Mittwoch, 25. November 2015

Something For The Toolshelf - Code Analysis Tools Used For Security Analysis Of Truecrypt

Recently the Bundesamt für Sicherheit in der Informationstechnik (BSI), an authority of the German government released a security analysis of Truecrypt. This analysis was carried out by the Fraunhofer-Institut für Sichere Informationstechnologie (SIT) in Darmstadt /Germany. This institute is part of the Frauenhofer society - a research organization spread across Germany.

From a software engineering perspective I was curious what approach the researches took to evaluate the code code base.



Apparently also the Truecrypt authors liked their goto. The study on goto (my translation):

To implement exception handling the usage of goto is generally accepted since the language C does not offer an own feature for that. New research concludes that meanwhile programmers are predominantly using goto in a sensible way.

Die Verwendung von goto wird jedoch im Allgemeinen zur Umsetzung einer Ausnahmebehandlung akzeptiert, da die Sprache C kein eigenes Konstrukt hierfür kennt. Neuere Untersuchungen haben ergeben, dass Programmierer mittlerweile die goto-Anweisung überwiegend nur noch in sinnvoller Weise verwenden. (original)

On that topic the study quotes An empirical study of goto in C, a paper which was pre-released in February 2015 and which was subject of my previous post.


Complexity Of The Source Code

To measure complexity the authors of the study employed a tool called Lizard which can deal with a bunch of languages including C, C++, Java, Python and Javascript

Here is the feature list taken from the Github page of Lizard:
  • the nloc (lines of code without comments),
  • CCN (cyclomatic complexity number),
  • token count of functions.
  • parameter count of functions.

As their measure of complexity the study uses the cyclomatic complexity:

As a measure for the complexity of the flow of control especially the cyclomatic complexity is being used. Values higher than 15 are an indicator for potential refactoring. Values above 30 are usually accompanied by flawed code. (my translation)

Als Maß für die Kontrollflusskomplexität wird insbesondere die zyklomatische Komplexität verwendet. Werte größer 15 sind ein Indiz dafür, dass Refaktorierung sinnvoll ist. Werte über 30 gehen oft mit fehlerhaftem Code einher. (original)

Code Duplicates

To find identical pieces of source code the autors of the study use Duplo, a duplicate finder for C and C++. With its default settings the tools consideres three and more identical  lines of code as duplicates. 


Static Code Analysis

For this kind of analysis three tools where used: Coverity, Cppcheck and the Clang Static Analyzer. The interesting point here is that there where almost no overlaps in the errors found by the three tools. Which brings me to the conclusion that it is a sensible investment to integrate more than one static analyzer in the Continuous Integration chain.

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