ta_signed_header is not clear

[xlyu]

Hi,
Happy New Year!
I realize optee-os has implemented a feature with open trusted excue environment, which can load dynamic trusted applications in run-time OS. That is great.
In optee-os, I get TA including two parts:one parts is TA_SIGNED_HEADER,another part is TA_BODY which come from trusted application's elf file. TA_SIGNED_HEADER defined at kta_types.h:
typedef struct kta_signed_header {
uint32_t magic;
uint16_t size_of_signed_header;
uint16_t size_of_signature;
uint32_t sign_hash_type; /* see t_hash_type /
uint32_t signature_type; / see t_signature_type /
uint32_t hash_type; / see t_hash_type /
uint32_t payload_type; / see enum kta_payload_type /
uint32_t flags; / reserved /
uint32_t size_of_payload;
uint32_t sw_vers_nbr;
uint32_t load_address;
uint32_t startup_address;
uint32_t spare; / reserved */
} kta_signed_header_t;
I got a question about TA_SIGNED_HEADER:
Is this(struct kta_signed_header ) not a part of Global Platform's standard, and maybe come from STM's TEE project? Since I can't find the definition of the struct's variable in optee-os,such as signature_type,hash_type,payload_type. and there is no public key handle variable in struct kta_signed_header, means only can use default key to verify signed header.
Does this mean we can redefine the TA's format, as a example, define TA_SIGNED_HEADER and TA_BODY in two separate code fragments?
Thanks.

Best regards.
xlyu