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DESIGN.md

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TLSAudit Design Document

Documentation of architectural drivers and design rationales.

Architectural drivers

  • Minimal amount of dependencies so that the tool can be used out-of-the-box, without any additional installation steps on standard Linux distributions
  • Modular architecture so that the tool can be easily extended to additional web servers, etc. (or the support/maintenance can be dropped for deprecated servers without affecting others)

Architecture

To achieve modularity, TLSAudit uses the pipes-and-filters architecture. Moreover, pipes-and-filters is a natural fit to the task at hand:

  1. Read Nginx configuration
  2. Parse TLS options
  3. Check if there are any weak or insecure options
  4. Generate and output a report

Data structures

Dictionary D of all Nginx TLS configuration options, with keys being the individual options in a hierarchical notation A:B:C and values being {secure|weak|insecure}.

Filters

  • Parser: read Nginx configuration file (provided as argument) and extract a list L with TLS configuration options (hierarchical notation A:B:C)
  • Checker: take L and dictionary D as input, output list R containing configuration options which are either weak or insecure
  • Reporter: take R as input and generate a simple command line report (if needed, different report formats can be added later)

Implementation

To ensure minimal amount of dependencies and maximum portability, TLSAudit is implemented as a Bash script. While TLSAudit would be easier to implement in a modern scripting language like Python, most Linux distributions come with the Bash shell pre-installed so that a Bash script can be used out-of-the-box.

Files

  • tlsaudit.sh is the main script
  • lib/parser.sh contains the parser code
  • lib/checker.sh contains the checker code
  • lib/reporter.sh contains the reporter code