Iso7816_4Padding Class

Definition

Namespace: Bodu.Security.Cryptography

Assembly: Bodu.Security.Cryptography.dll

Package: Bodu.Security.Cryptography 1.2.0

Source: Iso7816_4Padding.cs

Implements the ISO/IEC 7816-4 padding scheme (also known as "one-and-zeros" or bit padding). The first pad byte is 0x80 and remaining pad bytes are 0x00.

public sealed class Iso7816_4Padding : IPaddingStrategy

Inheritance: object

Iso7816_4Padding

Implements: IPaddingStrategy

Inherited Members: 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

using Bodu.Security.Cryptography;

IPaddingStrategy padding = new Iso7816_4Padding();
byte[] padded = padding.Pad(plaintext, blockSize: 128); // 128 bits = 16 bytes

// padded ends with 0x80 followed by zero or more 0x00 bytes.
byte[] recovered = padding.Unpad(padded, blockSize: 128);

Remarks

A full block of padding is always added when the input is already block-aligned so that Unpad(ReadOnlySpan<byte>, int) can unambiguously recover the original length by locating the terminator. The scheme is widely used in smart-card protocols, SHA-3/Keccak and CMAC. Unpad(ReadOnlySpan<byte>, int) validates in constant time over the final block to resist padding-oracle side channels.

When to choose ISO/IEC 7816-4. Pick this when interoperating with smart-card, EMV, or ISO crypto tooling - the 0x80/0x00 sentinel scheme is the standard there. It is also the padding used by the SHA-3 / Keccak family and by CMAC. For general-purpose .NET / Java / OpenSSL interop prefer Pkcs7Padding; for AEAD modes that handle their own alignment use NoPadding.

Constructors