Algorithms and protocols for creating signatures to documents, and verifying such signatures. These are normally asymmetric, for symmetric signatures see [mac].

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Proof for composed signatures

Assumes that we have 3 signature algorithms, $S^A$ with key pair $(sk^A,pk^A)$, $S^B$ with key pair $(sk^B,pk^B)$,$S^C$ with key pair $(sk^C,pk^C)$. We denote by $\epsilon$, $\epsilon'$ and ...
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RSA Signature - Multiple Use Weakness

I cite from Fundamentals of Computer Security (Chapter 7 on Digital Signature, Paragraph 7.3 on RSA Signatures, page 289): Multiple uses of the RSA Signature scheme tend to weaken it. The way out ...
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278 views

Implementing Paillier Signature Scheme in Delphi

I've been trying to implement the Paillier Signature Scheme in Delphi, but I can't get it to work and I don't know where the problem is. First of all, I got my info about the scheme from this paper. ...
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13 views

PKCS#7 signed data structure in signed PDF document

Is it mandatory to include PKCS#7 data (OID 1.2.840.113549.1.7.1) octet string into the sequence of PKCS#7 signed data? I mean if you want to sign PDF, you are basically adding PKCS#7 container ...
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18 views

Device intercommunication with commands

I want to create a smart house project, and in that i bought some simple RF modules. Those modules don't support crypto out of the box but i want to connect them to a device that i would program to ...
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53 views

Collision attacks on digital signatures

After reading this document about MD5 collision attacks, I still don't understand how collisions can make digital signatures insecure. In the paper, the researchers created two files with the same ...
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83 views

Why not send the identity in the encrypted message?

I've recently started reading the book "Applied Cryptography" written by Bruce Schneier. Quite a few times I stumbled across protocols who send the identity outside of the encrypted message (see step ...
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28 views

Signature constructor using Self-signed certificate

I've the following scenario: One application signs JWT access/id tokens using the private key contained in a self-signed certificate, and then passes its public key to other parties to validate that ...
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62 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However Alice is a bad girl and ...
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42 views

Is signing a message just encrypting it with private key? [duplicate]

I have a simple question, When I sign a message (in RSA) does the program encrypt the text with my private key? Because I can decrypt it with my public key. Yes or no. Is signing a message just ...
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58 views

chameleon signature vs regular signatures

I am trying to understand the practical usage of sanitizable signatures particularly on Chameleon Hashing and Signatures. Chameleon hash, or trapdoor function allow parties with the knowledge of the ...
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109 views

Two questions on EMSA-PKCS1-v1_5

If I implement EMSA-PKCS1-v1_5 in the following two non-standard ways, what kind of things could go wrong? The padding structure will be referred as (00|01|PS|00|DER(Digest Algo)|Digest), where | is ...
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RSA - Why should we sign hash rather than raw content? [duplicate]

Apart from obvious performance considerations, is there any mathematical or crypto reasons that imply that we sign a hash rather than a raw content ? I read that it was because the hash must fit in ...
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62 views

Asymmetric sign in public enviroment

I have RTS game, where all players run game and server just relays messages. Game can generate and store text file on player pc. I want to allow some players to be moderators, so I need to sign or ...
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71 views

processing time for multiplication and exponentiation in pairing base cryptography

I'm using the Boneh-Boyen-Shacham signature scheme and want to estimate complexity in my scheme. As reported in "Scott M., Efficient Implementation of Cryptographic pairings", if we set parameters ...
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32 views

Validity of ElGamal signature variation

I'm trying to solve excersise 7.6 from Hoffstein - Introduction to Mathematical Cryptography page 459 (http://goo.gl/oRyInT) Let $p$ be a prime and let $i$ and $j$ be integers with $gcd(j, p − 1) = ...
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25 views

signed message susceptible to block re-ordering , block deletion , block replication

We would implement a Public Key Cryptography (PKC) based digital signature by breaking the message into blocks and signing each block independently. One of the issues associated with digital ...
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124 views

Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack

While reading a literature on signature schemes, I came across the concept of Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack. Can anyone point me to the paper ...
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71 views

advantages of hashing over elliptic curve signatures for a proof of work protocol

I'm trying to create a proof-of-work protocol for a proof-of-concept software, and it's basically something like this: ...
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121 views

Possible Digital Signature Hack?

I am starting to learn more about cryptography and I just read more about how asymmetric keys can make a digital certificate, and I would like if someone could explain me why the following case can't ...
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51 views

Advantages of using intermediate hash over full hash in digital signature application

Description of intermediate hashes Intermediate (or partial) hashes are canonical forms of digest state that can be transferred from one hash implementation to another, so that the other, limited ...
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52 views

How to know private key is computed from specific partial private key?

In a certificate-less cryptography, I have learned that – to resolve the key escrow problem of IBE – the concept of a partial private key is used. Now, consider the following Scenario: After ...
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129 views

Going Blind, Group or Ring?

I have several problems approaching the following problem: Let's assume that we have Alice, Bob and Cathy. Alice wants to present a message to Cathy, showing her that someone else has signed it (Bob), ...
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173 views

How to safely sign a 6 characters String?

I have to decide, whether a document, which I am given, was correctly signed by a private key. my Ideas is to sign the document id using RSA with the private key and to print the following onto the ...
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What length should the padding be when encrypting or signing with RSA?

I am wondering what length the padding should be when encrypting or signing with RSA. Does it matter what length the padding is, and if so — what length should it be? Another point: Should it be ...
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456 views

Verify Signature Failed [closed]

I am writing a small module which will verify signed message. Message will be signed using private key in Smart Card. The inputs are: Signed Message Original Message Public Key / Certificate with ...
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Why is 2 the inverse of 10?

I have one question about the ECDSA signature scheme. When Bob wants to send a message to Alice that is to be signed she makes following things (with for example $A = (5,1)$, $d=7$, $q=19$). ...
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How does the signature checking work in DKIM?

As far as I understand DKIM works like this: DKIM is not used to encrypt anything, the only purpose is to mark mails that are not really sent from the claimed domain as spam. the DKIM-enabled ...
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556 views

Fiat-Shamir signature [closed]

I have a question about Fiat-Shamir signature: A hash function is h(w)=w mod 2011 and w1=2623, w2=3269, w3=1938. What is h=? and how to determine k.t bits?