...
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### Brute Force AES Calculations

I have an encryption service in which the user decides the length and the type of key, so I would like to build a tool that educates the user on the brute force times for the key they created if using ...
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### Is splitting AES ecrypted data safe?

Say I have a key, an iv and an AES/GCM/NoPadding encoded string and I want to split this information between three people such that only jointly can they reveal the ...
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### AES mix column stage

In a PDF related to AES algorithm for mix column stage is written: The multiplication mentioned above is performed over a Galois Field. The mathematics behind this is beyond the scope of this ...
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### Can DH_anon really be exploited by an attacker?

General consensus is that DH_anon (and ECDH_anon) ciphersuites should be disabled since they offer no way to verify if the server is the one you intend to communicate with. However, I have never run ...
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### Showing that $2^{N-1}\equiv1\pmod N$ when $N=2^p-1$ for prime $p$

I got this question on a previous exam and I got it wrong. I've gone back through it several times since then, but I can't seem to get it. I would really like to know how to do it, so if someone could ...
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### File format of an $2048$ bits RSA public key

From here, there are $14$ bytes specifying the file format of the key. I am still quite confused about the format bytes. For example, the following public key 30 82 01 0a 02 82 01 01 00 8e a3 d1 c7 ...
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### Is Paillier cryptosystem commutative?

Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier?
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I've got an API spec that specifies NRPAD and FPAD as possible padding schemes. I see these being used together with the Korean SEED algorithm. The SEED specification however is void of any padding ...
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### Complexity of preimage resistance

Why is the complexity of pre-image resistance $2$ raised to the power of $n$? I have been looking in everything lecture about pre-image resistance, but I still didn't know the answer.
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### symmetric encryption A5/1 and A5/2 algorithms

where does the key (Kc) used to generate the keystream comes from and also where does the 22bits counter comes from
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### How do I safely anonymize/hash a unique identifier to protect privacy?

I am building a system to collect a unique identifier (MAC addresses from 802.11 probe requests). The system will have several collection points over a large area, submitting to a central database. I ...
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### How represent message in Menezes–Vanstone elliptic curve cryptography

I ask about represent message in Menezes–Vanstone elliptic curve cryptography I now encrypt function as follow $C_1 = (M_1 * K_1) mod\ P$ $C_2=(M2 * k_2) mod\ P$ My question is about how much the ...
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### how to calculate non linearity of AES S-box?

S-box has to satisfy different design criteria. How to calculate non-linearity , propagation criteria for an AES S-box?
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### How can a good encryptor be made?

I am making an encryptor software for a stream cipher with my own PRNG as a project for an inter school science competition. How can I make one so that after it generates the pseudo random nos. it can ...
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### Fast root finding algorithm for Binary Goppa codes decoding using linearised and affine polynomials

I am trying to implement the root finding algorithm from the following paper - Finding roots of polynomials over finite fields by Sergei V. Fedorenko, Peter V. Trifonov link : ...
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### AES: Changing plaintext to state

Can someone explain this to me? For example how M chanes to 0c? Changing plaintext to state:
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### Is python a secure programming language for cryptography?

I know Python is a powerful programming language but is it secure for cryptography? I mean is it possible to reverse engineer the program (written in python) and discover the algorithm of cryptography ...
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### Is a RSA 2048 bits public key secure [duplicate]

I realize servers such as Google, Yahoo, which use RSA has 2048 bits public key. After comparing those keys, I realize that the public keys share a common property, that is first 9 bytes and last 5 ...
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### The Short Integer Solution (SIS) problem for square matrices

The short (or small) integer solution (SIS) problem is as follows: given an integer $q$, a matrix $A \in \mathbb Z^{n\times m}_q$, and a real $\beta$, find a nonzero integer vector $e\in \mathbb Z^m$ ...
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### Why do we need password in a server which uses TLS?

Suppose a server uses TLS to protect communication between us and the server. I observe that in the TLS handshake protocol, password is not mentioned anywhere. Then why do we need to have a ...
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### Crypto libary with Commutative Encryption

I want to implement Mental Poker in JavaScript as a toy program and lead in to a larger serious project so I did my research and found Massey-Omura cryptosystem and the Shamir three-pass protocol ...
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### A5/1 and LFSR incrementation

I am working on A5/1 and I'm not sure to all understand about it. We consider that we receive a burst(228 bits-sequence) to encrypt every 4.615 milliseconds. So when we have initialized our LFSR's ...
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### Can public key be recovered from ciphertext & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM. The ...
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### Security of RSA with $\gcd(pq, (p-1)(q-1))\ne 1$

The Congress of ThéOùÇa enacted that civilian use of any public-key encryption system is authorized on the territory of ThéOùÇa, subject to meeting certain security requirements published by the ...
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### When homomorphic encryption goes wrong?

Consider I have two ciphertext $c_1$ and $c_2$ encrypted using RSA encryption. By definition if I multiply them I'd get $c_1.c_2 \ modN$. My question is what would happen if $c_1.c_2 >N$. Can we ...
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### Show that the equal difference property exits for a modified DES encryption system

My cryptology professor gave us this problem on a past homework assignment and I only managed to get one of the 3 parts correct. Needless to say, I want to know how to do the other two parts as well. ...
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### What, cryptographically speaking, is a “long message”?

I have read about long message attacks on some cryptographic hash functions. However, I don't quite understand what is being referred to as a "long message". Also, do long message attacks only apply ...
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### CRC32 vs. low 32 bits of cryptographic hash

I was having a discussion with a colleague yesterday whose education and experience exceeded mine. He said something yesterday that sounded incorrect to me intuitively, but I don't have the knowledge ...
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### what is contained in a public key certificate

Public key certificate is a digitally signed document which verifies the sender is indeed the person. May I know how can the receiver tell the sender is indeed the person solely based on information ...
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### Simplest code for 64-bit block RSA-like encryption/decryption and key generation

Looking for the simplest code in C. Need a set of functions that will first generate a public/private 64-bit key pair, and then the function to code/decode a given 64-bit block, no built-in checksum ...
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### Type of cipher used where ciphertext has no discernible pattern, spaces. Type?

What type of cipher could give ciphertext where for example random ASCII chars between say F-z (symbols and numerals inclusive), but with only a few spaces? Frequency of chars shows some similarities ...
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### signed message susceptible to block re-ordering , block deletion , block replication

We would implement a Public Key Cryptography (PKC) based digital signature by breaking the message into blocks and signing each block independently. One of the issues associated with digital ...
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### RSA Decryption given n, e, and phi(n)

my cryptography professor gave us this problem for extra credit a while back and I attempted it but I didn't get it correct. I have gone back to it, but I'm even more lost now than I was the first ...
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### AES— Brute force attack versus Known plain text attack

I am taking a codes and cryptology course and the following is a questions on a past exam that I could not and still can't solve: ...
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### Why is it hard to calculate Logarithm on Diffie Hellman?

i read something about Diffie Hellman. What i don't understand: Alice selects a randomly generated Number, calculates X = g^x mod p and sends X to Bob. If she calculates g^x, she needs to calcluate ...
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