Problems verifying a signed message

A friend of mine, Keybase username [arcticlight](https://keybase.io/arcticlight), sent me a signed, encrypted message generated by Keybase's web interface. When I attempt to decrypt this message, I get an error saying `Error: Cannot verify username, no self-signed proofs given`. My friend does have what appear to be valid Twitter and GitHub proofs on their Keybase profile. When my friend sends me an unsigned encrypted message, everything works fine.

Start by reproducing the signed, encrypted message flow from Keybase's web interface and compare it with the unsigned encrypted case. Trace the `Cannot verify username, no self-signed proofs given` error and the friend's Twitter and GitHub proofs; done means identifying why the signed message fails verification and confirming successful decryption.

Written by the indexing model from the issue text.