at88sc018 ATMEL Corporation, at88sc018 Datasheet - Page 16

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

2.
2.1.
16
1.6.5.2. When the AT88SC018 is Locked
When the AT88SC018 is locked, the security delays from
The first command run after powerup or a reset must be either VerifyFlash or Startup. If the first command is Startup,
then VerifyFlash cannot be run until the next power cycle. If the first command is VerifyFlash, then the next command
must be Startup. After Startup, the next command must always be Challenge Response.
No other command can be run until ChallengeResponse has successfully completed. Any attempt to run another
command prior to ChallengeResponse or a failure of the ChallengeResponse command will cause the AT88SC018 to
lock up until the next power cycle or reset assertion.
A complete and successful authentication sequence (Auth_1 & Auth_2) must be run prior to those commands that
require it: EncryptPassword, Encryption_1, Encryption_2 and GrindBytes. Failure to run the authentication sequence
will result in an error code in the status register but no delay.
When the AT88SC018 is locked, the following commands are disabled: WriteMemoryEncrypted, ReadMemoryDigest
and Lock. WriteMemory is available only for Read/Write memory (the region between RWBound and F-Bound).
ReadMemory is only available for ReadOnly + ReadWrite memory (the region between address 0x110 and F-Bound).
Any attempt to violate these restrictions will result in a BadCmd error message but no penalty.
CMC
The AT88SC018 supports the mutual authentication sequence of the CRF chip in a manner such that the shared
secrets are not ever exposed on the AT88SC018 or CRF busses. This section describes that mutual authentication
sequence. To be consistent with the parameter names in the command descriptions, the AT88SC018 is referred to by
its alternate name of CMC.
Nomenclature
X
Y
C
CH, C
F2
G, G
ID
K
Q
CryptoCompanion Chip
i
A
ID
, Y
i
E
i
The subscript ‘i’ indicates a key index in the CRF memory array. CRF contains 4 sets of key values, only those
from a single set can be used in a successful authentication sequence.
The superscripts ‘A’ and ‘E’ indicate the two possible phases of the crypto setup for CRF. ‘A’ indicates the
authentication phase which prefaces all cryptographic communication with CRF. The ‘E’ indicates the optional
encryption phase.
The initial cryptogram state from CRF to CMC. It is the state generated as a result of a previous authentication
or encryption sequence and is unique.
These values are the challenge and response during the mutual authentication & encryption sequences. CH
is the authentication challenge to CRF from CMC. C
the copy of this computed within CMC. CH
encryption response from CRF to CMC, C
This is the Atmel proprietary algorithm implemented within CMC and CRF. [A, B, C] = F2(X, Y, Z) indicates
that X, Y & Z are inputs to the F2 algorithm and that execution of the algorithm on these inputs yields the set
of outputs A, B & C.
The secret stored in CRF or computed on CMC from ID and Fn.
This is the unique serial or identification number for CRF which is obtained from the Nc register within the CRF
EEPROM.
This is a constant generated by the external system in a manner of its choosing. It should typically be a
function of the ID number and an external secret, but may also include other information about the item to
which CRF is attached, the system configuration or other values held external to CMC. CMC treats K
constant and does not interpret its value.
These are random values created in the RNG of CMC which are used as part of the authentication and
encryption sequences.
CRF Authentication
E
is the copy of this computed within CMC.
E
Section 1.6.3
is the encryption challenge to CRF from CMC. C
i
A
is the authentication response from CRF to CMC, C
apply.
5277C–CryptoCompanion–9/09
i
E
ID
is the
as a
A
is
A