How do organisations get started with Challenge Handshake Authentication Protocol?

What CHAP Is Good For, and What It Is Not

CHAP is a challenge-response authentication method, so the first decision is whether an organisation actually needs a legacy protocol at all. It is usually only worth considering where older network or remote-access equipment still requires it, and even then it should be treated as a compatibility measure rather than a preferred control. For new designs, stronger authentication is the better default.

Because CHAP relies on older trust assumptions and is weaker than modern phishing-resistant or certificate-based approaches, it should never be the starting point for a new high-risk access path. If the business case is only “it is available,” that is a signal to choose a different method instead of trying to harden CHAP into a modern control.

How to Contain CHAP If You Must Use It

If CHAP is unavoidable, constrain it to low-risk, tightly controlled internal use cases. The practical objective is to reduce where the protocol can operate, limit which systems accept it, and keep it out of internet-facing or broadly reachable services. That makes the authentication weakness less dangerous because the protocol is exposed to fewer untrusted actors and fewer lateral movement opportunities.

Network segmentation matters because CHAP should be treated as a compatibility island, not a general authentication standard. Restrict it to trusted zones, isolate older devices or applications that depend on it, and avoid mixing it with broader enterprise access patterns where a single weak link can become a wider credential-reuse or replay problem.

The Network Ports and Protocols Security Guide is useful here because CHAP decisions often sit inside a wider protocol-hardening exercise, where legacy services and exposed ports should be reviewed together rather than one at a time.

Migration Plan and Control Checks for Legacy Authentication

Start by inventorying every place CHAP is still enabled, then decide whether each instance can be removed, replaced, or isolated. That review should include devices, remote-access paths, and any inherited configurations where the protocol may have survived simply because no one challenged it. The right outcome is usually retirement or replacement, not long-term acceptance.

As part of the migration path, choose a stronger alternative that matches the use case, such as modern federated authentication, MFA-backed access, or certificate-based methods where appropriate. The goal is to move away from shared legacy assumptions and toward controls that are easier to monitor, revoke, and defend against replay or credential theft.

For a broader control reference, NIST SP 800-63 Digital Identity Guidelines helps frame stronger authenticator choices, while the IANA registries are useful when you are checking protocol and identifier context during a legacy review.

Risk and Threat Considerations

CHAP’s main risk is not that it is impossible to deploy safely, but that it can become an accepted weak point in an otherwise stronger environment. Once it is allowed into trusted paths, it tends to linger, especially on internal systems that are hard to replace. That creates a target for attackers who look for older authentication boundaries, weak segmentation, and places where legacy access still reaches meaningful assets.

Failure mechanism: The protocol remains in use longer than intended, often behind the assumption that “internal only” is good enough. If an attacker gains foothold on the same network or compromises a dependent device, the weaker authentication path can become part of the attack chain.

Impact: The result can be unauthorized access, easier lateral movement, and a harder migration later because the organisation has built operational dependence around a legacy method that should have been retired sooner.

Practitioner Guidance

What to prioritise: Treat CHAP as a temporary exception that needs an owner, a retirement date, and a business justification. If nobody can explain why it still exists, the likely answer is that it should not.

What to verify: Confirm where CHAP is configured, what assets depend on it, and whether those paths are isolated from higher-value systems. If the protocol reaches production or remote-access services without strong segmentation, the risk is materially higher.

Decision rule: If CHAP is needed only for convenience, remove it; if it is needed for compatibility, restrict it to the smallest possible internal scope and move the affected systems onto a replacement plan.

Practitioner takeaway: The safe way to “start” with CHAP is usually to start the exit plan first, because legacy authentication is tolerable only when its scope is narrow, its exposure is controlled, and its replacement is already on the roadmap.

Related resources from NHI Mgmt Group

• How do organisations get started with Multifactor Authentication?
• What is an example of Challenge Handshake Authentication Protocol in practice?
• How do organisations get started with Authentication Tag?
• How do organisations get started with MAC Authentication Bypass?