System.Formats.Asn1 (9.0.10)

Published 2026-02-04 09:32:15 +03:30 by kayer

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To install the package using NuGet, run the following command:

dotnet add package --source kayer --version 9.0.10 System.Formats.Asn1

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Provides classes that can read and write the ASN.1 BER, CER, and DER data formats.

About

Provides functionality for parsing, encoding, and decoding data using Abstract Syntax Notation One (ASN.1). ASN.1 is a standard interface description language for defining data structures that can be serialized and deserialized in a cross-platform way.

Key Features

Parse ASN.1 data into .NET types.
Encode .NET types into ASN.1 format.
Support for BER, CER, DER: Handles Basic Encoding Rules (BER), Canonical Encoding Rules (CER), and Distinguished Encoding Rules (DER).

How to Use

Parsing ASN.1 data:

using System.Formats.Asn1;
using System.Numerics;

// Sample ASN.1 encoded data (DER format)
byte[] asn1Data = [0x30, 0x09, 0x02, 0x01, 0x01, 0x02, 0x01, 0x02, 0x02, 0x01, 0x03];

// Create an AsnReader to parse the data
AsnReader reader = new(asn1Data, AsnEncodingRules.DER);

// Parse the sequence
AsnReader sequenceReader = reader.ReadSequence();

// Read integers from the sequence
BigInteger firstInt = sequenceReader.ReadInteger();
BigInteger secondInt = sequenceReader.ReadInteger();
BigInteger thirdInt = sequenceReader.ReadInteger();

Console.WriteLine($"First integer: {firstInt}");
Console.WriteLine($"Second integer: {secondInt}");
Console.WriteLine($"Third integer: {thirdInt}");

// First integer: 1
// Second integer: 2
// Third integer: 3

Decoding ASN.1 data using AsnDecoder:

using System.Formats.Asn1;
using System.Numerics;
using System.Text;

// Sample ASN.1 encoded data
byte[] booleanData = [0x01, 0x01, 0xFF]; // BOOLEAN TRUE
byte[] integerData = [0x02, 0x01, 0x05]; // INTEGER 5
byte[] octetStringData = [0x04, 0x03, 0x41, 0x42, 0x43]; // OCTET STRING "ABC"
byte[] objectIdentifierData = [0x06, 0x03, 0x2A, 0x03, 0x04]; // OBJECT IDENTIFIER 1.2.3.4
byte[] utf8StringData = [0x0C, 0x05, 0x48, 0x65, 0x6C, 0x6C, 0x6F]; // UTF8String "Hello"

int bytesConsumed;

bool booleanValue = AsnDecoder.ReadBoolean(booleanData, AsnEncodingRules.DER, out bytesConsumed);
Console.WriteLine($"Decoded BOOLEAN value: {booleanValue}, Bytes consumed: {bytesConsumed}");
// Decoded BOOLEAN value: True, Bytes consumed: 3

BigInteger integerValue = AsnDecoder.ReadInteger(integerData, AsnEncodingRules.DER, out bytesConsumed);
Console.WriteLine($"Decoded INTEGER value: {integerValue}, Bytes consumed: {bytesConsumed}");
// Decoded INTEGER value: 5, Bytes consumed: 3

byte[] octetStringValue = AsnDecoder.ReadOctetString(octetStringData, AsnEncodingRules.DER, out bytesConsumed);
Console.WriteLine($"Decoded OCTET STRING value: {Encoding.ASCII.GetString(octetStringValue)}, Bytes consumed: {bytesConsumed}");
// Decoded OCTET STRING value: ABC, Bytes consumed: 5

string objectIdentifierValue = AsnDecoder.ReadObjectIdentifier(objectIdentifierData, AsnEncodingRules.DER, out bytesConsumed);
Console.WriteLine($"Decoded OBJECT IDENTIFIER value: {objectIdentifierValue}, Bytes consumed: {bytesConsumed}");
// Decoded OBJECT IDENTIFIER value: 1.2.3.4, Bytes consumed: 5

string utf8StringValue = AsnDecoder.ReadCharacterString(utf8StringData, AsnEncodingRules.DER, UniversalTagNumber.UTF8String, out bytesConsumed);
Console.WriteLine($"Decoded UTF8String value: {utf8StringValue}, Bytes consumed: {bytesConsumed}");
// Decoded UTF8String value: Hello, Bytes consumed: 7

Encoding ASN.1 data:

// Create an AsnWriter to encode data
AsnWriter writer = new(AsnEncodingRules.DER);

// Create a scope for the sequence
using (AsnWriter.Scope scope = writer.PushSequence())
{
    // Write integers to the sequence
    writer.WriteInteger(1);
    writer.WriteInteger(2);
    writer.WriteInteger(3);
}

// Get the encoded data
byte[] encodedData = writer.Encode();

Console.WriteLine($"Encoded ASN.1 Data: {BitConverter.ToString(encodedData)}");

// Encoded ASN.1 Data: 30-09-02-01-01-02-01-02-02-01-03

Main Types

The main types provided by this library are:

System.Formats.Asn1.AsnReader
System.Formats.Asn1.AsnWriter
System.Formats.Asn1.AsnDecoder
System.Formats.Asn1.AsnEncodingRules

Additional Documentation

Feedback & Contributing

System.Formats.Asn1 is released as open source under the MIT license. Bug reports and contributions are welcome at the GitHub repository.

https://go.microsoft.com/fwlink/?LinkID=799421

ID	Version	Target Framework
System.Buffers	4.5.1	.NETFramework4.6.2
System.Memory	4.5.5	.NETFramework4.6.2
System.ValueTuple	4.5.0	.NETFramework4.6.2
System.Buffers	4.5.1	.NETStandard2.0
System.Memory	4.5.5	.NETStandard2.0

Details

NuGet

2026-02-04 09:32:15 +03:30

123

Microsoft

Project website

Repository website

292 KiB

Assets (2)

system.formats.asn1.9.0.10.nupkg 290 KiB

system.formats.asn1.nuspec 1.7 KiB

Versions (4) View all

9.0.1

2026-02-20

9.0.0

2026-02-20

9.0.10

2026-02-04

5.0.0