Public key encrypt/decrypt app

Hi all,
Does anyone know of a public key encrypt/decrypt ipad app (IOS5).  I use gpgtools on the imac (lion 7.2) and put spreadsheets, docs, and the like into dropbox.  I have the dropbox app on the ipad.  It opens non-encrypted files just fine; however, if they are encrypted - no soap. I need something that works with dropbox, or provides a dropbox-like repository.
Searching the store gives me a couple of email encrypters but nothing for files. 
Many thanks for any help,
Best,

By how much is the file size increasing? Depending on how you do the actual encryption, it can easily grow a bit due to varying headers and some padding, but it shouldn't be a significant part of the file size if the file is reasonably big.
If, however, the file size grows by some significant factor (say your output is 2 time the size of the input), then there is some problem that you should look into.

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