Private Execution
Private execution is Aleo's computation model. Program functions run off-chain on the user's device (or a delegated prover), not on every validator. The user provides private inputs locally, SnarkVM executes the function, and the output is a zero-knowledge proof that the computation was correct. Only this proof, along with encrypted outputs and nullifiers, goes to the blockchain. Validators verify the proof without ever seeing the private inputs.
This differs from transparent blockchains like Ethereum, where every validator re-executes every transaction and all inputs are visible in calldata. On Aleo, the blockchain only sees that a valid computation occurred and what its public effects are (like mapping updates in the finalize phase). Transfer amounts, user balances, and application secrets stay hidden.
The tradeoff is that proof generation is computationally heavy. Client-side proving can take seconds to minutes depending on program complexity, which is why delegated proving services exist for users on constrained devices.