ATECC508A datasheet(63/109 Pages) MICROCHIP

63 / 109 page

counts even if the power is interrupted during the counting operation. In some power loss conditions, the

counter may increment by a value of more than one.

Counter<0> may be attached to some keys to limit their use; Counter<1> is never attached to any key.

When Counter<0> is attached to a key, the counter will be incremented with each use of the key until the

counter has reached its maximum value at which point use of the key will no longer be permitted. The

number of legal uses for a key can be controlled by initializing the Counter<0> to a non-zero value at

configuration time. Contact Microchip for details.

Table 9-12. Input Parameters

Name

Size

Notes

Opcode Counter

0x24

Param1

Mode

Bit 7-1:

Must be zero.

Bit 0:

0 = Read the value of the specified counter.

1 = Increment the value of the specified counter.

Param2

KeyID

The counter to be incremented. Only zero and one are legal values.

Table 9-13. Output Parameter

Name

Size

Notes

Count

4 or 1

Generally, this will be the current binary value of the counter.

If KeyID points to in invalid counter ID, a Parse Error will be returned.

If a requested increment fails, then an Exec error will be returned.

9.4

DeriveKey Command

The device combines the current value of a key with the nonce stored in TempKey using SHA-256 and

places the result into the target key slot. SlotConfig<TargetKey>.Bit13 must be set or DeriveKey will

return an error. DeriveKey always returns an error if KeyConfig indicates that the slot contains an ECC

private key, if the configuration zone has not been locked, or if the TargetKey slot is individually locked

using SlotLocked.

If SlotConfig<TargetKey>.Bit12 is zero, the source key that will be combined with TempKey is the target

key as specified in the command line (Roll Key operation). If SlotConfig<TargetKey>.Bit12 is one, the

source key is the parent key of the target key, which is found in SlotConfig<TargetKey>.WriteKey (Create

Key operation).

Prior to execution of this command, the Nonce command must have been run to create a valid nonce in

TempKey. If KeyConfig.ReqRandom is one for the source key, this nonce must have been created with

the internal RNG or an error will be returned. In all cases, Mode<2> must match the state of

TempKey.SourceFlag or the command will return an error.

If SlotConfig<TargetKey>.Bit15 is set, an input MAC must be present and have been computed as

follows:

SHA-256(ParentKey, Opcode, Param1, Param2, SN<8>, SN<0:1>)

where the ParentKey ID is always SlotConfig<TargetKey>.WriteKey.

If performing a Roll Key operation and KeyConfig<TargetKey>.ReqAuth is one, then the appropriate

authorization must have been performed using KeyConfig<TargetKey>.AuthKey prior to the execution of

ATECC508A

Security Commands

Datasheet Complete

DS20005927A-page 63

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