Lazy evaluation is the default in Haskell, but that doesn't mean strict evaluation is unavailable.

Here's an example of a type definition that specifies strict evaluation https://github.com/vincenthz/hs-tls/blob/master/core/Network...

See? They don't have to switch languages after all.

This is an excellent point, and I didn't mean to imply that it's impossible to implement TLS securely in Haskell (though my original comment did seem to; I plan to fix that shortly). Only that there are more natural choices that give the same primary advantage (a strong algebraic type system).

Why don't you test the library before making assumptions about it's runtime characteristics. How about doing the slightest bit of research on the creator?

Simple(ish) example of using strictness annotations with folds:

http://www.haskell.org/haskellwiki/Foldr_Foldl_Foldl%27

There is a TLS implementation in OCaml in progress, it still has a long way to go though: https://github.com/mirleft/ocaml-tls

Could you elaborate on how lazy evaluation is problematic for such a project?

In cryptography, for most operations, you need to be sure that the operation takes the same amount of time for all possible inputs. Otherwise, you leak information.

The classic example of this is checking string equality with strncmp(): this takes a different amount of time depending on how similar the strings are. If one string is secret and the other is controlled by an attacker, the attacker can use a clock and multiple attempts to discover the secret.

Obviously this particular one isn't relevant to SSL, but there are a number of other possibilities to worry about in most languages, most obviously short-circuiting operations like boolean AND/OR. Lazy evaluation makes every operation short-circuit, so you need to worry about this in every operation.

It can be done, but it's harder than it needs to be.

So we should choose the approach that gives us trivial attacks that reveal 64K straight out of Compton to the approach that may be slightly harder to defend against timing attacks?

This is such an obvious false dichotomy that I'm sure most people will notice, but I'm pointing it out anyway.

We could use something that gives both advantages, like the OCaml I already mentioned. Or, we could take a hybrid approach, where something like Haskell generates C code that provably can't have buffer problems. Or, we could statically verify that the library is written in a known-memory-safe subset of C++. Or, we could use a language like Rust, which (once it's eventually complete) seems ideal for this sort of application.

I think the "define a strict, branchless DSL" approach is the right one, if you're going with Haskell. Then use the type system to ensure that only that stuff can touch key data. No problems with laziness or timing attacks, if the core of that is implemented correctly.

Nope. This is a common troll whenever any Haskell project is mentioned. It's despicable FUD and just plain wrong. Haskell makes it very easy and lightweight to add strictness annotations to your data structures; far, far easier than it is to add laziness to a strict-by-default language.

Not him, but I don't think the regular lazy evaluation worry about building up a million thunks and GC hell would be as much of a problem as it being awkward to not have things happen too fast and leave side channel attacks from timing.