# All Questions

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### When NIST disallows the use of 1024-bit keys, what effect will that have on SHA-3 (with max. 512 bits)?

Quoting the article Gone in 60 Months or Less: The National Institute of Standards and Technology (NIST) has disallowed the use of 1024-bit keys after 31 December 2013 because they are insecure. ...
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### Would RSA make sense if we used no computers?

I was recently wondering - would RSA be useful if we brought it to, say, medieval times? Could you choose the keys so that you could encrypt/decrypt messages quite easily, but factoring the private ...
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### how to iteratively calculate a^emod n with modulus n sized 4096 bits

In most sites the exponent of the RSA public key is 24 bits. But the modulus can get to 4096 bits size. I have an accelerator that can get max. 2112 bit size modulus. It calculates ...
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### Why are cryptography algorithms not exported to certain countries?

There have been strict laws about the export of crypto software to certain countries. I can understand the intent, but never gauged the fact that there is nothing stopping these countries from ...
3k views

### Hybrid encryption with RSA and AES versus spliting into multiple RSA messages?

I've done research about this subject, but I can't find the answer I'm looking for. The problem is that the string I want to send doesn't fit into the RSA key that the client have, and during ...
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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… ...
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### Is this really the correct way to do an IND-CPA test?

In a description of IND-CPA (indistinguishability under the chosen plaintext attack), I have been reading the following, simple test: The adversary can generate as many messages as he wants. Then, ...
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### Verifying Self-signed SSL Client Certificates

I have a service and I want to authenticate my clients using SSL client certificates. Now I want the key exchange process to be as simple as possible, kind of like SSH: You generate a keypair and ...
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### Understanding elliptic curve encryption

I'm having a hard time understanding the elliptic curve encryption. One thing thing I don't understand is listing all the points on the curve (mod p). Suppose I have the following elliptic curve: y^2 ...
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### Why must curve25519 shared secret be hashed?

When using the curve25519 DH function, D.J. Bernstein recommends hashing the shared secret before using it as a session key for a symmetric block cipher. Why is that? Hashing won't increase the ...
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### Who's talking to who encryption - does this concept work?

With all the NSA stuff in the news, I've been thinking about how to ensure the "who's talking to who" is just as private as the contents of the messages. I had an idea on the subject, about which I've ...
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### Detail about reactive simulatability framework

I'm trying to understand the framework of reactive simulatability using *"PfWa2_00AsyncModel"* from this publication which is a tech report behind the paper A model for Asynchronous Reactive Systems ...
1k views

### Are NIST's changes to Keccak/SHA-3 problematic?

NIST is working on standardizing SHA-3. They have selected Keccak as the basis for SHA-3, and they plan to make some small changes to it; the result (with NIST's changes) will be standardized as ...
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### how to mathematically prove a key exchange algorithm [closed]

I want to know the basic methodology that can be used to prove that a key exchange algorithm is secure. I am not asking about any specific algorithm. I want to know what should be proven and how to ...
999 views

### Is it possible to create an open-source SecurID?

As far as I understand it, the hardware key-fob two-factor systems such as RSA SecurID depend on secret algorithms, and employ tamper-resistant hardware to prevent reverse engineering. Is there some ...
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5k views

### How to decode an OTP message?

First off, I'm extremely sorry if this comes off as a "homework dump", but to clarify, it isn't. I don't want the answer, I want to know how to get to the answer. My cryptography professor gave us an ...
274 views

### Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...