1
vote
0answers
20 views

If you use an AES key just once, do you need to use IV, and/or pad the message? [duplicate]

I am developing an application that is going to use AES encryption. Since it is going to use a different key for every message encrypted... Would it be secure to use a constant IV? (i.e null bytes) ...
2
votes
1answer
154 views

Is F' a pseudorandom function when F is composed with G, a pseudorandom generator?

If $F$ is a pseudorandom function, is $F'$ also a pseudorandom function in the following: $$ F'_k(x)=F_k(G(x)) \space \space \text, $$ where $G$ is $a$ pseudorandom generator? Also, does the other ...
4
votes
3answers
128 views

Why are there $2^{56}$ possible DES keys when there are 64 key bits?

On forums I read DES has $2^{56}$ possible keys so it takes x times to brute force it with hardware x. But there are 64 total bits of which are 8 parity bits. But those parity bits are a ...
0
votes
0answers
40 views

Symmetric encryption vulnerable when encrypting and decrypting are the same?

To my understanding, symmetric encryption is where encrypting and decrypting data can occur with the same key. It's possible for symmetric encryption that the encrypting and decrypting algorithms are ...
-1
votes
1answer
49 views

Understanding the cryptography used in a file [closed]

I use a software that stores a raw binary file with information, and exports it to a text file. I have access to the data in the original binary file. You can find a sample of the contents of the raw ...
2
votes
0answers
42 views

Example of Projective Coordinates

Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
1
vote
1answer
87 views

Cycling hashing in PBKDF's and their limitations in strength?

I hope this question isn't too similar to one that's already been asked. I also want to point out I know part the answer already, AFAIK: I just want some expert input on this. Let's model a hash that ...
1
vote
0answers
73 views

Convert projective to affine coordinates in ECC? [closed]

I am working with my project. I use projective coordinates but when I convert to affine coordinates, I can't get it. Can anyone help me? Projective Coordinates $(X,Y,Z)$ to Affine Coordinates ...
1
vote
1answer
72 views

Non-numeric Diffie-Hellman?

It may seem that this is a programming question, but I just need advice on the cryptography side of the question. I want to implement the Diffie-Hellman key exchange algorithm on iOS (since no free ...
1
vote
1answer
44 views

XOR or add in one time pads? [duplicate]

Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)?
1
vote
2answers
157 views

Recommendation for lightweight algorithm for partial message encryption

I have designed a specific client and server program, which sends a file from client to server in 32k chunks. I want to encrypt only part of the data. More specifically: in each 32k chunk passing ...
0
votes
0answers
149 views

Strength of TripleDES (DESede) in Java (Sun JCE)?

I'm introducing Jasypt to a spring-boot project. The default algorithm for storing passwords with it is PBEWithMD5AndDES. Since I've got some reservations on using that cipher, I'm looking into ...
4
votes
0answers
84 views

How can I implement decryption for NTRU homomorphic encryption scheme?

I have come across this paper On-the-fly multiparty computation via on-the-cloud Multikey from Fully Homomorphic Encryption by Lopez-Alt et al., where authors describe a NTRU-based homomorphic ...
4
votes
1answer
104 views

Could we share a secret key using the Birthday problem?

I stumbled upon this code on-line, it seems obvious to me that generating all 2^40 keys in trivial time can always be achieved as can hashing each and everyone of them, using the SHARED Salt that ...
6
votes
2answers
139 views

The difficulty of computing discrete logs

I understand that in Diffie-Hellman it should be hard to compute $a$ given $g$ and $g^a$. In computational Diffie-Hellman, it appears to be hard to compute $(g^{ab})$ from $g^a$ and $g^b$. As for ...
3
votes
1answer
461 views

Should AES.decrypt(ct, wrong_key) return blank or wrong result?

I am trying to use AES as cipher for an application I am building. I am using a JavaScript library (https://code.google.com/p/crypto-js/) to perform encryption and decryption with AES. When I ...
5
votes
1answer
136 views

Encryption scheme like RSA where encryption is the inverse of decryption

In RSA, it is basically equivalent to use the private key $d$ to encrypt as it is to use the public key $e$ to encrypt. They are exactly inverses: $e=d^{-1}$. I need to know, are there other public ...
1
vote
1answer
87 views

SHA256 for large files

I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size. What should be my input after 1st 64KB ...
1
vote
0answers
66 views

Diffie-Hellman, RSA and the types of public key cryptography

Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different ...
0
votes
0answers
33 views

How to calculate unicity distance of Fleissner grille?

I need to calculate unicity distance of Fleissners grille of $M \times M$ size. All I know is that plaint text redundancy equals $2$. The alphabet is not specified. Is it possible to calculate its ...
0
votes
0answers
98 views

splitting the plaintext and ciphertext into blocks

Say I was to use RSA with a given value of n. I choose to split the plaintext and ciphertext written in a 27 letter alphabet into blocks with k and m characters resp. How would I find the largest ...
5
votes
0answers
30 views

OTR AKE protocol implementations security

While looking at the different versions of OTR protocol I discovered a strange thing: there is no trace of the patch for the weaknesses that were noted in “Finite-State Security Analysis of OTR ...
4
votes
1answer
145 views

Determining if Server/Client's TLS configuration is Vulnerable to SLOTH

In the context of SSL/TLS protocol and SLOTH vulnerability. I want to find out if certain websites(webservers) or applications that use TLS are vulnerable. I need some guidance for this. My idea is ...
3
votes
1answer
151 views

Unable to understand hash function representations

I have some hash function representations, which I find it hard to understand. I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations ...
4
votes
2answers
124 views

Name and security of these non-invertible functions?

I would like to learn more about a specific set of non invertible functions: The function should accept 2 inputs: one hidden and the other visible. The output and the function should also be ...
0
votes
0answers
28 views

Uniformly distributed sub-sequences of a main PRG sequence

Let $ g_s $ be a pseudo-random generator that generates uniform distributions of numbers ($s$ : seed) of a fixed bit-size. One wants to compare the pseudo-randomness of certain subsets of elements ...
2
votes
2answers
75 views

BOOLEAN FUNCTIONS: generate a function $f: \{0, 1\}^n \rightarrow \{0, 1\}$ from a $n \times n$ S-Box

I want to calculate the hamming weight of a S-Box using this formula: $\text{hw}(f) = \sum_{x=0}^{2^n-1} f(x)$. Where $f: \{0, 1\}^n \rightarrow \{0, 1\}$ My problem is that I don't know how to get ...
5
votes
0answers
31 views

Understanding the definition of HGD

On the section 4.2, page 10, of the paper Order-Preserving Symmetric Encryption, the authors define two subroutines: the first one is called $HGD$ and the second one is $GetCoins$. I have doubts ...
0
votes
0answers
73 views

Semaev summation polynomials

I am little confused how this attack works. We have the points $P, Q$ such that $Q = nP$. We let $u_{1} $and $u_{2}$ such that $R(x,y)=u_{1}P+u_{2}Q$. Then if we find the solution $x_1,...,x_n$ of the ...
0
votes
1answer
51 views

Computing the cardinality of the co-domain of specific modular exponentiations

Consider the following function: $f: \mathbb{Z}_n \rightarrow Y,~x \mapsto x^e \bmod n$, where $n = p \cdot q$ is an RSA modulus and $gcd(\varphi(n),e) \neq 1$ (different as required for a public ...
0
votes
0answers
83 views

Proof that this is not a secure pseudorandom function

$p$ is a large prime number. Consider the following function $F:\mathbb Z^*_p \times \mathbb D\rightarrow\mathbb Z^*_p$ where $\mathbb D=2,....,p-1$. $F_k(x)=x^k \bmod p$ Proof that it's ...
1
vote
1answer
131 views

Limitations of Elliptic Curve Cryptography?

Simple question, what are the limitations of ECC, both in terms of application and how secure it is? I heard that the NSA were able to read emails a few years back due to a backdoor they had ...
0
votes
0answers
30 views

Using Montgomery ladder to calculate the coordintes

In one of my assignments I need to solve the below: For a Montgomery curve $3v^2 = u^3+u^2+u$ over ${\mathbb{F}}_{11}$ and point $P = (9,8)$. I need to compute $x$ coordinate of $3P$ using ...
2
votes
1answer
81 views

Which ciphers produce random ciphertext?

I already know AES produces a "random" output. 5e4e6440826d6afc4535fbf078455f791159701a9df624ddd4e4dda84523b6a7 Its ciphertext doesn't follow a pattern and is ...
1
vote
0answers
57 views

Proving pseudorandom generators

Can anyone please help me on how to prove or disprove (by counterexample) whether the following function $G'$ is a PRG (Pseudorandom Generator) given that $G$ is a PRG. $$G'(s) = ...
1
vote
4answers
135 views

Is it safe to use XOR to encrypt data key using master key

I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way ...
1
vote
1answer
50 views

Is this a secure keyed hashing construction?

I need a PRF for use with PBKDF2, however, the only thing I have is the AES block cipher primitive. I'm attempting to derive a keyed hash function from the block cipher. The design is based on the ...
10
votes
8answers
2k views

Are there any advantages in using proprietary encryption?

Proprietary software generally relies on the fact that in keeping the encryption algorithm private, it gets an extra layer of security implying "Security through Obscurity." Obviously this phrase has ...
3
votes
0answers
64 views

Why reveal MAC-keys after using them?

As far as my understanding goes MACs are used to determine whether the received message comes from a source that has access to a MAC-key which is known by both parties. Some crypto protocols reveal ...
1
vote
0answers
42 views

Algebraic relationship between Original Key and Sub Key of DES

Does there exist any sorts of algebraic relationship between Original and Sub Key of DES? I understand that by solving K-Maps of 64-bit Input/48-bit Output, I can get 16 algebraic relationships ...
3
votes
1answer
117 views

Practical attack on an impractical implementation of Rijndael (AES?)

My understanding of the cryptanalysis of AES, is based on what I've read on Wikipedia and my intuition, I have nothing but self-taught education on the subject. So I want you to imagine: I have only ...
7
votes
5answers
296 views

Does frequent key change weaken encryption?

Following scenario: We are using OTR for communication between Alice and Bob which means after each successfull message exchange a re-keying happens for both parties leading to new AES-keys for the ...
1
vote
1answer
86 views

Encrypting and Authenticating The Simplex Communication Between Embedded Devices

I am planning to build temperature sensor nodes for my home heater control. Central device will control the heater using temperature data read by nodes. These nodes will send temperature data to ...
3
votes
1answer
108 views

Why gcd(r,(p-1)/r) needs to be 1 in benaloh cryptosystem

I recently discovered the benaloh cryptosystem. I am working with the system as it is discribed in the following link: https://en.wikipedia.org/wiki/Benaloh_cryptosystem However I need some help in ...
1
vote
2answers
38 views

Are there any disadvantages of using libsodiums helpers for en-/decoding/comparision instead of the native ones?

Libsodium has some helpers, which allow hexdecimal decoding, encoding and also constant-time string comparison. So if you use the php binding libsodium-php you ...
0
votes
3answers
60 views

Defining Symmetric vs Asymmetric cryptosystems

I'm writing a project on the advantages and disadvantages of symmetric vs asymmetric cryptosystems. At the moment I am trying to define both systems using mathematical notation. Under the heading ...
1
vote
0answers
58 views

Encryption technology for DARPA

I'm working on a short story taking place in the near future in which a hacker gains access to the DARPA mainframe and files related to a highly classified DARPA project. Being ignorant about state ...
3
votes
1answer
74 views

4 x E = D in Simplified AES how it's possible?

Can anyone explain how it's possible through hexadecimal or Binary 4 x E= D
2
votes
1answer
73 views

Does the time to evaluate a hash function depend on the function input size?

Suppose we have a (variable-input size) hash function modeled as a random oracle. Can it be consistent to say that the time to evaluate this function depends on the input size ?
5
votes
1answer
127 views

Can somebody help me understand RC4 Spritz? (Three Questions)

So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic ...

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