Atmel AT88SA102S [DATASHEET] 14
8584H−CRYPTO−9/2012
6.1 MAC
Computes a SHA-256 digest of a key stored inside the chip, an input challenge and other information on the chip. The output
of this command is the digest of this message.
If the message includes the serial number of the chip, then the response is said to be diversified. Protocols that utilize
diversified responses may be more secure because two AT88SA102S chips with same key will return different responses to
an identical challenge based on their unique serial number.
Table 6-1. Input Parameters
Name Size Notes
Opcode
MAC 1 0x08
Param1
Mode 1 Controls which fields within the chip are used in the message
Param2
KeyID 2 Which internal key is to be used in the message
Data
Challenge 32 Input portion of message to be digested
Table 6-2. Output Parameters
Name Size Notes
Response 32 SHA-256 digest
Regardless of the value of mode, the first 512-bit block of the message that will be hashed with the SHA-256 algorithm will
consist of:
256-bits key[KeyID]
256-bits challenge
The second block consists of the following information:
8-bits Opcode (always 0x08)
8-bits Mode
16-bits KeyID
64-bits Secret Fuses including BurnFuse and BurnSecure enable (or zeros, see Table 6-3)
24-bits Status Fuses including FuseDisable (or zeros, see Table 6-3)
8-bits Fuse MfrID fuses, (Fuse[88:95]) (never zero’d out)
32-bits Fuse SN, (Fuse[96:127]) (or zeros, see Table 6-3)
16-bits ROM MfrID (never zero’d out)
16-bits ROM SN (or zeros, see Table 6-3)
1-bit ‘1’ pad
255-bit ‘0’ pad
64-bit Total length of message in bits (512+192=704), excluding pad and length
