Re: Size of Entropy with Dpapi Encrypted Connection String

From: charlestek (charlestek_at_yahoo.com)
Date: 03/15/05 

Date: Mon, 14 Mar 2005 18:28:16 -0800

Alex,

I am doing TWO things with the dpapi.
I am decrypting my text encryption string, stored in my web config,
already encrypted by the dpapi once.
as well as decrypting a dpapi encrypted aes binary symmetric key stored
in the web config as well.

The connection string is used for my database access by the classes that
need it, and the symmetric key is used to encrypt and decrypt info in a
table in my database. Each encrypted row in my database has an IV for
that row stored as well.

For some reason, it Appeared that if I didn't use a binary entropy value
that was the same number of bytes as the symmetric aes binary key, I had
problems with encrypting/decrypting the symmetric aes binary key with
the dpapi.
That however could be coincidence, and I had some other bug
that was causing the problem.

In addition, now that I have the dpapi encrypted binary
aes key in my web config, when I use a class to encrypt and
decrypt some arbitrary text, I'm getting an invalid keysize
error upon decryption only. I forwarded the code about this particular
issue to Dominick recently.

If you read the MSDN documentation about the innards of the dpapi it is
hard for the lay person such as myself to understand the mathematics of
the entropy in the dpapi algorithm.

Phil

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