AT88SC0404C-PI Atmel, AT88SC0404C-PI Datasheet - Page 17

• Manufacturer Part Number: AT88SC0404C-PI
• Manufacturer: Atmel

Specifications of AT88SC0404C-PI

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Package Type: PDIP
• Mounting: Through Hole
• Pin Count: 8
• Operating Temperature Classification: Industrial
• Lead Free Status / RoHS Status: Not Compliant

5.1.2. Mutual Authentication
16
The use of a mutual authentication protocol further protects access to user zones. Any one of four key sets is available
for assignment to any user zone through configuration of access registers. Each key set consists of a secret seed, a
cryptogram, and a session encryption key. A Verify Crypto command exists to allow the use of any one of the key sets
to enter authentication mode. Each successful entry into authentication mode renders the mode active until the next
call to the Verify Crypto command or device reset. Only one key set may be active at anytime. Unsuccessful calls of the
Verify Crypto command exits authentication mode and decrements the value of the authentication attempts counter
(AAC) register. Decrementing AAC to $00 permanently disables the corresponding key set and permanently renders
the corresponding user zone(s) under protection inaccessible.
Entry into authentication mode is a process through which the host and Atmel
authenticate one another. First, the host generates a 64-bit random number, reads a current cryptogram from the
device, and uses this information in conjunction with the corresponding secret seed to generate a 64-bit challenge for
the device. The host also generates a new cryptogram and session encryption key in the process. The host then sends
the challenge and random number to the device by calling the Verify Crypto command. The device utilizes the random
number from the host to generate its own challenge, new cryptogram and session encryption key. It then compares its
challenge to the one from the host. If the challenges match, then the device declares the host authentic, overwrites its
corresponding current cryptogram and session encryption key with the new ones. To complete the mutual
authentication, the host reads the new cryptogram from the device and compares it with its newly calculated
cryptogram. The new cryptogram from the device serves as a challenge to the host. If the cryptograms match then the
device is authentic. Only an authentic pair of host and device can generate the same challenges and cryptograms.
Mutual authentication requires the use of the Verify Authentication variant of the Verify Crypto command (see
“Atmel CryptoMemory Synchronous Command
Command
Figure 4. The Mutual Authentication Process
Atmel AT88SC0104/0204/0404/0808/1616/3216/6416/12816/25616C
CryptoMemory Device
Device Info, Cryptogram
Set
Compute Session Key
Compute Challenge A
Compute Challenge B
,” on page
Verify Challenge A
[Secret Seed]
Allow Access
45).
Command/Communications
Set
Verify Authentication
Read Config Zone
Read Config Zone
,” on page
28
or
Table
34,
“Atmel CryptoMemory Asynchronous
®
Read Device Info, Cryptogram
Compute Secret Seed
Generate Random Number
Compute Challenge A
Compute Challenge B
Compute Session Key
Read Challenge B
Verify Challenge B
Allow Access
CryptoMemory
Host Logic
®
device mutually
5211C–SMIC–01/10
Table
25,