Add scramble xormask

[keeshux]

Rebase of #121

Fixes #38

cc @XMB5

[HosseyNJF]

Why this isn't being merged?

[x0r2d2]

Why this isn't being merged?

+1
Hopefully, will be merged soon.

[keeshux]

@XMB5 I notice your additions in the copyright header. While I have no issue with crediting one's work (goes without saying), it's impossible to track authorship on a line by line basis. In fact the header is more of a Xcode placeholder.

Would you be okay with being credited in a different manner? E.g. in README, LICENSE or wherever else you're okay with. As is, I'm not sure about merging this as I don't want this to cause trouble in the future.

Feel free to contact me privately on me@davidederosa.com for more insight.

[keeshux]

Other than that, the "official" Tunnelblick patch takes a string as input. Do you confirm this PR only supports a single byte XOR mask?

[XMB5]

@keeshux I'm fine with being credited in any way, for example in the README, LICENSE, at the top of the file, or even only in git log (i.e. not written down in any file, only in git metadata).

And yes, this patch only supports a single byte mask--see ConfigurationParser.swift line 470:

optXorMask = Character($0[1]).asciiValue

Although the official patch supports multiple bytes, in practice, people often use only 1 byte because it is sufficient to evade firewalls (for example, ExpressVPN does this, although they use a custom option name instead of scramble xormask).

[keeshux]

Nice! Please check out last 2 commits.

[x0r2d2]

@keeshux Am I right that you plan to merge it soon?

[XMB5]

@keeshux The new commits look good. My one comment is that maybe we should document this feature somewhere, perhaps in the README? Here's some text we could use:

--scramble xormask <character> -- XOR all incoming and outgoing bytes by the ascii value of this character

• Only single-byte masks supported
• See https://tunnelblick.net/cOpenvpn_xorpatch.html for details