ATSHA204 ATMEL [ATMEL Corporation], ATSHA204 Datasheet - Page 8

• Manufacturer Part Number: ATSHA204
• Description: Atmel CryptoAuthentication
• Manufacturer: ATMEL [ATMEL Corporation]

Read operations depend on the state of IsSecret and EncryptRead according to the following table:
Table 2-3.
The 4-bit WriteConfig field is interpreted by the Write and DeriveKey commands as shown in Table 2-4 and Table 2-5, where
X means “don’t care.”
Note:
Table 2-4.
Table 2-5.
Note:
IsSecret
Bit 15
Bit 15
0
0
1
X
0
1
0
1
X
0
0
1
1
1.
Bit 14
Bit 14
X
X
X
X
X
EncryptRead
0
0
0
1
Read Operation Permission
The tables overlap. For example, a code of 0110 indicates a slot that can be written in encrypted form using the
write command and also can be the target of an unauthorized DeriveKey command with the target as the source.
Write Configuration Bits – Write Command
Write Configuration Bits – Derivekey Command
The source key for the computation performed by the DeriveKey command can either be the key directly
specified in Param2 (the “Target”) or the key at slotConfig[Param2].WriteKey (the “Parent”)
See Section 3.3 for more details.
0
1
0
1
Bit 13
Bit 13
X
X
0
1
1
1
1
1
0
Description
Clear text reads are always permitted from this slot.
Slots set to this state should never be used as key storage.
Either 4 or 32 bytes may be read at a time.
Prohibited. No security is guaranteed for slots using this code.
Reads are never permitted from this slot.
Slots set to this state can still be used for key storage.
Reads from this slot are encrypted using the encryption algorithm documented in the Read
command description (See Section 8.12).
The encryption key is in the slot specified by ReadKey. 4-byte reads and writes are prohibited.
Bit 12
Bit 12
X
X
X
X
X
0
0
1
1
Source Key
Mode Name
Encrypt
Always
Target
Target
Parent
Parent
Never
Never
–
(1)
Description
Clear text writes are always permitted on this slot. Slots set to
“always” should never be used as key storage. Either 4 or 32 bytes
may be written to this slot.
Writes are never permitted on this slot using the Write command
Slots set to “never” can still be used as key storage.
Writes are never permitted on this slot using the Write command
Slots set to “never” can still be used as key storage.
Writes to this slot require a properly computed MAC, and the input
data must be encrypted by the system with WriteKey using the
encryption algorithm documented in the Write command description
(Section 8.13). 4-byte writes to this slot are prohibited.
Description
DeriveKey command can be run without authorizing MAC (Roll).
Authorizing MAC required for DeriveKey command (Roll).
DeriveKey command can be run without authorizing MAC (Create).
Authorizing MAC required for DeriveKey command (Create).
Slots with this value in the WriteConfig field may not be used as the
target of the DeriveKey command.
Atmel ATSHA204 [DATASHEET]
8740D−CRYPTO−3/12
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