Asn1DecoderNet5 1.6.0

ASN1Decoder

This library aims to facilitate the parsing of ASN.1 data. It provides a data decoder and a set of methods for their parsing.

NuGet package

Decoding

The class Asn1DecoderNet5.Decoder is used for decoding DER data. Specifically, the static method Decode returns an Asn1DecoderNet5.Interfaces.ITag object.

ITag decodedDataStructure = Asn1DecoderNet5.Decoder.Decode(dataByteArray);

Working with the decoded data

Get a string representation

To obtain the string representation of the ASN.1 structure, you can utilize this extension method:

string result = decodedDataStructure.ToPrettyString(" | ", 128);

This method accepts two parameters. The first parameter is a string used to control the indentation of each element. The second parameter is the maximum length of a single line in the resulting string, not including the indentation.

The resulting string will appear as follows:

SEQUENCE
| OBJECT_IDENTIFIER 1.2.840.113549.1.7.2, signedData, PKCS #7
| [0]
|  | SEQUENCE
|  |  | INTEGER 1
|  |  | SET
...

Check if the data is X.509 v3 certificate

To check if the data is actual X.509 certificate use this extension method:

bool isCert = decodedDataStructure.IsCertificate();

Get items SubjectAlternativeName

To get items from the Subject Alternative Name (SAN), you can refer to the unit tests provided in the source code. The unit tests in the linked file will demonstrate how to use the library to extract and work with items from the SAN in ASN.1 data.

TL;DR:

[Fact]
public void Should_GetSan_GetsSanWithMailFromCert()
{
    var tag = Decoder.Decode(Sources.NormalCertificateWithEmailInSan);
    var ok = tag.TryGetSubjectAlternativeName(out var san);
    Assert.True(ok);
    Assert.NotEmpty(san);
    Tags.SAN.Rfc822Name email = null;
    foreach (var item in san)
    {
        if (item.ItemKind == Tags.SAN.SanItemKind.Rfc822Name)
        {
            email = (Tags.SAN.Rfc822Name)item;
            break;
        }
    }
    Assert.NotNull(email);
    Assert.Equal("kral@ica.cz", email.Content);
}