ATECC508A datasheet(30/109 Pages) MICROCHIP

30 / 109 page

The public key corresponding to the generated private key is returned to the system, and the device can

also use another internally stored key to create a MAC or signature (using the Sign(Internal)

command) covering the new public key.

3.2.4

Created Secret Keys

There may be a need to have unique ephemeral symmetric keys on each client; a function also supported

by the ATECC508A. With this mechanism, a parent key (that is specified by SlotConfig.WriteKey) is

combined with a fixed or random nonce to create a unique key, which is then used for any cryptographic

purpose.

The ability to create unique keys is especially useful if the parent key has usage restrictions (see Sections

High Endurance Monotonic Counters and Limited Use Key (Slot 15 only)). In this mode, the limited use

parent can be employed to create an unlimited use child key. Because the child key is useful only for this

particular host-client pair, attacks on its value are less valuable.

This capability is also implemented using the DeriveKey command. Prior to execution of the

DeriveKey command, the Nonce command must be run to load the nonce value into TempKey.

3.2.5

High Endurance Monotonic Counters

The ATECC508A supports two independent high endurance nonvolatile monotonic counters that can

count to a value of 2,097,151. Their value never decreases and the storage elements are protected

against count loss if the power is interrupted during an incrementing operation. The current value of the

two counters can be read using the Counter command, which can also be used to increment the

counters. There is no way to reset the counters.

The counters can be used in one of two methods:

•

Cryptographic Counters:

In this mode, the Counter command is used to increment the value of the counters and the current

value can be read via the same command. The two counters are independent.

•

Limited Key Use:

Counter<0> can be attached to any one (or more) of keys 0 – 14 via the SlotConfig.LimitedUse bit.

If this bit is set, then any use of the keys will cause the counter to increment automatically prior to

the operation being performed. If the counter has reached its limit, then the command will return an

error code, and no counter change will occur. Use of the keys for fewer than 2,097,151 times is

facilitated by initializing the counters in the configuration zone to a lower value. Contact Microchip

for details.

The GenKey, Read, and Write commands ignore the monotonic counter limited use feature. It is also

ignored for the copied slot during CheckMac/Copy.

3.2.6

Limited Use Key (Slot 15 only)

If SlotConfig<15>.LimitedUse is set, usage of key number 15 is limited through a different mechanism

than the limitation described in the previous section (which applies only to Slots 0 through 14).

Prior to any use of Key 15 by a command, the following takes place:

•

If all bytes in LastKeyUse are 0x00, then return error.

•

Starting at bit 7 of the first byte of LastKeyUse (byte 68 in Configuration zone), clear to zero the first

bit, which is currently a one. If byte 68 is 0x00, then check bit 7 of byte 69, and so forth up through

byte 83. Only a single bit is cleared each time prior to using Key 15.

ATECC508A

Security Information

Datasheet Complete

DS20005927A-page 30

ATECC508A Arkusz danych(PDF) 30 Page - Microchip Technology

ATECC508A Arkusz danych(HTML) 30 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Arkusz danych Pobierz

Link URL