RFC 5116 defines AEAD algorithms. IETF AEAD Limits (Draft) describes how to limit the use of keys in order to bound the advantage given to an attacker.
NOTE: This is irrelevant to the plaintext bit length limitation (2^39 - 256), which is already defined in AES-GCM 5.2.1.1.
DSP0277 defines a 64-bit sequence number. The default value is the maximum 64-bit value: 0xFFFFFFFFFFFFFFFF.
The Integrator can set LIBSPDM_DATA_MAX_SPDM_SESSION_SEQUENCE_NUMBER to override the default
value, such as 0xFFFFFFFF (32-bit) or 0xFFFFFF (24-bit).
The Integrator may query LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_REQ_DIR and
LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_RSP_DIR to get the current number of messages that have been
encrypted / decrypted in the request and response directions, and trigger may trigger a KEY_UPDATE
accordingly.
If KEY_UPDATE is not sent before the maximum sequence number is reached, the SPDM session will be
terminated.