If you want, you could stop the project now and happily use GPG on your BBB. But if you do, you would miss out on adding some extra protection with the CryptoCape, specifically, the Trusted Platform Module (TPM). In the upcoming sections, we will use the TPM to protect our GPG private key.
The TPM is a cryptographic co-processor. The TPM on the CryptoCape is Atmel's embedded I2C version, which conforms to version 1.2 of the TPM spec published by the Trusted Computing Group (TCG). The TCG is an industry consortium that maintains and develops open specifications for trusted computing. Trusted in this sense is the definition from RFC 4949: a system that operates as expected, according to design and policy.
Cryptographically, TPM 1.2 is limited. It implements the RSA algorithm, SHA-1, has an internal random number generator, and some limited storage. It does not provide any symmetric ciphers. These limitations were a result of the...