# 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, which has ...
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### Public key decryption mathematical analogy

To clarify, I'm talking about digital-signatures, not public key encryption. When I encrypt something with a private key, then it should be decryptable with a public key, as I've understood how ...
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### How would low-precision Gaussian sampling impact the security of BLISS?

For digital signature, I implemented BLISS in my cryptographic suite, and wrote the Gaussian sampler based on Lattice Signatures and Bimodal Gaussians. But unlike the reference implementation and ...
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### Is it possible to turn an image (e.g. a photo) into a cryptographic hash? [on hold]

I am looking for a way to turn an image (e.g. a photo captured on a phone) into a cryptographic hash (e.g. SHA256). Is this possible? If so, how?
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### Using a single Ed25519 key for encryption and signature

The libsodium documentation contains a function crypto_sign_ed25519_pk_to_curve25519 that converts an Ed25519 key into a Curve25519 one, so it can be used for both ...
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### Replacing signer with simulator

Assume we can prove security of digital signature scheme against key-only (no message) attacks. Now we want to prove security against adaptive chosen message attack. We use random oracle model. The ...
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### How to forge signatures in the Schnorr scheme if $r=g^k$ is eliminated?

I need some help to demonstrate how to forge signatures in the Schnorr scheme if I eliminate the random string $r=g^k$ used in the hash – using $H(M)$ instead of $H(M||r)$. How would one be able to ...
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### Can I discard a specific X509 signature from file?

I'm writing a program to sign files using X.509 certificates and .NET framework classes. My users can sign the same file more than once without any problem (like a revision process). So, a file may ...
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### Are there any signatures based on matrix multiplication with noise?

Are there any signatures based on matrix multiplication with noise? Representing the message as a matrix and multiplying with some randomness coming from another matrix such that the signature itself ...
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### Is this RSA signing and verification process secure?

I need to verify that messages in a communications program are from valid senders. Below is a highlevel outline of how I think the process would work. The connections themselves are done over TLS. The ...
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### Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
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### Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...
81 views

### Strange notation using dollar sign

In the paper Multi-Signatures in the Plain Public-Key Model and a General Forking Lemma, the authors Bellare and Neven use notation which looks like left arrow with dollar sign above it. Authors ...
386 views

### When would I need DSA as opposed to RSA for digital signature?

The digital signature algorithm encrypts a hash using the senders private key and the receiver's public key. This multiple encryption is a pretty expensive process since public key encryption is so ...
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### 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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### Digital signature with collision

Let's assume a digital signature scheme such that there's a probability of 0.2 for two random messages to have the same signature. How can I exploit this sheme? I'm having difficulties in finding an ...
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### Is this a good choice of a digital signature scheme?

This is a concrete instantiation of Rabin-Williams signatures. Specifically: The private key is 2 primes $p, q$. The public key is their product $N = pq$ and is approximately 3072 bits long. the ...
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### Are there any signature schemes for underpowered devices (8-bit microcontroller)?

I am currently researching into a small scale home automation system, aiming for cost. The system architecture is basically one master and several slaves which are connected in parallel. Recently i'...
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### How to sign a large file for random-access reading?

I need to write an "Authoring" application which produces large files. These files must be signed so that the "Consuming" application knows that it was authored with a matching key. The consuming ...
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### How to generate an RSASSA-PSS signature with MGF1-SHA256?

As part of rooting a device, I need to generate a 256-byte RSASSA-PSS signature using SHA256 as the hash and MGF1-SHA256 as the mask function, for an update file I created. I can choose any 32-byte ...
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### Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
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### Single-scalar multiplication with sign bit

I want to know if there's an "easy" timing-free way to compute the sign of $y$-coordinate of $r G$, for a secret scalar $r$ and $G$ the generator of an elliptic curve. We have several choices for ...
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### Get $a$ such that quadratic residue has a solution (Rabin)

My task is to implement Rabin signature. I have trouble with choosing padding a such that $$x^2 \equiv a \pmod n$$ has a solution. In that context, $n=p\cdot q$ is composite, where $p$ and $q$ are ...
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### Does a key need to be signed if it is being used to decrypt a message that is already signed?

I am trying to better understand authentication. Lets say I have posted my 128-bit AES symmetric key on some forum, encrypted asymmetrically to my friend using 256-bit ECC (25519). The forum isn't ...
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### What is the probability of attacking SHA1 used in RSA signature with small exponent?

There is RSA signature check which has following properties: RSA modulus N which is 2048-bit RSA public exponent equal 41 (0x29) Genuine Signature uses EMSA-PKCS1-v1_5 padding of SHA1 hash, however ...
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### check user signed in group signature

I have $N$ users, all of them creating a group digital signature. Also I have user $A$. How can I check if user a signed or not signet in this signature? Is it possible ? Are there other methods how I ...
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### One-way hash on encrypted data, result hidden from hasher

I'm looking for a one-way hash function that can be performed by A on an encrypted piece of data E(D) provided by B, without the performer A able to figure out D or H(D). This similar to HMAC(Message, ...
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### Can I get successful signature verification with just altering message and signature?

Assuming I can modify a message and also modify the verification signature, and I also have the public-key but not the private-key. Can I create a message that can be verified with a signature that I ...
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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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### Do other one-time signature schemes exist?

I'm curious to know if there are any one-time signature schemes other than Lamport's or its variants (Merkle trees are one such variant). The first I've discovered is called "Bins and Balls" which ...
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### Why can’t DSA be used for encryption?

This question at StackOverflow mentions that DSA cannot be used for encrypt. But Both RSA and DSA can be used to generate public and private keys, right? (Or am I wrong?). Then why can't I use the ...
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### What happens if someone implements tree-base signature scheme incorrectly?

I'm learning about signature schemes and read about Merkele's tree-base signature scheme. There are paragraphs about how the key and signings are generated. Using so-called tree structure and pseudo ...
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### Why are there $q^2$ keys for each equivalence class in Pedersen-van Heyst Signature Scheme?

How do you know there are $q^2$ keys for each equivalence class in the Pedersen-van Heyst Signature Scheme? My textbook says this is "easy to see", however, I am not seeing it. Is it because in the ...
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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 ...
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### How do I prove the tracing part in a ring signature model?

I have a question about the article “efficient and multi-level privacy-preserving communication protocol for VANET” by H. Xiong et al. I need the ID of malicious vehicle, but I could not prove how I ...
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### signature, hashing schemes

I have 20 friends. we create message(s) (1...i) and tar them up with a file messages.hashes(1..i). We sign these tars with our ...
In the lectures I see, hash functions are always used when we want to sign a document $d$. My question is why they are used in digital signatures? Maybe, because it is more easy and fast to calculate ...
I'm trying to reverse engineer a key exchange protocol which is based on the Diffie-Hellman key exchange scheme and faced with the following problem: Let $g$ be the generator, $m$ the modulus. Alice ...