Skip to content

æternity naming system


This document describes the first draft of the æternity naming system, short AENS.


Entities native to most blockchain systems are addressed or identified by their hashes, which are generally n bit numbers displayed in a hex or base64/base58 notation, all of which are somewhat unfriendly to the humans trying to use these systems.


A solution to a similar problem is the Domain Name System, or DNS, which should be familiar to most people, providing human readable names for IP addresses. The issue with DNS is its centralization and it was conjectured by Zooko that a decentralized system can't have human-meaningful names while still being secure. This conjecture has been proven to be false by a number of systems, one example being NameCoin, which was debuted in 2011. It allowed users to associate names with a number of key-value pairs. The NameCoin network still exists today but sees barely any usage.

A more recent effort is ENS, the Ethereum Name Service, which enables users to claim names via a set of smart contracts. ENS is currently running a two year trial deployment, during which users can claim name with a .eth postfix, e.g. mywallet.eth. ENS currently allows users to associate a single 32 byte array of data with a node, typically used for a hash.


Names are part of a namespace, which works just like DNS, e.g. mywallet.test or привет.test are part of the same .test namespace.


Lima protocol upgrade is introducing final .chain registration namespace. It also retires .test namespace. We will also not include mechanisms similar to the sunrise and landrush periods, which are common for DNS, where registration is restricted to small select groups and trademark holders in order to avoid name squatting, before the general public can start claiming names.


It is unclear what a good mechanism for a naming system would look like. If we imagine two actors both being interested in the same name, what would a »fair« solution be to resolve this?

Fees are the main mechanism to discourage spam and squatting. We lock the governance fee in an account without private key access. Starting out with locking could allow us an easier path for future update to the fee structures, as it doesn't involve miners.

Every entry in the .test namespace pays the same amount of fees. After Lima .test namespace is no longer available to claim. Entries in .chain namespace are differentiated regarding fees by their length.

The new mechanism planted in Lima hard fork introduces auctions. We make auction parameters depend on name length.

An auction starts when a valid claim transaction following preclaim transaction has auction triggering parameter. Currently auction starts when revealed name is 12 characters or shorter.

For the names subject to auction, a claim transaction is an attempt of a name claim. It can be followed by another claim from an account different than one set in preclaim for given name.

For names longer than 12 characters, a claim transaction sets ownership of a name.

There is finite amount of time when the follow up claim in an auction is allowed. This time is expressed in height delta computed from function of length of the name.

The function will return higher value for shorter names. In practice it means that the shorter the name, the longer another claim transaction is valid. We are starting with extremely long time that makes claim for short name final. It will protect attractive names until this functionality is exposed to larger audience.

Claim transaction becomes a bid in an auction.

Furthermore, the initial fee for name is a value of the function of the name's length. It is decreasing function: for shorter names have higher initial fee.

Also bidding by claim transaction is constrained by price progression. Each new bid has to be higher than the previous bid by a certain margin, determined by a percentage of the price (currently 5%) defined in governance.

All, functions, base fee, free length value and price progression may be subject to changes with governance mechanism. Non-bidding path of the name claim is purposed for development or testing.

Each entry has a fixed expiration date on claim after which the entry should transition into the revoked state. Once it reaches this state, the name will be released, i.e. transition into the unclaimed state, after which it could be claimed again.

To prevent the entry from expiring a user can, at any point before reaching the expiration date, update the entry, which pushes the expiration date into the future by the time delta of the registration time and the update time, e.g. if a user posts an update one week after claiming their name, the expiration date gets pushed one week further into the future. The main motivation of this expiration date is to prevent situations where the private keys, which control the name, are lost, making the name unusable as well.

The salted (blind) preclaim followed in a later generation by a name revealing claim was introduced to avoid front-running. At the same time it introduces problems in UX, two transactions are needed, the salt needs to be remembered/stored, etc. By the introduction (in Lima) of auctions the front-running is no longer an issue - hence, from Ceres onwards, the preclaim is optional. The user can then initiate an auction (or immediately claim long names) directly with a NameClaimTx (with salt = 0). Note: it is still possible to do a preclaim followed by a claim!


The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

AENS Entry

This is the entry as it should be stored by a node.

  name         size (bytes)
 ------------ ----
| owner      | 32 |
 ------------ ----
| expires_by | 32 |
 ------------ ----
| client_ttl | 8  |
 ------------ ----
| pointers   |    |
 ------------ ----

owner: the account, which controls this entry.

expires_by: the blockheight after which the entry goes into the revoked state. This value MUST NOT be further than 180000 blocks (Note: used to be 50000 before Iris protocol upgrade) into the future.

client_ttl: a suggestion as to how long any clients should cache pointers. Measured in seconds. (TODO: should have a reasonable upper limit, e.g. 86400 seconds, and probably a different name to not be confused with the general TTL for transactions)

This entry is only relevant for clients and has no consensus impact.

pointers: a dictionary with all the values this entry points towards. This can have multiple entries, e.g. a payment address associated with the name and an oracle address associated with the name.


Names MUST be normalized according to IDNA2008 before hashing, as described in uts-46 and SHOULD be stored in their ASCII representation. The parameters to be used for normalization and validation are:

CheckBidi=true # important for registrars, to restrict names
CheckJoiners=true # important for registrars, to restrict names

See also rfc3491 and rfc3492.

Names SHOULD be at most 253 characters long, in order to enable interoperability with DNS.


A name is split up into labels by the FULL STOP (U+002E .) character. These labels will also be referred to as namespaces, e.g. mywallet.test can be understood as the mywallet namespace in the chain namespace.

Any label that is not at the top level, e.g. chain, MUST be longer than three characters.

Labels SHOULD be at most 63 characters long and the full path of all names and namespaces SHOULD be at most 253 characters long, in order to enable interoperability with DNS.


A registrar controls who is allowed to claim names in their namespace and under what circumstances they are allowed to do so.

The only available registrars up to Lima version will be hard-coded ones, which own the . and .test namespaces.

From Lima we will support .chain and limit .test namespace. .test names will expire without an option of updating TTL. We will use expiration mechanism to purge .test names.

The . namespace registrar is restricted and MUST NOT allow anyone to claim any names in its namespace.

The .test namespace registrar allows users to claim any name that is valid according to the validation rules if the name is currently not claimed and they pay the appropriate fee.

Commitment Scheme

Claiming a name requires a commitment scheme, which enables the claimant to commit to a name and after the commitment has been accepted into the chain, reveal the name to finish the process.

A commitment should be binding, i.e. the claimant cannot change the value they committed to without changing the actual commitment and hiding, so that a malicious miner learns nothing about the value the claimant has committed until they chose to reveal that value. This prevents malicious miners from front running, i.e. upon seeing a claim transaction, including their own claim request for the same name instead of the original claimant's one.

After the claim transaction the aens protocol is carried in clear text, in order to support auctions.


Names are generally only referred to in hashed form.

Until Lima protocol upgrade

We are going to adopt the NameHash as defined by the ENS in EIP-137 using Blake2b (256 bits digest) instead.

def namehash(name):
  if name == '':
    return '\0' * 32
    label, _, remainder = name.partition('.')
    return Blake2b(namehash(remainder) + Blake2b(label))

From Lima protocol upgrade

From Lima we don't use NameHash anymore. Instead, it is a 32 byte Blake2b hash of the IDNA encoded UTF-8 name.


       unclaimed ◄────────── revoked
         │   ▲                   ▲
         │   │                   │
         │   │                   │
pre-claim│   │ expire     expire │
 (claim) │   │            revoke │
         │   │                   │   transfer
         │   │                   │ ┌────┐
         ▼   │                   │ │    │
  pre-claimed/auction ─────► claimed ◄──┘
pre-claim | | expire       ||
 (claim)  | |              ||  _
          | |       revoke || | | transfer
          v |              || | v
pre-claimed|auction ---> claimed
         | ^    <timeout>  | ^
         | |               | |
          -                 -
        claim            update

The pointers field in the name entry: * On claim transaction, is initialized to the empty dictionary. * On update transaction, is replaced with the pointers in the transaction.

Note that expire is not an explicit message that is part of the protocol.

Protocol fees and protection times

Here is the function of initial bidding price depending on name length for Lima protocol upgrade.

 ------------- -------------
| name length | initial fee (unit 10^14) |
 ------------- -------------
| 31          | 3           |
 ------------- -------------
| 30          | 5           |
 ------------- -------------
| 29          | 8           |
 ------------- -------------
| 28          | 13          |
 ------------- -------------
| 27          | 21          |
 ------------- -------------
| 26          | 34          |
 ------------- -------------
| 25          | 55          |
 ------------- -------------
| 24          | 89          |
 ------------- -------------
| 23          | 144         |
 ------------- -------------
| 22          | 233         |
 ------------- -------------
| 21          | 377         |
 ------------- -------------
| 20          | 610         |
 ------------- -------------
| 19          | 987         |
 ------------- -------------
| 18          | 1597        |
 ------------- -------------
| 17          | 2584        |
 ------------- -------------
| 16          | 4181        |
 ------------- -------------
| 15          | 6765        |
 ------------- -------------
| 14          | 10946       |
 ------------- -------------
| 13          | 17711       |
 ------------- -------------
| 12          | 28657       |
 ------------- -------------
| 11          | 46368       |
 ------------- -------------
| 10          | 75025       |
 ------------- -------------
| 9           | 121393      |
 ------------- -------------
| 8           | 196418      |
 ------------- -------------
| 7           | 317811      |
 ------------- -------------
| 6           | 514229      |
 ------------- -------------
| 5           | 832040      |
 ------------- -------------
| 4           | 1346269     |
 ------------- -------------
| 3           | 2178309     |
 ------------- -------------
| 2           | 3524578     |
 ------------- -------------
| 1           | 5702887     |
 ------------- -------------

Here is the function of timeout required to close the auction. It depends on name length. Timeout is expressed in blocks. Non zero value means that there must be no follow up claim for the number of blocks defined here.

Until Ceres protocol upgrade

 ------------- -------------
| name length | time out    |
 ------------- -------------
| 13+         | 0           |
 ------------- -------------
| 9-12        | 480         |
 ------------- -------------
| 5-8         | 14880       |
 ------------- -------------
| 1-4         | 29760       |
 ------------- -------------

From Ceres protocol upgrade

| name length | time out |

| 13+ | 0 |

| 9-12 | 480 |

| 5-8 | 960 |

| 1-4 | 2400 |

From Ceres, each time a new (successful!) bid is made for a name the auction is extended for up to 120 key-blocks/generations. I.e. after the bid there is always at least 120 generations to make a higher bid.


Send a pre-claim transaction containing a hash commitment. This transaction starts the claiming process.

 ------------ ----
| commitment | 32 |
 ------------ ----

A client interacting with the blockchain should generate a warning if a user tries to claim a name that is not available.

The pre-claim has an implicit expiration attached to it. A pre-claim MUST be considered invalid after 300 blocks, i.e. about two days at 10 minute block time.

The hash commitment for the pre-claim is computed as follows:

commitment := Hash(NameHash(name) + name_salt)

Note: since Ceres the preclaim is optional.


 ---------------- ----
| name           | 63 |
 ---------------- ----
| name_salt      | 32 |
 ---------------- ----|
| name_fee       | 32 |
 ---------------- ----

Flow for a user:

  1. (optional) wait n blocks, s.t. that the block including the pre-claim cannot be reversed whp
  2. send claim transaction to reveal name and pay the associated fee
  3. (Lima) send follow up claim transaction as overbid to initial claim

From Lima transaction version is 2.

The first claim after a pre-claim transaction MUST be signed by the same private key as a pre-claim transaction containing a commitment to the name and nonce.

If the time delta of pre-claim and claim is bigger than 300 blocks, then the claim MUST be rejected.

If the time delta of subsequent claim is bigger than governance defined values then this claim MUST be rejected.

If the name_fee doesn't meet governance requirements it MUST be rejected.

From Lima hardfork, the subsequent claim that takes part in auction MUST have name_salt equal to 0

From Lima hardfork only the first claim transaction MUST be signed by the same private key as a pre-claim transaction containing a commitment to the name and nonce.

A claim transaction MUST NOT be in included in the same block as its pre-claim.

The claim transaction, apart from standard transaction fee, locks additional fee in a restricted account (account with no private key access). See also mechanisms section.

From Ceres hardfork the pre-claim is optional, and an auction can be started (or direct claim can be made) with a claim having name_salt equal to 0.


 ------------ ----
| hash       | 32 |
 ------------ ----
| expire_by  | 8  |
 ------------ ----
| client_ttl | 8  |
 ------------ ----
| pointers   |    |
 ------------ ----

The update transaction MUST be signed by the owner of the name entry to be updated.

The expire_by MUST NOT be more than 180000 blocks (Note: used to be 50000 before Iris protocol upgrade) into the future.

update transaction may be used to extend the lease of the name. We do not require an additional fee for extending the lease.

The pointers field SHOULD NOT contain multiple entries with the same key. The pointers can point to one of: account address, oracle id, channel id or contract id, and from Ceres 1024 bytes of uninterpreted data (a bytearray).

From Iris protocol upgrade, the following limitations on pointers apply: - No duplicate keys (a key can only be present once in a list of pointers). - Keys are not longer than 256 bytes - The list of pointers is not longer than 32.

From Ceres hardfork, a new pointer target type is introduced: - A key can point to up to 1024 bytes of uninterpreted data (a bytearray)

Note: An update containing the new pointer target type MUST use version 2 of the serialization; and, an update not containing the new target type MUST use version 1 of the serialization.


 ------------ ----
| target     | 32 |
 ------------ ----
| hash       | 32 |
 ------------ ----

The transfer transaction MUST be signed by the owner of the name entry to be transferred.


 ------------ ----
| hash       | 32 |
 ------------ ----

The revoke transaction MUST be signed by the owner of a name entry.

After the revoke transaction has been included in the chain, the name enters the revoked state. After a fixed timeout of 2016 blocks, the name will be available for claiming again.


We are going to store the AENS entries in an ESMT and use the hash of a name, as defined above, as a pointer to the entry data. If there's no entry for a given hash then that pointer will point to an empty hash or to the hash of that entry data otherwise.


Giving users plenty time to prepare for a launch of the naming system is of utmost importance given the allocation rules, i.e. first come first serve, of this first draft. This also includes giving users the proper tools, i.e. a GUI, in order to level the playing field as to who is able to actually register names.

Since we don't have an auction protocol at launch, we could hold auctions on Ethereum to establish an initial allocation of names, just like our ERC-20 token.

(possible) Future extensions


A later version of the name service should allow every user to become a registrar and encode their registration logic in a smart contract. A simplification would be that registrars have to submit the claim transaction themselves and just set the owner to whoever they want to give the name to.

These sub-labels allow for further customisation and also for users to associate with particular namespaces, e.g. a cryptographic cat breeding game might associate a name entry with every of its cats such as unicorn.kitty.test and then transferring that name to the person, who adopts the cat. The authorization policies for these will need some flexibility seeing as the owner of a namespace might want to prevent or allow users creating sub-sub-labels, e.g. the owner of unicorn.kitty.test creating rarest.unicorn.kitty.test.


Using (Vickrey) auctions instead of a simple, first come first serve approach for new claims, might allow a better mechanism for price discovery without having to go through a secondary market.

URI Schema

We are currently using the same schema as DNS, which might be problematic since this comes with a big slew of expectations as to what can and can't be done.

See this post about problems of urls or this IPFS spec issue for some discussions.

Decentralized name exchange

Having the exchange for names on chain would enable us to transfer names in a trustless manner. Plus having the bids recorded on chain could also facilitate better price discovery.


Allowing users to register their own namespaces and become registrars themselves, i.e. if I own mywallet.chain, I can then allow others to register name.mywallet.chain.

Consider a voting mechanism to introduce new TLDs.


  • investigate possibility to integrate with ENS
  • add interoperability with
  • add support for

Light clients

A light client might only be interested in the history or integrity particular name and thus require some lightweight mechanism for this, which is currently not possible.

Fee lottery

It was suggested that the fees for the .chain namespace could be distributed to random accounts via a lottery.


[1] Kalodner, Harry A., et al. "An Empirical Study of Namecoin and Lessons for Decentralized Namespace Design." WEIS. 2015.

[2] Ali, Muneeb, et al. "Blockstack: A Global Naming and Storage System Secured by Blockchains." USENIX Annual Technical Conference. 2016.