How to achieve Base64 URL safe encoding in C#?

You can use class Base64UrlEncoder from namespace Microsoft.IdentityModel.Tokens.

const string StringToEncode = "He=llo+Wo/rld"; var encodedStr = Base64UrlEncoder.Encode(StringToEncode); var decodedStr = Base64UrlEncoder.Decode(encodedStr); if (decodedStr == StringToEncode) Console.WriteLine("It works!"); else Console.WriteLine("Dangit!"); 

Microsoft.IdentityModel.Tokens is a NuGet package that has to be downloaded.

Another option, if you are using ASP.NET Core, would be to use Microsoft.AspNetCore.WebUtilities.WebEncoders.Base64UrlEncode.

If you are not using ASP.NET Core, the WebEncoders source is available under the Apache 2.0 License.

Based off the answers here with some performance improvements, we've published a very easy to use url-safe base64 implementation to NuGet with the source code available on GitHub (MIT licensed).

Usage is as easy as

var bytes = Encoding.UTF8.GetBytes("Foo"); var encoded = UrlBase64.Encode(bytes); var decoded = UrlBase64.Decode(encoded); 

To get an URL-safe base64-like encoding, but not "base64url" according to RFC4648, use System.Web.HttpServerUtility.UrlTokenEncode(bytes) to encode, and System.Web.HttpServerUtility.UrlTokenDecode(bytes) to decode.

In .NET 9 you can do this without any extra packages using Base64Url:

ReadOnlySpan<byte> bytes = ...; string encoded = Base64Url.EncodeToString(bytes); 

Simplest solution: (with no padding)

private static string Base64UrlEncode(string input) { var inputBytes = System.Text.Encoding.UTF8.GetBytes(input); // Special "url-safe" base64 encode. return Convert.ToBase64String(inputBytes) .Replace('+', '-') // replace URL unsafe characters with safe ones .Replace('/', '_') // replace URL unsafe characters with safe ones .Replace("=", ""); // no padding } 

Credit goes to: Tholle

 public string Decode(string str) { byte[] decbuff = Convert.FromBase64String(str.Replace(",", "=").Replace("-", "+").Replace("/", "_")); return System.Text.Encoding.UTF8.GetString(decbuff); } public string Encode(string input) { byte[] encbuff = Encoding.UTF8.GetBytes(input ?? ""); return Convert.ToBase64String(encbuff).Replace("=", ",").Replace("+", "-").Replace("_", "/"); } 

This is the way to do it to align with JavaScript!

In .NET 9.0 there is the Base64Url class. It also supports spans.

Example:

using System.Buffers.Text; var base64UrlEncoded = Base64Url.EncodeToString(url); 

The Microsoft.Bcl.Memory package provides the Base64Url type for .NET Framework 4.6.2 and .NET Standard 2.0.

Here is another method to decode an url-safe base64 was encode by same way with Marc. I just don't get why 4-length%4 worked(it does).

As follows, only the origin's bit length are common multiple of 6 and 8, base64 do not append "=" to result.

1 2 3 4 5 6 7 8|1 2 3 4 5 6 7 8|1 2 3 4 5 6 7 8 1 2 3 4 5 6|1 2 3 4 5 6|1 2 3 4 5 6|1 2 3 4 5 6 "==" "=" 

So we can do it conversely, if result's bit length can't divisible by 8, it has been appended:

base64String = base64String.Replace("-", "+").Replace("_", "/"); var base64 = Encoding.ASCII.GetBytes(base64String); var padding = base64.Length * 3 % 4;//(base64.Length*6 % 8)/2 if (padding != 0) { base64String = base64String.PadRight(base64String.Length + padding, '='); } return Convert.FromBase64String(base64String); 

Karanvir Kang's answer is a good one and I voted for it. However, it does leave an odd character on the end of the string (indicating the number of padding characters removed). Here is my solution.

var bytesToEncode = System.Text.Encoding.UTF8.GetBytes("StringToEncode"); var bytesEncodedPadded = HttpServerUtility.UrlTokenEncode(bytesToEncode); var objectIdBase64 = bytesEncodedPadded.Substring(0, bytesEncodedPadded.Length - 1); 

Using Microsoft cryptographic engine in UWP.

uint length = 32; IBuffer buffer = CryptographicBuffer.GenerateRandom(length); string base64Str = CryptographicBuffer.EncodeToBase64String(buffer) // ensure url safe .TrimEnd('=').Replace('+', '-').Replace('/', '_'); return base64Str;