Learn in the textbookUser Authentication (Knowledge-Based and Possession-Based)
DefinitionA password (パスワード) is a secret string only the user knows, paired with a user ID for knowledge-based authentication.
ExplanationThe kinds of information used to confirm identity are called authentication factors (認証要素), and there are three: knowledge, possession, and biometrics. A password falls under knowledge, and its weakness is that anyone who knows it is treated as the user. The main threats are eavesdropping (盗聴), which captures data in transit, and the brute-force attack (総当たり攻撃), which tries every possible string one after another.
AnalogyIt is like the password to a secret clubhouse: whoever says it is treated as a member, so it becomes useless the moment it leaks.
Memory hookpass + word: the word that lets you pass.