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No, change addresses are optional. The protocol allows transactions with one input and one output: https://en.bitcoin.it/wiki/Transaction#Principle_example_of_

• ikeboy 12y ago
  Yes, but that's if you want it all to go to one place. I don't see any specific design choice involving change addresses that seems specifically for anonymity.
  • jordigh 12y ago
    Change addresses aren't part of the design at all. Multiple outputs are. By convention, an output to an address you control is called a change address, but it's just a convention on top of the protocol, not something the protocol is aware of. And yes, their purpose is very explicitly extra anonymity. Gavin named a branch without change addresses a "noprivacy" branch: http://bitcoin.stackexchange.com/questions/1629/why-does-bitcoin-send-the-change-to-a-different-address#comment2139_1629 http://bitcoin.stackexchange.com/questions/1629/why-does-bit...
    • deleted 12y ago
      [deleted]
    • ikeboy 12y ago
      >By convention, an output to an address you control is called a change address, but it's just a convention on top of the protocol, not something the protocol is aware of. I'm aware of that, it's part of what I was trying to say. >Gavin named a branch without change addresses a "noprivacy" branch: That branch apparently just sends it to the sending address. There are other reasons not to reuse addresses unrelated to anonymity, see https://en.bitcoin.it/wiki/Address_reuse https://en.bitcoin.it/wiki/Address_reuse. So I still don't see a design choice that is specifically for anonymity.
    • markburns 12y ago
      Anonymity and lack of susceptibility to a certain class of quantum computing attacks