# All Questions

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### Does OpenTSA support PKCS11 to talk to HSMs?

We are planning to implement the time-stamping service (RFC 3161) using OpenTSA wanted to know: Does OpenTSA support PKCS-11 (Cryptoki) to talk to HSMs? BTW: I did not find documentation or much ...
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### Types of cryptography

We have cryptography based on hard problems from number theory, like DDH. When we speak about symmetric cryptography with AES, a mode of encryption (CBC, ...), what is the type of problem ? What is ...
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### Mutual authentication with Public Key and session Key

I am trying to understand two protocols for mutual authentication and if they are secure or not. $K$ is the session key, and it's calculated $k=H(TimeStamp)$. Are the following both cases secure? ...
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### RSA encryption and signature padding flaw

This is Oxford's computer security exam question: Suppose that Bob has published an RSA encryption key $ke$ (retaining in secret the corresponding decryption key $kd$), and Alice has published a ...
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### Commutative Encryption with RSA scheme?

I wanted to know how I could manage to do what I'm going to tell you next, with the RSA encryption/decryption scheme. So Alice and Bob each have a public key $(n, e)$ and a private key $(p, q, d)$; ...
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### Autocorrelation in Autokey

I know that Vigenère can broken using auto-correlation (as explained at cryptool-online.org). Now my question is: Why does this also work with autokey (tested it using crypttool)? To prove that I ...
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### Bilinear pairing

I am working on Efficient Construction of Pairings which are being realized by Miller's algorithm. In this algorithm the basic steps are point doubling and line function computation point addition ...
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### Secure Secret sharing

I'm trying to come up with a new way to do oblivious transfer that is faster and requires less computation than existing methods. The basis of my method is shamir secret sharing. Below is an example ...
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### Blowfish vs. Twofish regarding power consumption

If I wanted to use Blowfish or Twofish to provide security on a device where power consumption is crucial. Regarding power consumption, which one would win? Generally, which algorithms are known to ...
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### Looking for crypto with derived keys?

I am looking for cryptographic algorithm or combination of them. Basically I need an algorithm, which can generate private key and for this key can be computed multiple keys based on some seed. So a ...
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### For enciphering messages with AES in CTR mode, do I need a different key for each message?

I have written a program to run AES in CTR mode with keys of 128,192 or 256 bits and checked it gives correct results with the data given in section F.5 at ...
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### Berlekamp-Massey algorithm, correct stepping

I'm trying to use the Berlekamp-Massey algorithm on the following bit sequence: 0 1 0 0 1 0 0 1 0 1 I have the correct answer and most of the approach to get there, but I'm unable to fill in what I ...
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### Constructing of 16x16 Involutory Binary Matrices of Branch Number 7

In the PDF “Algebraic Construction of 16×16 Binary Matrices of Branch Number 7 with One Fixed Point”, it was given that: ...
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### P10 to P8 in S-DES

I am new to cryptography. During my learning I am facing a problem with S-DES. I am confused where P10 to P8 come from, and I’m ...
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### What constitutes a “description of B” for probabilistic encryption as defined in Cryptology 6.3.4?

On page 21 of the Rivest's Cryptology chapter, he defines a trapdoor predicate as a boolean function for which it is easy to choose an x such that ...
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### Special random distribution algorithm

I am implementing ring signatures as a part of an authorization system. Since the number of users could get high enough to make computation on end-user devices infeasible, I am thinking of ...
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### RSA Key Blinding

I was looking the answer to the following question (Timing attack on modular exponentiation), discussing the Private Key Blinding as a countermeasure for timing attacks. Therefore I'm asking if ...
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### Performance analysis of roaming authentication protocol using pbc library

Recently, I have surveyed a few research papers related to roaming authentication protocol for wireless networks. For example: “Efficient Privacy-Preserving Authentication in Wireless Mobile Networks” ...
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### The advantages of Merkle Signature and One time Signature

In Merkle Signature, it also requires one-time signature to be used once for a message. The signature in Merkle scheme is even longer compared to Lamport one time signature. The verifier also has more ...
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### Decrypt a public encrypted message and Sign a signature, how the math is different?

As I understand, when you want to send a confidential message to someone, you encrypt the message with his public key. And he use his private key to decrypt the message. At the same time, one can use ...
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### Predicting Google Authenticator OTP Codes

I use Google Authenticator to generate OTP codes for logging in. As you know, the numbers change every 30 seconds or so, and (AFAIK) use an RSA key to generate those numbers. If someone were to ...
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### Is container format relevant to security of encrypted message inside?

Still trying to design a fully binary cryptography container format for my mobile app, I am here asking if container is ever relevant. Thanks to Apple, I cannot use GPG directly because I can neither ...
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### Is G is a secure PRG?

Is the following function is secure PRG? Given F is a secure PRG and k is choosen random from key space K. $G(x) = F(k,x) \oplus F(k,x \oplus 1^s)$ My solution - $x \oplus 1^s = x'$ so G(x) ...
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### Mapping integers to Ed25519 and back again?

I would like to map integer values to points on Ed25519, and then back again. Is there a technique that takes advantage of the specific structure of Ed25519?
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### Shor's Algorithm values

I'm working with Shor's algorithm and I have a question regarding the following step $$a^r -1 = (a^{r/2}+1)(a^{r/2}-1)=0 \pmod n$$ Now what is going to be the result if ${r/2}$ was -1? this will ...
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### Smart card Strong authentication / Verification ( fingerprints)

I'm trying to make a strong authentication software and embedded software in a java card. I have found many papers and publications about the subject… too much information to process and I'm working ...
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### Does not using padding mean a lack of security?

I've read several texts which say that if the entire plaintext is a multiple of the block-size padding is not required (and not using padding would not mean a loss of security). I generally disagree ...
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### Accelerated hashing on consumer-grade CPU?

Question is a follow-up to this one. The question was about accelerating SHA1. I am writing an application, where I do have a choice of hash algorithm, as long as it's a strong one. I want to be able ...
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### CBC MAC and DES combined question?

Suppose that we want to develop a MAC scheme which is as secure as Triple-DES CBC-MAC and at the same time as efficient as Single-DES CBC-MAC. We come up with the following idea: Except the last ...
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### Generalize the Merkle-Damgard construction for any compression function

I am trying to figure out this question: Generalize the Merkle-Damgard construction for any compression func­tion that compresses by at least one bit . You should refer to a general input length ...
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### Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
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### Why does computing g^a * g^{-a} with the PBC library result in zero?

My example code is as follows: /* * Example 1 * 1) Calculate g^a * 2) calculate g^{-a} * 3) multiply g^a * g^{-a} * */ Note: here ...
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### Cryptography Implementation in software

I am trying to implement a password manager in C and I had a question about the proper steps in implementing the crypto. I looked at some implementations, google talks on crypto and what the standards ...
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### Is anyone aware of Du atallah multiplicative secret sharing scheme for dot products for > 2 party scenario?

I am working on Du Atallah's multiplicative secret sharing scheme for more than 2 party scenario. Is anyone aware of its multiparty version (more than 2 parties). The paper for 2 party can be found ...
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