In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information from plain text into code or cipher. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts are distinct in cryptography. In classical cryptography, ciphers were distinguished from codes. Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, “UQJHSE” could be the code for “Proceed to the following coordinates”. When using a cipher the original information is known as plaintext, and the encrypted form as ciphertext. The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it; it should resemble random gibberish to those not intended to read it.

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Vice is a practice or a behavior or habit considered immoral, depraved, or degrading in the associated society. In more minor usage, vice can refer to a fault, a defect, an infirmity, or merely a bad habit. Synonyms for vice include fault, depravity, sin, iniquity, wickedness, and corruption. The modern English term that best captures its original meaning is the word vicious, which means "full of vice". In this sense, the word vice comes from the Latin word vitium, meaning "failing or defect". Vice is the opposite of virtue.

Depending on the country or jurisdiction, vice crimes may or may not be treated as a separate category in the criminal codes. Even in jurisdictions where vice is not explicitly delineated in the legal code, the term vice is often used in law enforcement and judicial systems as an umbrella for crimes involving activities that are considered inherently immoral, regardless of the legality or objective harm involved.

In the United Kingdom, the term vice is commonly used in law and law enforcement to refer to criminal offenses related to prostitution and pornography. In the United States, the term is also used to refer to crimes related to gambling, alcohol, and drugs.