# Tagged Questions

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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### Are there any digital signatures valid for multiple pieces of data?

Are there any digital signature algorithms that can be used to produce signatures valid for multiple pieces of data? For example: Pick a private key $k_{private}$, which has public key $k_{public}$. ...
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### RSA signatures without padding?

Suppose I have a message $M$ for which I generate an RSA-2048 digital signature as follows: $H = H(M)$, $H(M)$ being the SHA-256 of the message $M$ $S = H^d \bmod N$ Assume $N = pq$ is properly ...
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### RSA Signature : Process of Sign the message and Verify

I have read that the RSA numeric signature works as the following: Generation of keys : $p,q,N,e,d$ Process of signing the message $m$ (which is BigInteger) : it uses the secret key $sk=(p,q,d)$ so ...
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### What are the differences between X9.31 RSA operation and PKCS#1 RSA operation?

NIST and other - mainly older - standards often don't just mention PKCS#1 RSA algorithms but also X9.31 RSA algorithms. What are the differences between X9.31 and PKCS#1 (v2.1) with regards to key ...
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### Why do openssl elliptic curve digital signatures differ by one byte [duplicate]

For some curves defined in Openssl 1.0.2h if I generate a key and generate a digital signature the size of the signature block changes by one byte. Why does this happen? My test file is, y.sh ...
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### In which situation is HMAC mandatory rather than signature? [duplicate]

I’ve seen that the question has been asked already but this is still confusing to me. In a digital signature, Alice sends a message M and the ...
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### Could this “symmetric RSA” scheme provide key compromise resistant communications?

This question, and fkraiem's answer to it, made me wonder about the security and practicality of using "symmetric RSA" to provide a partially compromise-resistant secure channel. Specifically, assume ...
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### Forgery attack against Textbook RSA with simple redundancy

I know how to forge vanilla Textbook RSA message signatures (easy). I've learnt that by adding a good redundancy to the message, it cannot be forged anymore. How can one add redundancy so that the ...
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### Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...
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### Is it possible for Alice and Bob to both sign a message “simultaneously”?

Let's say that there is a message which is considered valid if signed by both Alice and Bob. Alice could sign the message and then give it to Bob, so that he can sign it and give it back to her. But,...
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### Is PKCS7 a signature format or a certificate format?

I always though PKCS7 was a signature format. However, on the net I find several references to PKCS7 being a certificate format - for example, this talks about PKCS7 certificate: Extract raw ...
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### comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
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### Need help understanding this exercise's solution

We were given this exercise, which asks us to identify the types of keys used on this diagram: The solution was Kxa -> A's private key Kya -> A's public key KxB -> B's private key My question ...
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### Problem with applying threshold scheme

For a report on threshold signature schemes, I have to explain a threshold signature scheme and give a simple example with numbers. A threshold signature scheme is a scheme in which a network of n ...