AT88SC0404CA-MJTG Atmel, AT88SC0404CA-MJTG Datasheet - Page 16

• Manufacturer Part Number: AT88SC0404CA-MJTG
• Description: CRYPTOMEM 4KBIT 4 ZONE MOD J TWI
• Manufacturer: Atmel
• Series: CryptoMemory®r

Specifications of AT88SC0404CA-MJTG

• Format - Memory: EEPROMs - Serial
• Memory Type: EEPROM
• Memory Size: 4K (512 x 8)
• Speed: 4MHz
• Interface: I²C, 2-Wire Serial
• Voltage - Supply: 2.7 V ~ 3.6 V
• Operating Temperature: 0°C ~ 70°C
• Package / Case: M2 J, Smart Card Module
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.1.2. Authentication Protocol
8664C–CRYPT–01/10
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 for the
current key set 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 and
identification information 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 the 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 new 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. Activating mutual authentication requires the use of the Verify Authentication variant of
the Verify CRYPTO command (see Section
Figure 6. The Mutual Authentication Process
CryptoMemory Device
Device Info, Cryptogram
Compute Session Key
Compute Challenge A
Compute Challenge B
Verify Challenge A
[Secret Seed]
Allow Access
8.2, Command Set
Command/Communications
Atmel AT88SC0104/0204/0404/0808/CA
Verify Authentication
Read Config Zone
Read Config Zone
and Section
10.3, Command Set
®
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
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