Computer Science AS · Security, privacy and data integrity. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Data has integrity when it is accurate and has not been changed by mistake. Two processes protect it. Validation is an automatic check by the software that data is reasonable and follows the rules. Verification checks that data has been copied correctly from its source, at entry or during transfer.
Neither one proves the data is true. A wrong date of birth can still be a sensible date and pass every validation check.
During transfer, bits can flip. A parity bit is added to each byte so the number of 1s is even (even parity) or odd (odd parity). The receiver counts the 1s again. A checksum is a value calculated from the whole block and sent with it.
Do not mix up validation and verification. Validation asks whether the data is sensible; verification asks whether it matches the source. Neither one checks that the data is correct.
Answer: The check digit is 5, so the full code is 23515.
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