integrity-methods as

Validation & verification

What is validation?

• Validation is an automated process where a computer checks if a user input is sensible and meets the program’s requirements

• There are seven categories of validation which can be carried out on fields and data types, these are

  • Range check

  • Format check

  • Length check

  • Presence check

  • Existence check

  • Limit check

  • Check digit

• There can be occasions where more than one type of validation will be used on a field

• An example of this could be a password field which could have a length, presence and type check on it

What is verification?

• Verification is the act of checking data is accurate when being transferred or entered into a system

• Verification methods include:

  • Parity check (transfer)

  • Checksum (transfer)

  • Double entry checking (entry)

  • Visual checks (entry)

Validation methods

What is a check digit?

• A check digit is the last digit included in a code or sequence, used to detect errors in numeric data entry

• Examples of errors that a check digit can help to identify are:

  • Incorrect digits entered

  • Omitted or extra digits

  • Phonetic errors

• Added to the end of a numerical sequence they ensure validity of the data

• Calculated using standardised algorithms to ensure widespread compatibility

• Examples of where check digits can be used include:

  • ISBN book numbers

  • Barcodes

ISBN book numbers

• Each book has a unique ISBN number that identifies the book

• A standard ISBN number may be ten digits, for example, 965-448-765-9

• The check digit value is the final digit (9 in this example).

• This number is chosen specifically so that when the algorithm is completed the result is a whole number (an integer) with no remainder parts

• A check digit algorithm is performed on the ISBN number and if the result is a whole number, then the ISBN is valid

Barcodes

• Barcodes consist of black and white lines which can be scanned using barcode scanners

• Barcode scanners shine a laser on the black and white lines which reflect light into the scanner

• The scanner reads the distance between these lines as numbers and can identify the item

• Barcodes also use a set of digits to uniquely identify each item

• The final digit on a barcode is usually the check digit, this can be used to validate and authenticate an item

Verification methods

What is a parity check?

• A parity check determines whether bits in a transmission have been corrupted

• Every byte transmitted has one of its bits allocated as a parity bit

• The sender and receiver must agree before transmission whether they are using odd or even parity

• If odd parity is used then there must be an odd number of 1’s in the byte, including the parity bit

• If even parity is used then there must be an even number of 1’s in the byte, including the parity bit

• The value of the parity bit is determined by counting the number of 1’s in the byte, including the parity bit

• If the number of 1’s does not match the agreed parity then an error has occurred

• Parity checks only check that an error has occurred, they do not reveal where the error(s) occurred

Even parity

• Below is an arbitrary binary string

• If an even parity bit is used then all bits in the byte, including the parity bit, must add up to an even number

  • There are four 1’s in the byte

  • This means the parity bit must be 0 otherwise the whole byte, including the parity bit, would add up to five which is an odd number

Odd parity

• Below is an arbitrary binary string

• If an odd parity bit is used then all bits in the byte, including the parity bit, must add up to an odd number

  • There are four 1’s in the byte. This means the parity bit must be a 1 otherwise the whole byte, including the parity bit, would add up to four which is an even number

• The table below shows a number of examples of the agreed parity between a sender and receiver and the parity bit used for each byte