ATECC508A datasheet(17/109 Pages) MICROCHIP

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Bit

Name

Description

1 = The key stored in the slot is intended for verification usage and cannot be used by the

MAC or HMAC commands. When this key is used to generate or modify TempKey, then

that value may not be used by the MAC and HMAC commands. Also cannot be used with

the SHA command in HMAC mode.

3-0

ReadKey

Use this KeyID to encrypt data being read from this slot using the Read command. See more

information in the description for bit 6 in this table, the Section Read Command, and Table

2-7 for more details.

0x0 = Then this slot can be the source for the CheckMac/Copy operation. See Section

Password Checking.

Do not use zero as a default. Do not set this field to zero unless the CheckMac/

Copy operation is explicitly desired, regardless of any other read/write restrictions.

Slots containing private keys can never be read and this field has a different meaning:

Bit 3: 0 = ECDH master secret will be output in the clear.

1 = Master secret will be written into slot N+1. (Can only be set to 1 for even number

slots and should always be 0 for odd number slots)

This bit is ignored if Bit 2 is zero.

Bit 2: 0 = ECDH operation is not permitted for this key.

1 = ECDH operation is permitted for this key.

Bit 1: 0 = Internal signatures of messages are not enabled.

1 = Internal signatures of messages generated by GenDig or GenKey are enabled.

Bit 0: 0 = External signatures of arbitrary messages are not enabled.

1 = External signatures of arbitrary messages are enabled.

For slots containing public keys that can be validated (PubInfo is one, see Section KeyConfig

(Bytes 96 through 127), this field stores the KeyID that should be used to perform the

validation.

2.2.2

Read Permissions

Read operations for most data slots are controlled by the state of IsSecret and EncryptRead, according to

the following table. ECC private keys can never be read under any circumstances.

Table 2-7. 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

Section Read Command. The encryption key is in the slot specified by ReadKey.

4-byte reads and writes are prohibited.

ATECC508A

Device Organization

Datasheet Complete

DS20005927A-page 17

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