Definition
Output registration is the CoinJoin phase in which each participant tells the coordinator which outputs they want the final transaction to create, redeeming the blinded credentials they earned during input registration. Because the credentials are cryptographically blinded, the coordinator can verify that the requested output value is backed by registered input value without learning which participant's input it came from. This unlinkability between the registration steps is the heart of how a modern CoinJoin protects privacy.
The role of a fresh identity
To prevent the coordinator from joining the dots, participants register outputs using a new network identity, typically a fresh Tor connection separate from the one used for inputs. If a wallet leaked the same circuit or IP across both phases, the coordinator could link an input to an output and collapse the participant's anonymity set. The discipline of identity separation is therefore enforced by the wallet, not left to the user.
Standardized outputs and change
Participants generally request standardized denominations so their mixed outputs are indistinguishable from everyone else's, plus an optional change output for any leftover value. That change is the weak link, since it is the non-standard amount, and how it is later handled determines whether privacy survives. Output registration thus sets up the spending decisions that follow the mix.
See also equal-output CoinJoin.
In Simple Terms
Output registration is the CoinJoin phase in which each participant tells the coordinator which outputs they want the final transaction to create, redeeming the blinded…