# All Questions

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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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### How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
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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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### Group Signature Scheme without Opening but with Revocation

After reading many papers about group signature schemes, I saw that basically all of them employ the possibility of "signature opening": The Group Manager (GM) can identify any signature made by his ...
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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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### Undefined $E_y(1,r_{i,j,1})$ notation in cryptography paper, suspect ElGamal-like

I'm trying to understand a paper that uses the notation $E_y(1,r_{i,j,1})$ (full text available in link, used just once on Page #35, 6th page of pdf, Section 3.3, Step 1c) in the context of an ...
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### x509 CA trust question

I'm trying to understand the logic of CAs, trust and client certificates. I have a general understanding but am having a tough time bridging some gaps. In a hypothetical situation a software system ...
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### Tiger Tree Hash vs generic Merkle Tree

Is there any advantage of using Tiger Tree Hash over any other hash function organized as the Merkle tree? Are there maybe any properties of TIGER that, say, SHA2 or BLAKE in Merkle tree do not have? ...
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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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### How can I decode a Hill Cipher without a key? [duplicate]

On my exam, we had to solve this problem: message matrix is: [20, 19, 14; 17, 0 10] and the ciphertext matrix is: ...
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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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### Cryptographic library quality [closed]

I've been working on a project that will require secure communication over the internet, so I've been thinking of TLS 1.2. After looking around I chose Botan but then I thought about using a more ...
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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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### What is a 'secret key factory'? What precisely is it doing? [closed]

I have found a Java implementation of AES CBC mode that runs in Netbeans. The lines below appear to create the key from password and salt: ...
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### Sequence of Encrypting RSA like Chaum Blinding scheme

I'd be a noob in cryptography but reading up a little on RSA, I do get some understanding and I want to specifically resolve this issue. UPDATED Lets say we have the following values in place: ...
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### Client puzzle using hash

When a server is under attack, it send the client the following data: Nonce - a byte array of Y length Hash - the hash digest of the puzzle solution The client has to find X such as ...
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### RSA timing attack

Given an RSA implementation that uses Montgomery multiplications and CIOS exp algo, but NOT CRT. Given a decryption1 oracle that takes chosen cipher text and responds the plain text and the time it ...
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### What is the idea behind hashing the QueryString in OAuth?

In OAuth 1.0a and 2.0 using MAC Authorization, I need to generate a hash of all the QueryString Parameters, which requires normalization (alphabetical ordering) of them. I'm trying to understand what ...
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### McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...