Rainbow Electronics AT88SA100S - Manual (Page 13)

AT88SA100S [ Preliminary]
13
8558A–SMEM–03/09
4.1. MAC
Computes a SHA-256 digest of the key, challenge and other fixed information on the chip to generate an output
response. If MemValid is not set, indicating that no valid key is stored in the SRAM, then this command will return an
error. The hashed message includes the following bytes, concatenated in this order:
256 bits Key (Stored in Sram)
256 bits Challenge
8 bits Opcode (always 0x01)
8 bits Mode input
16 bits Param2 input
88 bits All 0’s
8 bits MfrID Fuse[88-95]
32 bits SerialNum Fuse[96-127], or 0’s
16 bits ROM MfrID
16 bits ROM SN), or 0’s
1 bit 1’s – SHA-256 padding
255 bits 0’s – SHA-256 padding
64 bits Length (704) per SHA-256
Table 7. Input Parameters
Name Size Notes
Opcode MAC 1 0x08
Param2 Zero 2 Must be 0x00 00
Data Challenge 32 Input portion of message to be digested
Table 8. Output Parameters
Name Size Notes
Response 32 SHA-256 digest
Table 9. Mode Encoding
Bit Notes
6 If set, then the 4 bytes of Serial Number Fuses and the two bytes of ROM SN will be included in the
message, otherwise these bits will be set to 0 in the message.
0-5, 7 Ignored, must be all 0.