2
votes
2answers
95 views

PRNG determinism (and java.security.SecureRandom)

Looking at getDefaultPRNG() in java.security.SecureRandom makes me very unsure about how to use it. On my desktop, it uses sun.security.provider.NativePRNG, which reads from ...
1
vote
1answer
223 views

Can we quantify strength of encryption scheme ?

Was wondering if we have any (or can we come up with) "units" for strength of encryption like in Physics. Most of our comparative analysis of encryption schemes are based on number of S boxes or ...
0
votes
2answers
52 views

Is the DES F-function injective for a given subkey?

Is it possible for two different half-block inputs to the DES F-function, with the same round subkey, to produce the same output? That is, if we feed two different half-block inputs $b_1$ and $b_2$ ...
0
votes
0answers
47 views

Is basic RSA secure? [duplicate]

I'm pretty new to cryptography, had RSA in my math lectures a few years back and decided to try it myself. I've implemented a rather basic version of RSA using a hash from a passphrase to create the ...
0
votes
0answers
53 views

Decrypting the CipherValue in a PSKC file [migrated]

This is the opposite of what I was doing in this question - Encryption and HMAC in a PSKC file The spec is there at https://tools.ietf.org/rfc/rfc6030.txt The Data/seed is encrypted with AES-128-CBC ...
0
votes
0answers
112 views

Preventing Quantum Attacks on Cryptography [duplicate]

With the advancement of technology in quantum computing, it's becoming more evident that we need to start thinking about protecting the future integrity of our cryptographic standards. What can we do ...
4
votes
1answer
108 views

What cryptography is suitable to motivate High School students to learn math?

A High School math teacher in the Bronx asked me if I knew of any way to use cryptography in a way that motivates students (15 to 18 years old) to learn math. I do know that many of them want to ...
1
vote
1answer
142 views

Attack an stream cypher using 2 XORed LFSRs

We know that the Key were generated by 2 16Bit LFSRs (output of both is XORed together -> key) I already extracted a 64 Bit key sequence, but how can I calculate the polynom of the LFSRs (and the ...
0
votes
1answer
88 views

Possible to know who is the owner of a message encrypted with RSA public key

Given the scenario in which I want to send 10 messages either to Stalio or Olio. I encrypt these messages with their respective public keys using textbook RSA, before sending the messages to their ...
0
votes
0answers
66 views

Formal proof of theorem concerning the Random Oracle Model

Reading a book on cryptography by Douglas R. Stinson I've met the following theorem, which is stated without proof (see here). Thereby, $\mathcal{F^{X,Y}}$ denotes the set of all functions from ...
0
votes
0answers
27 views

How to use NaCl with Java under Windows [migrated]

I recently found the library Libsodium and was glad that there are also Bindings for Java. Unfortunately, the libraries does not appear to work with Windows beacause they were developed for other ...
2
votes
2answers
138 views

Solving Quadratic equations in Galois Field (2^163)

Hello I am working on implementing a message to elliptic curve point mapping hardware circuit I have done some research and found out the koblitz mapping method: I will be using a field of binary ...
0
votes
2answers
111 views

DES generating the same ciphertext for different plaintexts and identical key

Is it possible to get the same output for DES while the inputs are different while using the same key? The key should not have to be a weak key. If yes could you give me a hint how to show how to do ...
1
vote
2answers
86 views

Do I have to transfer the private key to digitally sign a remote document?

I'm trying to digitally sign a document which is uploaded by a user. I want the user to sign that document using his digital signing certificate (DSC). Should I: transfer the file to the user, and ...
1
vote
0answers
46 views

Is there a way to “shorten” a Merkle chain?

If I have a Merkle chain of 3 items, is it possible to create a zero knowledge proof of the existance of a correct chain between hash 1 and hash 3? Editing to clarify (Thanks Ricky), what I mean my a ...
3
votes
2answers
67 views

Power analysis and exponentiation by squaring

I am trying to understand how one can retrieve the secret exponent via a simple power analysis. Lets suppose that the exponentiation by squaring algorithm is implemented in its simplest form : ...
8
votes
1answer
596 views

What are the security implications of multiple hashing?

There are plenty of questions on this site about hashing passwords. However, none of them quite cover this topic. One of those links covers using multiple different hash algorithms; one covers general ...
8
votes
4answers
199 views

How are random numbers for RSA generated? [duplicate]

The RSA public key encryption requires two very large prime numbers as part of its encryption process that serve as secrets. These are typically generated with cryptographically secure random number ...
2
votes
2answers
82 views

Can I simulate iterated AES-ECB with other block cipher modes?

I am trying to write some code using the Web Crypto API (http://www.w3.org/TR/WebCryptoAPI/#algorithm-overview) which provides only some of the block cipher modes for AES, intentionally excluding ...
0
votes
0answers
27 views

what is wrong in my Rijndael that gives me this? [migrated]

I'm using the Rijndael classes from .net System.Security to Encrypt my RSA Keys this is how I set it up: ...
2
votes
1answer
73 views

Diffusion in Stream Cipher

The diffusion property of a cipher defined by Shannon refers to the ability of a cipher to cause a lot off bits in the cipher text to be modified, when even a single bit in the plaintext is flips. ...
0
votes
1answer
88 views

Prime Numbers in Discrete Log

I am implementing a security protocol based on discrete log. I came across the equation $p = kq + 1$. Understand that based on number theories that both $p$ and $q$ should be large enough to be ...
-1
votes
0answers
63 views

How to verify the result of repeated squaring method

I am wondering that is there any way to check that the result of repeated squaring is correct or not Suppose we have a calculator (like Casio FX 570ES, ...), and we want to calculate x^d ≡ n If any ...
1
vote
1answer
76 views

Luby-Rackoff on Feistel ciphers [closed]

On page 46 of these lecture notes, it seems to say that if we have a Feistel cipher, and plaintexts $(L_0, R_0)$ and $(L_0^*, R_0^*)$ with corresponding encryptions, then we can determine the key? But ...
3
votes
2answers
134 views

Why would an Initialization Vector be supplied externally?

My software uses a 3rd party encryption appliance (DataSecure). One of the capabilities they allow is for the client software to supply an IV while doing CBC encryption. Why would they not generate ...
0
votes
0answers
30 views

AFV11 scheme simplification

I tried to implement AFV11 scheme http://eprint.iacr.org/2011/410 and faced with performance issues. In order to reduce this issue I have made some simplifications to the scheme. Does the following ...
-2
votes
1answer
67 views

Which Block cipher mode should I use? [closed]

Which of the Block cipher mode is MOST secure? I dont care about the performance just the most secure
-2
votes
1answer
65 views

What is Initialization vector (IV) [closed]

I am not the best cryptologer and therefore I have some questions so I learn more and get better. Heres the questions: What is Initialization vector (IV)? MUST I use it or not?
-2
votes
0answers
45 views

Example related to Algorithm to invert VMPC function

I am new with VMPC one way function. I understood the concept from vmpcfunction.com. But I can not understand algorithm of inverting VMPC function.I am not getting any example of it with detailed ...
0
votes
1answer
54 views

Encryption and HMAC in a PSKC file

This is the PSKC standard https://tools.ietf.org/rfc/rfc6030.txt In Section 6.1 6.1. Encryption Based on Pre-Shared Keys They have the following ...
1
vote
2answers
74 views

Chosen plaintext vs Chosen ciphertext

What is the difference between chosen plaintext and chosen ciphertext attack? In both of these adversary has access to paintext-ciphertext pairs.Then where lies the difference?
0
votes
1answer
70 views

Embedded devices Authentication, Integrity and Confidentiality

Embedded devices send messages to the server. The server occasionally sends messages to individual devices(Reboot, upgrade firmware etc) After some research this is my ad-hoc solution: 1) Each ...
1
vote
1answer
52 views

test vectors for 3DES seem to in fact be testing DES - not 3DES

NIST SP 800-20 Appendix A has what presumably are supposed to be test vectors for 3DES except almost all of the test vectors utilize 8-byte keys and not the 24-byte keys that 3DES is supposed to have. ...
2
votes
2answers
67 views

Security concern about reducing hash value using modulo operation

As stated in the title, what I am looking for is information about a "technique" that I would like to use in some of my algorithms. Sometimes I need to map a hash function's result into a range of ...
1
vote
2answers
109 views

how to let other people respond to emails only decrypt-able with my private key

First of all I have to say it's a homework question but since I have no one to consult with, I ended up here :) Suppose a case in which you are the manager of a company and all employees encrypt ...
3
votes
1answer
99 views

Second pre-image resistance vs Collision resistance

From Wikipedia: Second pre-image resistance Given an input $m_1$ it should be difficult to find another input $m_2$ such that $m_1$ ≠ $m_2$ and $\operatorname{hash}(m_1) = ...
1
vote
2answers
88 views

Significance of 3mod4 in squares and square roots mod n?

Why do most literature while discussing squares or square root modulo a prime P, consider P to be congruent to 3 mod 4?
-1
votes
1answer
50 views

Modular Reduction of polynomials in GF(2^m)

Hello I am having trouble understanding the algorithm implementation in hardware of the reduction process over galois fields of F(2^163) In the following process it ...
-2
votes
4answers
215 views

Do Brute-Force Attacks and Cryptanalysis refute Kerckhoffs's principle? [closed]

According to Kerckhoffs's principle "A cryptosystem should be secure even if everything about the system, except the key, is public knowledge." Now I want to throw in a provoking formula of mine which ...
3
votes
2answers
56 views

How many times can a key be used for HMAC-SHA256 before it needs to be rotated?

If I wanted to use hmac for proving that a value hadn't been tampered with, how many times can I use a key before it needs to be rotated?
0
votes
2answers
103 views

Brute force against computational security

One-time pad is secure under brute force with respect to either of the definitions \begin{align} \Pr[M = m] &= \Pr[M = m | C = c]\\ \Pr[C = c | M = m_0] &= \Pr[C = c | M = m_1] \end{align} ...
3
votes
1answer
82 views

Proving the existence of a pseudorandom function

I've been reading the Introduction to Modern Cryptography book by Katz and Lindell as part of my own learning and have come across this exercise which I am not sure how to approach. The exercise is: ...
0
votes
0answers
33 views

Modifying algebraic secrecy message to use digital certificates

I have the following message: sign((M’, T$_A$, sign((encrypt((encrypt(M, $K_{pbB}$), M’), K), T$_B$), $K_{sB}$)), $K_{sA}$) Sign is used for signature generation. Encrypt is used for ...
0
votes
1answer
53 views

Calculate number of chips to solve bit commitment using hash function

I have a problem that I don't know how to solve Assume that H is a cryptographic hash function with output size 80 bits. Assume that ABC123 is a specifically designed line of hardware chips for ...
1
vote
1answer
50 views

Associative but NOT Commutative Reducing Function Construction with Existing Hash Function(s)

Is it possible to construct a binary reducing function based on any existing cryptographic hash function satisfying the associative property but not the commutative property? So formally: Using an ...
1
vote
0answers
54 views

Obliviously computing the Least common multiple of two poylnomials

Consider I have two polynomials $f_1$ and $f_2$ of the same degree. I want to secure them (using any kind of encryption except FHE) and outsource them to an untrusted server. I want him to compute the ...
5
votes
2answers
91 views

power consumption in a XOR

I'm trying to understand how a XOR affect traces of power consumption in a Differential Power Analysis on smartcards. What's the difference in energy radiated in a $1 \oplus 1$ and in a $0 \oplus 1$? ...
2
votes
1answer
66 views

Encrypting decryption key

What's that property called when a scheme is secure even if you encrypt the decryption key? Some schemes have problems when your plaintext is the decryption key (or just the key if symmetric).
3
votes
1answer
58 views

PBKDF vs HKDF for pretty long key

I'm developing a messenger application with encrypted chats. In the first version of the app I've used PBKDF2 (10000 iterations, SHA1, random salt) to extend a short user password and generate keys ...
2
votes
1answer
67 views

Is AES-GCM length extension attack possible using authenticated decryption?

I am looking to encrypt a piece of data using AES-GCM with a full 16-byte GCM Tag and send it over the network using UDP. Is it safe to assume using the AEAD nature of AES-GCM that performing ...

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