在「NIST to forbid requirement of specific passwords character composition (mastodon.social)」這邊看到的消息，出自 Fediverse 上的「Lukasz Olejnik: "GREAT change is approaching. NIST will standardis…" - Mastodon」這則，在講密碼規則中不得要求「混合字元」，像是要求要有「至少一個大寫 + 一個小寫 + 一個特殊符號」這樣的條件被禁止了。
現行的 NIST Special Publication 800-63B 是在 2017 年發表的第三版：「NIST Special Publication 800-63B」，這個版本關於混合字元的說明是 SHOULD NOT：
Verifiers SHOULD NOT impose other composition rules (e.g., requiring mixtures of different character types or prohibiting consecutively repeated characters) for memorized secrets. Verifiers SHOULD NOT require memorized secrets to be changed arbitrarily (e.g., periodically). However, verifiers SHALL force a change if there is evidence of compromise of the authenticator.
這次第四版 draft (目前可以在「https://pages.nist.gov/800-63-4/sp800-63b.html」這邊看到) 則是改成 SHALL NOT：
Verifiers and CSPs SHALL NOT impose other composition rules (e.g., requiring mixtures of different character types) for passwords.
這邊的 SHOULD NOT 與 SHALL NOT 有定義在文件開頭，這邊的定義與 RFC 2119 類似：
The terms “SHALL” and “SHALL NOT” indicate requirements to be followed strictly in order to conform to the publication and from which no deviation is permitted.
The terms “SHOULD” and “SHOULD NOT” indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required, or that (in the negative form) a certain possibility or course of action is discouraged but not prohibited.
也就是說從建議變成強制性的要求了。
NIST SP 800-63B 算是重要的 reference，我記得前陣子有看到社群在蒐集整理密碼要求，要送到政府單位當作外部意見的，裡面也是引用了不少 NIST SP 800-63B 的內容，但一時間沒找到... (好像是放在 HackMD 上？)