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Base64 Encoder/Decoder in C#

, 19 Nov 2003
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An implementation of Base64 encoding/decoding in C#

Introduction

The code implements the encoding and decoding mechanism of Base64, which is widely used in e-Mail encoding and also .NET Viewstate encoding.

Background

It is written based on RFC 1341, using VS.NET 2003.

Notes

I didn't implement filtering and inserting carriage return and newline etc.

Code Listing

Encoder source

using System;

namespace TestBase64
{
  /// <summary>
  /// Summary description for Base64Encoder.
  /// </summary>
  public class Base64Encoder
  {
    byte[] source;
    int length,length2;
    int blockCount;
    int paddingCount;
    public Base64Encoder(byte[] input)
    {
      source=input;
      length=input.Length;
      if((length % 3)==0)
      {
        paddingCount=0;
        blockCount=length/3;
      }
      else
      {
        paddingCount=3-(length % 3);//need to add padding
        blockCount=(length+paddingCount) / 3;
      }
      length2=length+paddingCount;//or blockCount *3
    }

    public char[] GetEncoded()
    {
      byte[] source2;
      source2=new byte[length2];
      //copy data over insert padding
      for (int x=0; x<length2;x++)
      {
        if (x<length)
        {
          source2[x]=source[x];
        }
        else
        {
          source2[x]=0;
        }
      }
      
      byte b1, b2, b3;
      byte temp, temp1, temp2, temp3, temp4;
      byte[] buffer=new byte[blockCount*4];
      char[] result=new char[blockCount*4];
      for (int x=0;x<blockCount;x++)
      {
        b1=source2[x*3];
        b2=source2[x*3+1];
        b3=source2[x*3+2];

        temp1=(byte)((b1 & 252)>>2);//first

        temp=(byte)((b1 & 3)<<4);
        temp2=(byte)((b2 & 240)>>4);
        temp2+=temp; //second

        temp=(byte)((b2 & 15)<<2);
        temp3=(byte)((b3 & 192)>>6);
        temp3+=temp; //third

        temp4=(byte)(b3 & 63); //fourth

        buffer[x*4]=temp1;
        buffer[x*4+1]=temp2;
        buffer[x*4+2]=temp3;
        buffer[x*4+3]=temp4;

      }

      for (int x=0; x<blockCount*4;x++)
      {
        result[x]=sixbit2char(buffer[x]);
      }

      //covert last "A"s to "=", based on paddingCount
      switch (paddingCount)
      {
        case 0:break;
        case 1:result[blockCount*4-1]='=';break;
        case 2:result[blockCount*4-1]='=';
          result[blockCount*4-2]='=';
          break;
        default:break;
      }
      return result;
    }

    private char sixbit2char(byte b)
    {
      char[] lookupTable=new char[64]
          {  'A','B','C','D','E','F','G','H','I','J','K','L','M',
            'N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
            'a','b','c','d','e','f','g','h','i','j','k','l','m',
            'n','o','p','q','r','s','t','u','v','w','x','y','z',
            '0','1','2','3','4','5','6','7','8','9','+','/'};

      if((b>=0) &&(b<=63))
      {
        return lookupTable[(int)b];
      }
      else
      {
        //should not happen;
        return ' ';
      }
    }
  }
}

Decoder source

using System;

namespace TestBase64
{
  /// <summary>
  /// Summary description for Base64Decoder.
  /// </summary>
  public class Base64Decoder
  {
    char[] source;
    int length, length2, length3;
    int blockCount;
    int paddingCount;
    public Base64Decoder(char[] input)
    {
      int temp=0;
      source=input;
      length=input.Length;

      //find how many padding are there
      for (int x=0;x<2;x++)
      {
        if(input[length-x-1]=='=')
          temp++;
      }
      paddingCount=temp;
      //calculate the blockCount;
      //assuming all whitespace and carriage returns/newline were removed.
      blockCount=length/4;
      length2=blockCount*3;
    }

    public byte[] GetDecoded()
    {
      byte[] buffer=new byte[length];//first conversion result
      byte[] buffer2=new byte[length2];//decoded array with padding

      for(int x=0;x<length;x++)
      {
        buffer[x]=char2sixbit(source[x]);
      }

      byte b, b1,b2,b3;
      byte temp1, temp2, temp3, temp4;

      for(int x=0;x<blockCount;x++)
      {
        temp1=buffer[x*4];
        temp2=buffer[x*4+1];
        temp3=buffer[x*4+2];
        temp4=buffer[x*4+3];        

        b=(byte)(temp1<<2);
        b1=(byte)((temp2 & 48)>>4);
        b1+=b;

        b=(byte)((temp2 & 15)<<4);
        b2=(byte)((temp3 & 60)>>2);
        b2+=b;

        b=(byte)((temp3 & 3)<<6);
        b3=temp4;
        b3+=b;

        buffer2[x*3]=b1;
        buffer2[x*3+1]=b2;
        buffer2[x*3+2]=b3;
      }
      //remove paddings
      length3=length2-paddingCount;
      byte[] result=new byte[length3];

      for(int x=0;x<length3;x++)
      {
        result[x]=buffer2[x];
      }

      return result;
    }

    private byte char2sixbit(char c)
    {
      char[] lookupTable=new char[64]
          {  

    'A','B','C','D','E','F','G','H','I','J','K','L','M','N',
    'O','P','Q','R','S','T','U','V','W','X','Y', 'Z',
    'a','b','c','d','e','f','g','h','i','j','k','l','m','n',
    'o','p','q','r','s','t','u','v','w','x','y','z',
    '0','1','2','3','4','5','6','7','8','9','+','/'};
      if(c=='=')
        return 0;
      else
      {
        for (int x=0;x<64;x++)
        {
          if (lookupTable[x]==c)
            return (byte)x;
        }
        //should not reach here
        return 0;
      }

    }

  }
}

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

wchvic
Web Developer
Canada Canada
No Biography provided

Comments and Discussions

 
QuestionYou are a livesaver Thank you Pinmemberdl4gbe16-Oct-12 10:13 

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