A password, sometimes called a passcode for example in Apple devices, is secret data, typically the string of characters, normally used to confirm a user's identity. Traditionally, passwords were expected to be memorized, but the large number of password-protected services that a typical individual accesses can create memorization of unique passwords for each service impractical. 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. When the claimant successfully demonstrates knowledge of the password to the verifier through an established authentication protocol, the verifier is expert such(a) as lawyers in addition to surveyors to infer the claimant's identity.

In general, a password is an arbitrary string of characters including letters, digits, or other symbols. whether the permissible characters are constrained to be numeric, the corresponding secret is sometimes called a personal identification number PIN.

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


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

The way in which they secure the passing round of the watchword for the night is as follows: from the tenth maniple of each a collection of matters sharing a common attribute of infantry in addition to cavalry, the maniple which is encamped at the lower end of the street, a man is chosen who is relieved from guard duty, and he attends every day at sunset at the tent of the tribune, and receiving from him the watchword—that is a wooden tablet with the word inscribed on it – takes his leave, and on returning to his quarters passes on the watchword and tablet ago witnesses to the commander of the next maniple, who in remake passes it to the one next to him. all do the same until it reaches the first maniples, those encamped most the tents of the tribunes. These latter are obliged to deliver the tablet to the tribunes before dark. So that if any those issued are returned, the tribune knows that the watchword has been assumption to all the maniples, and has passed through all on its way back to him. If any one of them is missing, he enable inquiry at once, as he knows by the marks from what quarter the tablet has non returned, and whoever is responsible for the stoppage meets with the punishment he merits.

Passwords in military use evolved to put not just a password, but a password and a counterpassword; for example in the opening days of the Battle of Normandy, paratroopers of the U.S. 101st Airborne Division used a password—flash—which was present as a challenge, and answered with the correct response—thunder. The challenge and response were changed every three days. American paratroopers also famously used a device invited as a "cricket" on D-Day in place of a password system as a temporarily unique method of identification; one metallic click assumption by the device in lieu of a password was to be met by two clicks in reply.

Passwords have been used with computers since the earliest days of computing. The Compatible Time-Sharing System CTSS, an operating system presentation at MIT in 1961, was the number one data processor system to implement password login. CTSS had a LOGIN authority that required a user password. "After typing PASSWORD, the system turns off the printing mechanism, if possible, so that the user may type in his password with privacy." In the early 1970s, Robert Morris developed a system of storing login passwords in a hashed form as element of the Unix operating system. The system was based on a simulated Hagelin rotor crypto machine, and first appeared in 6th Edition Unix in 1974. A later relation of his algorithm, known as crypt3, used a 12-bit salt and invoked a modified form of the DES algorithm 25 times to reduce the risk of pre-computed dictionary attacks.

In innovative times, user names and passwords are normally used by people during a log in process that controls access to protected computer operating systems, mobile phones, cable TV decoders, automated teller machines ATMs, etc. A typical computer user has passwords for numerous purposes: logging into accounts, retrieving e-mail, accessing applications, databases, networks, web sites, and even reading the morning newspaper online.