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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Why is public key cryptography not widely used in governments? [closed]

Are there any practical limitations? Govt driving license, passport, SSN could be digitally signed making it easy for anyone to validate. They can have a qr code in them which can be easily validated ...
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240 views

RSA Signature : Process of Sign the message and Verify

I have read that the RSA numeric signature works as the following: Generation of keys : $p,q,N,e,d$ Process of signing the message $m$ (which is BigInteger) : it uses the secret key $sk=(p,q,d)$ so ...
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69 views

Boneh-Boyen like signature scheme

Full Boneh-Boyen signature scheme defines a pair of secret keys (SK) $a \in \mathbb{Z}_n$ and $b \in \mathbb{Z}_n$ and a pair of public keys (PK) $A = G^a \in \mathbb{G}$ and $B = G^b \in \mathbb{G}$. ...
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53 views

Is signing a message just encrypting it with private key? [duplicate]

I have a simple question, When I sign a message (in RSA) does the program encrypt the text with my private key? Because I can decrypt it with my public key. Yes or no. Is signing a message just ...
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544 views

Existential Forgery on textbook RSA signatures

Can an adversary who haven't seen the message before forge the signature of that message? The adversary has seen $σ_1 = (m_1)^d \bmod N$ and $σ_2 = (m_2)^d \bmod N$ He forges $m' = m_1\cdot m_2$ $σ' ...
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88 views

advantages of hashing over elliptic curve signatures for a proof of work protocol

I'm trying to create a proof-of-work protocol for a proof-of-concept software, and it's basically something like this: ...
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75 views

exchanging private key between service and iPhone app - digital signing

I need to do digital signing of my request data which will be sent to the server. My server sends distinct private keys to her clients after authentication and expects all responses to be digitally ...
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104 views

Is it possible (how difficult) to find MORE than one valid RSA signature?

Is it possible (how difficult) to find more than one valid RSA signatures for a given message m (after padded) and a public key e...
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182 views

A way around digital signatures?

Scenario: I have to protect the integrity of some files that will be exchanged between entities $A$, $B$, $C$. Entity $A$ creates the file (e.g. configuration) and sends it to $B$ and $C$. Entities $A$...
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159 views

The advantages of Merkle Signature and One time Signature

In Merkle Signature, it also requires one-time signature to be used once for a message. The signature in Merkle scheme is even longer compared to Lamport one time signature. The verifier also has more ...
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1answer
134 views

Group Signature Scheme without Opening but with Revocation

After reading many papers about group signature schemes, I saw that basically all of them employ the possibility of "signature opening": The Group Manager (GM) can identify any signature made by his ...
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117 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 $s=\text{sign}(sk,m)$ (for a private key $sk$ and a message $m$) into a signature $s'...
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113 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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41 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 ...
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64 views

How to specify last $t$ bits are only sent when a signature is sent?

I have read that in cases where there is a limit on the amount of data sent over the network, one idea is to sent only $t$ bits of data rather than sending all the bits. For example, in the Schnorr ...
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97 views

Factorization or discrete logarithm is difficult for an attacker?

I have read that difficulty in breaking many algorithms are based either on Factorization or discrete logarithm. I am reading about schemes that are similar to RSA which make use of integer ...
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80 views

LogSpace Merkle Traversal

I am studying LogSpace Merkle Tree Traversal algorithm in "Post Quantum Cryptography". I don't understand the Table 1 on page 58. My question is: Why within of the $2^h$ rounds for $NEED_h$ exist ...
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104 views

Password checking algorithm

I'm trying to reverse engineer a key exchange protocol which is based on the Diffie-Hellman key exchange scheme and faced with the following problem: Let $g$ be the generator, $m$ the modulus. Alice ...
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61 views

Conditions for proving that a signcryption scheme is secure

If I'm able to prove that any scheme satisfies confidentiality ad unforgeability conditions, will it be a valid signcryption scheme, without explicit signature and encryption parts ?
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235 views

Most frequently used digital signature schemes in the recent years

I am looking to understand if there are any hard figures on which digital signature schemes are most commonly in use today. I'm only really interested in what is employed recently (ie. last couple ...
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1answer
259 views

Collision attacks on digital signatures

After reading this document about MD5 collision attacks, I still don't understand how collisions can make digital signatures insecure. In the paper, the researchers created two files with the same ...
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2answers
183 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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2answers
110 views

Needed: signature over a collection of hashes

I'm looking for some kind of crypto-based data structure that will allow me to produce a signature over a set of hashes. Call this a SignedSetOfHashes. I want to be ...
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1answer
50 views

Breaking the Rabin Signature system with chosen message attack

I heard that we can break the Rabin Signature system using chosen-message attack. I can't find a message to ask for its signature in order to spoof my message M. Any suggestions?
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1answer
647 views

Is RSA with SHA1 broken?

I am using CryptSignMessage to sign a string/file. Is using RSASha1 insecure? I know Sha1 is broken as a hashing algorithm, but does that also mean that using it for signing with RSA is broken?
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263 views

Why do we need to compute message digest of a message first while signing it?

Why it is more efficient to compute a message digest of message and digitally sign it then, rather than sign the message directly?
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1answer
41 views

Why hash function are used in digital signatures? [duplicate]

In the lectures I see, hash functions are always used when we want to sign a document $d$. My question is why they are used in digital signatures? Maybe, because it is more easy and fast to calculate ...
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2answers
36 views

Is ssl_sign safe as it is using OPENSSL_PKCS1_PADDING

I've been hearing a lot of scare talk about PKCS1 padding attacks. Is PKCS1 v1.5 safe in signatures as it is practically transporting only message digest? I'm using it in one of my applications so i'...
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32 views

Aggregation signature and verification

I'm not even sure of the appropriate terminology to use to describe my problem so bear with me if the explanation is not exactly formal. Imagine I have a simple digital calculator, with a screen and ...
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1answer
69 views

Fast Forward Hash Signatures

As a follow up to the Q/A session: Small Quantum Signatures - Reality check needed I have implemented the discussed idea for a new short-quantum-safe signature system using fast-forwarding hash. It ...
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56 views

How can I prove I have a certain Facebook account by signature?

I would like to know how to prove I have certain Facebook account (or that I can login to that account).
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491 views

SSL / TLS digital signature exchange

If server is sending its digital signature, in which message / where does the digitally signature is provided to the client. Is it after the server_hello message because there the public key of the ...
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1answer
114 views

anonymous signature implementation and usage?

This is one of the question asked in my class. Implement a anonymous digital signature. So it means hiding signers information. i could not find any article in anonymous digital signing. Also another ...
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1answer
241 views

Is this EdDSA modification secure?

I am hoping to employ a signed set membership system which is valid iff each signer's contribution to the set is present. The system should allow for two or more mutually exclusive signed sets to be ...
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1answer
350 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. ...
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19 views

Digital signature with collision

Let's assume a digital signature scheme such that there's a probability of 0.2 for two random messages to have the same signature. How can I exploit this sheme? I'm having difficulties in finding an ...
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1answer
27 views

Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
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1answer
39 views

can session key be be used as digital signature?

if two communicating parties share a (symmetric) session key, k. When one of the party wants to send a message 'm' to other, is it okay use {m}k as a digital signature?
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79 views

Doubts about Authenticated Data Structures logic

I am studying the theory of authenticated data structure, like Merkle Tree and I have a doubt: why use them? I explain better: why to be sure, for example, that a cloud provider didn't modify my files ...
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1answer
75 views

Stern identification scheme to signature scheme

I'm trying to understand the comment in the page 103 of the book Postquantum Cryptography. about convert the identification Stern procedure for signing. Can you write an example of signature of this ...
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1answer
29 views

Reordering of multiple signed blocks

I would like to refer you to page 430 of the Handbook of Applied Crypto, where the authors said "... reordering of multiple signed blocks presents a security risk..." This statement was made in ...
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71 views

Weak Boneh-Boyen Signature in Composite order group

In the paper Ring Signatures of Sub-linear Size Without Random Oracles, authors have remarked that the scheme is instantiable in composite order setting, too. I am attaching the following reference ...
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1answer
50 views

Using Permutation polynomial to compute a MAC

Is the following MAC secure? For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$. Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is ...
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82 views

Asymmetric sign in public enviroment

I have RTS game, where all players run game and server just relays messages. Game can generate and store text file on player pc. I want to allow some players to be moderators, so I need to sign or ...
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60 views

what does rsaSha512Sign do?

I have the following function: ...
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1answer
82 views

Signature scheme doesn't seem to hold

I can't seem to verify the signature scheme described below. Key Generation Public Key: $$y_1=g^{a_1}y^{a_2} \pmod p$$ $$y_2=g^{b_1}y^{b_2} \pmod p$$ $g$ denotes a generator of $Z_p^*$ and $y$ ...
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1answer
75 views

Efficiently show/prove knowledge of third party secret without leaking information

Say Alice publishes (i.e. all parties in the universe) a key or certificate $x$ and sends a secret $s$ to Bob. Bob then publishes some data $d$ (his identity or a message or smt.) and an ...
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1answer
182 views

Proof for composed signatures

Assumes that we have 3 signature algorithms, $S^A$ with key pair $(sk^A,pk^A)$, $S^B$ with key pair $(sk^B,pk^B)$,$S^C$ with key pair $(sk^C,pk^C)$. We denote by $\epsilon$, $\epsilon'$ and $\epsilon''...
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243 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 ...
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31 views

check user signed in group signature

I have $N$ users, all of them creating a group digital signature. Also I have user $A$. How can I check if user a signed or not signet in this signature? Is it possible ? Are there other methods how I ...