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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Bitcoin multi-sign and the amount of storage it required

I read this paper (Threshold-optimal DSA/ECDSA signatures and an application to Bitcoin wallet security), the authors said that in the optimal threshold signature that they propose players requires ...
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1answer
863 views

What characters are valid in PGP encrypted and signed messages?

What characters may be present in a PGP encrypted message or a PGP signature? For example, do encrypted messages only use the Roman alphabet + some numbers and symbols? Can the character set be ...
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2answers
129 views

Detecting encryption in real-time?

Is there anyway to detect encryption in real-time through a common signature or pattern recognition. Say, a file is being encrypted using an AES-256 cipher, if I have access to the file stream - can ...
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1answer
32k views

How does RSA signature verification work?

I understand how the RSA algorithm works for encryption and decryption purposes but I don't get how signing is done. Here's what I (think) I know and is common practice: If I have a message that I ...
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0answers
51 views

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 $k_{public}$. ...
2
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1answer
305 views

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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1answer
259 views

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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583 views

Can an adversary forge an RSA signature while not having seen the message?

Can an adversary who hasen't seen the message before, forge the signature of that message? The adversary has seen $σ_1 = (m_1)^d \bmod N$ and $σ_2 = (m_2)^d \bmod N$ He forges $m' = m_1\cdot m_2$ $σ'...
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3answers
91 views

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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0answers
39 views

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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0answers
36 views

Is it possible to turn an image (e.g. a photo) into a cryptographic hash? [closed]

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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62 views

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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62 views

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 ...
6
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1answer
73 views

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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1answer
49 views

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 ...
6
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81 views

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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2answers
61 views

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 ...
2
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1answer
129 views

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 ...
11
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1answer
484 views

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 ...
5
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1answer
82 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 ...
3
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1answer
387 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 ...
0
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1answer
496 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 ...
11
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1answer
154 views

Explanation and proof of a well-know probabilistic lemma

Pointcheval and Stern in their paper on "Security proofs for Signature Schemes" state the following "well-known" probabilistic lemma: Let $A \subset X \times Y$, such that $\mathrm{Pr}[A(x, y)] \...
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1answer
45 views

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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53 views

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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1answer
46 views

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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1answer
127 views

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 ...
2
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1answer
122 views

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 ...
6
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1answer
1k views

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 ...
16
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2answers
281 views

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,...
2
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1answer
69 views

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 ...
2
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2answers
83 views

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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1answer
54 views

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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2answers
84 views

Chosen-Message-Attack RSA-Signature

I know that because of the multplicative property of RSA $s =(s_1s_2) \bmod n = (m_1m_2)^d \bmod n$ If Oscar wants to sign now an own message $m$ he chooses another message $m_1$ with $\gcd(m_1,n)=...
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1answer
19 views

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 ...
4
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1answer
58 views

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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2answers
751 views

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'...
4
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1answer
434 views

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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104 views

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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1answer
49 views

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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1answer
26 views

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 ...
2
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1answer
69 views

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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2answers
80 views

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 ...
3
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1answer
188 views

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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0answers
32 views

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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1answer
254 views

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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1answer
53 views

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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1answer
72 views

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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2answers
5k views

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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32 views

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 ...