[botan-devel] Format Preserving Encryption - Using it with words and names

S J zx78 at live.com
Wed May 6 22:32:42 EDT 2015




Hello,
I have several questions I was hoping someone could assist with,

1. Can you  point me to the location of the source code for just the FPE module (including any dependencies)?  I might try to use the C++ source in my .NET project

I found on GitHub this file, botan/src/cmd/fpe.cpp   What are the other files I need to make a complete library for just the FPE module.

2. I want to use this FPE to encrypt strings like words and names.  After experimenting with a C# port I found of the FPE module, I found it throws an exception if the string is too long.  In my case I am converting the string to a base 52 number (where A = 0, B = 1, C = 2.....y = 50, z = 51)  Then converting that to base 10 before encrypting.  Then I convert the encrypted result back to base 52 to get the result as  a string.  Since the modulus is 52^N where N is the number of characters in my string, this value can grow quite large as N increases.  Therefore I was wondering if you are imposing a restriction on this value and why?  

What modification can you suggest to allow for longer strings?  (Alternatively I was considering to break the plaintext string into fragments if it was too long and encrypt the fragments individually before putting them back together again)

Thanks for any help

Joseph

 		 	   		  
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