AT88SA102S_11 ATMEL [ATMEL Corporation], AT88SA102S_11 Datasheet - Page 5

• Manufacturer Part Number: AT88SA102S_11
• Description: Atmel CryptoAuthentication Product Authentication Chip
• Manufacturer: ATMEL [ATMEL Corporation]

1.6
1.6.1
1.7
SHA-256 Computation
AT88SA102S performs only one cryptographic calculation – a keyed digest of an input challenge. It includes optionally various
other information stored on the chip within the digested message.
AT88SA102S computes the SHA-256 digest based on the algorithm documented here:
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
Throughout this document, the complete message processed by the AT88SA102S chip is documented. According to the
above specification, this always includes a single bit of ‘1’ pad after the message, followed by a 64-bit value representing the
total number of bits being hashed (less pad and length). If the length is less than 447 (512-64-1), then the necessary number
of ‘0’ bits are included between the ‘1’ pad and ‘length’ to stretch the last message block out to 512-bits.
When using standard libraries to calculate the SHA-256 digest, these pad and length bits should probably not be passed to the
library as most standard software implementations of the algorithm add them in automatically.
SHA Computation Example
In order to ensure that there is no ambiguity, the following example vector is provided in addition to the sample vectors in the
NIST document. In this example, all values are listed in hex format. For all but the key, bytes are listed in the order that they
appear on the bus – first on the bus is listed on the left side of the page. The key value below is listed in the same order as the
challenge, so the 01 at the left of the key string corresponds to the first byte in the SHA-256 document.
SHA Computation Example
Security Features
The AT88SA102S incorporates a number of physical security features designed to protect the keys from release. These
include an active shield over the entire surface of the part, internal memory encryption, internal clock generation, glitch
protection, voltage tamper detection and other physical design features.
Pre-programmed keys stored on the AT88SA102S are encrypted in such a way as to make retrieval of their values via outside
analysis very difficult.
Both the clock and logic supply voltage are internally generated, preventing any direct attack via the pins on these two signals.
Key
Challenge
Opcode
Mode
KeyID
Secret Fuses
Status Fuses
Fuse MfrID
Fuse SN
ROMMfrID
ROM SN
The 88-bytes over which the digest is calculated are:
And the resulting digest is:
01030507090B0D0F11131517191B1D1F21232527292B2D2F31333537393B3D3F
020406080A0C0E10121416181A1C1E20222426282A2C2E30323436383A3C3E40
08
50 (all optional information included in message)
0000111122223333
445566
77
8899AABB
CCDD
EEFF
0103…3D3F0204…3E400850FFFF00001111…EEFF
6CA7129C8DA9CE80EA6357DDCFB1DDCBBBD89ED373419A5A332D728B42642C62
Atmel AT88SA102S [DATASHEET]
8584G−CRYPTO−9/11
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