Tagged Questions

2
votes
1answer
106 views

Why is verification using DSA slower than verification with RSA?

We read in literature that verification of a digital signature is slower using DSA than if we used RSA. Why is this? DSA parameter generation: choose prime number $p$ choose prime number $q$ such ...
-1
votes
1answer
92 views

What length should the padding be when encrypting or signing with RSA?

Does it matter what length the padding is? If so - what length should it be? (Another point: Should it be random?)
3
votes
1answer
166 views

Secure encrypt-then-sign with RSA

I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt. However, I have encrypted data that I need to sign, to prove the author of ...
2
votes
4answers
203 views

Tamper-proofing log files

Problem Overview I want to securely store log files so the contents are secret, and they can't be modified without detection. The files will be encrypted using authenticated encryption (AES in GCM ...
2
votes
1answer
112 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
0answers
104 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 ...
1
vote
3answers
496 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
2answers
464 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 ...
1
vote
3answers
349 views

What is the length of an RSA signature?

Is it the same as the bits of the key (So a 2048 bit system will yield a 2048 bit signature)? At most as the key? Or something else entirely?
0
votes
1answer
50 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 ...
1
vote
2answers
2k 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 ...
0
votes
1answer
121 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 ...
3
votes
2answers
806 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 ...
1
vote
1answer
190 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 ...
2
votes
2answers
100 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
130 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
2answers
591 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 ...
3
votes
3answers
504 views

Why hash or salt when signing?

I've seen an example of how to sign using RSA. Besides the signing itself (s = m^d mod n) it also hashes and adds an IV. Why is that needed?
2
votes
1answer
454 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 ...
5
votes
2answers
812 views

What are advantages of using a HMAC over RSA with SHA-1 hashes?

I am currently studying for an exam and this was a previous question: Give one advantage of using HMACs over using RSA to sign SHA-1 hashes. My thoughts are that it has something to do with the ...
3
votes
2answers
2k 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
219 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. ...
2
votes
1answer
112 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 ...
4
votes
1answer
201 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 ...
6
votes
2answers
271 views

What is the key strength reduction encrypting only 160 bits of data using RSA1024 for signatures

I am attempting to determine the strength of an incorrectly implemented 1024 bit RSA signature scheme. The weakness in the implementation is that the padding data lacks random numbers. As a result, ...
5
votes
1answer
115 views

Including a “purpose” designation in a digital signature

A signature of some data can mean many different things, such as: This is a message I sent, this is a certificate I validated,... So I was surprised that common signing schemes don't include a ...
4
votes
1answer
452 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 ...
2
votes
2answers
446 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 ...
2
votes
1answer
403 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 ...
4
votes
2answers
431 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
734 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 ...
6
votes
1answer
1k views

How do other, non-RSA algorithms, compare to the PKCS #1 standard?

Arguably the PKCS suite of standards have a profit-oriented bias as they are promoted by RSA and promote their algorithms over others in the form of RFCs and other means. I'm considering the ...