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MrMick - Decoding Base64 files!!

Posted on 1998-04-03
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Last Modified: 2012-06-21
Hi there,

MrMick very kindly answered a question of mine a few day ago and provided me with a routine to encode a file into base64.  I've used this routine and it works fine but would now like the ability in my app to decode these files as well.

Has anyone got a VB sub that will do this?

Thanks

Pete
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Question by:peterwest
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6 Comments
 
LVL 6

Expert Comment

by:clifABB
ID: 1460287
Most encryption routines will decrypt if the encrypted object is run through the encryption again.
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LVL 6

Expert Comment

by:clifABB
ID: 1460288
Make a backup of the file first!
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LVL 2

Author Comment

by:peterwest
ID: 1460289
I don't think Base64 will decrypt the file by running it through again!!!  I've already tried that and it didn't work.
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LVL 2

Accepted Solution

by:
sbmc earned 50 total points
ID: 1460290
Base64 encoding works in chunks of three bytes converted to four bytes. Decoding works by grabbing 4 byte chunks and converting these 4 bytes into 3 bytes as follows:
   1. grab 4 bytes
   2. convert to binary ie 32 bits
   3. remove 1st 2 bits of every byte
   4. divide the resulting 24 bits into 3 8bit chunks
   5. convert each 8 bit string into a byte
   6. repeat 1-6 for each group of 4 byte strings in your file

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Author Comment

by:peterwest
ID: 1460291
Thanks,

I've already got the necessary routine to decode Base64 but it is useful to understand how it works - maybe i'll even write my own routine as the one i'm using at the moment is a little convoluted and inefficient (or at least it would appear so).

Pete

0
 
LVL 2

Author Comment

by:peterwest
ID: 1460292
Thanks,

I've already got the necessary routine to decode Base64 but it is useful to understand how it works - maybe i'll even write my own routine as the one i'm using at the moment is a little convoluted and inefficient (or at least it would appear so).

Pete

0

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