Accounts and addresses

The Tezos ledger currently supports two types of accounts that can hold tokens (and be the destinations of transactions), identified by distinct addresses:

  • A user account (or implicit account) is a non-programmable account, whose tokens are spendable and delegatable by the owner of a private key. Its address is the hash of the public key, prefixed by tz1, tz2, tz3 or tz4.

  • A smart contract is a programmable account, associated with some Michelson code and a piece of data storage. The address of a smart contract is a unique hash that depends on the operation that led to its creation, called origination, prefixed by KT1. This is why smart contracts are also called originated accounts.

Finally, addresses prefixed with sr1 identify Smart Rollups.

User accounts

From the economic protocol’s point of view, user accounts are considered as a particular case of smart contracts that always succeed in receiving tokens or tickets, and do nothing else. Transferring toward a user account succeeds even if the address of the account has never appeared on the chain before. This is why user accounts are also called implicit accounts.

Transactions that are signed by the private key corresponding to the public key hash, i.e. address of the account can spend its tokens. Each prefix for addresses denotes a different cryptographic signing scheme. They are briefly described below from a user point of view.

The sizes of public keys, secret keys and signatures may differ between the different schemes but addresses are always 20 bytes long.

tz1: Ed25519

Addresses that start with the tz1 prefix are hashes of Ed25519 public keys and signatures must be produced by using the EdDSA signature scheme with the Curve25519 curve. This is the default scheme of Octez when, e.g., generating key pairs. It is also the recommended cryptographic scheme to use because it offers better security guarantees than EcDSA and has good performance on most hardware. It may not be available in all wallets or on all dedicated chips which is why Tezos supports multiple schemes.

tz2: Secp256k1

Addresses that start with the tz2 prefix are hashes of Secp256k1 public keys and signatures must be produced by using the EcDSA signature scheme with the Secp256k1 curve. Secp256k1 is notably the cryptographic scheme used by Bitcoin and Ethereum. This means that private keys and addresses used on Bitcoin can also be used on Tezos.

tz3: P-256

Addresses that start with the tz3 prefix are hashes of P-256 public keys and signatures must be produced by using the EcDSA signature scheme with the P-256 curve, also known as Secp256r1. This is one of the curves for EcDSA recommended by NIST. It is also often the only cryptographic scheme supported by HSMs (Hardware Security Modules) of cloud providers.

tz4: BLS

Addresses that start with the tz4 prefix are hashes of BLS public keys and signatures must be produced by using the BLS signature scheme with the BLS12-381 curve. One particularity of BLS signatures is that they are aggregatable. This means that multiple signatures can be aggregated into one, and later verified as having been produced for the correct expected public keys. This allows for numerous applications like mutli-signatures schemes, multi-party key exchanges, signatures compaction, etc. BLS is notably used by Zcash and Ethereum 2.0.

Smart contracts

A transaction to a smart contract address can provide data and optionally some tokens, and triggers the execution of the code, which may read and update the storage. The transaction can succeed or fail, according to the transaction semantics.