ATECC508A datasheet(90/109 Pages) MICROCHIP

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Table 9-55. Output Parameter

Name

Size

Notes

Response

Returns a value of zero if the signature of the message can be verified using the public key.

Returns a value of one if the signature does not match, or another error code if there is some

form of parsing or execution error.

The message to be used for the ECDSA Verify operation depends on the mode as follows:

•

Stored, External, and ValidateExternal Modes

The contents of TempKey should contain the SHA-256 digest of the message.

•

Validate or Invalidate Mode

The contents of TempKey should contain a digest of the PublicKey at KeyID. It must have been

generated using the GenKey command over the KeyID slot. The device then generates a message

based on the same format as the Sign(Internal) command, except that the parameter and

state bytes are copied from the input parameter OtherData. The message is formatted as follows:

32 bytes

TempKey (must have been generated by GenKey)

1 byte

Sign Opcode

10 bytes

OtherData<0:9>

1 byte

SN<8>

4 bytes

OtherData<10:13>

2 bytes

SN<0:1>

5 bytes

OtherData<14:18>

This message is hashed using SHA-256 and used as the message input to the ECC Verify operation.

9.21

Write Command

The Write command writes either one four byte word or an 8-word block of 32 bytes to one of the

EEPROM zones on the device. Depending upon the value of the WriteConfig byte for this slot, the data

may be required to be encrypted by the system prior to being sent to the device. This command cannot

be used to write slots configured as ECC private keys (see Section PrivWrite Command).

The following restrictions apply to writes within zones using this command:

•

Configuration Zone: If the configuration zone is locked or Zone<6> is set, then this command

returns an error; otherwise the bytes are written as requested. Any attempt to write any byte for

which writes are permanently prohibited (see Section EEPROM Configuration Zone) results in a

command error with no modifications to the EEPROM.

•

OTP Zone: If the OTP zone is unlocked, then all bytes can be written with this command. If the

OTP zone is locked and the OTPmode byte in the configuration zone is read-only, then this

command returns an error; otherwise, OTP mode should be consumption and this command sets to

zero those bits in the OTP zone that correspond to the zero bits in the input parameter Value. When

the data and OTP zones are locked, encrypted writes to the OTP zone are never permitted

regardless of OTPmode.

•

Data Zone: If the data zone is unlocked, then all bytes in all zones can be written with either plain

text or encrypted data. After the data zone is locked, the values within the SlotConfig.WriteConfig

bytes control access to the data slots. If the WriteConfig bits for this slot are set to Always, then the

ATECC508A

Security Commands

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