Designing public vs. private state: what goes where and why

Short summary

Midnight smart contracts store data across three distinct layers: public ledger (on-chain and visible), private state (off-chain in wallets, hidden), and transaction transcripts (revealed by disclose() calls). A critical misconception: marking a field as non-exported doesn't make it private—both exported and non-exported ledger fields are on-chain and publicly readable. Use witness functions for private data; disclose() explicitly marks transitions to public state.

• •Three data layers in Midnight: public ledger (on-chain), private state (off-chain), transaction transcript (disclosed values)
• •Non-exported fields are still on-chain—export controls API visibility, not privacy
• •Use witness functions for private data; disclose() explicitly marks transitions to public state

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