OpenPGP private key backup utility suitable for printing
Due to metadata and redundancy, OpenPGP secret keys are significantly larger than just the "secret bits". The secret key contains a complete copy of the public key. Since the public key generally doesn't need to be escrowed, only archiving 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, OCR, QR code, or the like) and paperkey can use them to transform your existing public key into a secret key.
Homepage: https://www.jabberwocky.com/software/paperkey/