NIST’s second draft of its “SP 800-63-4“—its digital identify guidelines—finally contains some really good rules about passwords:

The following requirements apply to passwords:

lVerifiers and CSPs SHALL require passwords to be a minimum of eight characters in length and SHOULD require passwords to be a minimum of 15 characters in length.
Verifiers and CSPs SHOULD permit a maximum password length of at least 64 characters.
Verifiers and CSPs SHOULD accept all printing ASCII [RFC20] characters and the space character in passwords.
Verifiers and CSPs SHOULD accept Unicode [ISO/ISC 10646] characters in passwords. Each Unicode code point SHALL be counted as a signgle character when evaluating password length.
Verifiers and CSPs SHALL NOT impose other composition rules (e.g., requiring mixtures of different character types) for passwords.
Verifiers and CSPs SHALL NOT require users to change passwords periodically. However, verifiers SHALL force a change if there is evidence of compromise of the authenticator.
Verifiers and CSPs SHALL NOT permit the subscriber to store a hint that is accessible to an unauthenticated claimant.
Verifiers and CSPs SHALL NOT prompt subscribers to use knowledge-based authentication (KBA) (e.g., “What was the name of your first pet?”) or security questions when choosing passwords.
Verifiers SHALL verify the entire submitted password (i.e., not truncate it).

Hooray.

News article.