A reasonable way to achieve a long term backup of
OpenPGP (GnuPG, PGP, etc) keys is to print them
out on paper. Due to metadata and redundancy,
OpenPGP secret keys are significantly larger than
just the "secret bits". In fact, the secret key
contains a complete copy of the public key. Since
the public key generally doesn't need to be backed
up in this way (most people have many copies of it
on various keyservers, Web pages, etc), only
extracting the secret parts can be a real
advantage. Paperkey extracts just those secret
bytes and prints them. To reconstruct, you
re-enter those bytes (whether by hand or via OCR),
and paperkey can use them to transform your
existing public key into a secret key.
