# All Questions

92 views

### Limit the length of AES encoded output to certain value

First let me be clear upfront that am not Crypto expert. I'm having a problem where I will have to use NFC card. Now given the limitation of NFC cards memory sizes, I will need to constraint my system ...
91 views

### How secure is Shamir's Secret Sharing for password sharing when attacker has t-1 shares?

I am designing protocol to share a random generated n long password between k parties using Shamir's Secret Sharing. I know that share alone does not reveal much information about the original ...
24 views

### What happens when domain parameter $q$ in DSA is not prime number

Suppose that attacker creates domain parameters $(p,q,g)$ where $q$ is not prime number (but $q$ still divides $p-1$) and that signer generates new key pair using these domain parameters. How exactly ...
48 views

### How to store keypair generated by RSA in a textfile?

I'm trying to write an encryption decryption program using Openssl-RSA. There are only two operations. User stores the data and retrieves it whenever he needs. To decrypt something, we need the ...
159 views

### Santa Claus' secret permutation

This December, $N$ friends play secret santa: they select a random permutation $\sigma$ of $N$ (without fixed point). For Santa Claus, everyone has to bring a gift to the next person in the ...
39 views

### can session key be be used as digital signature?

if two communicating parties share a (symmetric) session key, k. When one of the party wants to send a message 'm' to other, is it okay use {m}k as a digital signature?
68 views

### Fast Forward Hash Signatures

As a follow up to the Q/A session: Small Quantum Signatures - Reality check needed I have implemented the discussed idea for a new short-quantum-safe signature system using fast-forwarding hash. It ...
56 views

### Is there a fast implementation of RSA for Microcontrollers?

Zhe Liu, Johann Großschädl, and Ilya Kizhvatov. "Efficient and Side-Channel Resistant RSA Implementation for 8-bit AVR Microcontrollers" describes a fast implementation, but only contains a sketch of ...
72 views

### Doubts about Authenticated Data Structures logic

I am studying the theory of authenticated data structure, like Merkle Tree and I have a doubt: why use them? I explain better: why to be sure, for example, that a cloud provider didn't modify my files ...
24 views

### Does threshold crypto (m-of-n) guarantee that m peers discover the plain text?

In a threshold cryptosystem, is there any guarantee that all $m$ peers participating in retrieving a plain-text will all retrieve it? If not, is it possible to provide such a guarantee? For instance ...
47 views

### How to test the speed of an Authenticated Encryption algorithm?

I am trying to implement Authenticated Encryption algorithms using CUDA. Most of Authenticated Encryption algorithms have short message length like 64, 254..., 4094 (Byte). these message lengths ...
185 views

### Different tools return different ciphertext value for equal input

I have a Luna G5 Safenet HSM and I want to encrypt a text file containing testtest with 3DES-ECB algorithm. So in the first step ...
57 views

### Is it secure to encrypt random key with block cipher in ECB mode?

If we have a random key $K$ which is 256-bit, and have a block cipher $C$ which has a block size of 128-bit. Is it safe to encrypt $K$ with $C$ in ECB mode? This problem can be generalized to given a ...
58 views

### NMaster key from n secret key

I have to derive master key from N secret key. With the help of master key, i can collect all the secret keys which is used to derive master key. key1, key2,..keyN ==> single master key and single ...
51 views

### what is the fastest and efficient method to perform modular multiplication?

I'm working on a code that needs to perform modular multiplication of big numbers several times. Since the operation takes place several times, using division to find the remainder is very expensive. ...
228 views

### RSA enc/decryption with multiple prime modulus using CRT

Every information I found on internet about RSA-CRT encryption/decryption uses only two primes. I'm interested in my project in doing that using multiple (up to 8) primes. The general idea is to ...
71 views

### Lightweight Cryptography and Gate Equivalents [closed]

If I design a lightweight cryptographic algorithm, how do I calculate gate equivalents (GE)?
41 views

### Differential Cryptanalysis

How do I find the differential characteristics using techniques Shrinking ? How do I extract the key on Differential Cryptanalysis using the technique Shrinking in Blockcipher Algorithm? Shrinking ...
84 views

### RSA message integrity

I wish to send some small data that RSA alone can encrypt, and I send a shared secret along with it. ...
90 views

### Usefulness of Damgård–Jurik

I am trying to understand what are the benefits of using Damgård–Jurik over Paillier. I understand that expansion factor decreases as s increases. But isn't it the ...
37 views

### Deletion complexity in a RSA accumulator

My question is about the existence of a dynamic RSA accumulator with deletion of an element in O(1) time. Do you know some practical implementation?
96 views

### 2 Part Encryption

Can anyone tell me if an encryption / decryption scheme like the following exists? Encrypted1 = SomeCryptoFunction(Data, Key1) ...
64 views

### Largest number that could be factored in milli seconds

Considering a home pc/laptop as machine used (Say typical 2.4 GHz, 16GB RAM, 4 core processor) for running any factorization algorithm. What would be the largest number that could be factored into its ...
32 views

### how to prove sequence y uphold golomb's third axiom

given $\{ x_k \}$ is a m-seq of order $n$, we define $\{ y_k \}$ to be a $m$ digits number: $$y_i=x_ix_{i+1}...x_{i+m-1}$$ for every integer $n \ge m \ge 1$ how can I show that $\{ y_k \}$ upholds ...
49 views

### Applying Vigenere on small strings with sorting capability

I am new to cryptography and have a question about a use of Vigenere cipher in the case of small strings. I'd like to encrypt keywords that are smaller than 10 characters. If I use Vigenere ...
64 views

### Optimal same-base exponentiation?

I've (finally) implemented the answer to this question in our library, which stated how to transform montgomery curves (and points) to weierstrass curves (and points). Now, for scalar multiplication, ...
1k views

### How is the One Time Pad (OTP) perfectly secure?

The Wikipedia entry on One Time Pads (OTPs) states that if this cipher is used properly; ie, the keys are truly random and each "part" of the key is independent of every other "part", it's ...
110 views

### Message security and also program copy detection

Imagine I have client and server running on different machines, each as a separate software. I want to ensure: message authenticity, integrity and confidentiality at least of messages coming from ...
31 views

### Clarification on the state of the art of qubit commitment

What is the current state of research on quibit commitment? It seems that the answer is not 2001 but it seems to me that a lot of these pdf are referring to a old protocols of quantum bit commitment ...
203 views

### Why Merkle Tree doesn't suffer Birthday attack?

I am trying to understand why Merkle Tree doesn't suffer the birthday attack? Can you help me? Thank you!
23 views

### How to calculate Private Key in RSA using Extended Euclidean Algorithm [duplicate]

I have googled for about 2 hours now and still haven't found an explanation. The wiki article just makes me more confused and so has every other similar question I've found on StackExchange. Here's an ...
162 views

### Modular Arithmetic in RSA

Consider the following the following RSA public key $pk = (N, e) = (1457, 1307)$. (a) Knowing that $187^2 \equiv 1 \pmod {1457}$ find the factorization of $N$. (b) Given the factorization of $N$ ...
33 views

### Can knowing part of what was used to generate an md5 hash make it vulnerable? [duplicate]

Say I am able to ask a black box MD5 generator to generate 1,000,000 hashes given input $STRING$ Where $STRING$ is an arbitrary ...
149 views

### Random Coin Flip

Quoting an old question: Consider the following protocol for two parties A and B to flip a fair coin (more complicated versions of this might be used for Internet gambling): A trusted ...
42 views

### elliptic curve multiplication with negative factor

I'm learning the multiplication operation on EC. From most material I can found, the multiplication $nP$ is just: $$nP=P+P+\cdots +P+P$$ For negative factor, i.e. $(-n)P$, by above definition and the ...
88 views

### Unconditionally Secure Authentication

I'm trying to add the authentication for my One-Time Pad implementation. I know that to provide Unconditionally Secure Authentication I need to use the One-Time MAC authentication. But I don't ...
45 views

### How do different block sizes affect the throughput of GPU implementations of AES?

I am confused about the effect of different block sizes on AES performance. As you can see here, there is a huge gap between the throughput of different block sizes. As far as I know, every 16 bytes ...
85 views

### Probability approximation of no collisions

I am comparing the actual probability of no collisions to the probability approximation formula of no collisions from the Understanding Cryptography text. The approximation is as follows: ...
78 views

### Is there short period in AES 128 key schedule?

I am wondering if for some particular keys the AES 128 key schedule lead to a periodic pattern for the round keys. The key schedule is only 10 rounds, but I am also wondering in the general case where ...
35 views

MonkeyDuplex constructions defined by Keccak authors has padding in every duplex block. Why only last duplex block is padded in NORX? Is it because NORX has domain separation, or simply because ...
63 views

### What are requirements of the audio input to be encrypted using AES?

I want to inquire that what are requirements of the audio input to be encrypted using AES. Is encrypting a mp3 file different from encrypting an aac file? Thanks!
70 views

### Implicit authentication aritcle

First, I want to know what is the logarithm used in the following system of equations (from the paper Flexible and Robust Privacy-Preserving Implicit Authentication - Domingo-Ferrer, Wu, ...
82 views

### What are the security implications of an AES implementation that uses only 8-bit byte operations on the cipher state?

Some AES implementations in crypto libraries make use only 8-bit byte operations on the cipher state, like in the lorawan-parser (cf lib/aes.h). When I try to understand the implications of that, I ...
29 views

### (Looking for reference) Variants of Diffie-Hellman

Sorry for asking a non-pure-crypto question but I think that crypto.SE might be the right place to find the right people to answer this: I remember having seen a few years ago, online and in HTML ...
110 views

### Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
52 views

### A standard extension of ECIES for multiple recipients (broadcast / multiparty)?

I have one sender, and a small number (~5) of recipients. The sender knows each recipient's public EC key. I want the sender to broadcast a single message in such a way that any one of the recipients ...
378 views

### What is cryptographic agility?

I keep seeing the term "Cryptographic Agility" referenced. What does it mean? For instance: https://msdn.microsoft.com/en-us/library/windows/desktop/bb204775(v=vs.85).aspx One of the key value ...
44 views

### How do I prove that a bit by bit PKE scheme (that is IND-CPA secure) for an n-bit message is not IND-CCA-2 secure?

Gen generates Pk and Sk (l bits each), Enc encrypts m (length l) but by bit using each bit of Pk respectively, Dec decrypts ciphertext bit by bit using each bit of Sk respectively. How do I prove this ...
Consider the following protocol for two parties to flip a fair coin: Trusted party $T$ publishes her public key $p_k$ A chooses a random bit $b_A$, encrypts it under $p_k$, and announces the ...