Base64 Encode/Decode Functions for ASP

Category:

ASP, HTML and XML

Type:

Snippets

Difficulty:

Intermediate

Author:

Markus Hartsmar

Version Compatibility: ASP

More information:

See comments for more detail.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
' (None)

Code:

' Functions to provide encoding/decoding of strings with Base64.
' 
' Encoding: myEncodedString = base64_encode( inputString )
' Decoding: myDecodedString = base64_decode( encodedInputString )
'
' Programmed by Markus Hartsmar for ShameDesigns in 2002. 
' Email me at: mark@shamedesigns.com
' Visit our website at: http://www.shamedesigns.com/
'

Dim Base64Chars
	Base64Chars =	"ABCDEFGHIJKLMNOPQRSTUVWXYZ" & _
			"abcdefghijklmnopqrstuvwxyz" & _
			"0123456789" & _
			"+/"

' Functions for encoding string to Base64
	Public Function base64_encode( byVal strIn )
		Dim c1, c2, c3, w1, w2, w3, w4, n, strOut
		For n = 1 To Len( strIn ) Step 3
			c1 = Asc( Mid( strIn, n, 1 ) )
			c2 = Asc( Mid( strIn, n + 1, 1 ) + Chr(0) )
			c3 = Asc( Mid( strIn, n + 2, 1 ) + Chr(0) )
			w1 = Int( c1 / 4 ) : w2 = ( c1 And 3 ) * 16 + Int( c2 / 16 )
			If Len( strIn ) >= n + 1 Then 
				w3 = ( c2 And 15 ) * 4 + Int( c3 / 64 ) 
			Else 
				w3 = -1
			End If
			If Len( strIn ) >= n + 2 Then 
				w4 = c3 And 63 
			Else 
				w4 = -1
			End If
			strOut = strOut + mimeencode( w1 ) + mimeencode( w2 ) + _
					  mimeencode( w3 ) + mimeencode( w4 )
		Next
		base64_encode = strOut
	End Function

Private Function mimeencode( byVal intIn )
		If intIn >= 0 Then 
			mimeencode = Mid( Base64Chars, intIn + 1, 1 ) 
		Else 
			mimeencode = ""
		End If
	End Function

' Function to decode string from Base64
	Public Function base64_decode( byVal strIn )
		Dim w1, w2, w3, w4, n, strOut
		For n = 1 To Len( strIn ) Step 4
			w1 = mimedecode( Mid( strIn, n, 1 ) )
			w2 = mimedecode( Mid( strIn, n + 1, 1 ) )
			w3 = mimedecode( Mid( strIn, n + 2, 1 ) )
			w4 = mimedecode( Mid( strIn, n + 3, 1 ) )
			If w2 >= 0 Then _
				strOut = strOut + _
					Chr( ( ( w1 * 4 + Int( w2 / 16 ) ) And 255 ) )
			If w3 >= 0 Then _
				strOut = strOut + _
					Chr( ( ( w2 * 16 + Int( w3 / 4 ) ) And 255 ) )
			If w4 >= 0 Then _
				strOut = strOut + _
					Chr( ( ( w3 * 64 + w4 ) And 255 ) )
		Next
		base64_decode = strOut
	End Function

Private Function mimedecode( byVal strIn )
		If Len( strIn ) = 0 Then 
			mimedecode = -1 : Exit Function
		Else
			mimedecode = InStr( Base64Chars, strIn ) - 1
		End If
	End Function