另一种写法：
private string Encode64( string Message) { char [] Base64Code = new char [] { ' 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 ' , ' + ' , ' / ' , ' = ' }; byte empty = ( byte ) 0 ; System.Collections.ArrayList byteMessage = new System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes (Message)); System.Text.StringBuilder outmessage; int messageLen = byteMessage.Count; int page = messageLen / 3 ; int use = 0 ; if ((use = messageLen % 3 ) > 0 ) { for ( int i = 0 ; i < 3 - use; i ++ ) byteMessage.Add(empty); page ++ ; } outmessage = new System.Text.StringBuilder(page * 4 ); for ( int i = 0 ; i < page; i ++ ) { byte [] instr = new byte [ 3 ]; instr[ 0 ] = ( byte )byteMessage[i * 3 ]; instr[ 1 ] = ( byte )byteMessage[i * 3 + 1 ]; instr[ 2 ] = ( byte )byteMessage[i * 3 + 2 ]; int [] outstr = new int [ 4 ]; outstr[ 0 ] = instr[ 0 ] >> 2 ; outstr[ 1 ] = ((instr[ 0 ] & 0x03 ) << 4 ) ^ (instr[ 1 ] >> 4 ); if ( ! instr[ 1 ].Equals(empty)) outstr[ 2 ] = ((instr[ 1 ] & 0x0f ) << 2 ) ^ (instr[ 2 ] >> 6 ); else outstr[ 2 ] = 64 ; if ( ! instr[ 2 ].Equals(empty)) outstr[ 3 ] = (instr[ 2 ] & 0x3f ); else outstr[ 3 ] = 64 ; outmessage.Append(Base64Code[outstr[ 0 ]]); outmessage.Append(Base64Code[outstr[ 1 ]]); outmessage.Append(Base64Code[outstr[ 2 ]]); outmessage.Append(Base64Code[outstr[ 3 ]]); } return outmessage.ToString(); } private string Decode64( string Message) { string Base64Code = " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/= " ; int page = Message.Length / 4 ; System.Collections.ArrayList outMessage = new System.Collections.ArrayList(page * 3 ); char []message = Message.ToCharArray(); for ( int i = 0 ; i < page; i ++ ) { byte []instr = new byte [ 4 ]; instr[ 0 ] = ( byte )Base64Code.IndexOf(message[i * 4 ]); instr[ 1 ] = ( byte )Base64Code.IndexOf(message[i * 4 + 1 ]); instr[ 2 ] = ( byte )Base64Code.IndexOf(message[i * 4 + 2 ]); instr[ 3 ] = ( byte )Base64Code.IndexOf(message[i * 4 + 3 ]); byte []outstr = new byte [ 3 ]; outstr[ 0 ] = ( byte )((instr[ 0 ] << 2 ) ^ ((instr[ 1 ] & 0x30 ) >> 4 )); if (instr[ 2 ] != 64 ) { outstr[ 1 ] = ( byte )((instr[ 1 ] << 4 ) ^ ((instr[ 2 ] & 0x3c ) >> 2 )); } else { outstr[ 2 ] = 0 ; } if (instr[ 3 ] != 64 ) { outstr[ 2 ] = ( byte )((instr[ 2 ] << 6 ) ^ instr[ 3 ]); } else { outstr[ 2 ] = 0 ; } outMessage.Add(outstr[ 0 ]); if (outstr[ 1 ] != 0 ) outMessage.Add(outstr[ 1 ]); if (outstr[ 2 ] != 0 ) outMessage.Add(outstr[ 2 ]); } byte []outbyte = ( byte [])outMessage.ToArray(Type.GetType( " System.Byte " )); return System.Text.Encoding.Default.GetString(outbyte); }转载于:https://www.cnblogs.com/tuyile006/archive/2008/01/17/1043207.html
相关资源：数据结构—成绩单生成器