# All Questions

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### how do I learn cryptography, and where? [on hold]

I want to learn cryptography, but I don't know how to go about it. I have tried asking around, but i still have no idea as to where it is taught. Any help?
53 views

### Question on BPP and NP (polynomial time) [closed]

Informally, BPP is the class of languages that can be decided by a probabilistic algorithm in polynomial time with an arrow probability of most 1/3 on any instance. More formally, a language L is in ...
54 views

### Bijective Multivariate Public Key Cryptography

Is there any scheme in Multivariate Public Key Cryptography with bijective trapdoor function such that is unbroken actually? I have investigated and I have found only surjective or nor subjective. ...
336 views

### Fiat-Shamir signature [closed]

I have a question about Fiat-Shamir signature: A hash function is h(w)=w mod 2011 and w1=2623, w2=3269, w3=1938. What is h=? and how to determine k.t bits?
367 views

### Why is there a strong distinction between stream and block ciphers? [duplicate]

If I don't err, in the literature a stream cipher is one in which each plaintext bit is processed individually, commonly via xor-ing with one bit of a random or pseudo-random bit stream, while a block ...
133 views

### OpenPGP Brainwallet [closed]

This question is an intersection of two pieces of technology. The first is on Hierarchical Deterministic Wallets from the Bitcoin Space. The second is on OpenPGP key generation. Has anyone created a ...
550 views

### Would this simple encrypted chat program be feasible using One Time Pads?

Lets say I want to build a simple chat program that has encryption that is impossible to crack for anyone, even a theoretical government with a massive super computer. Ok here's my idea. You'll need ...
187 views

### Does a playlist of songs or movies mixed together contain enough random enough for OTP key material?

Ok hypothetical scenario. Lets say I want to generate a lot of key material quickly for a one-time pad. This key material will be divided up and used for many different messages in the future. I ...
246 views

### Why shouldn't one build a MAC by XORing multiple message blocks?

I found this simple proposal for a MAC algorithm: Let the MAC of message M (which consists of message blocks $M_1$,$M_2$, ..., $M_n$) be the AES encryption with key K of the XOR of all the ...
536 views

### finding collision for truncated SHA1 hash output

Suppose we truncate only 40 bits of sha1 hash output.hence it is insecure.how can we find two message as input which gives first 40 bits of hash as same value i.e we have to find collision for first ...
206 views

### IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG?

I am using a AutoSeededRNG from Crypto++ to generate IVs for use in CBC encryption. I am encoding the IVs using Base64 for future use (decryption). I notice that ...
176 views

### Any techniques for evading frequency based crypt analysis without encrypting?

Are there any general techniques for evading frequency based crypt analysis without using any encrypting techniques
94 views

### RSA public key security issue

The public key for RSA is $[e,n]$. Since $n = p * q$, are $p$ and $q$ already exposed because it takes no effort to figure out $p$ and $q$ from $n$?
559 views

### Is it possible to generate an RSA SHA1 signature only from a public key?

Is it possible to generate signature only from Public key. See example below where i have valid signature but what if I change hash ? Is then any way to do this? Public key(160 bytes): ...
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### Storing the activation status of a product and expire details Android [closed]

In my Android application, it's required to store the activation status of the software and keep track of the activation expire date. What is the best way to store this information? Is it safe to ...
72 views

### What is the best (thoroughly covering) textbook for application of LFSRs in cryptography? [closed]

What is the best (thoroughly covering) textbook for application of LFSRs in cryptography? (Beside Cipher Systems by Beker & Piper)
218 views

### Multi layer encryption with ECB mode [closed]

if i use the 2 of the same key with 2 of the same algoritm when encrypting in ECB like when i have 2 blocks of the same color and i encrypt the 2 blocks with the same color the cipher text should not ...
516 views

### 128-bit Pseudorandom number Generator

Is there any 128-bit pseudorandom number generator available? I tried the Blum Blum Shub Generator, but I can't produce a 128-bit pseudo-random number. Maybe before I produce a 128-bit pseudorandom ...
60 views

### cryptography permutation [closed]

Let $\pi$ be a permutation of the integers $0$ through $2^n-1$ (the integers that can be represented in $n$ bits). For example, $\pi$ could be used as a substitution cipher in which each plaintext ...
172 views

### AES implementation in java that allows key of 320-bit length [closed]

I need an implementation of AES(Rijndael) in java that allows use of a 320-bit key. Please suggest a reliable implementation
244 views

### Encrypting with private key in Public Key InfraStructure [closed]

In Public key infra structure, The MD5 of the data is encrypted with private key of sender and this encypted md5 along with the data is again encryted using AES or 3DES algo. here key used to encrypt ...
537 views

### Advantages of each encryption mode [closed]

What is the advantages of each encryption mode to other encryption mode.. for example what are advantages of CBC to PCBC, CBC to CFB just like that. so that I can filter what would be the best ...
139 views

### Can someone tell if my Hand Cipher is secure? [closed]

In easy steps, this is how it works: Convert txt to numbers. mod 1-26. Generate random numbers (by my other cipher) equal to plain txt. Write random numbers under txt numbers. Like this: ...
234 views

### How to calculate cycles per byte [closed]

I have this data: processor clock frequency: 2,1 ghz message length: 16 byte Speed: 4,3 Mbytes/s how can calculate cycles and cycles per byte?
905 views

### Decrypting encrypted files if i have the original files(Plain Text attack) [closed]

I have the following A Encrypted file and the same file in its original(not encrypted) form Now will it be possible to find the encryption/decryption key by comparing the the above two files are ...
67 views

### AES ENCRYPTION ALGORITHM [closed]

What is the amount of decrease in the probability of decrypting a data encrypted using an AES algorithm? (That is by introducing each round out of ten whole rounds, how the probability of decryption ...
242 views

### What kind of attacks is this code vulnerable to? [closed]

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For every set of twin primes $y,z$ let $n=8z^{2}y$ and ${e}=z^{3}+2yz$. Then I claim: $$\cfrac{4e}{n}=\cfrac{1}{2}+\cfrac{1}{y}+\cfrac{1}{z},$$ That this is true can be seen simplifying the ...