Common input ownership heuristic
Also · CIOH · Multi-input heuristic
The common input ownership heuristic assumes that all inputs of a transaction belong to the same person. It is the main tool for clustering addresses, and collaborative transactions defeat it.
When a transaction spends several inputs, each must be signed by its owner. The simplest reading is that 1 owner signed them all. Satoshi Nakamoto noted this leak in the Bitcoin white paper. Chain analysis turns it into its workhorse. Every transaction with multiple inputs merges those addresses, and the addresses they are later linked to, into 1 cluster.
The heuristic is usually right for ordinary wallets, which is why consolidating UTXOs fuses their histories. It is wrong by construction for CoinJoin and PayJoin, where inputs come from different people. The more such transactions exist, the less any analyst can trust the rule for the chain as a whole. Coin control is the everyday way to avoid feeding it.
In French · Heuristique de propriété commune des entrées