The decryption of a ciphertext described in the previous page is triggered by an on-chain smart contract, and will expose the underlying plaintext to the public. For some use cases, for example accessing your private confidential token balance, a public decryption is not desired. Reencryption comes in to play when a user wants to access their own private data without revealing it to any other third party.

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How it Works

The idea behind reencryption is that the user generates on the client-side an ephemeral private/public keypair. The user will then ask the covalidator to decrypt an on-chain handle, and immediately reencrypt the plaintext using the user’s generated public key. This way, only the user can decrypt the reencrypted ciphertext using the ephemeral private key. A sequence diagram of the reencryption flow can be found in the Decryption Mechanisms page.

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Access Control

Access control is of particular importance in the reencrypt flow. A reencrypt request is valid only if the two following conditions are met:
  • the user requesting a reencryption must have access to the handle. This on-chain validation prevents other people seeing your own private data, and vice-versa.
  • the user requesting a reencryption must sign an EIP-712 message over the ephemeral public key they generated, using the same address that has access to the handle. This ensures that it’s indeed the user that requested a reencryption to that ephemeral public key, and not some malicious actor.

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Requesting a Reencryption

A reencryption does not require any on-chain transaction. On the contract side, we simply require that the handle is publicly readable. For example, for a confidential token contract, the mapping of user address to confidential balance can be made public. Once the handle to be reencrypted is retrieved on the client side, we can use the JS SDK’s reencryptor to request a reencryption. The SDK will perform all the low-level steps, such as generating an ephemeral keypair and signing the EIP-712 message, and will return the plaintext value.