A.4 Central vs. Local Verification

While passwords that are used as a separate authentication factor are often centrally verified by the CSP’s verifier, those that are used as an activation factor for a multi-factor authenticator are either verified locally by the authenticator or used to derive the authenticator output, which will be incorrect if the wrong activation factor is used. Both of these situations are referred to as “local verification.”

The attack surfaces and vulnerabilities for central and local verification are very different. Accordingly, the requirements for centrally verified passwords differ from those verified locally. Centrally verified passwords require the verifier (i.e., an online resource) to store salted and iteratively hashed verification secrets for all of the subscribers’ passwords. Although the salting and hashing process increases the computational effort to determine the passwords from the hashes, the verifier is an attractive target for attackers, particularly those interested in compromising an arbitrary subscriber rather than a specific one.

Local verifiers do not have the same concerns with large-scale attacks on a central online verifier but depend on the physical security of the authenticator and the integrity of its associated endpoint. To the extent that the authenticator stores the activation factor, that factor must be protected against physical and side-channel (e.g., power and timing analysis) attacks on the authenticator. When the activation factor is entered through the associated endpoint, the endpoint needs to be free of malware (e.g., key-logging software). Since such threats are less dependent on the length and complexity of the password, these requirements are relaxed for local verification.

Online password-guessing attacks are a similar threat to centrally and locally verified passwords. Throttling is the primary defense against online attacks and can be particularly challenging for local verifiers because of the limited ability of some authenticators to securely store information about unsuccessful attempts. Throttling of local activation factors can be done in one of two ways. The authenticator itself could handle the throttling by keeping count of invalid activation attempts or, when activated incorrectly, the authenticator could produce an invalid authenticator output that will be rejected and throttled by the verifier.

1. Yleiskatsaus

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1.2 Tunnistetut vaatimukset

1.3 Liittyvät säädökset

2. Tunnistetut vaatimukset

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