# All Questions

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### 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 ...
22 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 ...
285 views

### Can you help me understand PFS and wPFS?

Every time I encounter the concepts of PFS (perfect forward secrecy) and wPFS (weak perfect forward secrecy), I feel uncertain about them. My understanding is that: PFS ensures that, if the ...
808 views

### Winternitz One-Time Signature

I am reading the page 38 in this "Post Quantum Cryptography" book (Equations 8 and 9). My question is, why to compute the verification key $Y$, $f$ is applied $2^w-1$ times? Are there any security ...
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### 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 ...
12k views

### What is the lowest level of mathematics required in order to understand how encryption algorithms work?

What mathematical fields of knowledge would be required in order to get a good understanding of encryption algorithms? Is it basic algebra, or is there a "higher education" mathematical field ...
5k views

### What is the meaning of “trapdoor” in cryptography?

I do not really understand the meaning of a "trapdoor" in cryptography, so here are my questions: What is the meaning of trapdoor and how can I convert a word or string using a trapdoor in ...
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 ...
13k views

### How cryptographically secure was the original WW2 Enigma machine, from a modern viewpoint?

If cryptanalysts today were to crack the original Enigma machine, “how fast” or “how easily” could they do it? What methods would they use? The original cracking was significantly helped by operator ...
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 ...
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### 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 ...
50 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. ...
40 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 ...
83 views

### Deletion in RSA Accumulator

I am studying RSA Dynamic Accumulator and I have a question: why is simpler to calculate the new accumulator value after a deletion if is known the secret ϕ(n)? Is possible to calculate the deletion ...
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### 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?
62 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 ...
282 views

### Decoding base64 encoded message with a key

I am pentesting a database that where I found data which was base64 encoded. I tried the usual method of decoding base64, which didn't work. Later, I found in ...
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 ...
1k views

### Reasons for Chinese SM2 Digital Signature Algorithm

In the IETF RFC draft named "SM2 Digital Signature Algorithm" a signature algorithm is specified. The RFC does however not mention why this signature algorithm has been defined. Nor does it specify ...
2k views

### What is a Non-Interactive Zero Knowledge Proof?

I understand the concept of a Zero Knowledge Proof thanks to the easy to understand analogy of Alibaba's cave. However, this seems to require interaction between the verifier and the other party. I ...
14k views

### Why is AES resistant to known-plaintext attacks?

At least it's my understanding that AES isn't affected by known-plaintext. Is it immune to such an attack, or just resistant? Does this vary for chosen-plaintext?
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 ...
188 views

### Is my protocol that uses hybrid cryptography and AES-GCM secure?

I'm having a lot of trouble trying to understand how to implement AES-GCM. My usecase: Person A sent me a file with a gauranteed unique name. I want to be assured it was from person A, and that no ...
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 ...
27 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 ...
196 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!
145 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 ...
83 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 ...
82 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: ...
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 ...
37 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 ...
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### 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 ...
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### How can IND-CPA encryption be identity revealing?

This is problem 10 of Chapter 4 "Symmetric Encryption" (pdf) from Lecture notes by Bellare and Rogaway: An IND-CPA secure encryption scheme might not conceal identities, in the following sense: ...
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### 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 ...
104 views

### Multiple NTRU public keys for the same private key?

An NTRU public key is generated essentially by multiplying the inverse of a polynomial $f$ by a polynomial $g$. The polynomial $f$ is the private key; $g$ is discarded. My question is: Is it insecure ...
34 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 ...
132 views

### Could Riemann hypothesis solve certainly RSA?

I don't have the background for dealing with Riemann hypothesis but is well known that covers the prime distribution below a specified number. In order to solve the RSA problem you have to factor the ...
51 views

### key exchange using hashing with preshared secret

I came upon an idea the other day that I had some questions about. I am not a security professional but I do study with an amateur interest and have not heard of this particular idea before. There ...
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 ...
58 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!
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 ...
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 ...
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### Does including the size of the hashed data improve security over just the hash

Trying to settle a discussion at work. We are mostly concerned with pre-image resistance. Suppose we have a common secure hash function $H$ (e.g. SHA-1/SHA-2) and some message $M$ we want to hash. ...
65 views

### Does DES support different keys that lead to the same result?

While bruteforcing a ciphertext, I've found multiple keys which produce the same result. Mode is DES with ECB and PKCS5 padding. ciphertext is ...
62 views

### RSA Optimal Asymmetric Encryption Padding Beginner

I'm new to the OAEP scheme. I learn it from the Wikipedia page. Link The page does not explain a proper setup for of the system. So I'm not sure if the output of the padding scheme which contains ...
78 views

### How to verify CA certificate from Yubico with openssl?

I'm going to verify the CA certificate from Yubico. I copied the whole certificate from -----BEGIN CERTIFICATE----- to ...
112 views

### Given PRNG $G(s)$, why is $G(s) || G(s+1)$ not a PRNG?

I have given a pseudorandom Generator $G(s)$, $|s|=n$ whose expansion $l(n)$ is $>2n$. I also know that $G^\prime(s) := G(s_1,\ldots,s_{\lfloor\frac{n}{2}\rfloor})$ is a pseudorandom generator. Now ...
5k views

### Is there any opensource white-box implementation of AES or DES?

I googled it and give me no result. There is a binary executable of white-box implementation of DES (scroll down), but no source code provided. The same page also links various papers about ...