How do I encode and decode a base64 string?

Question

How do I return a base64 encoded string given a string?
How do I decode a base64 encoded string into a string?

If this is a "sharing the knowledge" question and answer, I think we're looking for something a bit more in-depth. Also a quick search of SO turns up: http://stackoverflow.com/a/7368168/419 — Kev, Aug 01 '12 at 01:46
Ask yourself do you really need to do this? Remember base64 is primarily intended for representing binary data in ASCII, for storing in a char field in a database or sending via email (where new lines could be injected). Do you really want to take character data, convert it to bytes, then convert it back to character data, this time unreadable and with no hint of what the original encoding was ? — bbsimonbb, Apr 14 '16 at 08:22
Why should we care about the original encoding? We encode the string into the bytes using UTF8 representation, which can represent all the possible string characters. We then serialize that data and on the other end we deserialize that data and we reconstruct the same string that we originally had (string object doesn't hold the information about encoding used anyway). So why is there any concern related to the encoding used? We can consider it like a proprietary way of representing the serialized data, which we shouldn't be interested at anyway. — Mladen B., Mar 12 '19 at 11:08

score 2319 · Accepted Answer · edited Feb 17 '23 at 01:31

2319

Encode

public static string Base64Encode(string plainText) 
{
  var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
  return System.Convert.ToBase64String(plainTextBytes);
}

Decode

public static string Base64Decode(string base64EncodedData) 
{
  var base64EncodedBytes = System.Convert.FromBase64String(base64EncodedData);
  return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
}

edited Feb 17 '23 at 01:31

John Smith

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answered Jul 31 '12 at 15:06

Kevin Driedger

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Null checks for input strings in both functions and the solution is perfect :) – Sverrir Sigmundarson Mar 29 '14 at 23:05
31

@SverrirSigmundarson: That or make them extension methods. – T.J. Crowder Dec 30 '14 at 12:38
89

@SverrirSigmundarson - Why do a null check? He's not the one dereferencing the input string. Null checks should prevent `NullReferenceException` in your own code, not somebody else's. – qxn Feb 02 '15 at 18:44
2

Alternate suggestion: Contracts (`Contract.Requires(plainText != null)`) and your code is perfect :) – Clément Jul 08 '15 at 07:11
18

@ken And somebody else will say "you should only expose errors in your own code, not somebody else's", invoking the principle of least surprise, spiced with "fail early" and "proper encapsulation". Sometimes this means wrapping errors of lower-level components, sometimes something else entirely. In this case, I'll agree that wrapping a deref error is definitely dubious (plus we're all slowly agreeing to the fact that null as a concept is a bit of a hack to begin with), but we can still see some effects otherwise: the parameter name given in the exception might not be correct if left unchecked. – tne Aug 19 '15 at 08:57
7

return System.Text.Encoding.UTF8.GetString(base64EncodedBytes, 0, base64EncodedBytes.Length); for windows phone 8 – steveen zoleko Dec 09 '15 at 17:26
1

All of you are wrong; examples should be simple and this isn't cs101. – Ed S. Oct 06 '22 at 01:03

score 165 · Answer 2 · answered Aug 03 '20 at 23:13

165

One liner code:

Note: Use System and System.Text directives.

Encode:

string encodedStr = Convert.ToBase64String(Encoding.UTF8.GetBytes("inputStr"));

Decode:

string inputStr = Encoding.UTF8.GetString(Convert.FromBase64String(encodedStr));

answered Aug 03 '20 at 23:13

Zeigeist

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Thanks for remembering to include mention of the namespaces - people always just assume that – stimms Feb 04 '21 at 22:07
3

@stimms any serious IDE will provide these to you though ;) – derHugo Apr 30 '21 at 14:46
3

@derHugo if the namespace located in an assembly which is not referenced by default, then even a serious IDE can't help :) – RAPTOR May 06 '21 at 08:51
3

@RAPTOR well in this case also adding the `using` statements wouldn't help much ;) – derHugo May 06 '21 at 11:48
3

@derHugo that's true of course, but if we know the namespace we can guess the assembly name. (at least it helped me several times) – RAPTOR May 06 '21 at 12:32
@RAPTOR VS does that too – Ed S. Oct 06 '22 at 01:08
and this is System; what are we talking about? – Ed S. Oct 06 '22 at 01:09

score 61 · Answer 3 · answered Mar 17 '16 at 20:46

I'm sharing my implementation with some neat features:

uses Extension Methods for Encoding class. Rationale is that someone may need to support different types of encodings (not only UTF8).
Another improvement is failing gracefully with null result for null entry - it's very useful in real life scenarios and supports equivalence for X=decode(encode(X)).

Remark: Remember that to use Extension Method you have to (!) import the namespace with using keyword (in this case using MyApplication.Helpers.Encoding).

Code:

namespace MyApplication.Helpers.Encoding
{
    public static class EncodingForBase64
    {
        public static string EncodeBase64(this System.Text.Encoding encoding, string text)
        {
            if (text == null)
            {
                return null;
            }

            byte[] textAsBytes = encoding.GetBytes(text);
            return System.Convert.ToBase64String(textAsBytes);
        }

        public static string DecodeBase64(this System.Text.Encoding encoding, string encodedText)
        {
            if (encodedText == null)
            {
                return null;
            }

            byte[] textAsBytes = System.Convert.FromBase64String(encodedText);
            return encoding.GetString(textAsBytes);
        }
    }
}

Usage example:

using MyApplication.Helpers.Encoding; // !!!

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Test1();
            Test2();
        }

        static void Test1()
        {
            string textEncoded = System.Text.Encoding.UTF8.EncodeBase64("test1...");
            System.Diagnostics.Debug.Assert(textEncoded == "dGVzdDEuLi4=");

            string textDecoded = System.Text.Encoding.UTF8.DecodeBase64(textEncoded);
            System.Diagnostics.Debug.Assert(textDecoded == "test1...");
        }

        static void Test2()
        {
            string textEncoded = System.Text.Encoding.UTF8.EncodeBase64(null);
            System.Diagnostics.Debug.Assert(textEncoded == null);

            string textDecoded = System.Text.Encoding.UTF8.DecodeBase64(textEncoded);
            System.Diagnostics.Debug.Assert(textDecoded == null);
        }
    }
}

Returning `null` in case of `null` is a very inconsistent behaviour. No other .net API that works with strings does that. — t3chb0t, Jun 22 '18 at 06:10
@t3chb0t feel free to adjust it to your needs. As the way it's presented here was adjusted to ours. This is not a public API ;) — andrew.fox, Jun 22 '18 at 09:35

score 49 · Answer 4 · edited Jun 19 '18 at 09:56

Based on the answers by Andrew Fox and Cebe, I turned it around and made them string extensions instead of Base64String extensions.

public static class StringExtensions
{
    public static string ToBase64(this string text)
    {
        return ToBase64(text, Encoding.UTF8);
    }

    public static string ToBase64(this string text, Encoding encoding)
    {
        if (string.IsNullOrEmpty(text))
        {
            return text;
        }

        byte[] textAsBytes = encoding.GetBytes(text);
        return Convert.ToBase64String(textAsBytes);
    }

    public static bool TryParseBase64(this string text, out string decodedText)
    {
        return TryParseBase64(text, Encoding.UTF8, out decodedText);
    }

    public static bool TryParseBase64(this string text, Encoding encoding, out string decodedText)
    {
        if (string.IsNullOrEmpty(text))
        {
            decodedText = text;
            return false;
        }

        try
        {
            byte[] textAsBytes = Convert.FromBase64String(text);
            decodedText = encoding.GetString(textAsBytes);
            return true;
        }
        catch (Exception)
        {
            decodedText = null;
            return false;
        }
    }
}

I would add a ParseBase64(this string text, Encoding encoding, out string decodedText) (to populate the exception if needed, and call that on the TryParseBase64 — João Antunes, Sep 19 '19 at 09:19

score 25 · Answer 5 · answered Apr 13 '16 at 08:05

A slight variation on andrew.fox answer, as the string to decode might not be a correct base64 encoded string:

using System;

namespace Service.Support
{
    public static class Base64
    {
        public static string ToBase64(this System.Text.Encoding encoding, string text)
        {
            if (text == null)
            {
                return null;
            }

            byte[] textAsBytes = encoding.GetBytes(text);
            return Convert.ToBase64String(textAsBytes);
        }

        public static bool TryParseBase64(this System.Text.Encoding encoding, string encodedText, out string decodedText)
        {
            if (encodedText == null)
            {
                decodedText = null;
                return false;
            }

            try
            {
                byte[] textAsBytes = Convert.FromBase64String(encodedText);
                decodedText = encoding.GetString(textAsBytes);
                return true;
            }
            catch (Exception)
            {
                decodedText = null;
                return false;   
            }
        }
    }
}

juliushuck · Answer 6 · 2020-03-24T16:33:03.360

15

URL safe Base64 Encoding/Decoding

public static class Base64Url
{
    public static string Encode(string text)
    {
        return Convert.ToBase64String(Encoding.UTF8.GetBytes(text)).TrimEnd('=').Replace('+', '-')
            .Replace('/', '_');
    }

    public static string Decode(string text)
    {
        text = text.Replace('_', '/').Replace('-', '+');
        switch (text.Length % 4)
        {
            case 2:
                text += "==";
                break;
            case 3:
                text += "=";
                break;
        }
        return Encoding.UTF8.GetString(Convert.FromBase64String(text));
    }
}

edited Mar 24 '20 at 16:33

answered Mar 18 '20 at 11:27

juliushuck

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Note that using `Replace()` and `TrimEnd()` several times in a row will allocate new strings that will instantly become garbage for the GC. Instead, you can use `StringBuilder` with a specified capacity to avoid the extra heap allocations. – Lucas Nov 23 '21 at 01:14

score 14 · Answer 7 · edited Feb 19 '20 at 15:04

14

You can use below routine to convert string to base64 format

public static string ToBase64(string s)
{
    byte[] buffer = System.Text.Encoding.Unicode.GetBytes(s);
    return System.Convert.ToBase64String(buffer);
}

Also you can use very good online tool OnlineUtility.in to encode string in base64 format

edited Feb 19 '20 at 15:04

Daniel

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answered Jul 31 '19 at 14:40

chetan chaphekar

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Online tools don't help in this situation -- He's asking how to CODE IT. I often wonder why people say "Check out this online tool!", because the OP didn't ask for an online tool :D – Momoro Oct 29 '19 at 03:19

score 11 · Answer 8 · edited Jun 24 '21 at 08:53

11

// Encoding
string passw = "tes123";
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(passw);
string pass = System.Convert.ToBase64String(plainTextBytes);

// Normal
var encodedTextBytes = Convert.FromBase64String(pass);
string plainText = Encoding.UTF8.GetString(encodedTextBytes);

edited Jun 24 '21 at 08:53

Josef

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answered Jun 24 '21 at 06:55

Ghazi Hur

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Sameera R. · Answer 9 · 2019-06-05T04:18:55.837

    using System;
    using System.Text;

    public static class Base64Conversions
    {
        public static string EncodeBase64(this string text, Encoding encoding = null)
        { 
            if (text == null) return null;

            encoding = encoding ?? Encoding.UTF8;
            var bytes = encoding.GetBytes(text);
            return Convert.ToBase64String(bytes);
        }

        public static string DecodeBase64(this string encodedText, Encoding encoding = null)
        {
            if (encodedText == null) return null;

            encoding = encoding ?? Encoding.UTF8;
            var bytes = Convert.FromBase64String(encodedText);
            return encoding.GetString(bytes);
        }
    }

Usage

    var text = "Sample Text";
    var base64 = text.EncodeBase64();
    base64 = text.EncodeBase64(Encoding.UTF8); //or with Encoding

score 4 · Answer 10 · answered Jun 22 '19 at 00:19

For those that simply want to encode/decode individual base64 digits:

public static int DecodeBase64Digit(char digit, string digit62 = "+-.~", string digit63 = "/_,")
{
    if (digit >= 'A' && digit <= 'Z') return digit - 'A';
    if (digit >= 'a' && digit <= 'z') return digit + (26 - 'a');
    if (digit >= '0' && digit <= '9') return digit + (52 - '0');
    if (digit62.IndexOf(digit) > -1)  return 62;
    if (digit63.IndexOf(digit) > -1)  return 63;
    return -1;
}

public static char EncodeBase64Digit(int digit, char digit62 = '+', char digit63 = '/')
{
    digit &= 63;
    if (digit < 52)
        return (char)(digit < 26 ? digit + 'A' : digit + ('a' - 26));
    else if (digit < 62)
        return (char)(digit + ('0' - 52));
    else
        return digit == 62 ? digit62 : digit63;
}

There are various versions of Base64 that disagree about what to use for digits 62 and 63, so DecodeBase64Digit can tolerate several of these.

Momoro · Answer 11 · 2019-10-17T09:02:11.227

You can display it like this:

var strOriginal = richTextBox1.Text;

byte[] byt = System.Text.Encoding.ASCII.GetBytes(strOriginal);

// convert the byte array to a Base64 string
string strModified = Convert.ToBase64String(byt);

richTextBox1.Text = "" + strModified;

Now, converting it back.

var base64EncodedBytes = System.Convert.FromBase64String(richTextBox1.Text);

richTextBox1.Text = "" + System.Text.Encoding.ASCII.GetString(base64EncodedBytes);
MessageBox.Show("Done Converting! (ASCII from base64)");

I hope this helps!

score 1 · Answer 12 · answered Feb 01 '23 at 12:18

To encode a string into a base64 string in C#, you can use the Convert.ToBase64String method:

string originalString = "Hello World";
string encodedString = Convert.ToBase64String(Encoding.UTF8.GetBytes(originalString));

To decode a base64 encoded string into a string in C#, you can use the Convert.FromBase64String method:

string encodedString = "SGVsbG8gV29ybGQ=";
string originalString = Encoding.UTF8.GetString(Convert.FromBase64String(encodedString));

How do I encode and decode a base64 string?

12 Answers12

Encode

Decode

Linked

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