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AT88SC0808CA-SU

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Atmel AT88SC0808CA [Summary DATASHEET]
5204FS−CRYPTO−12/11
13
11.5 Cryptographic Message Authentication Codes
AT88SC0808CA implements a data validity check function in the standard, authentication or encryption modes of operation.
In the standard mode, data validity check is done through a Modification Detection Code (MDC), in which the host may read
an MDC from the device in order to verify that the data sent was received correctly.
In authentication and encryption modes, the data validity check becomes more powerful since it provides a bidirectional data
integrity check and data origin authentication capability in the form of a Message Authentication Codes (MAC). Only the
host/device that carried out a valid authentication is capable of computing a valid MAC. While operating in the authentication
or encryption modes, the use of MAC is required. For an ingoing command, if the device calculates a MAC different from the
MAC transmitted by the host, not only is the command abandoned but the security privilege is revoked. A new authentication
and/or encryption activation will be required to reactivate the MAC.
11.6 Encryption
The data exchanged between the device and the host during read, write and verify password commands may be encrypted to
ensure data confidentiality.
The issuer may choose to require encryption for a user zone by settings made in the configuration memory. Any one of four
keys may be selected for use with a user zone. In this case, activation of the encryption mode is required in order to read/write
data in the zone and only encrypted data will be transmitted. Even if not required, the host may still elect to activate encryption
provided the proper keys are known.
11.7 Supervisor Mode
Enabling this feature allows the holder of one specific password to gain full access to all eight password sets, including the
ability to change passwords.
11.8 Modify Forbidden
No write access is allowed in a user zone protected with this feature at any time. The user zone must be written during device
personalization prior to blowing the security fuses.
11.9 Program Only
For a user zones protected by this feature, data can only be programmed (bits change from a “1” to a “0”), but not erased (bits
change from a “0” to a “1”).
Atmel AT88SC0808CA [Summary DATASHEET]
5204FS−CRYPTO−12/11
14
12. Protocol Selection
The AT88SC0808CA supports two different communication protocols.
• Smartcard Applications:
Smartcard applications use ISO 7816-B protocol in asynchronous T = 0 mode for compatibility and interoperability
with industry standard smartcard readers.
• Embedded Applications:
A two-wire serial interface provides fast and efficient connectivity with other logic devices or microcontrollers.
The power-up sequence determines establishes the communication protocol for use within that power cycle. Protocol
selection is allowed only during power-up.
12.1 Synchronous Two-wire Serial Interface
The synchronous mode is the default mode after power up. This is due to the presence of an internal pull-up on RST. For
embedded applications using CryptoMemory in standard plastic packages, this is the only available communication protocol.
• Power-up V
CC
, RST goes high also
• After stable V
CC
, SCL(CLK) and SDA(I/O) may be driven
• Once synchronous mode has been selected, it is not possible to switch to asynchronous mode without first powering
off the device
Figure 12-1. Synchronous Two-wire Protocol
V
cc
I/O-SDA
RST
CLK-SCL
1
2
3
4 5
Note: Five clock pulses must be sent before the first command is issued.
Atmel AT88SC0808CA [Summary DATASHEET]
5204FS−CRYPTO−12/11
15
12.2 Asynchronous T = 0 Protocol
This power-up sequence complies to ISO 7816-3 for a cold reset in smart card applications.
• V
CC
goes high; RST, I/O (SDA) and CLK (SCL) are low
• Set I/O (SDA) in receive mode
• Provide a clock signal to CLK (SCL)
• RST goes high after 400 clock cycles
The device will respond with a 64-bit ATR code, including historical bytes to indicate the memory density within the
CryptoMemory family.
Once asynchronous mode has been selected, it is not possible to switch to synchronous mode without first powering off the
device.
Figure 12-2. Asynchronous T = 0 Protocol (Gemplus Patent)
V
cc
I/O-SDA
RST
CLK-SCL
ATR
13. Initial Device Programming
Enabling the security features of CryptoMemory requires prior personalization. Personalization entails setting up of desired
access rights by zones, passwords and key values, programming these values into the configuration memory with verification
using simple write and read commands, and then blowing fuses to lock this information in place.
Gaining access to the configuration memory requires successful presentation of a secure (or transport) code. The initial
signature of the secure (transport) code for the AT88SC0808CA device is $22 E8 3F. This is the same as the Write 7
password. The user may elect to change the signature of the secure code anytime after successful presentation.
After writing and verifying data in the configuration memory, the security fuses must be blown to lock this information in the
device. For additional information on personalizing CryptoMemory, please see the application notes Programming
CryptoMemory for Embedded Applications and Initializing CryptoMemory for Smart Card Applications from the product page at
www.atmel.com/products/securemem.
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AT88SC0808CA-SU

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