AT88SC0404C-PI Atmel, AT88SC0404C-PI Datasheet - Page 18

• 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

5.1.3. Data Encryption
5.1.4. Encrypted Checksum
5211C–SMIC–01/10
Atmel AT88SC0104/0204/0404/0808/1616/3216/6416/12816/25616C
Atmel
the confidentiality of data during read-write accesses and verify password operations. To enable encryption, the host
must call the Verify Crypto command with a valid session encryption key when the device is already in active
authentication mode. The session encryption key must belong to the active authentication key set. The host may
enable encryption at any time after which data content of communication between host and device user zones
becomes encrypted. If a user zone configuration in the Access Register requires encryption, however, then the host
must enter encryption mode and must encrypt all data content to and from the zone in the remainder of the active
encryption session in order to communicate with the zone. CryptoMemory does not encrypt system zone data except
for password and password attempt counters. Passwords and password attempt counters require encryption during
active authentication or encryption modes.
Each successful entry into encryption 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 both encryption and authentication modes 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. Activating encryption is similar in
process to activating authentication with the exception that the session encryption key replaces the secret seed. The
process uses the Verify Encryption variant of the Verify Crypto command (see
Synchronous Command
45).
Figure 5. Encryption Activation Process from Active Authentication Mode
CryptoMemory implements a data validity check function in the form of an encrypted checksum. This checksum
provides a bi-directional data integrity check and data origin authentication capability in the form of a Message
Authentication Code (MAC): only the host/device that carried out a valid authentication is capable of computing a valid
MAC. When writing data to the CryptoMemory device in authentication or encryption communication modes, the host
must send a valid checksum immediately following the write command. If the checksum is invalid, the device rejects the
write command and resets the device security privileges. The host must reinitiate entry into authentication and, if
applicable, encryption modes to continue. The use of checksum is optional when reading data. Calls to the read
checksum command resets device security so its use is recommended only at the completion of all data read
operations from the device.
®
CryptoMemory
Session Key, Cryptogram
CryptoMemory Device
Compute Challenge A
Compute Challenge B
Verify Challenge A
Enable Encryption
®
allows the use of encryption between a host system and the CryptoMemory device to protect
Set
,” on page
28
or
Command/Communications
Table
Read Config Zone
Verify Encryption
34,
“Atmel CryptoMemory Asynchronous Command
Session Key, Cryptogram
Generate Random Number
Compute Challenge A
Compute Challenge B
Read Challenge B
Verify Challenge B
Table
Host Logic
25,
“Atmel CryptoMemory
Set
,” on page
17