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posted by martyb on Saturday December 02 2017, @01:48PM   Printer-friendly
from the see-what-we-did-there? dept.

https://www.cossacklabs.com/blog/macros-in-crypto-c-code.html

Like death and taxes, one thing that you can be sure of is that using C macros in a modern software project will cause a debate. While for some macros remain a convenient and efficient way of achieving particular programming goals, for others they are opaque, introduce the unnecessary risk of coding errors, and reduce readability.

The criticism of macros is particularly acute in the wider security community. Among Cossack Labs' engineers and the core Themis crypto library contributors there are people who previously worked on auditing cryptographic implementations of critical code. Their typical knee-jerk reaction to macros was always "kill it with fire and never use it again". Taking no sides, we would like to assess both pros and cons of using such dangerous things as macros in security code (as we faced the issue when developing Themis) and suggest some techniques for lowering the accompanying risks.

We'll also discuss a custom "for-audit" build target for Themis designed specifically to generate source code that exposes the macros to inspection because we appreciate the need for security software to be subject to detailed source code scrutiny.


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  • (Score: 2) by Pino P on Saturday December 02 2017, @11:53PM

    by Pino P (4721) on Saturday December 02 2017, @11:53PM (#604467) Journal

    What's your feeling about code generators? Code to generate code?

    It depends on the difficulty of either formally proving the correctness of the code generators or auditing their output. The featured article is about making a code generator's output more auditable.

    How about templates?

    The key difference is that C++ templates are more type-safe than C preprocessor macros. But C preprocessor macros still have two advantages: availability on platforms with no C++ compiler (such as MOS 6502), and ability to use __FILE__ and __LINE__ at the place where a macro is used as opposed to where it is defined.

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