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

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ECDSA verification is too slow [on hold]

I found that ECDSA is too slow while verifying signatures; can you tell me why? I'm planing to speed it up, so what tips should I consider to make it fast?
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0answers
48 views

RSA and ECDSA algorithms [on hold]

Hi, i want to learn more about ECDSA and RSA Digital signatures , could you give me both Algorithms for sign and verify the data.
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1answer
90 views

Is there a method to combine encryption and ring signing?

There's the well-known question on whether to sign or encrypt first. However, if instead a message is to be ring-signed such that either recipient could be the actual signer, is there any scheme that ...
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1answer
124 views

Attack of an RSA signature scheme using PKCS#1 v1.5 encryption padding

My best interpretation of this question is that Java's crypto API has been subverted to perform RSA signature using PKCS#1 v1.5 encryption padding. Assume the signature $S$ of a message $M$ is ...
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1answer
123 views

Given a message and signature, find a public key that makes the signature valid (ECDSA)

This question is a variant on Given a message and signature, find a public key that makes the signature valid, which discusses the analogous question for RSA. It was suggested to me by this post over ...
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1answer
85 views

Why should a signature use PSS padding in RSA?

Suppose I send a message using AES (private keys already negotiated securely) and I send a hash of this message using RSA (encrypted with private key) with OAEP to verify the authenticity and ...
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1answer
43 views

Showing that security of a elgamal invariant is insecure

Original Elgamal signature is defined $S(m, \alpha) = (r, s)$, where $$r = g^k \bmod p$$ $$s = (m – r*α)k^{-1} \bmod (p – 1)$$ more information on Elgamal signature can be found here. Variant ...
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0answers
62 views

Threshold signatures vs. certificate authority+voting verification

Perhaps a silly question, but I am wondering what the advantages are of threshold signatures. Let's consider the following two signature schemes: $(t,n)$-threshold signature with a trusted dealer, ...
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49 views

How to know private key is computed from specific partial private key?

In a certificate-less cryptography, I have learned that – to resolve the key escrow problem of IBE – the concept of a partial private key is used. Now, consider the following Scenario: After ...
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1answer
65 views

Why do we encrypt-then mac but sign-then-encrypt?

This question was asked in comments on my answer to should we sign then encrypt or encrypt then sign. I think posing the question as a separate entity is best, so: The general advice for applying ...
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2answers
94 views

Convert SpookyHash to semi-secure 192bit hash [closed]

What do you think of converting SpookyHash into semi-secure 192bit hash function by this way: increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * ...
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0answers
40 views

Is there a malleable pubkey digital signature scheme?

I'm trying to find a special kind of Digital Signature Scheme. The scheme should allow me to transform a signature s=sign(sk,m) (for a private key sk and a message m) into a signature s'=sign(x,m) ...
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4answers
139 views

What is the difference between authenticate a document and sign a document?

Is it a kind of same? Authenticate means it is from sender. Also sign is done by the sender. Can someone please give a clear view about their relationship?
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0answers
59 views

How to compare different signature scheme's performance?

I am interested in comparing the computational performance of two signature schemes. However, I am unsure how to do that. My candidates are RSA and Shamir's ID Based Signature scheme. To get a fair ...
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2answers
215 views

How do I create a short signature? (e.g. less than 100 bytes)

I want to put information into a QR code and have it signed so that the authenticity of the information can be verified. But QR codes have limited storage capacity and when I used e.g. gpg I get ...
2
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1answer
111 views

Does changing the random number selected for each message increase security in Schnorr's scheme?

I was reading about Schnorr's scheme and in that for signing the signer generates a random number and continues with his operation. I am trying to implement this in a scenario where the signature ...
1
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1answer
143 views

Security Consideration on The Use of Random Number in Digital Signature

key-exchange protocol allows two parties to establish a shared key over public network. Lacking of authentication the original Diffie–Hellman key exchange is insecure under man-in- -the-middle ...
2
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1answer
141 views

Why the need to hash before signing small data?

I’ve got two questions: I’m doing the following: Data : uuid + int + nonce Signature: ECDSA(sha256(Data) ) To verify the signature: ...
5
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1answer
155 views

Is it possible to weaken a bitcoin private key by “using” it elsewhere?

What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ...
2
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1answer
36 views

ECDSA signature verifiable 1-way transformations

Alice signs a message $m$ with her private key, yielding a signature ($r$,$s$). I want to prove to someone else that I have this signature, but I don't want them to have the knowledge of what ...
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1answer
205 views

Verify Signature Failed [closed]

I am writing a small module which will verify signed message. Message will be signed using private key in Smart Card. The inputs are: Signed Message Original Message Public Key / Certificate with ...
6
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3answers
544 views

Lamport signature: How many signatures are need to forge a signature?

Lamport signature: Signing the message Note that now Alice's private key is used and should never be used again. The other 256 random numbers that she did not use for the signature she must never ...
2
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0answers
69 views

Looking for a detailed example of proof by reduction

I'm looking for a very detailed example of proof by reduction. Say we have two or three protocols (that have been proven secure) and we construct a new protocol. We want to provide a proof of security ...
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1answer
337 views

Is Curve25519-java secure?

I have only about 2 weeks of cryptography experience mostly in the form of questions on bitcoin.se. Is Curve25519-java up to date with current Curve25519 standards? Is Curve25519 itself secure? ...
3
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2answers
290 views

Signature based on public key cryptography and forgery

In the definition of existential unforgeability, there is no detail about the following questions. In general, can we suppose that a signer is also a possible adversary ? When generating a signature, ...
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1answer
61 views

how to use salt to sign a message and how is it effective?

I've had an assignment to sign a file using hash and salt, so I read about salt and I got why it's important when it comes to password, but not to sign messages. 1- how to sign using salt ? the only ...
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0answers
35 views

Distributed authentication in low trust environment

I would like to inquire if there is any Method to achieve the following: There is a list $L$ of $n$ entities that are allowed to perform a certain action. $L$ is cryptographically signed by some ...
3
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2answers
84 views

One-time digital signatures

Are there digital signatures for which, given two documents signed by the same key, one could derive the key? With such one-time signatures, one may be able to design a cryptocurrency based on ...
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1answer
96 views

Non-interactive Zero-knowledge proof signature validation without public key

I'm looking for a method for a scenario with following requirements: At least 3 people (A,B,C,...) are in a Network where they can broadcast messages to everyone but not communicate with a specific ...
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0answers
47 views

Probability of an ed25519 selective forgery?

What is the expected number of trials required to selectively forge ed25519? Please include how it is calculated.
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1answer
148 views

Why does Openssh use only SHA1 for signing and verifying of digital signatures?

I am learning SSH protocol. With my current understanding of SSH protocol, I think that message digest algorithms for using in digital signature should be derived from Key Exchange. But Openssh ...
3
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1answer
73 views

Should different key pairs be used for signing and encryption?

In the recent iOS Security white paper from Apple (February 2014), the section on iMessage discusses using two different asymmetric key types as part of its standard operation: When a user turns ...
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4answers
115 views

Are there use cases where a signature itself needs to be signed?

I'm writing some code to digitally sign certain files (JSON, if you must know), and I'm trying to understand the use cases, not being a crypto guy myself. I understand there are use cases where ...
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1answer
77 views

Can I use asymmetric encryption for more powerful write-protection?

I have a game that I am developing which uses a locally-stored internal database. It does not matter to me whether a user can read the file (which, to me, means I don't need a symmetric cipher), but I ...
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0answers
68 views

Generating a valid signature on El-Gamal without knowing the private key

Suppose we are given $p$, the large prime, $g$ which is the primitive root for $p$, $b$ which is calculated as $b=g^x$ mod $p$ where $x$ is the private key and $0<x<p-1$. Also suppose we know ...
5
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2answers
536 views

ElGamal signature without calculating the inverse

I stumbled upon this question in some textbook. Propose a variant of ElGamal signature scheme such that there is no need to calculate the inverse $k^{-1}$ as it is usually done using the EEA. ...
3
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1answer
288 views

ElGamal message signatures retrieving the secret value x

If the GCD(r, p-1) is small and the value k is used to sign a message using ElGamal is also small. Then the secret value of x can be determined. Why is this true? How would one retrieve x?
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1answer
711 views

How can one show that an ElGamal-like signature verification scheme is valid?

For an ElGamal-like signature scheme, I am given two things: The signing function, the verification function. How can I show that the verification function is valid? Example 1: Signing: $s := ...
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0answers
972 views

An existential forgery attack on ElGamal [closed]

From an old exam question: Consider this existential forgery attack on ElGamal. Choose $u$, and $v$ such that $\operatorname{gcd}(v, p - 1) = 1$. Compute $r := y^v g^u \mod p$ and $s := ...
2
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1answer
154 views

Non-standard signature security definition conforming ed25519 malleability

According to the paper “High-speed high-security signatures”… Malleability. We also see no relevance of "malleability" to the standard definition of signature security. Aside from the example, ...
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3answers
2k views

Why can't Diffie-Hellman be used for signing?

I understand that signing is often a case of hashing data and then encrypting the hash with the private key. What properties keep Diffie-Hellman from being useful for this?
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2answers
99 views

Digital Signature using symmetric key cryptography

Generally digital signature is a public key cryptography concept.But it needs high overhead. So is there any publication or link available where 'digital signature using symmetric key' has been ...
2
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1answer
68 views

Is ed25519 a “hash signature”

Writing my last question, I saw the hash-signature tag. I tried to research it best I could, but I'm simply overwhelmed in this field. I don't think it means to simply hash data before signing, but ...
6
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2answers
433 views

Why hash the message before signing it? Digital signature with RSA

Here's a method to sign the message with RSA: Why hash the data before signing it? Why not sign the whole message? It'll save time if you sign the hash value, but I've heard there are also security ...
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2answers
65 views

Shamir's ID based signatures - Notation issues

I am currently implementing Shamir's ID Based signature scheme as defined in the original paper. The sign and verify operation are defined as follows: Sign: $s = g * r^{f(t,m)} (\mod n)$ ...
3
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3answers
645 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 ...
-2
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1answer
105 views

Digital signatures under plain RSA

Show that digital signatures under plain RSA are insecure (Plain RSA means that signing is done by calculating $m^d\bmod n$, with $0\le m<n$, and no padding or hashing of $m$). Write an algorithm ...
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3answers
2k 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?
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3answers
151 views

How can we sign a contract digitally between two parties?

I'm trying to sign a contract with another party, without using handwritten signatures. I've just read through Applied Cryptography, but there doesn't seem to be a protocol that can solve this ...
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1answer
98 views

Certificate signature with SHA-1 and RSA: where do 1888 bits come from?

Plenty of X.509 Certificates use "PKCS#1 SHA1 with RSA encryption" as the Certificate Signature Algorithm for generating a 2048-bit signature. The SHA-1 hash function generates a hash value of 160 ...