12.2.4.1 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.

Bit 3130292827262524 
 CERTIFICATE_SIZE[12:5] 
Access  
Reset  
Bit 2322212019181716 
 CERTIFICATE_SIZE[4:0]SIG_CODE[1:0]BT_SIZE[16] 
Access  
Reset  
Bit 15141312111098 
 BT_SIZE[15:8] 
Access  
Reset  
Bit 76543210 
 BT_SIZE[7:0] 
Access  
Reset  

Bits 31:19 – CERTIFICATE_SIZE[12:0] Size of the of X.509 certificate chain, in bytes

Bits 18:17 – SIG_CODE[1:0] Code for the RSA signature length

ValueDescription
00 2048 bits
01 3072 bits
10 4096 bits
11 RFU

Bits 16:0 – BT_SIZE[16:0] Boot file size, in bytes