Verhoeff Class

Definition

Namespace

Bodu.IO.Hashing.CheckDigits

Assembly

Bodu.IO.Hashing.dll

Package

Bodu.IO.Hashing 1.0.0

Source

Verhoeff.Tables.cs

Computes the check digit of a decimal string using the Verhoeff algorithm. This class cannot be inherited.

public sealed class Verhoeff : CheckDigitAlgorithm

Inheritance

object

CheckValueAlgorithm

CheckDigitAlgorithm

Verhoeff

Inherited Members

CheckDigitAlgorithm.GetCurrentCheckValue()

CheckValueAlgorithm.Append(char)

CheckValueAlgorithm.CheckLength

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Extension Methods

ComparableExtensions.AtLeast<T>(T, T, IComparer<T>)

ComparableExtensions.AtMost<T>(T, T, IComparer<T>)

ComparableExtensions.IsEqualTo<T>(T, T, IComparer<T>)

ComparableExtensions.Max<T>(T, T, IComparer<T>)

ComparableExtensions.Min<T>(T, T, IComparer<T>)

Examples

// Single-call computation against an in-memory body.
char check = Verhoeff.Compute("236");   // '3'

// Full-sequence validation.
bool ok = Verhoeff.IsValid("2363");     // true

// Streaming use when the body is built up incrementally.
var algo = new Verhoeff();
algo.Append("236");
char d = algo.GetCurrentCheckDigit();   // '3'

Remarks

The Verhoeff algorithm, published by the Dutch mathematician Jacobus Verhoeff in 1969, was the first decimal-digit check-sum capable of detecting all single-digit substitution errors and all adjacent-digit transpositions. It achieves this by combining a position-dependent permutation with multiplication in the dihedral group D₅ , the group of symmetries of a regular pentagon.

In addition to single-digit and adjacent-transposition errors, Verhoeff also catches the common twin errors ( aa → bb) and a significant proportion of other mutation classes.

Worked example. For the body "236", the computed check digit is '3', and the resulting sequence "2363" is therefore valid under Verhoeff.

important

This algorithm is not cryptographically secure and should not be used for password hashing, digital signatures, or integrity validation in security-sensitive applications.

Constructors

Verhoeff()

Initializes a new instance of the Verhoeff class.

public Verhoeff()

Properties

AlgorithmName

Gets the canonical name of the algorithm, suitable for diagnostic output and logging.

public override string AlgorithmName { get; }

Property Value

string

A short, stable identifier such as "Luhn", "IBAN", or "ISO 7064 MOD 97-10".

Methods

Append(ReadOnlySpan<char>)

Absorbs the supplied characters into the running check-value state.

public override void Append(ReadOnlySpan<char> body)

Parameters

body ReadOnlySpan<char>

The characters to append. Each element must belong to the algorithm's accepted input alphabet. An empty span is a permitted no-op.

Exceptions

ArgumentOutOfRangeException

Thrown when body contains any character outside the algorithm's accepted input alphabet.

Compute(ReadOnlySpan<char>)

Computes the Verhoeff check digit for the supplied body of decimal digits without allocating a streaming instance.

public static char Compute(ReadOnlySpan<char> body)

Parameters

body ReadOnlySpan<char>

The body characters. Each must be an ASCII decimal digit ('0' to '9').

Returns

char

The check digit as an ASCII character in the range '0' to '9'.

Exceptions

ArgumentOutOfRangeException

Thrown when body contains any character outside the range '0' to '9'.

GetCurrentCheckDigit()

Returns the check digit computed for the body absorbed since the last Reset() (or since construction).

public override char GetCurrentCheckDigit()

Returns

char

The check digit as an ASCII character in the range '0' to '9'. For an empty body all built-in algorithms return '0'.

Remarks

This call is non-destructive; the running state is unaffected and the method may be invoked any number of times with identical results between appends.

IsValid(ReadOnlySpan<char>)

Determines whether the supplied sequence, comprising a body followed by a trailing Verhoeff check digit, is valid - that is, whether the final running value evaluates to zero.

public static bool IsValid(ReadOnlySpan<char> digitsIncludingCheck)

Parameters

digitsIncludingCheck ReadOnlySpan<char>

The complete sequence including the trailing check digit.

Returns

bool

true if the sequence evaluates as valid under Verhoeff; otherwise, false - including the case where digitsIncludingCheck is empty or contains a character outside the range '0' to '9'.

Reset()

Resets the algorithm to its initial state, discarding any characters previously absorbed.

public override void Reset()

Remarks

Equivalent in behavior to constructing a fresh instance of the same concrete type.

Applies to

Product	Versions
.NET	8, 10