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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How to prove that a commitment hides the decryption of an ElGamal ciphertext?

I've decided to remove a previous unanswered question of mine and break it down into smaller pieces so it's not such a loaded question. For this question I need to prove that I've committed to a ...
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76 views

Problem with applying threshold scheme

For a report on threshold signature schemes, I have to explain a threshold signature scheme and give a simple example with numbers. A threshold signature scheme is a scheme in which a network of n ...
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100 views

Limit the number of private key uses for RSASSA-PKCS1-v1_5 with SHA-256 signature?

Assuming all messages and their signatures are available to the attacker, is it secure to use the same RSA private key to sign many messages (roughly $10^{6}$) via PKCS#11 ...
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32 views

Residue requirements of Rabin-Williams primes?

I'm trying to determine the residue requirements of Rabin-Williams. An older copy of P1363's Public Key Cryptography states the following in Section 8.1.3.2 RW key pairs: An RW public key consists ...
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210 views

BER or DER X9.62 ECDSA signature

The signature format for ECDSA signatures can be encoded using ASN.1 integers according to X9.62 or it can comprise of two integers with the same size as the key size. In case the X9.62 format is ...
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100 views

Can CKM_RSA_PKCS signature be made secure by lowering its maximum input size?

The CKM_RSA_PKCS Mechanism in PKCS#11 v2.20 section 12.1.6 PKCS #1 v1.5 RSA is a signature scheme commonly used to implement RSASSA-PKCS1-v1_5 of PKCS#1 signature of data hashed externally to a ...
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212 views

How does Schnorr signature actually work?

I'm trying to get a grip on how Schnorr signature works. Suppose Alice sends Trent a tuple $(P, M)$, which contains a payload and a message to be signed by him. She then passes the certificate to Bob ...
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85 views

Homomorphic proxy re-signature

Alice has a value $a$ and she signs it using her secret key $d_1$ as: $s_1 = (r_1 * g^a)^{d_1} \bmod p$, and Bob has a value $b$ and he signs it using his secret key $d_2$ as: $s_2 = (r_2 * g^b)^{d_2} ...
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124 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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1answer
375 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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97 views

BLS signatures in the G-valued Random Oracle Model

This paper on semi-generic algorithms considers "non-standard properties of the employed hash function". For BLS signatures whose main group is $G$, I'm curious what can be shown when the hash ...
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646 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 ...
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202 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, ...
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2answers
319 views

What does $\Pi$ represent in cryptography?

I am doing a project in cryptography and while reading a tag generation algorithm for files, I got stuck with the meaning of $\Pi$. The screenshot of the algorithm is inserted below. Here the ...
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4answers
195 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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2answers
343 views

What security flaw exists in MAC authentication scenario?

What security flaw exists (if any) in the solution of this non-encrypted authentication scenario? An unencrypted message passes one-way from computer A to B. Its transmission is viewable by the ...
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1answer
44 views

Security of a signature scheme based on both factoring and discrete logarithms

I have seen this paper: A New Signature Scheme Based on Multiple Hard Number Theoretic Problems by Ismail and Tahat: In this paper, we propose a new signature scheme based on two hard number ...
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1answer
61 views

How are all necessary parameters shared between signer and verifier in ED25519 signature scheme?

I want to use ED25519 signature scheme in my application which requires frequent sharing of secret data between two entities in public domain. I know that Schnorr signature scheme has a key ...
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1answer
129 views

Why are cryptographically secure hashes required for digital signing (RSA or DSA)?

I know that a cryptographically secure hashing algorithm is required for proper message signing (SHA-1, or I think SHA-2 is the current suggested algorithm). However, why does the hashing algorithm ...
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2answers
150 views

Do I have to transfer the private key to digitally sign a remote document?

I'm trying to digitally sign a document which is uploaded by a user. I want the user to sign that document using his digital signing certificate (DSC). Should I: transfer the file to the user, and ...
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1answer
363 views

Security of chameleon hash functions

With the knowledge of the trapdoor, we are able to compute the same digest for differents messages. I've read that given two messages $m$, $m'$ and two numbers $r$, $r'$ such that ...
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2answers
117 views

Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$? [closed]

Is there an efficient way to map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
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1answer
5k views

Simple digital signature example with number

I've been looking for a simple which signs a number with some randomly generated key and then verified(decrypts the original number) with the public key, which is generated by the private. All the ...
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1answer
176 views

Merkle Signature Generation

In the section 2 (page 42) of the book "Post Quantum Cryptography", it says: Then he generates the one-time signature $\sigma_{\text{OTS}}$ of the digest using the $s$-th one-time signature key ...
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2answers
239 views

Digital Signature Scheme Count

My question is How I will be able to count digital signature Scheme that can sign many documents with one private key. There are signature scheme as long as exists private keys in the keys spaces? or ...
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1answer
215 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 ...
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45 views

Merkle signature scheme

I was browsing the Wikipedia article on Merkle signature schemes and noted that it says: The number of possible messages must be a power of two[…] Why is that? ...
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1answer
258 views

Signing/verification between Java and the OpenSSL

I'm trying to sign/verify data between a C application and a Java application. In java for now I was using the built-in JCE provider with SHA256withRSA as ...
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1answer
51 views

Winternitz Signature Scheme Verfication

I am reading page 39 in this "Post Quantum Cryptography" book. Why does equation 15 hold? There is no further knowledge about f and you definitely cannot use any power laws. So, why is ...
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1answer
629 views

The difference in size between ECDSA output and hash size

So if I use secp256k1 for example, I've got my key size of 256 bit, and say I sign a SHA256 hash of a message, with size 256 bit, I get an output of size 512bit. Why is there a difference between the ...
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1answer
114 views

Are there signatures that don't have subliminal channels?

Are there signatures that don't have subliminal channels and also don't require commitments or zero-knowledge proofs? DSA or Shorr signatures need a nonce which can leak valuable information. There ...
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3answers
201 views

How is the following different than RSA Signing of a document?

If the goal is to demonstrate that you are who you say you are, I think the following will work: Bob wants to know that you are Amy. Bob encrypts a number using Amy's public key and then asks her what ...
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1answer
108 views

How can a digital signature algorithm incorporate a random data if it is to be authenticated on a separate system

I am trying to understand how RSA digital signatures can incorporate any data from a PRNG into the final signature. Does this mean that separate implementations might fail to verify each others ...
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1answer
228 views

ElGamal digital signature. why mod p-1 in delta?

Im trying to figure out why $\delta$ in the signature part of ElGamal has mod $p-1$ when $\gamma$ has mod $p$? $\gamma = \alpha^k \mod p$ $\delta = (x-a\gamma)k^{-1} \mod p-1$
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145 views

Is it ok to send part of digital signature if we have bandwidth constraints?

When creating digital signatures is it ok to send part of it when we have bandwidth constraints?
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1answer
121 views

Sample RSA-style signature confusion

I'm trying to study a simplified TLS-style protocol, including verifying RSA signatures. It's an attempt to verify using only a valid certificate. However, I can't manage to get anything to verify ...
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2answers
420 views

DSA, RSA, ECDSA etc - which one is cheapest for signing?

For a protocol where the server presents its signature to prove authenticity (e.g. IKE/SIGMA/STS with only one party authenticated), it's essential that the signing is extremely cheap, while ...
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1answer
41 views

Can I get successful signature verification with just altering message and signature?

Assuming I can modify a message and also modify the verification signature, and I also have the public-key but not the private-key. Can I create a message that can be verified with a signature that I ...
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1answer
52 views

Calculate if a digital signature is valid

In the book An Introduction to Mathematical Cryptography, it mentions a section on digital signatures and a theoretical example. I am having difficulty understanding the book and I was wondering if ...
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1answer
63 views

Shouldn't a signature using ECDSA be exactly 96 bytes, not 102 or 103?

Attempting to use openssl to create a signature is confusing on several levels: If I'm using it to sign a hash that I've already created (HMAC-SHA-384-192, specifically), a. why must I specify ...
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1answer
65 views

setting the MGF hash to a different value other than the regular hash with openssl for PSS signatures

In PKCS1's Probabilistic Signature Mode you have the Hash and the MGF Hash. Both appear to be, by default, sha1, with the OpenSSL CLI client, however, I can change it to sha256 with the following: ...
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1answer
77 views

Which hash function is usually used in RSA?

I know there are several available, however I can't seem to find whether there is one standard one or not. I think I understand the process of digital signatures, just wondering which has function is ...
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1answer
59 views

Signature Verification: High level

I'm trying to understand how certificate signing and verification works conceptually. I know the classic example with asymmetric cryptography- the sender encrypts data with public key of receiver, ...
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1answer
70 views

Can Winternitz be easily converted to a many-time encryption scheme?

The Winternitz scheme is typically cited as being an OTS scheme. Can it also be used as a one-time encryption scheme? If it can be used as a one-time encryption scheme, then is it possible to easily ...
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1answer
113 views

RSA padding confusion attacks

Server A produces signed messages on request. You can tell server A what type of RSA padding to use in the signature (either RSASSA-PKCS1v1_5 or RSASSA-PSS). Either way, the message will be signed ...
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1answer
224 views

How do SignRecover and VerifyRecover work?

In PKCS#11, there are the SignRecover and VerifyRecover methods, where the data can be recovered from the signature. How do these methods work? Can I implement signrecover and verifyrecover with ...
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1answer
75 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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1answer
220 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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1answer
246 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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1answer
114 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 ...