# All Questions

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Consider a secure modern block cipher like AES/Serpent/Twofish. I hear everyone say that the complexity is $2^{128}$ for a 128 block cipher. But isn't the weak link the actual hashed and salted ...
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### Serpent block cipher : S0 to S7 functions unclear

I am presently implementing the serpent block cipher in C++ following the specifications. It's important to mention that I'm implementing the cipher in bitslice mode. You'll need the The full ...
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### How does an RSA signature look like?

I am using OpenSSL libs to generate signatures. Internally, I learn that a signature is a hash of the message with some padding added to it. I am trying to understand the structure of a signature. If ...
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### probability of N hash digits colliding

What is the probability of the first N hash digits colliding? for example i made a script that appends the first 5 digits of the file's sha1 hash to the name of the file. So will the probability of ...
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### Question about Fermat's little theorem

Why is $g^e \mod p = g^{e \mod (p-1)} \mod p$ if p is prime. I don't get it. It follows from Fermat's little theorem.
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### RSA smaller number work-out-by-hand not working - I think I made a mistake

I tried out the paper/pencil explanation @ http://sergematovic.tripod.com/rsa1.html, and it seemed to make sense just fine until I came to decryption. Here is what I worked out: Key Creation: Choose ...
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### The security of an encrypt and MAC

I would like to know what is the security of an encrypt and MAC with different keys for each transaction For example: the one time pad with k1 and the HMAC with k2 ...
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### What is the “shared secret” used for in IPSec VPN?

Can somebody explain what the "shared secret" and "password" do when opening/creating a VPN tunnel? In this specific case I setup a VPN to my Fritz!Box and I had to provide a shared secret (which was ...
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### Is the salt value a secret or can it be stored in cleartext just like the IV? [duplicate]

From Wikipedia I read that the IV is used to randomise the mapping of cleartext to cipher text and that the IV is usually stored (in cleartext) together with the encrypted record. ...
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### How is input message for SHA-2 padded?

I read about how is an input message prepared to be hashed by MD4,MD5 or SHA-1: Step1 Append padding bits The input message is "padded" (extended) so that its length (in bits) equals to 448 ...
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### Merkle Signature Generation

Section 2 (end of page 42) of *"Post_Quantum_Cryptography.pdf"* says: Then he generates the one-time signature $\sigma_{\text{OTS}}$ of the digest using the $s$-th one-time signature key $X_s$, ...
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### Lamport-Diffie + Security Proof

I am studying Lamport-Diffie signature scheme. In the lecture present the algorithm $A'$ for attempting to invert the one way function $f$, where $f$ is used to compute the public key. My question is ...
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### Lamport-Diffie + attempting to invert OWF

I am studying Lamport-Diffie signature scheme and in my lecture present the follow algorithm for attempting to invert the one way function $f$, where $f$ is used to compute the public key of this ...
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### definition and meaning of semantic security

I'm taking coursera cryptography course. The definition of semantic security is hard to understand. I tried to slightly restate it (the word "efficient" was in the original definition). Do I get it ...
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### What kind of adversary is a compromised party?

Imagine multiple parties executing a secure multiparty computation protocol to evaluate a function securely. Let Alice be one of the parties who is intended to get all the partial results and combine ...
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### Recommended authenticated stream cipher for minimum overhead?

I'm running my TCP/IP protocol secured by encrypting each packet with AES128/CBC, bundling a SHA256 HMAC over that packet. This causes quite a bit of space overhead for small packets, so at first I ...
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### The security of the AES secret itself

I am writing an application, running on a server, where multiple users access data from a database which is AES encrypted with a master secret. The master secret itself is initially randomly ...
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### Do I need to keep a 64-bit version number secret?

Assume the following structure: version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key) The version starts out ...
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### What key length is required to keep simple keyed “hash” secure?

In a previous question, I described a particular keyed "hash" that mapped a 5-digit input code into a 5-digit output code. It used a 8-bit key which is very insecure - more than 99% of the time, you ...
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### Physical Level Encryption

What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
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### How to hash a structure that needs to include that hash's outcome?

so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
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### Solving a discrete logarithm using GDlog

I am trying to calculate an x, such that t = g^x mod p (I need to crack a weak elgamal encryption for university). I found gdlog, but I cant figure out how I can use the input to calculate my x. Here ...
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### Certificate == signed public key

For primes p and q used to create a keypair, I understand that the following operation is used to create a signature: $M^d (\bmod\ N)$ where d and N have their usual meanings and M is the message. ...
308 views

### Ciphertext-only attack on Simplified DES

Is it possible to deduce the plaintext block or the key, given only a Simplified-DES ciphertext block (e.g. c=01110110)? I'm reading Cryptography And Network Security, by William Stallings and I'm bit ...
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### Voice Call Safety [closed]

When i was dealing with an assistant of my bank through mobile call, she asked me to insert my bank login code after a beep. I was wondering if this procedure is secure against a Man In the Middle ...
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### In which disciplinary category can cryptography be put?

Is it a multi-disciplinary, inter-disciplinary, cross-disciplinary, or maybe even trans-disciplinary? What are the basis to describe each kind? I mean, how can we infer by which disciplinary field we ...
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### Efficient algorithm for remainder calculation over prime field for ECC implementation?

I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
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### 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 ...
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### Weak Stream Cipher cryptanalysis

Hi I have a stream cipher which uses a keystream of: F(r) || F(r+1) || F(r+2) || ... Suppose F(r) is the RSA encryption algorithm: ...