Algorithms and protocols for creating signatures to documents, and verifying such signatures. These are normally asymmetric, for symmetric signatures see [mac].

learn more… | top users | synonyms

2
votes
1answer
373 views

Are RSA signatures deterministic?

If I sign the word HELLO with the mechanism "NONEwithRSA" with the same private key, do I always will have the same signature? A Java example always return ...
2
votes
1answer
147 views

Is Guillou-Quisquater existentially unforgeable against adaptive message attack under a random oracle model?

First of all, the Guillou-Quisquater digital signature scheme is: Note everything is $\bmod n$. Message is denoted by $m$. Private key: $s$ Public key: Hash function $H$, $e$, ...
6
votes
3answers
280 views

Is signing a hash instead of the full data considered secure?

I reference object in some of my code in hashes. The signature is itself is another object separate from the one I am signing (for obvious reason). I consider simpler to simply sign the reference to ...
2
votes
3answers
1k views

Is 512-bit RSA still safe for signature generation?

The standard CSP on Windows XP only supports RSA up to 512-bit, which means that it's the maximum key size I can use for authenticity verification of updates. The public key is embedded in the ...
2
votes
0answers
371 views

Determining the algorithm used to generate a digital signature

I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature. From the signed string, is it possible to find out what ...
4
votes
1answer
225 views

Why doesn't this replay attack work on ECDSA?

I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ...
16
votes
3answers
8k views

Should we sign-then-encrypt, or encrypt-then-sign?

We often want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
4
votes
0answers
166 views

Ring Signature - paper/code difference in trying to solve inverse trap door function?

there is a paper on ring signatures and a python implementation of it here. The Step 4 in the paper describes $y_s = v =C_k,_v(y_1, y_2, ... y_r)$ for all $1 \leq i \leq r$ where $i \neq s$. The ...
-2
votes
0answers
515 views

Fiat-Shamir signature [closed]

I have a question about Fiat-Shamir signature: A hash function is h(w)=w mod 2011 and w1=2623, w2=3269, w3=1938. What is h=? and how to determine k.t bits?
1
vote
1answer
1k views

How does a client verify a server certificate?

As far as I know, when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
2
votes
0answers
198 views

How do I encrypt with the private key? [duplicate]

Possible Duplicate: RSA encryption with private key and decryption with a public key This wording is creeping everywhere (e.g. there): "I encrypt with the private key" and even sometimes, ...
3
votes
2answers
330 views

Can I save space for short messages by using encryption with private key instead of a signature?

Let's say I have a message, a Private Key and a Public Key. Normally if you want to see if the message is unaltered and is from the sender you would have the message part + signature part, which you ...
3
votes
2answers
8k views

FIPS 140-2 Compliant Algorithms

Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES". Any suggestions would be much ...
2
votes
2answers
2k views

Is RSASSA-PKCS1-v1_5 a good signature scheme for new systems?

Is RSASSA-PKCS1-v1_5 a good signature scheme to recommend that people use in new systems? Is it believed to be secure and represent the state-of-the-art in RSA-based signatures? I understand that ...
2
votes
4answers
522 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 ...
6
votes
4answers
3k views

How are timestamps verified?

You put an input and the hash value comes as an output then when someone puts the input the hash function it is applied to see if it is the same hash original value is stored in some database , that ...
4
votes
2answers
190 views

Detect tampering of data

I have the following problem: There are $n$ users and each users fills in three data points per day, this are three integers between say $-10$ and $10$. I have access to the database and hence I am ...
1
vote
1answer
58 views

Design question for a service that signs messages on behalf of a user

I'm working on a messaging service that lets users author messages and have them signed with an RSA key. The key is used for identity purposes only and can be revoked, so compromising the private key ...
-2
votes
1answer
155 views

Why is 2 the inverse of 10?

I have one question about the ECDSA signature scheme. When Bob wants to send a message to Alice that is to be signed she makes following things (with for example $A = (5,1)$, $d=7$, $q=19$). ...
2
votes
1answer
439 views

Can we trust digital signatures?

Consider that Alice wants to send a digitally signed message to Bob. Mallory might be able to publish his public key under Alice's name and then impersonate Alice to send a message with an apparently ...
0
votes
1answer
187 views

RSA Signature - Multiple Use Weakness

I cite from Fundamentals of Computer Security (Chapter 7 on Digital Signature, Paragraph 7.3 on RSA Signatures, page 289): Multiple uses of the RSA Signature scheme tend to weaken it. The way out ...
10
votes
2answers
10k views

Signatures: RSA compared to ECDSA

I'm signing very small messages using RSA, and the signature and public key are added to every message, which requires a lot of space compared to the actual content. I'm considering switching to ...
7
votes
1answer
136 views

Why does it matter for a signature scheme to be without random oracles?

There is a profusion of articles proposing signature schemes without random oracles (see for yourself). What does that mean, and why does it matter?
3
votes
1answer
224 views

Chaum undeniable signature - justification for probability of misleading the verifier?

Can anyone explain me in details why does the following statement hold true in Chaum and van Antwerpen scheme for undeniable signature? The probability that a dishonest signer is able to ...
2
votes
1answer
153 views

Does it make sense to use slow hashes in digital signatures?

For storing passwords, it seems that the use of intentionally slow hash functions (like PBKDF2 and bcrypt) is now recommended. This is because most hashes are designed to be fast, which also makes ...
2
votes
2answers
274 views

Is the “Signed on date” of a PGP Signature Verified?

I noticed that PGP signatures have a "signed on" field. I was wondering if this is "trustworthy" information and if so how is it accomplished. For example, I can't see how it could be trusted ...
3
votes
2answers
2k views

Digital Signatures, Standard Hash Functions and MACs

I'm studying Hash functions and Digital Signatures in sequence, and came up with some doubts about their usage. First of all: What is the difference between hashing a document and signing it? And ...
7
votes
4answers
963 views

What is the signature scheme with the fastest batch verification protocol for multiple signers?

I'm looking for a scheme where signing may be costly (slow) but batch verification with different signers is the fastest possible. Modified ECDSA allows batch verification for different signers with ...
3
votes
2answers
2k views

How do digital certificates work, and why is it not possible to reverse engineer one from a signed file?

Digital certificates are used quite commonly these days, for signing files. They are used by various operating systems to ensure reliability and security. For example, Android requires that each of ...
2
votes
1answer
864 views

“Signing” with public key

For this question, the following caveats and assumptions hold: There exists a 2048-bit RSA key pair used exclusively for signing/verification The private key is kept completely private There exists ...
3
votes
2answers
125 views

When to prefer exchanging cryptographic certificates over exchanging only public keys?

Let's think of the following case: A group of peers want to exchange messages with each other. They use public-key cryptography to sign and encrypt messages. Anyone with any name can join the ...
3
votes
1answer
205 views

Safely use CryptSignAndEncryptMessage?

I am developing an application that sends messages which I want to encrypt and sign. The CryptoApi offers a function called CryptSignAndEncryptMessage. The description says, what this function ...
1
vote
1answer
176 views

RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?

Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
4
votes
2answers
2k views

Why DSA cannot be used for encryption?

Here it is mentioned 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 DSA public key to ...
5
votes
1answer
161 views

Digital signature for an expiring password

I would like to create a publicly available tool that is used to generate a password that gives a limited time access to a resource. My idea is to digitally sign the current date with a private key ...
5
votes
1answer
210 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, ...
2
votes
1answer
1k views

How to sign a message using RSA?

Assuming I already have a D, P, Q, etc of an RSA key: How do I now sign a message? If it matters – the message is around 100 bits. I don't know much about cryptography, but I can get these numbers ...
0
votes
1answer
267 views

Implementing Paillier Signature Scheme in Delphi

I've been trying to implement the Paillier Signature Scheme in Delphi, but I can't get it to work and I don't know where the problem is. First of all, I got my info about the scheme from this paper. ...
2
votes
1answer
71 views

Are there any signature schemes that protect against collusion by multiple parties?

Say I want to verify the identity of Alice, but Alice could be colluding with Bob to fool me. Is there any way to verify Alice's identity and also be sure that Bob is not impersonating Alice, e.g. ...
6
votes
2answers
7k views

Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509

What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"? Edit: I'm creating the ...
4
votes
2answers
378 views

X.509 CSR: Why does CA remove signature?

I just read this article on Wikipedia: Certificate Signing Request I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator. ...
3
votes
1answer
372 views

What is the computational cost of a public key certificate signature verification?

What is the computational cost of a certificate signature verification in terms of exponentiation, multiplication and other computation operations?
4
votes
1answer
170 views

Signing a GCM MAC

If I encrypt a message with AES-GCM, is it safe to use the MAC as the hash in a DSA/RSA signature? That is, if someone knows the AES key and nonce, will they be able to generate a different message ...
6
votes
1answer
338 views

Threshold Signatures for RSA and DSA

I have a few questions relating to threshold signatures: a scheme where $n$ participants hold a key share and any $t$ of them can conduct a protocol using their shares that results in a valid RSA or ...
3
votes
2answers
1k views

Proof of security for RSA signatures

I am new to here, I was having some problems with a problem I am working on: "For each of the following variants of the definition of security for signatures, state whether textbook RSA is secure ...
4
votes
1answer
915 views

Why is ElGamal considered non-deterministic?

One difference between RSA and ElGamal is that ElGamal isn't necessarily deterministic (while RSA is). What makes it non-deterministic? Is this advantageous to security? How else does this property ...
3
votes
1answer
1k views

Demonstrating the insecurity of an RSA signature encoding scheme

I'm working on problem 12.4 from Katz-Lindell. The problem is as follows: Given a public encoding function $\newcommand{\enc}{\operatorname{enc}}\enc$ and a textbook RSA signature scheme where ...
5
votes
2answers
677 views

Is a RSA-signature of some identifying data a safe way to implement a license key?

I have this idea of implementing a license key: After the user downloads the program, he connects to a website and sends his Windows product ID. The website, then, sends this back to him with a ...
5
votes
1answer
2k views

RSA-PSS salt size

One of the inputs of RSA-PSS signing and verification is the salt size. According to PKCS#1, you must know the salt size before the verfication is carried out. However, this makes interoperability ...
4
votes
3answers
808 views

public key cryptography and digital signature

I read the following from Understanding Public Key Cryptography on Microsoft TechNet: Using a private key to establish identity shows that the full encryption and decryption operation was ...