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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10answers
821 views

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 ...
35
votes
3answers
7k views

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 ...
24
votes
4answers
10k views

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 ?
16
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2answers
1k views

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 ...
0
votes
3answers
124 views

Is it ok to send user's private key away, even if protected with a SSL channel?

I'm developing a webserver that performs digital signatures of (xml, pdf and office) documents and then validates those signatures. My idea is: an user puts its SmartCard and through a PIN, he gets ...
-5
votes
2answers
107 views

Protection of online image file (ancient manuscript) [duplicate]

I am going to protect an image file (ancient manuscript) which will be available online for everyone to download. I want to protect the file in these situations: When it's on the server, I need to ...
14
votes
4answers
9k views

how digital signature verification process works

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 ...
8
votes
4answers
6k views

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 ...
9
votes
5answers
6k views

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 ...
7
votes
4answers
7k views

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 ...
10
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1answer
6k views

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?
4
votes
2answers
416 views

Is piping a `ssh-agent` signed message as a password secure?

There's an encrypted filesystem on a server I ssh into using public key authentication. Since a forwarded ssh-agent can deterministically sign a message (see also the ssh-agent protocol section ...
5
votes
2answers
2k views

Dealing with expired or revoked signing certificates with Infopath documents

Suppose I have an Infopath form that is digitally signed today by a valid, and active user. When that user leaves the company, we disable the account and revoke the certificate. This causes a problem ...
12
votes
1answer
321 views

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 ...
5
votes
3answers
787 views

Is there a way to accept signed requests without storing client's password in plaintext?

We are developing REST Web service. We will give Identifier and Secret string to each of our REST clients. When doing requests, clients will authenticate themselves using HMAC algorithm (they will ...
4
votes
3answers
4k views

What is the difference between an electronic signature and a digital signature

From Wikipedia: An electronic signature, or e-signature, is any electronic means that indicates either that a person adopts the contents of an electronic message, or more broadly that the ...
1
vote
1answer
211 views

is pkcs#7 suitable for signing and encrypting zip files?

I'm looking to protect zip files that I will be regularly sending to a 3rd party. I need to ensure strong confidentiality and non-repudation. I would like signing/encryption to be based on ...
1
vote
2answers
550 views

Signed request vs HTTP digest auth for API authentication?

By signed request I mean something like this (simplified example): Client creates a sig in his request: $sig = hash('sha256', $api_key.$data); which generates 7409ur0k0asidjko2j for example. He then ...
14
votes
6answers
1k views

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 ...
7
votes
4answers
574 views

What good, standard digital signature verification clients are widely or easily deployed?

I'm looking for a good way to publish data along with a digital signature (and ideally a timestamp) which is as easy as possible to verify. For example, imagine an election administrator who wants to ...
6
votes
1answer
85 views

Reading older mails signed with a certificate that has meanwhile expired

A few years ago I have used S/MIME certs to sign (and encrypt) my mails. The reason for which I stopped signing was the following: My (class 2) cert was issued on Jan. 1st 2008 (just a sample). It ...
5
votes
3answers
491 views

Digital Signature and Verification?

AFAIK , When Alice wants to write a message to Bob -- she uses Bob's public key and encrypt the message - and then Bob - using his private key - use to decrypt it. So public key is used to decrypt ...
3
votes
3answers
307 views

Is there an attack that can modify ciphertext while still allowing it to be decrypted?

Is there any way an encrypted file using AES-256 could be modified without alerting the file owner, ie., so it can still be decrypted with the same key? I know that without an initialization vector ...
2
votes
1answer
191 views

Is the `ssh-agent`'s DSA signature deterministic?

In my hopes to use ssh-agent to generate a signature as password I implicitly assumed a deterministic signature. DSA is however supposed to take random value k for signing. However that randomness is ...
1
vote
2answers
85 views

Digital Signatures of XML, PDF and Office Documents on every platform

I'm trying to develop a website that performs digital signatures on client-side and then sent the signed document to the server-side. I want to do the signatures on client, due to the fact of not ...
1
vote
1answer
226 views

Signature and Timestamp for Long Term Document Archival Question

I have a PDF document intended for long-term (many years, maybe decades) archival which I would like to digitally sign with my personal certificate to ensure its integrity. As far as I understand, I ...
0
votes
1answer
266 views

Where is RSA Digital signature used in the online banking world?

When i do online banking, i sign my digital transaction with a digipass. Ive been told that it uses a RSA-based digital signature scheme. But an rsa digital signature (1024 bit for the modulus) is a ...
-1
votes
4answers
205 views

Is it possible to digitally sign information with a password?

I'm creating a cloud storage service and need to have the ability to provide reliable security for clients. In my previous question, I used a different schematic and said I would post a new question. ...