Algorithms and protocols for creating signatures to documents, and verifying such signatures. These are normally asymmetric, for symmetric signatures see [mac].
2
votes
1answer
103 views
Are digital signatures secure for signing lots of small messages?
I need to sign the numbers from 1 to 1 billion (literally this, it's not an analogy) using a digital signature and then send these numbers in a particular order to someone. The message is not private ...
-1
votes
1answer
84 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
137 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
191 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 ...
-1
votes
0answers
25 views
Create groups of keys [closed]
I looking for a solution to encrypt, sign documents or email a key group and send to one customers. The group of keys are had already created user keys and I would like to use them.
Is not an option ...
4
votes
2answers
174 views
Signature schemes for underpowered devices (8bit 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 ...
7
votes
1answer
190 views
Alice trusts Bob only when Bob trusts Alice
some story first: Alice and Bob both have public/private key pairs. Now Bob wants Alice to sign his public key id. Alice agrees but only when Bob signs the public key id of her.
Is this something ...
2
votes
1answer
102 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
166 views
Are there any practical implementation of a homomorphic hashing or signature scheme?
A homomorphic hash function is a function $H : A \to B$ between two sets with some algebraic structure $(A, *)$ and $(B, \star)$ such that
$H$ is collision resistant, i.e. it is hard to find $x \neq ...
1
vote
1answer
65 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
193 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 ...
0
votes
0answers
37 views
ElGamal signature: Forging a signature of a specific form
I have a question I can't solve from one of the courses I'm currently taking:
Show that given a legitimate ElGamal signature $(S,R)$ on a given message $m$, an attacker
can compute a signature ...
1
vote
0answers
80 views
Are hash trees an alternative, quantum-resistant signature scheme which can replace RSA?
Can hash trees can provide quantum resistant signatures to replace RSA for signing securely? What is the key size and how many times can we use same key?
1
vote
0answers
84 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 ...
3
votes
1answer
89 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 ...
3
votes
1answer
421 views
What are the differences between a digital signature, a MAC and a hash?
A message may be accompanied with a digital signature, a MAC or a message hash, as a proof of some kind.
Which assurances does each primitive provide to the recipient?
What kind of keys are needed?
3
votes
3answers
755 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 ...
2
votes
0answers
100 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
votes
1answer
123 views
Fiat-Shamir signature
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?
0
votes
1answer
156 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
1answer
194 views
Can ElGamal encryption and ElGamal signatures be used together sharing the same key-pairs?
I'm working on a encryption system where each party can store exactly a single ElGamal private key in a device. This is a hardware limit. The system must be expanded to support signatures and ...
0
votes
0answers
37 views
How is sender's public attached and sent to receiver with signed XML? [closed]
In which form the public key of sender is attached with the signed xml document (.Net),inorder to get signature verified at the receiver's end?
2
votes
2answers
142 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 ...
2
votes
0answers
190 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, ...
0
votes
1answer
151 views
Hash collision resistance requirements for Lamport signatures
According to the original paper, Lamport one-time signature scheme uses two one-way functions: $F$ and $G$. The former one, $F$, is used to create a public key by hashing elements of the private key ...
1
vote
3answers
460 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
684 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
421 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
2answers
121 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 ...
2
votes
3answers
328 views
Is it possible to pick your Ed25519 public key?
Is it possible to generate an Ed25519 keypair that has a very similar public key as another keypair (fooling a casual visual comparison) or is this as hard as solving one of SHA-512 or the discrete ...
1
vote
3answers
326 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
5answers
271 views
Approach towards anonymous e-voting
I want to implement an internet-based e-voting system.
Voters shall be able to cast their vote for one out of n possible candidates. Each candidate has his own ballot-box kept by and at a trustworthy ...
-1
votes
1answer
146 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
4answers
177 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 ...
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
0answers
47 views
What happens when you use Windows credentials to sign a message?
I'm trying to dig into the messages that are exchanged when you sign a message using Windows credentials. I've modified the default service that is provided when you create a WCF service to use the ...
0
votes
1answer
122 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 ...
6
votes
1answer
108 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?
2
votes
1answer
124 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
1answer
118 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 ...
0
votes
1answer
118 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 ...
2
votes
2answers
711 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 ...
3
votes
2answers
728 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
360 views
Okay to use OpenSSL to encrypt then sign a message?
I am planning on encrypting a message then signing the message so the recipient can authenticate the source. Reading this article has me concerned that I'm doing something wrong.
My current plan is ...
1
vote
0answers
63 views
In S/MIME, are the same certificates always used to sign and encrypt messages?
My assumption is that S/MIME almost always utilizes certificates as follows:
My certificate can be used to allow people to encrypt messages and send them to me.
My certificate (the same ...
1
vote
1answer
181 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 ...
1
vote
2answers
99 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
124 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 ...
5
votes
1answer
305 views
Why are MACs in general deterministic, whereas digital signature constructions are randomized?
The fact is I'm not quite sure if my question statement is true, however all the MAC constructions I know of (e.g. CBC-MAC, CMAC, HMAC) are deterministic, whereas many constructions for digital ...
