ATECC508A datasheet(26/109 Pages) MICROCHIP

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at the time of data/OTP locking. After the data/OTP zones are locked, either the Read, CheckMac, or MAC

commands can be used to validate the slot contents prior to individual slot locking.

Note: Validation of a public key via the Verify command can occur regardless of the state of the

SlotLocked bit for that slot.

2.5

Static RAM (SRAM) Memory

The device includes an SRAM array that is used to store the input command or output result,

intermediate computation values, and/or an ephemeral key. The entire contents of this memory are

always invalidated whenever the device goes into Sleep mode or the power is removed. The ephemeral

key is named TempKey and can be used as an input to the MAC, HMAC, CheckMac, GenDig, Sign,

Verify, and DeriveKey commands. It is also used as the data protection (encryption or decryption) key

by the Read and Write commands.

2.5.1

TempKey

TempKey is a storage register in the SRAM array that can be used to store an ephemeral result value

from the Nonce, GenDig, SHA, or GenKey commands. The contents of the 32 byte data value in this

internally). The Info command can be used to return the value of the nine status/flag bits within this

Execution of GenDig or GenKey replaces the old contents of TempKey with the new calculated output,

which is a combination of the old TempKey value and other information. Execution of the Nonce

command or the copy mode of the CheckMac command completely replaces any previous output of the

GenDig or GenKey commands. This register contains the elements shown in the table below:

Table 2-16. TempKey Storage Register

Name

Length

Description

TempKey

256-bit (32 byte) Nonce (from Nonce command) or digest (from GenDig or GenKey(Digest)

commands).

KeyID

4 bits

If TempKey was generated by GenDig or GenKey, these bits indicate which key

was used in its computation. The four bits represent one of the slots of the Data

zone.

SourceFlag

1 bit

The source of the randomness in TempKey:

0 =

Internally generated random number (Rand).

1 =

Input seed only, no internal random generation (Input).

GenDigData

1 bit

0 = TempKey was not generated by GenDig.

1 = The contents of TempKey were generated by GenDig using one of the slots

in the Data zone (and TempKey.KeyID will be meaningful).

GenKeyData

1 bit

0 = TempKey.KeyID was not generated by GenKey.

1 = The contents of TempKey were generated by GenKey using one of the slots

in the Data zone (and TempKey.KeyID will be meaningful).

ATECC508A

Device Organization

Datasheet Complete

DS20005927A-page 26

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