Key agreement protocols and key transport protocols are the crucial components f

Question

Key agreement protocols and key transport protocols are the crucial components for all secure communications. For example, a fundamental part of SSL- and IPSec-based VPN protocols is the key agreement protocol. After a secure shared key is established between the parties, the parties can use efficient symmetric key encryption schemes, such as AES, to exchange subsequent messages.

Having backfround information on various attacks on key agreement protocols such as replay attack, impersonation attack, key compromised impersonation (KCI) attack, unknown key share (UKS) attack, etc.

Question

- Assess the ability of adversaries to attack these key agreement protocols.

- Find one commonly used (or proposed) key agreement protocol for some practical applications, and analyse whether the attacks that we have discussed could be mounted against your chosen protocol.

Explanation / Answer

1. Key agreement protocols are a fundamental building block for ensuring

authenticated and private communications between two parties over an insecure

network.Despite being authenticated, there exists adversaries who intend to

corrupt the communication.One of them is Key Compromise Impersonation (KCI).

A KCI attack involves an adversary that has obtained the private key of an

honest party.The adversary's aim is to impersonate a different user and try

to establish a valid session key with the corrupted party. This attack represents

a serious threat since a user may not even be aware that his computer was

hijacked and that a malicious party has obtained his private key.

In the real world, a KCI attack is carried through as a man-in-the-middle attack.

2. The below protocols have been chosen keeping in mind the complexity and efficiency

of the recovery-

LLK Protocol

The session key is computed from the expression (rAwB + rBwA)P. Although the authors have

conjectured that a KCI attack against the protocol is unfeasible, the following proves

the opposite.

SSEB Protocol

The SSEB key agreement protocol is derived from the expression (rArB + wAwB)P. The conjectured

security attributes include KCI resilience.

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