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Base 64 Encode / Decode


Base 64 encodeing is used to convert binary files to a "safe" format for transporting files through smtp (email) and other protocols. It is also used for basic authentication. With this code, you can decode the current UserName/Password who is visiting a protected page on your site by requesting one of the serverVariables.

Original Author: Lewis E. Moten III

Inputs

These two algorithims are expecting a string that is to be encoded or decoded.

Returns

Returns a string that was encoded or decoded.

Side Affects

The string returned from encoding with Base64 is not delimited by cariadge returns. Some formats that I have seen in the past, such as email - may continue to the next line after the 80th character.
Also, these functions work with Strings. (Not binary data). When working with binary data, some changes may need to come into place.

API Declarations

Copyright (C) 1999, Lewis Moten. All rights reserved.

Code

Const sBASE_64_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
' -----------------------------------------------------------------------------
Function Base64decode(ByVal asContents)
Dim lsResult
Dim lnPosition
Dim lsGroup64, lsGroupBinary
Dim Char1, Char2, Char3, Char4
Dim Byte1, Byte2, Byte3
If Len(asContents) Mod 4 > 0 Then asContents = asContents & String(4 - (Len(asContents) Mod 4), " ")
lsResult = ""

For lnPosition = 1 To Len(asContents) Step 4
lsGroupBinary = ""
lsGroup64 = Mid(asContents, lnPosition, 4)
Char1 = INSTR(sBASE_64_CHARACTERS, Mid(lsGroup64, 1, 1)) - 1
Char2 = INSTR(sBASE_64_CHARACTERS, Mid(lsGroup64, 2, 1)) - 1
Char3 = INSTR(sBASE_64_CHARACTERS, Mid(lsGroup64, 3, 1)) - 1
Char4 = INSTR(sBASE_64_CHARACTERS, Mid(lsGroup64, 4, 1)) - 1
Byte1 = Chr(((Char2 And 48) 16) Or (Char1 * 4) And &HFF)
Byte2 = lsGroupBinary & Chr(((Char3 And 60) 4) Or (Char2 * 16) And &HFF)
Byte3 = Chr((((Char3 And 3) * 64) And &HFF) Or (Char4 And 63))
lsGroupBinary = Byte1 & Byte2 & Byte3

lsResult = lsResult + lsGroupBinary
Next
Base64decode = lsResult
End Function
' -----------------------------------------------------------------------------
Function Base64encode(ByVal asContents)
Dim lnPosition
Dim lsResult
Dim Char1
Dim Char2
Dim Char3
Dim Char4
Dim Byte1
Dim Byte2
Dim Byte3
Dim SaveBits1
Dim SaveBits2
Dim lsGroupBinary
Dim lsGroup64

If Len(asContents) Mod 3 > 0 Then asContents = asContents & String(3 - (Len(asContents) Mod 3), " ")
lsResult = ""

For lnPosition = 1 To Len(asContents) Step 3
lsGroup64 = ""
lsGroupBinary = Mid(asContents, lnPosition, 3)
  
Byte1 = Asc(Mid(lsGroupBinary, 1, 1)): SaveBits1 = Byte1 And 3
Byte2 = Asc(Mid(lsGroupBinary, 2, 1)): SaveBits2 = Byte2 And 15
Byte3 = Asc(Mid(lsGroupBinary, 3, 1))
  
Char1 = Mid(sBASE_64_CHARACTERS, ((Byte1 And 252) 4) + 1, 1)
Char2 = Mid(sBASE_64_CHARACTERS, (((Byte2 And 240) 16) Or (SaveBits1 * 16) And &HFF) + 1, 1)
Char3 = Mid(sBASE_64_CHARACTERS, (((Byte3 And 192) 64) Or (SaveBits2 * 4) And &HFF) + 1, 1)
Char4 = Mid(sBASE_64_CHARACTERS, (Byte3 And 63) + 1, 1)
lsGroup64 = Char1 & Char2 & Char3 & Char4

lsResult = lsResult + lsGroup64
Next

Base64encode = lsResult
  
End Function
' -----------------------------------------------------------------------------

About this post

Posted: 2002-06-01
By: ArchiveBot
Viewed: 89 times

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ASP/ HTML

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