[AXS-61] Review ASN Engineering Specs

[bernardoaraujor]

ASN Engineering Specs were extracted from DAC Design Specification v0.5.docx and XAIN_Embedded Technical Specifications.pdf.

However both documents provide conflicting information, and some of them remain unclear and possibly outdated.

A review by @djordjeglbvc on the ASN section of the Engineering Specification document needs to be done to ensure all information is correct and presented properly.

Review items:

• libCrypto module
• Tiny Embedded module
• Server authentication key exchange
• Client public key authentication protocol
• Data encryption, decryption and validation

JIRA: AXS-61

[djordjeglbvc]

@vlad-ns would be better suited for reviewing this, as I wasn't directly involved in implementation of these modules

[vlad-ns]

1. Block diagrams for server authentication key exchange and client public key authentication protocol should be replaced with following images:

2. Add additional explanation for DH public key generation:

After physical connection is established, client generates a Diffie-Hellman (DH) private key. Based on the private key, client computes DH public key.

... using following formula: where g and p are previously configured constants on both side client and server.

3. In section Data encryption, decryption and validation bellow formulas add explanation: "A", "B", ... "F" are constants representing ASCII values of those characters

[vlad-ns]

review and update done.