# All Questions

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### How to calculate AES logarithm table?

I would like to know how to find multiplicative inverses in $\mathrm{GF}(2^8)$. I know how to multiply two elements of $\mathrm{GF}(2^8)$ (for example, I know that ...
79 views

### Is a Combined Linear Congruential Generator secure for cryptography? [closed]

I learnt that a Combined Linear Congruential Generator (cLCG) has better properties than a Linear Congruential Generator (LCG). For those who don't know what a cLCG is, here are three links that might ...
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### What is a good way to demonstrate elliptic curve cryptography?

For school (high school) I am writing an essay on elliptic curve cryptography. The assignment needs to include a practical part, so I decided to write a Python class for elliptic curves. This class is ...
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### How does ECDH arrive on a shared secret?

I read a brilliant, three part article on Elliptic Curve cryptography (one, two, three). It was able to explain Elliptic Curves to me in a way that didn't require a math degree to understand. The ...
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### Why are there no MACs inspired by block cipher modes other than CBC and CFB?

I've been studying message authentication codes and I was wondering why a MAC can only be produced with AES in CBC and CFB mode and why not the other modes such as ECB, OFB and counter. Why are CBC ...
57 views

### How are calculated numbers in AES S-box?

My question is how to calculate the 0x02 value of AES S-Box? I followed this explanation, but my answer is not correct. 0x02 is ...
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### RSA - Why should we sign hash rather than raw content? [duplicate]

Apart from obvious performance considerations, is there any mathematical or crypto reasons that imply that we sign a hash rather than a raw content ? I read that it was because the hash must fit in ...
64 views

### C# implementation of curve25519 to ed25519 conversions [closed]

WRT the selected answer here: Can curve25519 keys be used with ed25519 keys? Is there any c# implementation of this or equivalent? Thanks.
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### Relations between RSA and DLOG, factoring and DLOG

Definition: (The generalized Diffie-Hellman problem) Let $n=pq$ for two large primes $p,q$. Given $x, x^a, x^b,n$, find $x^{ab}\pmod{n}$. (1) Is there a known reduction from the GDH problem ...
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### Is it possible to decrypt this message with partially known data? [closed]

The following highlighted text must contains "547a5e0e008be33730158d63ce844e67" data. I don't know about encryption method and key. Is it possible to decrypt it? Or just give me some idea about ...
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### can anyone give the java code to encrypt files using paillier [closed]

I want to implement encryption on personal files using paillier encryption. Is it possible to encrypt files using this encryption..
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### emulating progressive encryption with RC4 / OpenSSL

PHP's OpenSSL bindings do not support progressive encryption by default. ie. if you do ...
443 views

### What is the SSL private key file format?

I was researching about how to encrypt with RSA. I understood everything but not the format of the private keys. In the phpseclib (RSA in PHP), you can import your private key (private.key format) ...
94 views

### Discrete logarithm modulo a smooth number

I am solving the discrete logarithm problem modulo $N$. $N$ is a composite number, I found its factors — lots of small primes and two big primes ($> 2^{50}$). Does the factorization of $N$ somehow ...
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### PKCS12 - private key protection [migrated]

I know that PKCS12 private key is protected by a password, but what is actually done with the password ? Does it use PBKDF to derive the key from password ? That would be a problem as if you change ...
25 views

### Attribute-based broadcast encryption with respect to ABE

What is the exact difference between attribute-based encryption (ABE) and attribute-based broadcast encryption (ABBE)? Is ABBE equivalent to broadcast encryption on top of ABE?
104 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 ...
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 ...
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### 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 $b_2$ ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
147 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
141 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 ...
115 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 ...
87 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 ...
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### 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 ...
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### 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 : ...
601 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 ...