What is an existential forgery attack? Existential forgery is a weak message related forgery against a cryptographic digital signature scheme. Existential forgery defines the outcome of an attack, not the way how or how often

## What is an existential forgery attack?

Existential forgery is a weak message related forgery against a cryptographic digital signature scheme. Existential forgery defines the outcome of an attack, not the way how or how often the attacker can interact with the attacked signer while the attack is performed ( Forgery and [ 1]).

**What is the significance of existential forgery attack in RSA digital signature?**

Existential forgery: adversary can create a pair (message, signature), s.t. the signature of the message is valid. A signature scheme can not be perfectly secure; it can only be computationally secure. Given enough time and adversary can always forge Alice’s signature on any message.

### How do you prevent an existential forgery attack?

A usual method to prevent existential forgery attack is on-way hash function and message redundancy. In 2004, Chang and Chang proposed a new digital signature scheme. The scheme is without using one-way hash function and any redundancy padding, which is very interesting to many designers.

**What is key only attack?**

1. In the signature scheme, adversary knows only the public key of the signer and therefore she can only check the validity of signatures of the messages given to her. Learn more in: Provable Security for Public Key Cryptosystems: How to Prove that the Cryptosystem is Secure.

## What is chosen message attack?

A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts. The goal of the attack is to gain information that reduces the security of the encryption scheme.

**Can you forge digital signature?**

A signing algorithm that, given a message and a private key, produces a signature, which is encrypted by the private key itself (so the digital signature cannot be forged without access to the private key).

### Can RSA signature be forged?

Note that N is part of both the public and the private RSA key. If all these conditions are there, the attacker is able, without any knowledge of the private key, to forge a RSA signature for pretty much any message, and have it accepted by the verifier.

**Can you forge a digital signature?**

## What is chosen-message attack?

**How does a known plaintext attack work?**

Known plaintext attack is a scenario in which the attacker has access to pairs of known plaintexts and their corresponding ciphertexts. The goal is to guess the secret key (or a number of secret keys) or to develop an algorithm which would allow him to decrypt any further messages.