possible mcrypt replacement - libsodium about openpgp-php

[DanielRuf]

Did I say so?

[singpolyma]

sounds worth investigating!

[jasekiw]

@singpolyma What learning resources do you recommend for learning how to contribute to this library?

[singpolyma]

@jasekiw if you want to learn more about the spec and fine the main one daunting, I've distilled some of the most necessary parts to https://github.com/singpolyma/openpgp-spec

If you're interested into helping with this mcrypt issue specifically, the mcrypt-using code is isolated to one file that's designed to be modular (so you could write another file with the same interface using libsodium, IIRC)

[singpolyma]

Looking over the code again, I think it only uses mcrypt for CAST5 support. So most operations will work without it.

[jasekiw]

After looking at libsodium more closely it seems that PHP will add it to the core extensions in PHP 7.2. However you can install the extension on 7.0+. So that leaves 7.1 completely unsupported and breaks < 7.0. I see two paths to go down.

1. Create a legacy branch to support < 7.0 with mcrypt and implement libsodium. This would require a version jump since the drop of support would be quite large. The only supported version that is dropped is PHP 5. This package would also require the installation of libsodium on php versions < 7.2.

2. Investigate what methods use CAST5 and see if we can remove mcrypt without replacing it with libsodium. is CAST5 operations necessary? This has the pros of supporting older versions of PHP as well as newer.

[singpolyma]

CAST5 is only necessary if you need to interoperate with someone using it as their symmetric algorithm. Unfortunately, gnupg defaults to CAST5 in most versions, so such interoperation is often desired.

[singpolyma]

Probably the best is to have compatible mcrypt and sodium wrappers in the library, and choose the right one a runtime based on what is installed, to keep compatibility with both popular and new versions of PHP.

[jasekiw]

I didn't think of that. That would be way better. PHP 7.1 would still be an odd version for people to install the package because the user would have to install libsodium seperately.

I cannot seem to find documentation on how to perform a CAST5 operation using libsodium. Have you seen anything?

I also found CAST5 in the list of supported algorithms in openssl. Maybe OpenSSL can be a polyfill?

[singpolyma]

I think sodium calls it cast128 -- same algorithm

[DanielRuf]

Why not use https://github.com/paragonie/sodium_compat?

[jedisct1]

The PECL extension supports PHP 7.0.x, 7.1.x and 7.2.x

[DanielRuf]

The PECL extension supports PHP 7.0.x, 7.1.x and 7.2.x

This is not an option here as this library should work on all systems with the right polyfills afaik.

[Rotzbua]

You can use openssl for encryption and signing. Only Idea and Twofish is not supported with openssl. (Only tested with php7.0)

[DanielRuf]

You can use openssl for encryption and signing. Only Idea and Twofish is not supported with openssl. (Only tested with php7.0)

No, this should not be done.

[Rotzbua]

No, this should not be done.

Why?

Mcrypt is used in this library for encrypting with cast5. Openssl supports cast5. -> Openssl can replace Mcrypt.

[DanielRuf]

We should use and move to libsodium.

[DanielRuf]

Because it makes no sense to reimplement mcrypt with openssl and libsodium is different. mcrypt support should be dropped in the future.

[Rotzbua]

@DanielRuf https://github.com/paragonie/sodium_compat#cryptography-primitives-provided do not list cipher cast5. Where did you read that the sodium library supports cipher cast5?

[DanielRuf]

Also see the comment of @singpolyma

I think sodium calls it cast128 -- same algorithm

[Rotzbua]

Did I say so?

More ore less, yes. You wrote:

We should use and move to libsodium.

So you have no clue about the sodium library, but you recommend it. No words...

@singpolyma Sodium do not support any cipher used by openpgp. https://secure.php.net/manual/en/ref.sodium.php

[singpolyma]

I'm happy to accept wrappers for any of openssl or sodium or whatever else for cast5/cast128 support. Should be no problem to support all of these options and use whatever is available on the system we're running on.

[DanielRuf]

@Rotzbua initially it was not my recommendation. See the first comment. I just said that I am also for supporting libsodium (or an alterntive) in some way.

I never wrote that it supports the gnupg / pgp algorithms ;-)

[DanielRuf]

Writing pure openssl wrappers is like writing your own crypto which is not recommended. I guess there is already a library for this eg by paragonie, ircmaxell and others.

[jedisct1]

libsodium does not support CAST5. In fact, in doesn't support any of the ciphers currently supported by GnuPG. So, files encrypted using OpenPGP-PHP could only be decrypted by the same tool.

[singpolyma]

I fail to see how wrapping openssl would be more dangerous than wrapping mcrypt.

I also remind people that mcrypt is only used for cast5 -- if you use AES that is supported directly by phpseclib so this whole question only matters if you application has a specific need for cast5 (which some do, of course)

[jedisct1]

That being said, CAST5 is a very simple algorithm, which can be easily rewritten in pure PHP.

[jasekiw]

@jedisct1 is there any current implementations of this in pure PHP? We don't want to reinvent the wheel if something is already out there.

[singpolyma]

Happy to accept PRs for wrapping other methods, but I've added an OpenSSL-based CAST5 wrapper to master now -- passes tests in PHP7.1 and 7.2 without warnings now (though there are warnings if using older versions of phpseclib -- have to figure out how to tell travis which versions to use with with PHP versions...)