Questions tagged [forgery]

Forgery is the process of making, adapting, or imitating objects, statistics, or documents with the intent to deceive.

43 questions
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Estimating the Security of SIS-Based Signature, by verifiying a subset of coordinates?

As I understood, the GPV signature scheme works as follows: KeyGen($1^n$) : Generate a Lattice with public $A \in Z_q^{n.m}$ and a secret trapdoor $t$. Sign $m$: compute $\vec y = H(m) \in Z_q^n$ ...
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Can randomness protect a list of signatures against forgery attacks?

Suppose we have a list of signatures $S = [s_1, .., s_n]$ for a list of messages $M = [m_1, .., m_n]$, and we want to verify that $S$ is a valid signature of $M$, so each $s_i$ should be valid for ...
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CBC MAC attack using Arbitrary-length Messages [duplicate]

This is from a lecture : The adversary sees the message-tag pair(m,τ), where m= (m1,m2,...,mn)The adversary sees the message-tag pair(m′,τ′), where m′= (m′1,m′2,...,m′n)The adversary computes m''=(m1,...
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Forging RSA1024 signature with e=3 where hash is right justified

I am trying to understand (in the frame of exponent 3) how to calculate a "forgery" in the case where the desired result is: xxxxxxxxxxx[...]xxxxxxxxxxxxxxxxxxxxHHHHHHHHHHH[...]HHHHHHHH where HH = a ...
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RSA Signature Forgery - Low Public Exponent + Improper Padding Validation? [duplicate]

Consider the following custom crypto: We have a signed message M1 with corresponding signature S. We have the 1024-bit modulus <...
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What is the difference between Forgery and Chosen-Message Attacks?

I did some researches about forgery attack and chosen-message attack. For me, forgery attacks are more focused on the verifiability whereas chosen-message attacks are similar to brute-force attacks. ...
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GMAC vs HMAC in message forgery and bandwidth

Saarinen in his work GCM, GHASH and Weak Keys says that; The GHASH algorithm belongs to a widely studied class of Wegman-Carter polynomial universal hashes. The security bounds known (this and ...
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What's wrong with this digital signature scheme?

With regards to user authentication... The server sends Alice a randomly chosen number. Alice signs the number and sends the signature back to the server. The server checks the signature using Alice'...
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What is the new attack on OCB2 and how does it work?

OCB2 is proposed by Rogaway, Efficient Instantiations of Tweakable Blockciphers and Refinements to Modes OCB and PMAC , and it is standardized in ISO/IEC 19772:2009. The author also provided a proof ...
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How difficult is it to practically detect a forgery in a cryptosystem?

If the encryption key that you use doesn't correspond to the decryption key used by the crypto system, it is assumed that it will not be possible to decrypt the message or you'll know that there has ...
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How can I resolve this basic MAC paradox I’m stumbling upon in my proof?

Suppose $S: K \times M \to T$ is a secure MAC. ($K$ = key space, $M$ = message space, $T = \{0,1\}^n$ = tag space.) $S$ being secure means that no matter what messages $m_1,...,m_q$ we throw at $S$ ...
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El Gamal existential forgery using Pointcheval–Stern signature algorithm

I found that there exists an algorithm that claims to make the El Gamal signature generation more secure. The algorithm can be found here as a pdf. I'm mainly interested in the two-parameter forgery ...
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How to forge signatures in the Schnorr scheme if $r=g^k$ is eliminated?

I need some help to demonstrate how to forge signatures in the Schnorr scheme if I eliminate the random string $r=g^k$ used in the hash – using $H(M)$ instead of $H(M||r)$. How would one be able to ...
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What is the probability of attacking SHA1 used in RSA signature with small exponent?

There is RSA signature check which has following properties: RSA modulus N which is 2048-bit RSA public exponent equal 41 (0x29) Genuine Signature uses EMSA-PKCS1-v1_5 padding of SHA1 hash, however ...
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In the Mac-forge experiment, the adversary is given access to a tag-generation oracle, which generates a tag for each message given by the adversary. The adversary's task is to generate a valid tag on ...
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Does key renewal increase complexity of MAC forgery?

Suppose I have encrypted messages sent to a device authenticated with a MAC keyed with a strong shared cryptographic key. This device can only process so many messages per unit of time. This ...
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Rogue CA Certificate MD5 Collision Control

Papers from Marc Stevens et al show that X509 certificates that rely on MD5 signatures can break the assumed security model, that is, it allows for a forged certificate to have the same signature as a ...
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How bad is it to use the identity function as hash for ECDSA?

I was recently asked whether a certain library supports the ECDSAwithNone Signature algorithm. Clearly this would mean ECDSA with the identity function as the hash function. I know this is a really ...
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Attacking RSA signature verification that ignores padding

I am looking at a RSA signature verification that is quite obviously flawed and am wondering if there's a way to exploit that flaw in practice. Signature is generated using RSA with PKCS 1.5 padding, ...
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Suppose I have a message $M$ for which I generate an RSA-2048 digital signature as follows: $H = H(M)$, $H(M)$ being the SHA-256 of the message $M$ $S = H^d \bmod N$ Assume $N = pq$ is properly ...
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Forgery attack on OCB

When using same nonce in OCB mode of authenticated encryption, how forgery attack can be done?
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How does hash function in Elgamal signature scheme prevent existential forgery attack?

I have heard that hashing the message M prevents an existential forgery attack. I was wondering how.
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Attacking unuauthenticated RSA

In symmetric cryptography, a scheme is not considered secure if the data transmitted is only encrypted. The adversary will be able to modify messages to generate encrypted messages of his choice ...
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Can you fake messages from recorded message-history?

Lets assume Eve has a lot of PGP conversation with Alice and records all those messages. Bob is also regularly communicating with PGP with Alice. If Bob doesn't care about not having a signature ...
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Why hash the message before signing it with RSA?

The diagram below illustrates the process of digitally signing a message with RSA: As diagram shows, the message is first hashed, and the signature is then computed on the hash, rather than on the ...
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Assume that we have a message $m$ of size $n$, and it is padded with two 01 bytes in front. Then the signature $s$ is computed using a private key $ks$. Can we ...
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Understanding the “cube-root math” behind an RSA signature forgery

I'm trying to understand the math outlined in this paper on a RSA signature forgery attack. I understand it except for one aspect of how the cube root (that makes the forged signature) is computed. ...
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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 ...