* g10/build-packet.c (do_encrypted_aead): New.
(do_symkey_enc): Handle version 5.
(build_packet): Support the ENCRYPTED_AEAD packet.
* g10/cipher.c (MIN_PARTIAL_SIZE): Remove unused macro.
(AEAD_ENC_BUFFER_SIZE): New macro.
(my_iobuf_write): New.
(write_header): Rename to write_cfb_header.  Adjust caller.
(set_ocb_nonce_and_ad): New.
(write_ocb_header): New.
(write_ocb_auth_tag): New.
(write_ocb_final_chunk): New.
(do_ocb_flush): New.
(do_ocb_free): New.
(cipher_filter_ocb): New.
* g10/filter.h (cipher_filter_context_t): Add fields for AEAD.
* g10/encrypt.c (encrypt_symmetric): For the use of a session key in
OCB mode.
(encrypt_seskey): Revamp to support OCB.
(use_aead): New.
(encrypt_simple): Support OCB.
(write_symkey_enc): Ditto.
(encrypt_crypt): Ditto.
(encrypt_filter): Handle OCB.
* g10/options.h (opt): Add field force_ocb.
* g10/gpg.c (oForceOCB): New.
(opts): New option "--force-ocb".
(main): Set force_ocb option.
* g10/gpgcompose.c (encrypt_seskey): New.
* g10/keygen.c (aead_available): New global var.
(keygen_set_std_prefs): Set AEAD feature by default in GNUPG mode. Add
parings of aead feature flag.
(keygen_get_std_prefs): Set aead flag.
(add_feature_aead): New.
(keygen_upd_std_prefs): Set OCB as preference if AEAD is enabled.
* g10/pkclist.c (select_aead_from_pklist): New.
(warn_missing_aead_from_pklist): New.
(select_mdc_from_pklist): Remove this unused function.