by Jon Matonis
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Also called bitcoin laundries, these web-based services charge bitcoin holders a nominal fee to receive different bitcoins than the ones initially transferred. The sites never handle national currencies like the dollar or euro so technically they are not exchanges.
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Vitalik Buterin of Bitcoin Magazine argues that [...] the core principles of the bitcoin protocol, such as user-defined anonymity and user-defined transactional privacy, remain intact due to optional mixing services.
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When it comes to bitcoin oversight, regulators and law enforcement must comprehend that which is able to be constrained versus that which is not able to be constrained.
- http://www.forbes.com/sites/jonmatonis/2013/06/05/the-politics-of-bitcoin-mixing-services