Base45Utility

A small, dependency-free Base45 encoding and decoding utility for .NET, implementing draft-faltstrom-base45-03 (the encoding used, among others, by the EU Digital COVID Certificate).

Features

• Encode/decode between raw bytes and Base45 strings.
• String helpers that treat text as UTF-8.
• Strict decoding: rejects illegal characters, invalid lengths, and out-of-range groups.
• Allocation-friendly Span overloads on modern targets.
• Multi-targets netstandard2.0, net8.0, net9.0, and net10.0.

Installation

The package is published to GitHub Packages. Add the source once (replacing USERNAME and TOKEN with a GitHub username and a personal access token that has the read:packages scope):

dotnet nuget add source "https://nuget.pkg.github.com/iupsilon/index.json" \
  --name github-iupsilon --username USERNAME --password TOKEN --store-password-in-clear-text

Then reference it from your project:

dotnet add package Base45Utility

<PackageReference Include="Base45Utility" Version="1.6.0" />

Usage

Encoding

Base45 is a lightweight, stateless type; a single instance can be reused.

using Base45Utility;

var base45 = new Base45();

// From a string (encoded as UTF-8)
string encoded = base45.Encode("Hello world");        // "%69 VD82EK4F.KEA2"

// From raw bytes
byte[] bytes = System.Text.Encoding.UTF8.GetBytes("Hello world");
string encodedFromBytes = base45.Encode(bytes);       // same result

Decoding

var base45 = new Base45();
const string input = "%69 VD82EK4F.KEA2";

byte[] decodedBytes = base45.Decode(input);           // raw bytes
string decodedText  = base45.DecodeAsString(input);   // "Hello world" (UTF-8)

Span overloads (net8.0 and later)

For hot paths, zero/low-allocation overloads are available:

var base45 = new Base45();

// Encode directly from a span of bytes
ReadOnlySpan<byte> payload = stackalloc byte[] { 1, 2, 3 };
string encoded = base45.Encode(payload);

// Decode into a caller-provided buffer; returns the number of bytes written
Span<byte> destination = stackalloc byte[32];
int written = base45.Decode("%69 VD82EK4F.KEA2".AsSpan(), destination);

Behavior and error handling

• String overloads assume UTF-8 for both directions.
• Empty input round-trips to empty output.
• null input throws ArgumentNullException.
• Decode throws InvalidOperationException for an illegal character, an invalid length (a Base45 string length is always 3n or 3n+2), or a group that decodes to a value outside the valid byte/two-byte range.
• The Span decode overload throws ArgumentException if the destination buffer is too small.

License

Licensed under the Apache License, Version 2.0.