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Questions tagged [digital-signature]

A digital signature (not to be confused with a digital certificate) is an electronic signature that is used to authenticate the identity of a message sender or document signer, and usually to ensure that the original message/document content is unchanged (document integrity).

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118 votes
6 answers

Why should one not use the same asymmetric key for encryption as they do for signing?

In an answer to a question about RSA and PGP, PulpSpy noted this: It is possible to generate an RSA key pair using GPG (for both encryption and signing -- you should not use the same key for both). ...
Iszi's user avatar
  • 27.1k
91 votes
4 answers

SSL Certificate framework 101: How does the browser actually verify the validity of a given server certificate?

(Sorry I know this is a complete noob question and at the risk of posting a somewhat duplicate topic. I have a basic understanding of public/private key, hashing, digital signature... I have been ...
SecurityNoob's user avatar
  • 1,021
83 votes
8 answers

Is it possible to "fake" being connected to a router?

A friend of mine is taking a UNIX systems class and mentioned to me that when they take exams they do so on their computers. That is all students are using their own computer/laptop. Students are not ...
Ryan's user avatar
  • 711
80 votes
3 answers

Does OpenPGP key expiration add to security?

I've created a new OpenPGP key to sign a software package in a source repository with an expiration date three years from now. It seemed like a good security measure, because if the key is compromised ...
Adam Matan's user avatar
  • 1,277
69 votes
4 answers

How does the digital signature verification process work?

I am not able to understand that how the digital signature is verified. I know that digital signature will be attached to the message and sent by sender to receiver. then receiver uses the public key ...
n92's user avatar
  • 879
67 votes
3 answers

Why shouldn't I bring a computer to a key-signing party?

I'm looking at the event description for the key-signing party at an upcoming BSD conference, and it's mentioned that I shouldn't bring my computer in to the event: Things to bring no computer What ...
Jules's user avatar
  • 1,240
66 votes
9 answers

Proving creation time/date of a screenshot

I have to produce a screenshot of a web page, and want to make sure others will know without any doubt that this screenshot has been produced today. That is, I would like to embed today's date in the ...
Matteo's user avatar
  • 763
65 votes
1 answer

Why would I sign my git commits with a GPG key when I already use an SSH key to authenticate myself when I push?

Simply put, I am wondering why would one need to sign one's commits with a GPG key when contributing to GitHub when one's already required to provide an SSH public key?
Mahmoud Tantawy's user avatar
64 votes
8 answers

Why do people still use/recommend MD5 if it has been proven weak since 1996?

It's still a commonly recommended way of hashing passwords, even if its insecurity had been proven in 1996: Therefore we suggest that in the future MD5 should no longer be implemented in applications ...
Marek Sebera's user avatar
  • 2,223
59 votes
2 answers

Would a digital signature have prevented the CCleaner compromise?

I read today about the CCleaner hack and how code was injected into their binary. People were able to download and install the compromised software before the company had noticed. Isn't this what ...
user avatar
58 votes
12 answers

Is it possible to make a video that is provably non-manipulated?

Suppose a student takes an exam at home. Since home-exams are prone to cheating, the student wants to be able to prove that he/she did not cheat. So the student puts cameras in the room, which ...
Erel Segal-Halevi's user avatar
52 votes
2 answers

Digital Certificate deployment: using two certs for each user?

At a large enterprise environment I have come across a deployment approach for Digital Certificates where each user is issued two (2) key pairs: One for signing documents, emails, etc. that is ...
George's user avatar
  • 2,813
50 votes
4 answers

How to achieve non-repudiation?

If I have a message that I need to send to another person, how do I achieve non repudiation ? Is digitally signing the message sufficient ?
user1157's user avatar
  • 1,797
49 votes
11 answers

Does hashing a file from an unsigned website give a false sense of security?

Consider this. Many websites with software downloads also make available MD5 or SHA1 hashes, for users to verify the integrity of the downloaded files. However, few of these sites actually use HTTPS ...
Iszi's user avatar
  • 27.1k
49 votes
4 answers

Can I use a private key as a public key and vice versa?

I have code to encrypt data using a public key and decrypt it using a private key. This is useful when a client wants to send data to a server and know that only the server can decrypt it. But say I ...
Graeme Perrow's user avatar
45 votes
3 answers

How safe are signed git tags? Only as safe as SHA-1 or somehow safer?

How safe are signed git tags? Especially because git uses SHA-1. There is contradictory information around. So if one verifies a git tag (git tag -v tagname), then checksouts the tag, and checks that ...
adrelanos's user avatar
  • 744
42 votes
2 answers

What is the actual value of a certificate fingerprint?

In a x509 digital certificate there is a "certificate fingerprint" section. It contains md5, sha1 and sha256. How are these obtained, and during the SSL connection, how are these values checked for?
Ashwin's user avatar
  • 1,607
41 votes
10 answers

Are there any OSes that verify program signatures before executing them?

If so, what are these OSes? Are they specially crafted? How difficult is it to apply this kind of program verification to the everyday OSes we use? If not, why haven't people invented such OSes? ...
Cyker's user avatar
  • 1,623
34 votes
6 answers

What does "signing" a file really mean?

I'm a bit new to security and trying to get the concepts properly. I'm wondering what exactly "signing" a file (a certificate, an apk file, or something else) means? Do we sign the whole file so ...
zgulser's user avatar
  • 491
30 votes
6 answers

Are documents truly "signed" by DocuSign?

I've never been happy with the explanation DocuSign gives for themselves in their own marketing material (e.g.
Dai's user avatar
  • 1,716
29 votes
7 answers

How can I be sure that I am using the real Facebook?

I type into my browser's address bar and press enter, then use Facebook. Could I actually be visiting a fake Facebook even if I see a URL of and a lock icon ...
again's user avatar
  • 974
29 votes
2 answers

Can you sign using a digital certificate itself?

Googling I saw several lectures saying that it is possible to sign using digital certificates. I am confused about that, because according to my knowledge it is possible to sign only using the private ...
juaninf's user avatar
  • 465
28 votes
7 answers

Why do we need HTTPS for static content? If we can have a checksum at the end signed by the private key, won't that prove the validity?

This method which I am talking about can improve caching of images, videos, and CSS by the ISP rather than just depending on the browser cache. And it also proves the validity of the sender. Is there ...
kalyan's user avatar
  • 447
28 votes
4 answers

How do the processes for digital certificates, signatures and ssl work?

I have been trying to understand how ssl works. Instead of Alice and Bob, lets consider client and server communication. Server has a digital certificate acquired from a CA. It also has public and ...
John Eipe's user avatar
  • 423
27 votes
2 answers

Does my PGP key really need to match the e-mail address for which I'll be using it?

In considering whether or not I want to join the big web o' trust and put my keys on a key server, I got to thinking about how it would affect my e-mail address' exposure. I generally try to keep my ...
Iszi's user avatar
  • 27.1k
24 votes
6 answers

What does "key with length of x bits" mean?

I'd like to know what it means to say "the cryptosystem C uses keys with a length of x bits". I do not understand what the bits length means... doesn't it depend on the encoding? The same word encodes ...
strauberry's user avatar
23 votes
4 answers

Verifying android application integrity from server side

I have android applications (Mobile banking) that connect to my server and do online transactions (via Internet/USSD/SMS), I want to make sure those clients are not tampered with and are the original ...
Silverfox's user avatar
  • 3,377
23 votes
9 answers

Deprecation of SHA1 code signing certificates on Windows

EDIT (7/7/2016) - see addition at the end of post I have been keenly following the issues with regards to Microsoft deprecating the use of SHA1 code-signing certificates for Windows executables (http:...
Kevin's user avatar
  • 331
22 votes
4 answers

What asymetric scheme provides the shortest signature, while being secure?

I've had a look at several signature schemes (DSA, ECDSA for the most common ones), and am wondering about whether there exist a scheme that would have the following properties : Be asymmetric (one ...
Wam's user avatar
  • 323
21 votes
3 answers

what is the difference between a mac and a digital signiture

I understand that a MAC algorithm takes a message and a private key as input and hashes them to a value. I understand that senders and receivers often use MACs to authenticate a message and check the ...
bernie2436's user avatar
  • 1,457
20 votes
3 answers

Can attackers change the public key of certificate during the SSL handshake

The communication is not encrypted during the SSL handshake. If an attacker conducts a man in the middle attack between server and client to capture the certificate, and change the public key in the ...
Grey's user avatar
  • 363
20 votes
7 answers

Is there a protocol that provides data integrity, but not encryption for HTTP?

HTTP I'm aware that HTTP sends plain text over the network which can be sniffed and modified if a MITM is performed. HTTPS On the other hand, HTTPS sends encrypted text over the network that can ...
MikeSchem's user avatar
  • 2,321
19 votes
2 answers

What exactly happens when I "validate" a digital signature?

Context: I'm filling my taxes and my country requires me to upload certain documents from my employer to verify the numbers I give to the government. These documents are "digitally signed", ...
WorldGov's user avatar
  • 333
19 votes
2 answers

JWT: Choosing between HMAC and RSA

It is my understanding that HMAC is a symmetric signing algorithm (single secret key) whereas RSA is an asymmetric signing algorithm (private/public key pair). I am trying to choose between these 2 ...
4Matt's user avatar
  • 415
16 votes
3 answers

License key / Serial number generator and checker

I need a serial number generator and accompanying checker. I would like to be able to set a salt (and maybe a length). The generator should only produce serial numbers that pass the test of the ...
Dave's user avatar
  • 261
16 votes
5 answers

A standard way to manually add a digital signature to a pdf file?

I've created a few certificates to use myself, but I find myself stumped when it comes to creating a certificate which contains a digital signature. First, how would I go about creating a standard ...
roman canada's user avatar
16 votes
3 answers

What are you saying when you sign a PGP key?

When you sign a PGP/GPG key, what exactly are you saying to everyone who sees your signature? Are you validating the person, or the email address? To explain what I mean, take the following two ...
IQAndreas's user avatar
  • 6,715
16 votes
3 answers

What is gained by hashing the last block on-device?

Recently I encountered the notion of "hashing the last block on-device". It means that when computing a digital signature, the hash that serves as input for the actual signature computation is not to ...
emboss's user avatar
  • 4,348
16 votes
2 answers

Which factors should I consider for devices that accept handwritten digital signatures?

These days many locations ask you to give your signature on a digital signature pad/device. As I am situated in Europe, the EU directive 1999/93/EC seems to regulate it. From what I have found out ...
Indrek's user avatar
  • 173
15 votes
1 answer

How does this unsigned exe launch without the windows 10 SmartScreen warning?

So, I have been working on my own project for which I have been looking into certificates and such. While browsing reddit I found a game which I can launch the exe file, expecting to get a Windows 10 ...
vbscript's user avatar
  • 153
15 votes
6 answers

Why not RSA-encrypt the entire document?

I have recently learned of a way for person B to verify that a document sent from person A is indeed from person A. Person A gives Person B his public RSA key. This must be done reliably. Person A ...
David Faux's user avatar
15 votes
3 answers

How do I produce a CA signed public key?

I have a need to have somebody else encrypt secret data with my public key that I can then decrypt with my private key. I have produced an RSA private/public key pair with OpenSSL gave them the public ...
user1683793's user avatar
14 votes
2 answers

What is meant with naïve sign & encrypt?

In his paper Defective Sign & Encrypt in S/MIME, PKCS#7, MOSS, PEM, PGP, and XML, Don Davis is often talking about the term naïve sign & encrypt After reading the paper, I'm not 100% ...
user1511417's user avatar
13 votes
2 answers

What is the meaning of GnuPG's --list-sigs output?

gpg --list-sigs gives me somethings like the following (I edited the output only to show the interesting/different rows): pub 2048R/4ACE309C 2016-11-01 uid lala_test2 <lala2@...
Lilás's user avatar
  • 339
13 votes
3 answers

Can signing too much compromise a private key?

Can a collection of many messages signed with the same private key be abused to either forge signatures so some (but not all possible) messages, or even worse to reconstruct that private key with less ...
Tobias Kienzler's user avatar
13 votes
3 answers

How are private keys handled in an enterprise?

We would like to start using digital signatures and possibly encryption for e-mails in our company. My knowledge of public-key cryptography is entirely theoretical with no practical experience. In ...
jgxvx's user avatar
  • 307
13 votes
1 answer

What are the problems with encrypted but unsigned data?

In another question's answer, D.W. wrote: Make sure there is authenticity protection for the encrypted data (e.g., encrypt and then sign/MAC): you will need both confidentiality and authenticity ...
Jean-Philippe Pellet's user avatar
13 votes
1 answer

How do certificates work in terms of encryption, hashing, and signing?

I think I might understand this stuff, but I want to be sure I've got the details correct. There is a lot of information out there on the high-level implementation of certificates, as well as the ...
Dave Hirsch's user avatar
12 votes
3 answers

Is it possible to use WebAuthn for digitally signing documents in the browser?

WebAuthn is a relatively new API for authentication, and it uses public key cryptography instead of something like passwords. I am wondering if it is possible to use the cryptographic part for a ...
Mad Scientist - on strike's user avatar
11 votes
2 answers

openssl verify signature

For S/MIME, I now know I can verify PKCS#7 detached signatures with: openssl smime -verify -in detachedsign.pem -content content.txt But what about non-MIME messages? So if I sign the message Hello, ...
Filipe Pina's user avatar

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