I wouldn't make that big of a leap. However, once I got the CSPs properly setup thanks to Alex, my "XP" problem went away. I actually have three apps using _cryptapi; one for testing (Uses the same _cryptapi on one machine for encrypting and decrypting). The second app encrypts the files and preps for distribution. The third is the GUI for users to look up & open customer files, etc.

The second and third apps could potentially be on any Windows OS and we have tested in both directions on W98, W2000, and now XP. (So far without problems).

Once again, I'm only working with file names not entire files so the strings are short. Also only using EncryptSessionStreamString, and DecryptSessionStreamString functions. And, the user app doesn't use DecryptSessionStreamString, it only uses EncryptSessionStreamString to recreate a file name the GUI app can use to locate a file.

At least for now, I am confident that things work the way they should.