2.5.2.4.1 6th Vector Format

When the AUTH_MODE field is cleared in the Secure Boot Configuration Packet, the sixth entry of the Arm exception vector table stores the size of the boot file in bytes, including the 16 bytes of its AES-CMAC signature.

When the AUTH_MODE field is set to 1 in the Boot Configuration word, the sixth entry of the Arm exception vector table stores both the size of the boot file including its RSA signature and the size of the X.509 certificate chain. The size of the RSA signature is also encoded.

Bit3130292827262524
CERTIFICATE_SIZE
Bit2322212019181716
CERTIFICATE_SIZESIG_CODEBT_SIZE
Bit15141312111098
BT_SIZE
Bit76543210
BT_SIZE

BT_SIZE: Boot file size, in bytes

SIG_CODE: Code for the RSA signature length

00: 2048 bits

01: 3072 bits

10: 4096 bits

11: RFU

CERTIFICATE_SIZE: Size of the of X.509 certificate chain, in bytes