# All Questions

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### RSA 896 vs 1024 vs 2048 in Javascript?

I am currently working on a secure messaging website and I had been using RSA 2048 for encryption, decryption and signing of messages but I found it to be EXTREMELY LAGGY so i've moved to 1024. I did ...
211 views

### What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
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### How does SSL secure the initial handshake?

I'm reading the SSL specs, and it seems that the initial handshake has no authenticity protection at all. What is to prevent, say, an attacker from overwriting the "available ciphers" list with one ...
387 views

### Some cryptography security questions

I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here :-). My friend said that when he used public ...
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### Hypothetical unknown cipher - security in obscurity?

I'm curious what would happen in the following scenario: Suppose an attacker gets a hold of a cipher-text of sufficiently large length. And suppose he has the means to verify a successful decryption. ...
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### Having 4096 bit keys and short (< 256 byte) messages, can I simply use the key as OTP?

Assumptions: Alice and Bob use (cryptographically secure, hardware-rng generated) 4096 bit keys. Each message is encrypted using a new key; meaning: once a key is used, it's destroyed. Alice and Bob ...
249 views

### Security considerations on “expand 32-byte k”-magic number in the Salsa20 famility of stream ciphers?

I'm currently examining the NaCl library written by Daniel J. Bernstein and I noticed that the library hard codes the sigma: ...
367 views

### Do we have to use an IV for AES encryption to be FIPS 140-2 compliant?

I asked this question Will our app be FIPS 140-2 compliant if we use our own AES algorithm implementation here before and although there are some different thoughts about this, the general consensus ...
370 views

### How does one use AES block cipher modes of operation?

This is the sequel to my previous question about AES block cipher modes of operation. (See: AES block cipher modes of operation) Now, here is my real problem. I have to use a block cipher with 8 bit ...
155 views

### Which platforms are most vulnerable to Simple Power Analyse Attack

In a "Simple Power Analyse Attack", the difference in power consumption during multiply or square operation is used. In the RSA decryption process with the "Square and Multiply" algorithm, both ...
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### How hard/easy will be to break a SHA-1 or SHA-256 hash if the attacker knows part of the original text?

I'm creating an algorithm to hash some text variables (20/30 characters long) to send them across an insecure channel. I'm not dealing with high security data, so no credits card numbers or any other ...
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### Rijndael: explanation of Rcon on Wikipedia?

I stumbled onto the explanation of Rijndael Rcon on Wikipedia, and I can't follow it. The example for Rcon indicates that Rcon(9) is 0x1b. That could make sense… ...
3k views

### What makes RSA secure by using prime numbers?

I am just learning about the RSA algorithm. Looking at the first two steps: Choose two distinct prime numbers $p$ and $q$. Compute $n = pq$. I have some probably stupid questions: Why do $p$ ...
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### How much does a successful Distinguishing Attack “break” the attacked stream cipher?

I started reading about the most recent cryptanalysis of RC4 and it's variants. One of the papers I just finished reading ("Two Linear Distinguishing Attacks on VMPC and RC4A and Weakness of RC4 ...
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I would like to know how much padding OpenSSL algorithms expect.
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### Can I construct a feasible stream cipher out of HMAC and a secure hash algorithm?

I have constructed a stream cipher from a secure hash algorithm and a HMAC. Here is a brief description of the algorithm: Let: (Actually Objective-C styled pseudo code) ...
431 views

### AES with different modes of operation

I'm taking up a cryptography class and this is for an assignment. We're asked to find the differences between AES/RSA in the different modes of operation vs the one timepad method. From wiki, I can ...
455 views

### Question regarding multiple SHA-256 rounds on a Bitcoin Brain Wallet passphrase…

I am attempting to come up with a way of memorizing a seed that could lead to any number of brain wallets for bitcoin. I need multiple wallets because a) I don't want all my eggs in one basket, and ...
507 views

### Is there an encryption/decryption algorithm that can give two different outputs?

The recent revelations that airport staff can detain travellers in an interrogation room and force them to give over passwords to encrypted-HDD laptops under threat of jail time has made me think ...
749 views

### Meet-in-the-middle with checking complexity

In regards to meet in the middle type attacks, I have been considering the amount of operations in order to successfully find a key given two sets of plaintext / ciphertext pairs. All of the sources I ...
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### Do any (non-hardware) RNGs exist which could be used to create an OTP for crypto purposes?

I've stumbled (jobwise) over a system where small messages (512 Bytes or less) are encrypted and decrypted using a simple XOR using a OTP. That OTP is created using a seed based on the individual user ...
981 views

### Am I insecurely implementing AES in Python? [closed]

My name is Pat, I'm a rising high school senior interested in Comp Sci. I've taken interest in cryptography following the NSA scandal. Since this is the first time I've ever implemented encryption ...
111 views

### Securing content and login with “same” password

I'm writing a client application that wants to store some secret information with a storage service. The client has to authenticate the user with the service and the service should not be able to ...
118 views

### What prevents continued hashing of a key from being used as a cipher when xored with plaintext? [duplicate]

This is just an idea I had while looking through some threads so take it as you will. Given a plaintext of any length and a key that a specific hash function is capable of taking as input(I mention ...
129 views

### Offline app authentication - embedding hashed password inside an encrypted file

I am working on an occasionally connected app. To allow the users to authenticate I created a profile which is encrypted and placed on the users machine. The first byte of the file contains the IV ...
431 views

### Is rainbow table attack applicable to any hash?

Typically when rainbow tables are discussed MD5 hash is used as an example. It's not quite clear whether this attack is specific just to MD5 or to a certain subset of hashes or to just any hash ...
4k views

### OpenSSL AES 256-bit Key Management

I am using C and OpenSSL to encrypt files. After experimenting with the OpenSSL command line utility, it makes you enter a passphrase that can be any length, but uses that to create a 256-bit key. ...
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### Is it possible to cryptographically prove when was the last time a ciphertext was decrypted/encrypted?

I want to provide a service that encrypts and decrypts documents and I want to provide the users with proof that I haven't stolen their secret key and read their documents. I know I can prove when a ...
2k views

### Bcrypt VS Scrypt, Again?

I found this article on SO, but the answer was short, and the subject was closed, What i don't understand, is: Which one of the two limits memory usage to avoid custom Hardware to break the password? ...
256 views

### IV Security Clarification

After doing lots of reading on SO and other websites relating to AES cryptography, I am trying to understand the security issues surrounding IV's. There seems to be a lot of confusion and ...
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I read that the Encrypt-then-MAC paradigm is provably secure. From what I understand, when using for example AES for encryption and HMAC_SHA256 for MAC generation (and the keys $K_1 \neq K_2$), this ...
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### Encrypt a single file, chunk-by-chunk, each chunk using different key (AES)

Encrypt a single file, chunk-by-chunk, each chunk using different key. I am a security newbie (only took 2 security courses before) But currently I am using this encryption method for my Android ...