Different key types
zkBob is based on complex cryptography. There are several keys needed for private transactions. The relationship between these keys is presented in the scheme below.
- Spending key () is the top secret key. It is used to derive other keys and to sign transactions. At a high level it is just a random 256-bit number which should be stored securely on the client side. The simplest way to get a spending key is to produce a random number. But in a production client software implementation more complex approaches should be used (e.g. hierarchical deterministic wallets). Concrete approaches for spending key derivation by a client are not discussed here.
- Transaction verifier key () is used for transaction signature verification. It's derived from the spending key and multiplied by the generator point in the JubJub elliptic curve field:
- Intermediate key () is derived from thekey by thehash function:. It is used in several cases:
- to obtain the account balance and transaction history
- to decrypt incoming notes
- Receiving key is used to decrypt incoming notes in the memo block. It is a combination of the intermediate key and ephemeral key generated for each note.
- Outgoing viewing key is used to decrypt the whole memo block in the transaction which is initiated by itself.
- Private payment address- is a set of random diversifiersand point