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Governance, Risk, Audit & Privacy · Intermediate

Check Digit

Extra digit calculated from other digits of a number to detect transcription and transposition errors.

Definition

Check digits, such as those produced by the Luhn algorithm for card numbers, are verified when data is entered. They are an input validation control.

Example

A credit card number's last digit is a Luhn check digit that detects most single-digit errors.

Exam tip

Check digits detect errors, not fraud; they are input controls.

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