Tag Archives: yassl

Is there a case for a unified SSL front?

There are many, sorry very many, different SSL libraries today that various programs may want to use. In the open source world at least, it is more and more common that SSL (and other crypto) using programs offer build options to build with either at least OpenSSL or GnuTLS and very often they also offer optinal build with NSS and possibly a few other SSL libraries.

In the curl project we just added support for library number nine. In the libcurl source code we have an internal API that each SSL library backend must provide, and all the libcurl source code is internally using only that single and fixed API to do SSL and crypto operations without even knowing which backend library that is actually providing the functionality. I talked about libcurl's internal SSL API before, and I asked about this on the libcurl list back in Feb 2011.

So, a common problem should be able to find a common solution. What if we fixed this in a way that would be possible for many projects to re-use? What if one project's ability to select from 9 different provider libraries could be leveraged by others. A single SSL API with a simplified API but that still provides the functionality most "simple" SSL-using applications need?

Marc Hörsken and I have discussed this a bit, and pidgin/libpurble came up as a possible contender that could use such a single SSL. I've also talked about it with Claes Jakobsson and Magnus Hagander for postgresql and I know since before that wget certainly could use it. When I've performed my talks on the seven SSL libraries of libcurl I've been approached by several people who have expressed a desire in seeing such an externalized API, and I remember the guys from cyassl among those. I'm sure there will be a few other interested parities as well if this takes off.

What remains to be answered is if it is possible to make it reality in a decent way.

Upsides:

  1. will reduce code from the libcurl code base - in the amount of 10K or more lines of C code, and it should be a decreased amount of "own" code for all projects that would decide to use thins single SSL library
  2. will allow other projects to use one out of many SSL libraries, hopefully benefiting end users as a result
  3. should get more people involved in the code as more projects would use it, hopefully ending up in better tested and polished source code

There are several downsides with a unified library, from the angle of curl/libcurl and myself:

  1. it will undoubtedly lead to more code being added and implemented that curl/libcurl won't need or use, thus grow the code base and the final binary
  2. the API of the unified library won't be possible to be as tightly integrated with the libcurl internals as it is today, so there will be some added code and logic needed
  3. it will require that we produce a lot of documentation for all the functions and structs in the API which takes time and effort
  4. the above mention points will deduct time from my other projects (hopefully to benefit others, but still)

Some problems that would have to dealt with:

  1. how to deal with libraries that don't provide functionality that the single SSL API does
  2. how to draw the line of what functionality to offer in the API, as the individual libraries will always provide richer and more complete APIs
  3. What is actually needed to get the work on this started for real? And if we do, what would we call the project...

PS, I know the term is more accurately "TLS" these days but somehow people (me included) seem to have gotten stuck with the word SSL to cover both SSL and TLS...

Top-3 curl changes in 2011

At the end of the year I thought it would be interesting to have a look back over the past twelve months and see what the biggest changes in the curl project were and what the most important bug-fixes were etc. I've turned into a little mini series of blog posts. The top-3s. First out, the top-3 changes.

Top-3 changes

In total I counted 29 notable changes brought during 2011. The most significant ones in my view are:

Change 1 - fancier protocol support in proxy strings

This may sound trivial, and the code certainly is, but with this change suddenly a lot of applications that use libcurl got better proxy support without having do anything at all. Previously the application would have to set what protocol type the proxy it would use is, even though libcurl has supported having the proxy specified as an environment variable for ages.

Having only the proxy name was useful but limiting. With this new change you can specify proxy type or rather proxy protocol by prefixing the proxy name like "socks4://magic-proxy.example.com" if you want a SOCKS4 proxy. libcurl now supports socks4, socks4a, socks5 or socks5h used as prefixes as well as http.

Change 2 - allow sending "empty" HTTP headers

Another minor change in code but possibly larger impact in usefulness for applications. We introduced a way for applications to change internal headers and to add new ones ages ago. We (or rather I) then made the choice that if you'd provide a header with only the name and a colon, that is with no contents on the right side, it would delete the internal header. That was not a clever move as later on people have wanted to add "blank" or "empty" headers that look exactly like that, but libcurl has then refused to.

There have been some more or less hackish work-arounds to trick libcurl into allowing an empty header, but now finally we introduce a nice and clean way for applications to pass in these kinds of empty headers:

Pass in an empty header that instead of a colon has a semicolon! This is an otherwise illegal header that wouldn't make sense, but libcurl will use that as a trigger that an empty header should be used and it will then replace the semicolon with a colon and things will be fine.

Change 3 - Added support for cyassl and axTLS

Proving that libcurl moves forward and into more and more markets, the number of supported SSL libraries grew to 7 this year. The all new cyassl backend that replaced the previously done yassl backend that was using cyassl's former OpenSSL emulation layer. Now we're using the native and pure API and things much cleaner. The possibly smallest available TLS library axTLS also got support.

Not all backends and not all SSL libraries are the same or support the same set of features, but then libcurl is used in many different scenarios and use cases and this way we offer more options to more users to craft libcurl for their particular needs. Our internal SSL backend API has managed quite well and proves to have been a worthy change. Adding support for yet another SSL library within libcurl is actually not a lot of work.

Change 4 - TSL-SRP

You may think number 4 of a top-3 list is weird, but I couldn't cut it off here! =) TLS-SRP has been waiting in the shadows for so long and all of a sudden two of the major SSL libraries have support for it in released versions and libcurl got support for using these features in both libraries during 2011.

cURL

libcurl, seven SSL libs and one SSH lib

I did a talk today at Fosdem with this title. The room only had 48 seats and it was completely packed with people standing everywhere it was possible around the seated guys.

The English slides from my talk are below. It was also recorded on video so I hope I'll be able to post once it becomes available online

What is this yassl really?

yassl is said to be Yet Another SSL library and I've been told that for example it is the preferred library used by the mysql camp. I got interested in this several years ago when I learned about it since I thought it was fun to see an alternative implementation of OpenSSL that still offers the same API.

Since then, I've amused myself by trying to build and run curl with it like every six months or so. I've made (lib)curl build fine with yassl (and its configure script also detects that it is an OpenSSL API emulated by yassl), but I've never seen it run the entire curl test suite through without failing at least one test!

I asked the mysql guy about how yassl has worked for them, but he kind of shrugged and admitted that they hadn't tried it much (and then I don't know really who he spoke for, the entire team or just he and his closest friends) but he said it worked for them.

Today I noticed the yassl version 1.9.6 that I downloaded, built and tried against curl. This time curl completely fails to build with it...

Let me also point out that it's not like I've not told the yassl team (person?) about these problems in the past. I have, and there have been adjustments that have been meant to address problems I've seen. I just can't make curl use it successfully... libcurl can still be built and run with OpenSSL, GnuTLS or NSS so it's not like we lack SSL library alternatives.

The same team/person seems to behind another SSL lib called Cyassl that's aimed for smaller footprint systems and I've heard whispers about people trying to get libcurl to build against that and it surely is going to be interesting to see where that leads!

libcurl built with yassl

yassl is a (in comparison) small SSL/TLS library that libcurl can be built to use instead of using one of the other SSL/TLS libraries libcurl supports (OpenSSL, GnuTLS, NSS and QSSL). However, yassl differs somewhat from the others in the way that it provides an OpenSSL-emulating API layer so that in libcurl we pretty much use exactly the same code for OpenSSL as we do for yassl.libcurl

yassl claimed this libcurl support for several years ago and indeed libcurl builds fine with it and you can even do some basic SSL operations with it, but the emulation is just not good enough to let the curl test suite go through so lots of stuff breaks when libcurl is built with yassl.

I did this same test 15 months ago and it had roughly the same problems then.

As far as I know, the other three main libraries are much more stable (the QSSL/QsoSSL library is only available on the AS/400 platform and thus I don't personally know much about how it performs) and thus they remain the libraries I recommend users to select from if they want something that's proven working.