Where does TimestampHashAlgorithmExtensions live in the IronPDF API?

TimestampHashAlgorithmExtensions is a class in the IronPdf.Signing namespace, shipped in IronPdf.dll. It extends the TimestampHashAlgorithms enum and derives from System.Object.

How do you get the OID string for a hash algorithm when signing a PDF in C#?

Call ToDigestAlgorithmOid on any TimestampHashAlgorithms enum value, for example TimestampHashAlgorithms.SHA256.ToDigestAlgorithmOid(). The method returns the dotted-decimal OID string that a timestamp authority requires in an RFC 3161 request.

Class TimestampHashAlgorithmExtensions

Helpers for TimestampHashAlgorithms.

Inheritance

System.Object

TimestampHashAlgorithmExtensions

Namespace: IronPdf.Signing

Assembly: IronPdf.dll

Syntax

public static class TimestampHashAlgorithmExtensions : Object

Converting a TimestampHashAlgorithms enum value into its corresponding OID string is the job TimestampHashAlgorithmExtensions handles. The single extension method it exposes, ToDigestAlgorithmOid, translates a hash algorithm selection into the dotted-decimal Object Identifier that RFC 3161 timestamp authorities expect when a PDF signature is being countersigned with a trusted timestamp.

When IronPDF applies a digital signature that includes a timestamp, the timestamp request must specify the digest algorithm as an OID rather than a human-readable name. ToDigestAlgorithmOid performs that translation cleanly, so calling code never has to hard-code strings like "2.16.840.1.101.3.4.2.1" for SHA-256. Instead, the algorithm is expressed as a TimestampHashAlgorithms enum value, and the extension method resolves the correct OID at the point of use.

Because ToDigestAlgorithmOid is a static extension method on TimestampHashAlgorithms, it reads as a natural call on the enum value itself:

using IronPdf.Signing;

string oid = TimestampHashAlgorithms.SHA256.ToDigestAlgorithmOid();
// oid now holds the OID string passed to the timestamp authority

This pattern keeps signing configuration readable and avoids magic strings scattered across a codebase. The class lives entirely in the IronPdf.Signing namespace alongside the signing and certificate types it supports, so no additional import is needed when working with PDF signature workflows.

For a broader look at PDF signing with timestamps, see the digital signature how-to and the PDF signing examples on the IronPDF site.

Methods

ToDigestAlgorithmOid(TimestampHashAlgorithms)

Returns the digest algorithm OID for the given timestamp hash algorithm. Unknown values default to SHA-1 (1.3.14.3.2.26). This is the single source of truth for the enum to OID mapping used by both the certificate based and HSM signing paths.

Declaration

public static string ToDigestAlgorithmOid(this TimestampHashAlgorithms algorithm)

Parameters

Type	Name	Description
TimestampHashAlgorithms	algorithm	The timestamp hash algorithm.

Returns

Type	Description
System.String	The digest algorithm OID string.