Polybius describes the system for the distribution of watchwords in the Roman military as follows: Sentries would challenge those wishing to enter an area to supply a password or watchword, and would only allow a person or group to pass if they knew the password. Passwords have been used since ancient times.

7 Alternatives to passwords for authentication.

4.4.3 Hash-based challenge–response methods.

4.4.2 Transmission through encrypted channels.

4.4.1 Simple transmission of the password.

4.4 Methods of verifying a password over a network.

4.2 Limits on the number of password guesses.

4.1 Rate at which an attacker can try guessed passwords.

4 Factors in the security of a password system.

2 Choosing a secure and memorable password.

A passphrase is similar to a password in usage, but the former is generally longer for added security. A memorized secret consisting of a sequence of words or other text separated by spaces is sometimes called a passphrase.

If the permissible characters are constrained to be numeric, the corresponding secret is sometimes called a personal identification number (PIN).ĭespite its name, a password does not need to be an actual word indeed, a non-word (in the dictionary sense) may be harder to guess, which is a desirable property of passwords. In general, a password is an arbitrary string of characters including letters, digits, or other symbols. When the claimant successfully demonstrates knowledge of the password to the verifier through an established authentication protocol, the verifier is able to infer the claimant's identity.

Using the terminology of the NIST Digital Identity Guidelines, the secret is held by a party called the claimant while the party verifying the identity of the claimant is called the verifier.

Traditionally, passwords were expected to be memorized, but the large number of password-protected services that a typical individual accesses can make memorization of unique passwords for each service impractical. A password, sometimes called a passcode (for example in Apple devices), is secret data, typically a string of characters, usually used to confirm a user's identity.

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