ATSHA204 datasheet(8/65 Pages) ATMEL

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Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

Read operations depend on the state of IsSecret and EncryptRead according to the following table:

Table 2-3.

Read Operation Permission

IsSecret

EncryptRead

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.

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:

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.

Table 2-4.

Write Configuration Bits – Write Command

Bit 15

Bit 14

Bit 13

Bit 12

Mode Name

Description

Always

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.

Never

Writes are never permitted on this slot using the Write command

Slots set to “never” can still be used as key storage.

Never

Writes are never permitted on this slot using the Write command

Slots set to “never” can still be used as key storage.

Encrypt

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.

Table 2-5.

Write Configuration Bits – Derivekey Command

Bit 15

Bit 14

Bit 13

Bit 12

Source Key

(1)

Description

Target

DeriveKey command can be run without authorizing MAC (Roll).

Target

Authorizing MAC required for DeriveKey command (Roll).

Parent

DeriveKey command can be run without authorizing MAC (Create).

Parent

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.

Note:

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.

ATSHA204 Datasheet(PDF) 8 Page - ATMEL Corporation

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