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Blockstack DID Method Specification

Abstract

Blockstack is a network for decentralized applications where users own their identities and data. Blockstack utilizes a public blockchain to implement a decentralized naming layer, which binds a user's human-readable username to their current public key and a pointer to their data storage buckets. The naming layer ensures that names are globally unique, that names can be arbitrary human-meaningful strings, and that names are owned and controlled by cryptographic key pairs such that only the owner of the private key can update the name's associated state.

The naming layer implements DIDs as a mapping between the initial name operation for a user's name and the name's current public key. The storage pointers in the naming layer are leveraged to point to the authoritative replica of the user's DID document.

Status of This Document

This document is not a W3C Standard nor is it on the W3C Standards Track. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

Comments regarding this document are welcome. Please file issues directly on Github.

1. System Overview

Blockstack's DID method is specified as part of its decentralized naming system. Each name in Blockstack has one or more corresponding DIDs, and each Blockstack DID corresponds to exactly one name -- even if the name was revoked by its owner, expired, or was re-registered to a different owner.

Blockstack is unique among decentralized identity systems in that it is not anchored to a specific blockchain or DLT implementation. The system is designed from the ground up to be portable, and has already been live-migrated from the Namecoin blockchain to the Bitcoin blockchain. The operational ethos of Blockstack is to leverage the must secure blockchain at all times -- that is, the one that is considered hardest to attack.

Blockstack's naming system and its DIDs transcend the underlying blockchain, and will continue to resolve to DID document objects (DDOs) even if the system migrates to a new blockchain in the future.

1.1 DID Lifecycle

Understanding how Blockstack DIDs operate requires understanding how Blockstack names operate. Fundamentally, a Blockstack DID is defined as a pointer to the nth name registered by an address. How this information is determined depends on the category of name being registered -- a DID can be derived from an on-chain name or an off-chain name. We call these DIDs on-chain DIDs and off-chain DIDs, respectively.

1.1.1 On-Chain DIDs

On-chain names are written directly to Blockstack's underlying blockchain. Instantiating an on-chain name requires two transactions -- a NAME_PREORDER transaction, and a NAME_REGISTRATION transaction. Upon successful confirmation of the NAME_REGISTRATION transaction, the system assigns name to an on-chain address indicated by the NAME_REGISTRATION transaction itself. This address is the name's owner.

Since these transactions are written to the blockchain, the blockchain provides a total ordering of name-to-address assignments. Thus, a DID instantiated for an on-chain name may be referenced by the name's owner address, and the number of names ever assigned to the owner address at the time of this DID's instantiation. For example, the DID did:stack:v0:15gxXgJyT5tM5A4Cbx99nwccynHYsBouzr-3 was instantiated when the fourth on-chain name was created and initially assigned to the address 15gxXgJyT5tM5A4Cbx99nwccynHYsBouzr (note that the index parameter -- the -3 -- starts counting from 0).

1.1.2 Off-chain DIDs

Off-chain names, sometimes called subdomains in the Blockstack literature, refer to names whose transaction histories are instantiated and stored outside of Blockstack's blockchain within Blockstack's Atlas peer network. Off-chain name transactions are encoded in batches, where each batch is hashed and written to the underlying blockchain through a transaction for an on-chain name. This provides them with the same safety properties as on-chain names -- off-chain names are globally unique, off-chain names can be arbitrary human-meaningful strings, off-chain names are owned by cryptographic key pairs, and all Blockstack nodes see the same linearized history of off-chain name operations.

Off-chain names are instantiated by an on-chain name, indicated by the off-chain name's suffix. For example, cicero.res_publica.id is an off-chain name whose initial transaction history is processed by the owner of the on-chain name res_publica.id. Note that the owner of res_publica.id does not own cicero.res_publica.id, and cannot issue well-formed name updates to it.

Off-chain names -- and by extension, their corresponding DIDs -- have different liveness properties than on-chain names. The Blockstack naming system protocol requires the owner of res_publica.id to not only propagate the signed transactions that instantiate and transfer ownership of cicero.res_publica.id. However, any on-chain name can process a name update for an off-chain name -- that is, an update that changes where the name's assocaited state resides. For details as to why this is the case, please refer to the Blockstack subdomain documentation.

An off-chain DID is similarly structured to an on-chain DID. Like on-chain names, each off-chain name is owned by an address (but not necessarily an address on the blockchain), and each Blockstack node sees the same sequence of off-chain name-to-address assignments. Thus, it has enough information to assign each off-chain name user a DID.

2. Blockstack DID Method

The namestring that shall identify this DID method is: stack

A DID that uses this method MUST begin with the following literal prefix: did:stack. The remainder of the DID is its namespace-specific identifier.

2.1 Namespace-Specific Identifier

The namespace-specific identifier (NSI) of the Blockstack DID encodes two pieces of information: an address, and an index.

The address shall be a base58check encoding of a version byte concatenated with the RIPEMD160 hash of a SHA256 hash of a DER-encoded secp256k1 public key. For example, in this Python 2 snippit:

import hashlib
import base58

pubkey = '042bc8aa4eb54d779c1fb8a2d5022aec8ed7fc2cc34d57356d9e1c417ce416773f45b0299ea7be347d14c69c403d9a03c8ec0ccf47533b4bee8cd002e5de81f945'
sha256_pubkey = hashlib.sha256(pubkey.decode('hex')).hexdigest()
# '18328b13b4df87cbcd190c083ef1d74487fc1383792f208f52c596b4588fb665'
ripemd160_sha256_pubkey = hashlib.new('ripemd160', sha256_pubkey.decode('hex')).hexdigest()
# '1651c1a6001d4750e46be8a02cc19550d4309b71'
version_byte = '\x00'
address = base58.b58check_encode(version_byte + ripemd160_sha256_pubkey.decode('hex'))
# '1331okvQ3Jr2efzaJE42Supevzfzg8ahYW'

The index shall be a non-negative monotonically-increasing integer.

The (address, index) pair uniquely identifies a DID. Blockstack's naming system ensures that the index increments monotonically each time a DID is instantiated (e.g. by incrementing it each time a name gets registered to the address).

2.2 Address Encodings

The address's version byte encodes whether or not a DID corresponds to an on-chain name transaction or an off-chain name transaction, and whether or not it corresponds to a mainnet or testnet address. The version bytes for each configuration shall be as follows:

On-chain names on mainnet: 0x00
On-chain names on testnet: 0x6f
Off-chain names on mainnet: 0x3f
Off-chain names on testnet: 0x7f

For example, the RIPEMD160 hash 1651c1a6001d4750e46be8a02cc19550d4309b71 would encode to the following base58check strings:

On-chain mainnet: 1331okvQ3Jr2efzaJE42Supevzfzg8ahYW
On-chain testnet: mhYy6p1NrLHHRnUC1o2QGq2ynzGhduVoEX
Off-chain mainnet: SPL1qbhYmg3EAyn2qf36zoyDamuRXm2Gjk
Off-chain testnet: t8xcrYmzDDhJWihaQWMW2qPZs4Po1PfvCB

3. Blockstack DID Operations

3.1 Creating a Blockstack DID

Creating a Blockstack DID requires registering a name -- be it on-chain or off-chain. To register an on-chain name, the user must send two transactions to Blockstack's underlying blockchain (currently Bitcoin) that implement the NAME_PREORDER and NAME_REGISTRATION commands. Details on the wire formats for these transactions can be found in Appendix A. Blockstack supplies both a graphical tool and a command-line tool for generating and broadcasting these transactions, as well as a reference library.

To register an off-chain name, the user must be able to submit a request to an off-chain registrar. Anyone with an on-chain name can use it to operate a registrar for off-chain names. A reference implementation can be found here.

To register an off-chain DID, the user must submit a JSON body as a HTTP POST request to the registrar's registration endpoint with the following format:

{
   "zonefile": "<zonefile encoding the location of the DDO>",
   "name": "<off-chain name, excluding the on-chain suffix>",
   "owner_address": "<b58check-encoded address that will own the name, with version byte \x00>",
}

For example, to register the name spqr on a registrar for res_publica.id:

$ curl -X POST -H 'Authorization: bearer API-KEY-IF-USED' -H 'Content-Type: application/json' \
> --data '{"zonefile": "$ORIGIN spqr\n$TTL 3600\n_https._tcp URI 10 1 \"https://gaia.blockstack.org/hub/1HgW81v6MxGD76UwNbHXBi6Zre2fK8TwNi/profile.json\"\n", \
>          "name": "spqr", \
>          "owner_address": "1HgW81v6MxGD76UwNbHXBi6Zre2fK8TwNi"}' \
> http://localhost:3000/register/

The zonefile field must be a well-formed DNS zonefile, and must have the following properties:

It must have its $ORIGIN field set to the off-chain name.
It must have at least one URI resource record that encodes an HTTP or HTTPS URL. Note that its name must be either _http._tcp or _https._tcp, per the URI record specification.
The HTTP or HTTPS URL must resolve to a JSON Web token signed by a secp256k1 public key that hashes to the owner_address field, per section 2.1.

Once the request is accepted, the registrar will issue a subsequent NAME_UPDATE transaction for its on-chain name and broadcast the batch of off-chain zone files it has accumulated to the Blockstack Atlas network (see Appendix A). The batch of off-chain names' zone files will be hashed, and the hash will be written to the blockchain as part of the NAME_UPDATE. This proves the existence of these off-chain names, as well as their corresponding DIDs.

Once the transaction confirms and the off-chain zone files are propagated to the peer network, any Blockstack node will be able to resolve the off-chain name's associated DID.

3.2 Storing a Blockstack DID's DDO

Each name in Blockstack, and by extention, each DID, must have one or more associated URLs. To resolve a DID (section 3.3), the DID's URLs must point to a well-formed signed DDO. It is up to the DID owner to sign and upload the DDO to the relevant location(s) so that DID resolution works as expected, and it is up to the DID owner to ensure that the DDO is well-formed. Resolvers should validate DDOs before returning them to clients.

In order for a DID to resolve to a DDO, the DDO must be encoded as a JSON web token, and must be signed by the secp256k1 private key whose public key hashes to the DID's address. This is used by the DID resolver to authenticate the DDO, thereby removing the need to trust the server(s) hosting the DDO with replying authentic data.

3.3 Resolving a Blockstack DID

Any Blockstack node with an up-to-date view of the underlying blockchain and a complete set of off-chain zone files can translate any name into its DID, and translate any DID into its name.

Since DID registration in Blockstack is achieved by first registering a name, the user must first determine the DID's NSI. To do so, the user simply requests it from a Blockstack node of their choice as a GET request to the node's /v1/dids/{:blockstack_did} endpoint. The response must be a JSON object with a public_key field containing the secp256k1 public key that hashes to the DID's address, and a document field containing the DDO. The DDO's publicKey field shall be an array of objects with one element, where the only element describes the public_key given in the top-level object.

For example:

$ curl -s https://core.blockstack.org/v1/dids/did:stack:v0:15gxXgJyT5tM5A4Cbx99nwccynHYsBouzr-0 | jq
{
   'public_key': '022af593b4449b37899b34244448726aa30e9de13c518f6184a29df40823d82840', 
   'document': { 
      ...
      '@context': 'https://w3id.org/did/v1', 
      'publicKey': [
         {
            'id': 'did:stack:v0:15gxXgJyT5tM5A4Cbx99nwccynHYsBouzr-0', 
            'type': 'secp256k1',
            'publicKeyHex': '022af593b4449b37899b34244448726aa30e9de13c518f6184a29df40823d82840'
         }
      ],
      ...
   }
}

3.4 Updating a Blockstack DID

The user can change their DDO at any time by uploading a new signed DDO to the relevant locations, per section 3.2, except for the publicKey field. In order to change the DID's public key, the user must transfer the underlying name to a new address.

If the DID corresponds to an on-chain name, then the user must send a NAME_TRANSFER transaction to send the name to the new address. Once the transaction is confirmed by the Blockstack network, the DID's public key will be updated. See Appendix A for the NAME_TRANSFER wire format. Blockstack provides a reference library for generating this transaction.

3.4.1 Off-Chain DID Updates

If the DID corresponds to an off-chain name, then the user must request that the registrar that instantiated the name to broadcast an off-chain name transfer operation. To do so, the user must submit a string with the following format to the registrar:

${name} TXT "owner=${new_address}" "seqn=${update_counter}" "parts=${length_of_zonefile_base64}" "zf0=${base64_part_0}" "zf1=${base64_part_1}" ... "sig=${base64_signature}"

The string is a well-formed DNS TXT record with the following fields:

The ${name} field is the subdomain name without the on-chain suffix (e.g. spqr in spqr.res_publica.id.
The ${new_address} field is the new owner address of the subdomain name.
The ${update_counter} field is a non-negative integer equal to the number of subdomain name operations that have occurred so far. It starts with 0 when the name is created, and must increment each time the name owner issues an off-chain name operation.
The ${length_of_zonefile_base64} field is equal to the length of the base64-encoded zone file for the off-chain name.
The fields zf0, zf1, zf2, etc. and their corresponding variables ${base64_part_0}, ${base64_part_1}, ${base64_part_2}, etc. correspond to 256-byte segments of the base64-encoded zone file. They must occur in a sequence of zf${n} where ${n} starts at 0 and increments by 1 until all segments of the zone file are represented.
The ${base64_signature} field is a secp256k1 signature over the resulting string, up to the sig= field, and base64-encoded. The signature must come from the secp256k1 private key that currently owns the name.

Thus to generate this TXT record for their DID, the user would do the following:

Base64-encode the off-chain DID's zone file.
Break the base64-encoded zone file into 256-byte segments.
Assemble the TXT record from the name, new address, update counter, and zone file segments.
Sign the resulting string with the DID's current private key.
Generate and append the sig=${base64_signature} field to the TXT record.

Sample code to generate these TXT records can be found in the Stacks Node reference implementation, under the blockstack.lib.subdomains package. For example, the Python 2 program here generates such a TXT record:

import blockstack

offchain_name = 'bar'
onchain_name = 'foo.test'
new_address = '1Jq3x8BAYz9Xy9AMfur5PXkDsWtmBBsNnC'
seqn = 1
privk = 'da1182302fee950e64241a4103646992b1bed7f6c4ced858282e493d57df33a501'
full_name = '{}.{}'.format(offchain_name, onchain_name)
zonefile = "$ORIGIN {}\n$TTL 3600\n_http._tcp\tIN\tURI\t10\t1\t\"https://gaia.blockstack.org/hub/{}/profile.json\"\n\n".format(offchain_name, new_address)

print blockstack.lib.subdomains.make_subdomain_txt(full_name, onchain_name, new_address, seqn, zonefile, privk)

The program prints a string such as:

bar TXT "owner=1Jq3x8BAYz9Xy9AMfur5PXkDsWtmBBsNnC" "seqn=1" "parts=1" "zf0=JE9SSUdJTiBiYXIKJFRUTCAzNjAwCl9odHRwLl90Y3AJSU4JVVJJCTEwCTEJImh0dHBzOi8vZ2FpYS5ibG9ja3N0YWNrLm9yZy9odWIvMUpxM3g4QkFZejlYeTlBTWZ1cjVQWGtEc1d0bUJCc05uQy9wcm9maWxlLmpzb24iCgo\=" "sig=QEA+88Nh6pqkXI9x3UhjIepiWEOsnO+u1bOBgqy+YyjrYIEfbYc2Q8YUY2n8sIQUPEO2wRC39bHQHAw+amxzJfkhAxcC/fZ0kYIoRlh2xPLnYkLsa5k2fCtXqkJAtsAttt/V"

(Note that the sig= field will differ between invocations, due to the way ECDSA signatures work).

Once this TXT record has been submitted to the name's original registrar, the registrar will pack it along with other such records into a single zone file, and issue a NAME_UPDATE transaction for the on-chain name to announce them to the rest of the peer network. The registrar will then propagate these TXT records to the peer network once the transaction confirms, thereby informing all Blockstack nodes of the new state of the off-chain DID.

3.4.2 Changing the Storage Locations of a DDO

If the user wants to change where the resolver will look for a DDO, they must do one of two things. If the DID corresponds to an on-chain name, then the user must send a NAME_UPDATE transaction for the underlying name, whose 20-byte hash field is the RIPEMD160 hash of the name's new zone file. See Appendix A for the wire format of NAME_UPDATE transactions.

If the DID corresponds to an off-chain name, then the user must submit a request to an off-chain name registrar to propagate a new zone file for the name. Unlike changing the public key, the user can ask any off-chain registrar to broadcast a new zone file. The method for doing this is described in section 3.4.1 -- the user simply changes the zone file contents instead of the address.

4. Deleting a Blockstack DID

If the user wants to delete their DID, they can do so by revoking the underlying name. To do this with an on-chain name, the user constructs and broadcasts a NAME_REVOKE transaction. Once confirmed, the DID will stop resolving.

To do this with an off-chain name, the user constructs and broadcasts a TXT record for their DID's underlying name that (1) changes the owner address to a "nothing-up-my-sleeve" address (such as 1111111111111111111114oLvT2 -- the base58-check encoding of 20 bytes of 0's), and (2) changes the zone file to include an unresolvable URL. This prevents the DID from resolving, and prevents it from being updated.

5. Security Considerations

This section briefly outlines possible ways to attack Blockstack's DID method, as well as countermeasures the Blockstack protocol and the user can take to defend against them.

5.1 Public Blockchain Attacks

Blockstack operates on top of a public blockchain, which could be attacked by a sufficiently pwowerful adversary -- such as rolling back and changing the chain's transaction history, denying new transactions for Blockstack's name operations, or eclipsing nodes.

Blockstack makes the first two attacks difficult by operating on top of the most secure blockchain -- currently Bitcoin. If the blockchain is attacked, or a stronger blockchain comes into being, the Blockstack community would migrate the Blockstack network to a new blockchain.

The underlying blockchain provides some immunity towards eclipse attacks, since a blockchain peer expects blocks to arrive at roughly fixed intervals and expects blocks to have a proof of an expenditure of an expensive resource (like electricity). In Bitcoin's case, the computational difficulty of finding new blocks puts a high lower bound on the computational effort required to eclipse a Bitcoin node -- in order to sustain 10-minute block times, the attacker must expend an equal amount of energy as the rest of the network. Moreover, the required expenditure rate (the "chain difficulty") decreases slowly enough that an attacker with less energy would have to spend months of time on the attack, giving the victim ample time to detect it. The countermeasures the blockchain employs to deter eclipse attacks are beyond the scope of this document, but it is worth pointing out that Blockstack's DID method benefits from them since they also help ensure that DID creation, updates and deletions get processed in a timely manner.

5.2 Blockstack Peer Network Attacks

Because Blockstack stores each DID's DDO's URL in its own peer network outside of its underlying blockchain, it is possible to eclipse Blockstack nodes and prevent them from seeing both off-chain DID operations and updates to on-chain DIDs. In an effort to make this as difficult as possible, the Blockstack peer network implements an unstructured overlay network -- nodes select a random sample of the peer graph as their neighbors. Moreover, Blockstack nodes strive to fetch a full replica of all zone files, and pull zone files from their neighbors in rarest-first order to prevent zone files from getting lost while they are propagating. This makes eclipsing a node maximally difficult -- an attacker would need to disrupt all of a the victim node's neighbor links.

In addition to this protocol-level countermeasure, a user has the option of uploading zone files manually to their preferred Blockstack nodes. If vigilent users have access to a replica of the zone files, they can re-seed Blockstack nodes that do not have them.

5.3 Stale Data and Replay Attacks

A DID's DDO is stored on a 3rd party storage provider. The DDO's public key is anchored to the blockchain, which means each time the DDO public key changes, all previous DDOs are invalidated. Similarly, the DDO's storage provider URLs are anchored to the blockchain, which means each time the DID's zone file changes, any stale DDOs will no longer be fetched. However, if the user changes other fields of their DDO, a malicious storage provider or a network adversary can serve a stale but otherwise valid DDO and the resolver will accept it.

The user has a choice of which storage providers host their DDO. If the storage provider serves stale data, the user can and should change their storage provider to one that will serve only fresh data. In addition, the user should use secure transport protocols like HTTPS to make replay attacks on the network difficult. For use cases where these are not sufficient to prevent replay attacks, the user should change their zone file and/or public key each time they change their DDO.

6. Privacy Considerations

Blockstack's DIDs are underpinned by Blockstack IDs (human readable names), and every Blockstack node records where every DID's DDO is hosted. However, users have the option of encrypting their DDOs so that only a select set of other users can decrypt them.

Blockstack's peer network and DID resolver use HTTP(S), meaning that intermediate middleboxes like CDNs and firewalls can cache data and log requests.

7. Reference Implementations

Blockstack implements a RESTful API for querying DIDs. It also implements a reference library for generating well-formed on-chain transactions, and it implements a Python library for generating off-chain DID operations. The Blockstack node reference implementation is available under the terms of the General Public Licence, version 3.

8. Resources

Many Blockstack developers communicate via the Blockstack Forum and via the Blockstack Slack. Interested developers are encouraged to join both.

Appendix A: On-chain Wire Formats

This section is for organizations who want to be able to create and send name operation transactions to the blockchain(s) Blockstack supports. It describes the transaction formats for the Bitcoin blockchain.

Only the transactions that affect DID creation, updates, resolution, and deletions are documented here. A full listing of all Blockstack transaction formats can be found here.

Transaction format

Each Bitcoin transaction for Blockstack contains signatures from two sets of keys: the name owner, and the payer. The owner scriptSig and scriptPubKey fields are generated from the key(s) that own the given name. The payer scriptSig and scriptPubKey fields are used to subsidize the operation. The owner keys do not pay for any operations; the owner keys only control the minimum amount of BTC required to make the transaction standard. The payer keys only pay for the transaction's fees, and (when required) they pay the name fee.

This construction is meant to allow the payer to be wholly separate from the owner. The principal that owns the name can fund their own transactions, or they can create a signed transaction that carries out the desired operation and request some other principal (e.g. a parent organization) to actually pay for and broadcast the transaction.

The general transaction layout is as follows:

Inputs	Outputs
Owner scriptSig (1)	`OP_RETURN <payload>` (2)
Payment scriptSig	Owner scriptPubKey (3)
Payment scriptSig... (4)
... (4)	... (5)

(1) The owner scriptSig is always the first input. (2) The OP_RETURN script that describes the name operation is always the first output. (3) The owner scriptPubKey is always the second output. (4) The payer can use as many payment inputs as (s)he likes. (5) At most one output will be the "change" scriptPubKey for the payer. Different operations require different outputs.

Payload Format

Each Blockstack transaction in Bitcoin describes the name operation within an OP_RETURN output. It encodes name ownership, name fees, and payments as scriptPubKey outputs. The specific operations are described below.

Each OP_RETURN payload always starts with the two-byte string id (called the "magic" bytes in this document), followed by a one-byte op that describes the operation.

NAME_PREORDER

Op: ?

Description: This transaction commits to the hash of a name. It is the first transaction of two transactions that must be sent to register a name in BNS.

Example: 6730ae09574d5935ffabe3dd63a9341ea54fafae62fde36c27738e9ee9c4e889

OP_RETURN wire format:

    0     2  3                                                  23             39
    |-----|--|--------------------------------------------------|--------------|
    magic op  hash_name(name.ns_id,script_pubkey,register_addr)   consensus hash

Inputs:

Payment scriptSig's

Outputs:

OP_RETURN payload
Payment scriptPubkey script for change
p2pkh scriptPubkey to the burn address (0x00000000000000000000000000000000000000)

Notes:

register_addr is a base58check-encoded ripemd160(sha256(pubkey)) (i.e. an address). This address must not have been used before in the underlying blockchain.
script_pubkey is either a p2pkh or p2sh compiled Bitcoin script for the payer's address.

NAME_REGISTRATION

Op: :

Description: This transaction reveals the name whose hash was announced by a previous NAME_PREORDER. It is the second of two transactions that must be sent to register a name in BNS.

When this transaction confirms, the corresponding Blockstack DID will be instantiated. It's address will be the owner address in this transaction, and its index will be equal to the number of names registered to this address previously.

Example: 55b8b42fc3e3d23cbc0f07d38edae6a451dfc512b770fd7903725f9e465b2925

OP_RETURN wire format (2 variations allowed):

Variation 1:

    0    2  3                             39
    |----|--|-----------------------------|
    magic op   name.ns_id (37 bytes)

Variation 2:

    0    2  3                                  39                  59
    |----|--|----------------------------------|-------------------|
    magic op   name.ns_id (37 bytes, 0-padded)       value

Inputs:

Payer scriptSig's

Outputs:

OP_RETURN payload
scriptPubkey for the owner's address
scriptPubkey for the payer's change

Notes:

Variation 1 simply registers the name. Variation 2 will register the name and set a name value simultaneously. This is used in practice to set a zone file hash for a name without the extra NAME_UPDATE transaction.
Both variations are supported. Variation 1 was designed for the time when Bitcoin only supported 40-byte OP_RETURN outputs.

NAME_RENEWAL

Op: :

Description: This transaction renews a name in BNS. The name must still be registered and not expired, and owned by the transaction sender.

Depending on which namespace the name was created in, you may never need to renew a name. However, in namespaces where names expire (such as .id), you will need to renew your name periodically to continue using its associated DID. If this is a problem, we recommend creating a name in a namespace without name expirations, so that NAME_UPDATE, NAME_TRANSFER and NAME_REVOKE -- the operations that underpin the DID's operations -- will work indefinitely.

Example: e543211b18e5d29fd3de7c0242cb017115f6a22ad5c6d51cf39e2b87447b7e65

OP_RETURN wire format (2 variations allowed):

Variation 1:

    0    2  3                             39
    |----|--|-----------------------------|
    magic op   name.ns_id (37 bytes)

Variation 2:

    0    2  3                                  39                  59
    |----|--|----------------------------------|-------------------|
    magic op   name.ns_id (37 bytes, 0-padded)       value

Inputs:

Payer scriptSig's

Outputs:

OP_RETURN payload
scriptPubkey for the owner's addess. This can be a different address than the current name owner (in which case, the name is renewed and transferred).
scriptPubkey for the payer's change
scriptPubkey for the burn address (to pay the name cost)

Notes:

This transaction is identical to a NAME_REGISTRATION, except for the presence of the fourth output that pays for the name cost (to the burn address).
Variation 1 simply renews the name. Variation 2 will both renew the name and set a new name value (in practice, the hash of a new zone file).
Both variations are supported. Variation 1 was designed for the time when Bitcoin only supported 40-byte OP_RETURN outputs.
This operation can be used to transfer a name to a new address by setting the second output (the first scriptPubkey) to be the scriptPubkey of the new owner key.

NAME_UPDATE

Op: +

Description: This transaction sets the name state for a name to the given value. In practice, this is used to announce new DNS zone file hashes to the Atlas network, and in doing so, change where the name's off-chain state resides. In DID terminology, this operation changes where the authoritative replica of the DID's DDO will be retrieved on the DID's lookup.

Example: e2029990fa75e9fc642f149dad196ac6b64b9c4a6db254f23a580b7508fc34d7

OP_RETURN wire format:

    0     2  3                                   19                      39
    |-----|--|-----------------------------------|-----------------------|
    magic op  hash128(name.ns_id,consensus hash)      zone file hash

Note that hash128(name.ns_id, consensus hash) is the first 16 bytes of a SHA256 hash over the name concatenated to the hexadecimal string of the consensus hash (not the bytes corresponding to that hex string). See the Method Glossary below.

Example: hash128("jude.id" + "8d8762c37d82360b84cf4d87f32f7754") == "d1062edb9ec9c85ad1aca6d37f2f5793".

The 20 byte zone file hash is computed from zone file data by using ripemd160(sha56(zone file data))

Inputs:

owner scriptSig
payment scriptSig's

Outputs:

OP_RETURN payload
owner's scriptPubkey
payment scriptPubkey change

NAME_TRANSFER

Op: >

Description: This transaction changes the public key hash that owns the name in BNS. When the name or its DID is looked up after this transaction confirms, the resolver will list the new public key as the owner.

Example: 7a0a3bb7d39b89c3638abc369c85b5c028d0a55d7804ba1953ff19b0125f3c24

OP_RETURN wire format:

    0     2  3    4                   20              36
    |-----|--|----|-------------------|---------------|
    magic op keep  hash128(name.ns_id) consensus hash
             data?

Inputs:

Owner scriptSig
Payment scriptSig's

Outputs:

OP_RETURN payload
new name owner's scriptPubkey
old name owner's scriptPubkey
payment scriptPubkey change

Notes:

The keep data? byte controls whether or not the name's 20-byte value is preserved (i.e. whether or not the name's associated zone file is preserved across the transfer). This value is either > to preserve it, or ~ to delete it. If you're simply re-keying, you should use >. You should only use ~ if you want to simultaneously dissociate the name (and its DID) from its off-chain state, like the DID's DDO.

NAME_REVOKE

Op: ~

Description: This transaction destroys a registered name. Its name state value in BNS will be cleared, and no further transactions will be able to affect the name until it expires (if its namespace allows it to expire at all). Once confirmed, this transaction ensures that neither the name nor the DID will resolve to a DDO.

Example: eb2e84a45cf411e528185a98cd5fb45ed349843a83d39fd4dff2de47adad8c8f

OP_RETURN wire format:

    0    2  3                             39
    |----|--|-----------------------------|
    magic op   name.ns_id (37 bytes)

Inputs:

owner scriptSig
payment scriptSig's

Outputs:

OP_RETURN payload
owner scriptPubkey
payment scriptPubkey change

Method Glossary

Some hashing primitives are used to construct the wire-format representation of each name operation. They are enumerated here:

B40_REGEX = '^[a-z0-9\-_.+]*$'

def is_b40(s):
    return isinstance(s, str) and re.match(B40_REGEX, s) is not None

def b40_to_bin(s):
    if not is_b40(s):
        raise ValueError('{} must only contain characters in the b40 char set'.format(s))
    return unhexlify(charset_to_hex(s, B40_CHARS))

def hexpad(x):
    return ('0' * (len(x) % 2)) + x

def charset_to_hex(s, original_charset):
    return hexpad(change_charset(s, original_charset, B16_CHARS))

def bin_hash160(s, hex_format=False):
    """ s is in hex or binary format
    """
    if hex_format and is_hex(s):
        s = unhexlify(s)
    return hashlib.new('ripemd160', bin_sha256(s)).digest()

def hex_hash160(s, hex_format=False):
    """ s is in hex or binary format
    """
    if hex_format and is_hex(s):
        s = unhexlify(s)
    return hexlify(bin_hash160(s))

def hash_name(name, script_pubkey, register_addr=None):
    """
    Generate the hash over a name and hex-string script pubkey.
    Returns the hex-encoded string RIPEMD160(SHA256(x)), where
    x is the byte string composed of the concatenation of the
    binary
    """
    bin_name = b40_to_bin(name)
    name_and_pubkey = bin_name + unhexlify(script_pubkey)

    if register_addr is not None:
        name_and_pubkey += str(register_addr)

    # make hex-encoded hash
    return hex_hash160(name_and_pubkey)

def hash128(data):
    """
    Hash a string of data by taking its 256-bit sha256 and truncating it to the
    first 16 bytes
    """
    return hexlify(bin_sha256(data)[0:16])

37 KiB Raw Blame History

Blockstack DID Method Specification

Abstract

Status of This Document

1. System Overview

1.1 DID Lifecycle

1.1.1 On-Chain DIDs

1.1.2 Off-chain DIDs

2. Blockstack DID Method

2.1 Namespace-Specific Identifier

2.2 Address Encodings

3. Blockstack DID Operations

3.1 Creating a Blockstack DID

3.2 Storing a Blockstack DID's DDO

3.3 Resolving a Blockstack DID

3.4 Updating a Blockstack DID

3.4.1 Off-Chain DID Updates

3.4.2 Changing the Storage Locations of a DDO

4. Deleting a Blockstack DID

5. Security Considerations

5.1 Public Blockchain Attacks

5.2 Blockstack Peer Network Attacks

5.3 Stale Data and Replay Attacks

6. Privacy Considerations

7. Reference Implementations

8. Resources

Appendix A: On-chain Wire Formats

Transaction format

Payload Format

NAME_PREORDER

NAME_REGISTRATION

NAME_RENEWAL

NAME_UPDATE

NAME_TRANSFER

NAME_REVOKE

Method Glossary

37 KiB

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