Zkopru account has 64 bytes address and is encoded with Base58Check algorithm. To understand how the Zkopru account works, you must know how the "viewing key" and the "spending key" work in Zkopru.

For compliance compatibility, Zkopru supports a viewing key system like ZCash. The encrypted memo field of a transaction includes private data that can decode the transaction details. Viewing key n, which is also a nullifier seed, is used to generate the public viewing key N = n*G where G is a constant generator EC point. With the public viewing key, the transaction sender makes an ephemeral shared key using ECDH, encrypts the transaction secrets, and puts them into the transaction's memo field. The latter 32 bytes of the total 64 bytes address stands for the public viewing key here.

The viewing key n also works as a seed value to generate the nullifiers to nullify the owner's UTXOs. Therefore, if Alice knows Bob's n, Alice can track the transactions by decoding the nullifiers and decrypting the memo field.

To prevent users from losing their keys, Zkopru derives a private spending key p from the Ethereum account's private key and then derive the nullifier seed from the p. And then, Zkopru uses p for EdDSA to verify the ownership of a UTXO to spend. Please note that a UTXO is a hash of poseidon(S, data, salt). It means that Zkopru uses S, which contains n, for its commitment in the commitment-nullifier scheme.



How to get

Where to use

Master seed

32 bytes

Randomly generated

Recover keys

Ethereum private key

32 bytes

Derived from the master seed with BIP39

Layer1 ECDSA

Ethereum public address

20 bytes

Derived from the Ethereum private key

Layer 1 interactions

p: Zkopru private spending key

254 bits

Derived from the Ethereum private key

Layer2 EdDSA

S: Zkopru public spending key

254 bits

Poseidon(p*G, n)

Commitment & ownership

n: Zkopru private viewing key & nullifier seed

254 bit

Derived from the Zkopru private key

Viewing txs & creating nullifiers

N: Zkopru public viewing key

32 bytes

N = n*G

Generating shared key(ECDH)

Zkopru public address

64 bytes

Concatenation of S and N

Layer 2 interactions

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