I believe that is likely to be the same encryption method, just it's private keys instead of the "protobuf" formatted wallet file.
Have you tried using a more recent version of the wallet application (ie.
Bitcoin Wallet for Android) and importing the "bitcoin-wallet-keys-YYYY-MM-DD" file?
If that doesn't work, you might be able to decrypt the file using the
openssl command with your bitcoin-wallet-keys-YYYY-MM-DD file:
openssl enc -d -aes-256-cbc -a -in bitcoin-wallet-keys-YYYY-MM-DD -out bitcoin-wallet-keys-YYYY-MM-DD-decrypted
Assuming that works without error, if you open the "decrypted" file in a text editor... do you see the keys listed?
