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What are the requirements of a nonce? <- Typically it is only required that a nonce is unique, however, in certain cases harsher requirements (such as randomness and unpredictability) are put.

The OAuth 1.0a specification states that:

A nonce is a random string, uniquely generated by the client to allow the server to verify that a request has never been made before and helps prevent replay attacks when requests are made over a non-secure channel. The nonce value MUST be unique across all requests with the same timestamp, client credentials, and token combinations.

Why does OAuth 1.0a require randomness?

Also I find it surprising that the spec says 'random' without explicitly requiring cryptographically secure randomness. What could be the benefit of a random, but not cryptographically secure random nonce? I suppose I should understand that the requirement of cryptographically secure randomness is implied here?

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  • $\begingroup$ OAuth basically defines a framework on how authentication tokens can be established. It doesn't go deep into security whatsoever. The authentication framework is secure, but only if it gets configured properly. For OAuth 2 there is a separate RFC with security requirements, which is very much needed. Strangely enough, OAuth 1 does specify requirements for the secrets used. Non-secure random RNG's may not be seeded properly (which may not be such a big issue if the RNG is always started with a fresh tim-stamp) and they are fast, but I'd use a large nonce from a well seeded CSPRNG anyway. $\endgroup$
    – Maarten Bodewes
    Jan 10, 2022 at 16:45

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