* Encrypt DEK in attestation demo pelz requests.
* Add support for encrypted pelz request fields.
* Fix demo encryption to match kmyth's aes_gcm.h
* Fix segmentation fault.
Freeing uninitialized charbuf.
* Clean up comments and constant names.
* Add additional demo output message.
* Use new derived key for encrypted message field.
* Fix compiler warnings.
Now ignoring 'cast discards const qualifier' warnings
in secure_socket_enclave.c because there seems to be no way
to avoid the warning when using EVP_PKEY_CTX_set_hkdf_md with sgxssl.