# Tagged Questions

Implementing a cipher or protocol is the process of taking it from its mathematical or algorithmic description and producing a working version, often in computer software or hardware. This tag should be used for any question discussing the various potential considerations and pitfalls of this ...

46 views

### Example of Projective Coordinates

Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
113 views

### Convert projective to affine coordinates in ECC? [closed]

I am working with my project. I use projective coordinates but when I convert to affine coordinates, I can't get it. Can anyone help me? Projective Coordinates $(X,Y,Z)$ to Affine Coordinates $(X,Y)$:...
61 views

### Reference AES-NI assembler code for AES-128-GCM? [closed]

I want to implement AES-128-GCM in assembler using Intel AES-NI instructions. I have found reference code in the Intel AES-NI Whitepaper but I don't see code for the GCM mode there (or indeed any use ...
158 views

### As a cryptographer, what are the things I should care about in my implementation of pairing functions?

As a beginner in cryptography, I do not know anything about different pairing types more than their names. So far, I know these names: Ate pairing, tate pairing, eta pairing, and r-ate pairing. I am ...
774 views

### Understanding the FMS attack on WEP

I am trying to implement the Fluhrer, Mantin and Shamir attack, one of the ways to break WEP. I seem to have hit on a problem. I have no idea whether or not it is a programming error, or if I don't ...
216 views

### Rotation table for 8 round DES

I'm trying to implement DES from scratch using the NIST paper and the Wikipedia article on DES. I got 16 round DES done, but I can't seem to get 8 round DES working. I figure it's because I got the ...
225 views

### Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks

Bitcoin uses SHA-256, Base58Check, ECDSA (Sep256k1) and RIPEMD-160 as the basis of its encryption (see this article for a short guide on how addresses are created). I would like to create an iOS-...
279 views

### Weil pairing implementation - low level programming language

I'm just started to studying elliptic curve cryptosystems. My one month-goal is to write a simple signature system based on the Weil-pairing. Some parts of it can be written without deeper ...
359 views

### How to properly format a PGP Message Block?

As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
196 views

### Setting protocol parameters to achieve concrete security

Background One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
209 views

### Standard serialization format for libsodium-based messages

Does anyone know of a standardized serialization format which can be (or already is) widely used for encrypted messages? For a variety of reasons (mostly complexity, age and poor support across a lot ...
76 views

294 views

### Discrete Logarithm (512 bits numbers) - Find exponent parameter

I'm trying to resolve a discrete logarithm equation: $$y = g^x \bmod p$$ Every parameter is a 512-bit number. I know the values for $g$, $y$ and $p$ and I need to find the $x$ value. Finally, I know ...
376 views

### What is the most light-weight symmetric cipher thats still usefull?

I need a very light encryption scheme which costs almost no performance during encryption (while decryption may be slow). I found 5 algorithms: RC4, DES, LED, PRESENT, and Piccolo. But how do I ...
372 views

### Performance bottlenecks in Paillier encryption

I'm implementing Paillier encryption and I'd like some recommendations about improving its performance. Firstly, I have to note the following: I have already set g=1+n to get rid of one ...
312 views

### Generating Diffie-Hellman parameters efficiently

I am working on an Android project for school and I am supposed to do a DHKE (Diffie Hellman Key Exchange). Everything works well. The problem is that it takes a lot of time (really a lot) to ...
104 views

Using homomorphic encryption, I would like to be able to take an encrypted integer and either add 1 or -1 for a new encrypted value. I do not want the encrypted value to be recoverable - just the ...
473 views

### How is multiplication inverted in IDEA's decryption round?

As we can see in the picture we have a multiplication in this algorithm, we know that two 16 bit inputs should have a 32 bit output, but here we just use 16 bits of the 32 bit output. For decryption ...
373 views

### Polynomial multiplication and division in2^128

I want to multiply and divide polynomials, and implement the extended Euclidean algorithm for polynomial greatest common divisors, over a Galois Field of size $2^{128}$. Moreover, I want to use the ...
3k views

### How can I implement the “Multiplication Modulo” and “Addition Modulo” operations in IDEA?

I am currently working on IDEA (International Data Encryption Algorithm), and I don't know how to perform Multiplication Modulo and Addition Modulo. This is how IDEA operates: IDEA operates on 64-...
906 views

### RSA 1024bit decryption performance

i want to know how many RSA 1024 bit long key decryption can a regular pentium4 computer do per second ? how to calculate RSA performance and determine its remaining time ?
23 views

### Why am I getting a wrong output when implementing Feige-Fiat-Shamir ID protocol?

I am trying to implement the Feige-Fiat-Shamir identification protocol. I've read another posting here on this site and I tried to adapt - however the end results always fail to match. Maybe because ...
25 views

### Audio Encryption in Voip SIP [closed]

I have some project encrypion real-time. I want use Voip SIP to implement the stream cipher. What I have done so far : Simple app android Voip SIP https://github.com/android/platform_development/...
40 views

### Why Rabin fingerprints assumes data is prefixed with a “1” bit?

(I know that a Rabin fingerprint is not a cryptographic hash, sorry in advance if my question is considered out of topic) In the paper Some applications of Rabin's fingerprinting method, it is ...
81 views

### Is it okay for a non-cryptographer to submit crypto code to an open source probject? [closed]

I am not a cryptographer, nor do I claim to be. However, at times I have wanted to contribute to open source cryptography projects such as libsodium. The maintainer of libsodium is a cryptographer, ...
117 views

### 128 Bit AES Issue

I'm trying to use the 128bit TI_aes implementation on my 16bit microcontroller and I'm having the weirdest issue. Every input where two bytes within a word are identical two nibbles within a byte ...
33 views

### Would buffering socket send resist timing attacks

I have been reading and thinking about timing attacks on cryptographic systems. The answer to this question mentions the following: "The way to defend against timing attacks is to make sure the time ...
348 views

### How to create a PEM file for storing an RSA key?

I have an RSA private key $\{d,n\}$ and a public key $\{e,n\}$, where $n$ is the modulus, and I also have the prime factors $p$ and $q$ of $n$. I want to create a PEM file containing this information,...
380 views

I have recently been playing with Chacha20-Poly1305 with libsodium, and all of the examples state the additional data portion of the tag is stored in plaintext when encrypted. But from what I can tell ...