DCP_BLOB_AUTHLEN
ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;