I have a LPC4370FET (flash-less, non AES part) that will be booted from its internal 128kB SRAM after loading the program image via USART0. The User Manual (5.3.3) tells me I need to send a 16 byte Boot Image Header in Table 24;
The answer is in Table 73 in section 7. It gives full description of the table items;
HASH_SIZE Size of the part of the image over which the hash value is
calculated in number of 512 Byte frames. Also size of the image copied to internal SRAM.
Hash size = 16 + HASH_SIZE x 512 Byte.