Before we go about this, could you tell us how much, if any, experience your friend has with cryptology?
[deleted, formerly addressed the difference between public and private encryption keys (not relevant)] Because the string is short, most likely a few possibilities will work.

In short, what I'm saying is that, while I'll give it a crack (and I'll give it to some friends that are much more computer-fluent to let them have a crack at it), if your friend has a good idea of what their doing, this might take a while [obscure reference to a coding sequence no longer relevant] More info concerning the code might shorten the process.

An option to decrypt this is to use a dictionary-style attack at the cyphertext. This is to say that you find a list of all 8-letter words and then see which ones match the rules for "buuconac". those rules would be:
-the second and third letters are the same (only in this case becuase it's a letter-letter substitution code)
-the fourth and last letters are the same (again, only in this case)
-no other letters are the same
-cyphertext "a" occurs once in the string, so it is likely to not be a common letter (listed in order of most frequent to least frequent, in the english language, the letter order is "E T A O N I S R H D L U F C M W P G Y B V K X J Q Z", source: Enchanted Mind, Cryptography )

Attached is my results (so far) after searching (visually and briefly, so there might be minor errors) through the 2000 most common words in the english language for some of the longer cyphertext strings. Hope this helps! (I'll post my results later after I make some real progress)