ATECC508A datasheet(28/109 Pages) MICROCHIP

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Security Information

3.1

Cryptographic Standards

The ATECC508A follows various industry standards for the computation of cryptographic results. These

reference documents are described in the sections below.

3.1.1

SHA-256

The ATECC508A MAC command calculates the digest of a secret key concatenated with the challenge or

nonce. It optionally includes various other pieces of information stored on the device within the digested

message. The ATECC508A computes the SHA-256 digest based upon the algorithm documented in the

following website:

http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf

The complete SHA-256 message processed by the ATECC508A is listed in Section Security Commands

for each of the particular commands that use the algorithm. Most standard software implementations of

the algorithm automatically add the appropriate number of pad and length bits to this message to match

the operation the device performs internally.

The SHA-256 algorithm is also used for encryption by taking the output digest of the hash algorithm and

XORing it with the plain text data to produce the ciphertext. Decryption is the reverse operation, in which

the ciphertext is XORed with the digest with the result being the plain text.

3.1.2

HMAC/SHA-256

The response to the challenge can also be computed using the HMAC algorithm based upon the

SHA-256 documented at the following website:

https://csrc.nist.gov/csrc/media/publications/fips/198/1/final/documents/fips-198-1_final.pdf

Because of the increased computation complexity, the HMAC command is not as flexible as the MAC

command, and the computation time is extended for HMAC. While the HMAC sequence is not necessary

to ensure the security of the digest, it is included for compatibility with various software packages.

3.1.3

Elliptic Curve Digital Signature Algorithm (ECDSA)

The ATECC508A computes and verifies the Elliptic Curve signatures according to the algorithm

documented in:

ANSI X9.62-2005 https://www.ansi.org/

FIPS 186-4 specification http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf

3.1.4

Elliptic Curve Diffie-Hellman (ECDH)

The ATECC508A executes the ECDH key agreement according to NIST Special Publication 800-56A

recommendations:

http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar2.pdf

https://csrc.nist.gov/csrc/media/publications/sp/800-56a/rev-2/final/documents/draft-sp-800-56a.pdf

The ATECC508A does not implement the KDF portions of these specifications.

ATECC508A

Security Information

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