Is reviewing the cryptographic aspects of a block of code on-topic for this site?
Code review is a different beast from the normal kind of Stack Exchange questions. “Review this code” isn't really a question, it can be very broad. It's more open-ended than the typical “problem to solve” archetype for Stack Exchange questions.
Stack Overflow has long been uneasy about code review questions, and now more and more often rejects them as too broad. There is a new site especially for code reviews. Partly due to the existence of this site, part of the Stack Overflow community wants to ban code review questions from SO and systematically migrate them to Code Review. This will officially happen once CR graduates, though there is some disagreement as to whether code review remains suitable on SO.
Code review is peculiar in that it isn't really a questions and answers site, but reuses the format for something a little different. “Askers” post working code and normally ask for feedback about a specific aspect, but “answers” may concern any aspect of the code. In practice, this seems to work.
I think code review on Cryptography SE clashes with the rest of the content here even more than on Stack Overflow. After all, straight coding questions are off-topic, even when they're about cryptographic code.
I propose to declare code review questions off-topic here and suggest posting on Code Review instead. Moderators can migrate questions that are posted here. Remember that Code Review is only for code that has no known bugs: for questions about non-working code, ask on Stack Overflow.
This isn't to say that any question with code is off-topic here, of course. But if the question is to review an aspect of the code (rather than, say, ask about possible algorithmic optimizations, or side channel implications of an implementation technique), then it's a poor fit for the site.
Cryptographers who are interested in participating in code reviews can browse the cryptography tag on Code Review.