at88sc018 ATMEL Corporation, at88sc018 Datasheet - Page 17

• Manufacturer Part Number: at88sc018
• Description: Cryptocompanion? Chip For Cryptomemory And Cryptorf
• Manufacturer: ATMEL Corporation

2.2.
3.
3.1.
5277C–CryptoCompanion–9/09
S
Authentication & Encryption Sequence
Table 14.
Command Descriptions
VerifyFlash
System sends information to the AT88SC018 which would typically be based on the state of an external nonvolatile
(e.g. FLASH) program store. If the input digest indicates a problem, the AT88SC018 will set up the status register to
indicate a RstLocked error code but will accept no commands until the next reset or power cycle. This command can
be run once only per reset.
If Mode.Bit [1:0] == 00, this command simply verifies that the incoming digest matches that stored in memory. This is
useful if the external ASIC has hardware that can verify the boot code, in which case that hardware would respond to
the return code of this command.
If Mode.Bit [1:0] == 01, this command implements a simple signature mechanism for an externally loaded module. In
this case the FlashDigest stored in EEPROM is a secret also known by the entity that generates legal download
images. The system sends both the download digest and the signature to the AT88SC018; the AT88SC018 generates
a comparison signature using its stored value and verifies that they are the same. This mode is useful if the external
system has some confidence in the boot code, but does not have sufficient space to implement a full public key
signature verification module.
If Mode.Bit [1:0] == 11, this command is disabled. If Mode.Bit [1:0] == 00 or 01, then VerifyFlash MUST run before
startup. Mode.Bit [1:0] == 10 should not be used, if it is the VerifyFlash command will return OK without any
computation or comparison being performed.
A.
B.
C.
D.
E.
F.
G.
A
, S
iA
Auth_1
Auth_2
Encrypt_1
Encrypt_2
CMC Command
These are the encryption keys generated as part of the authentication sequence – S
and S
encryption sequence are ignored.
Authentication & Encryption Sequence
i
A
is independently generated by CRF. Their value should be identical. The S keys generated by the
G = F1(F
Q
[CH
C
Q
[CH
Q
C
i
i
A
E
E
A
E
)
= RNG
= RNG
=? C
=? C
A
E
, C
, C
CMC Computation
A
E
A
E
, S
, S
n
, K
A
E
] = F2 (G, C, Q
] = F2 (S
ID
, ID)
CH
CH
A
A
E
, C
, Q
, Q
A
A
E
,
A
)
Dir.
⇐
⇒
⇐
⇒
⇐
ID, C
[CH, C
CH
C
[CH, C
CH
C
i
i
A
E
A
E
=? CH
=? CH
CRF Computation
i
i
A
E
CryptoCompanion Chip
, S
, S
i
i
A
E
] = F2(G
] = F2(S
i
i
A
, C
, C
i
, Q
i
A
, Q
A
)
E
A
)
is generated by CMC
CRF Command
Verify Crypto
Verify Crypto
Read Config
17