In unrelated, uncategorised other news, a secret… Erm, professional? cryptographer has joined Pivx…
Yeah, I’ll buy that for a dollar…
Zcash is provably private. DASH now wants someone to demonstrate that it isn’t !?!
OK. So, DASH has improved privacy over Bitcoin; essentially via the use of on-chain coin mixing through masternodes.
Essentially coinjoin - https://en.wikipedia.org/wiki/CoinJoin
Now, lets imagine a stage with a big pile of serialized bank notes (all of the DASH in circulation). A troop of dancers enters stage left and stage right. They proceed to frolic about in a seemingly dis-organised fashion, some of the dancers gather up the notes and start to re-arrange them into smaller piles of notes (masternodes). They then begin to dance back and forth between the piles of notes, swapping notes from each pile continually (making dark send transactions).
As the audience watches the show (because the blockchain is not encrypted in this regard), they can obviously see everything that takes place (all transactions), however they all clap excitedly in wonder and amazement.
The stage show is also televised and thus will remain in the archives forever (the blockchain). All dancers remain on the stage for the duration of the show! Anyone can play the show back in slow motion, repeatedly. They can fast forward and rewind it, time and time again to observe exactly what took place.
In this regard, it is clearly possible to work out which dancer moved which notes to where. It is difficult, although quite obviously do-able, given enough resources.
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With Zcash, (although coin mixing does not take place) some of the dancers are instead free to move (and make said z address transactions) behind a screen (or by dancing off stage left or stage right, perhaps even returning on the opposite side of the stage!). Through the use of Zk-SNARKs (i.e. the hidden screen or by some dancers being ‘backstage’) multiple un-linkable (private transactions) could take place between the dancers, with the entire audience being non the wiser!
Additional: The distinction between the on stage screen and being backstage (with Zcash) is actually quite relevant. Remembering that one or more dancers making private transactions could choose (or not) to demonstrate to the audience that a transaction took place. Imagine just half of the screen being illuminated to show that the transaction took place, a bit like shadow puppetry.
See: Anatomy of A Zcash Transaction - Electric Coin Company
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One is a real magic show and the other just an illusion!
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I get it, I really do. But, just for the sake of accuracy, this $100k challenge is currently only a proposal (being voted on by masternode owners right now) that has been organised by a passionate Dash supporter who, like quite a few others, has had to deal with far too many detractors that only offer opinion and no actual proof to support their position that the coin mixing in Dash can be analysed to reveal anything about the user and / or originating addresses.
Although I am glad that you see coin mixing as an on-chain process - some Dash enthusiasts aren’t even willing to concede that - as if Dash masternodes can somehow magically produce a jumble of transactions that don’t occur on the blockchain. Funny, non-technical people… 
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Indeed. I was simply trying to present an almost visual kind of analogy that anyone might reference.
Arguably, encryption only ever affords you more time in terms of privacy and anonymity. However, if that afforded time is greater than the entire history of you then it can be recognized to work in this regard. (i.e. Zcash).
With regards to the DASH challenge, it is a matter of certainty within an unknown time frame, reliant only on method and/or computational power! Breaking of encryption is unnecessary here, it only requires the correlation of big-data and/or a bit of social engineering, perhaps. That’s quite worrisome actually! 
Someone will complete the challenge eventually. Is it moral or ethical ? I’m undecided.
BlockSci claims to already have a tool for breaking Dash’s coinjoins…
Thank you - I just shared that link via the comments for that proposal.