IPNS Record and Protocol

The InterPlanetary File System (IPFS) is powered by content-addressed data, which by nature is immutable: changing an object would change its hash, and consequently its address, making it a different object altogether. However, there are several use cases where we benefit from having mutable data. This is where the InterPlanetary Naming System (IPNS) gets into the equation. IPNS records provide cryptographically verifiable, mutable pointers to objects.

2. IPNS Keys

2.1 Key Types

Implementations MUST support Ed25519 with signatures defined in [rfc8032]. Ed25519 is the current default key type.

Implementations SHOULD support RSA if they wish to interoperate with legacy IPNS names (RSA was used before Ed25519).

Implementations MAY support Secp256k1 and ECDSA for private use, but peers from the public IPFS swarm and DHT may not be able to resolve IPNS records signed by these optional key types.

When implementing support for key types, follow signature implementation notes from PeerID specs.

In all cases, the IPNS implementation MAY allow the user to enable/disable specific key types via configuration. Note that disabling support for compulsory key type will hinder IPNS interop.

2.2 Key Serialization Format

IPNS encodes keys in protobuf containing a KeyType and the encoded key in a Data field:

syntax = "proto2";

enum KeyType {
 RSA = 0;
 Ed25519 = 1;
 Secp256k1 = 2;
 ECDSA = 3;
}

// PublicKey
message PublicKey {
 required KeyType Type = 1;
 required bytes Data = 2;
}

// PrivateKey
message PrivateKey {
 required KeyType Type = 1;
 required bytes Data = 2;
}

Note:

Data encoding depends on KeyType (see Key Types)
Although private keys are not transmitted over the wire, the PrivateKey serialization format used to store keys on disk is also included as a reference for IPNS implementers who would like to import existing IPNS key pairs.
PublicKey and PrivateKey structures were originally defined in PeerID specification, and are currently the same in both libp2p and IPNS. If the PeerID specification ever changes in the future, definition from this file takes the precedence.

4. IPNS Record

A logical IPNS Record is a data structure containing the following fields:

Value (bytes)
- It can be any path, such as a /ipns/{ipns-key} path to another IPNS record, a DNSLink path (/ipns/example.com) or an immutable IPFS path (/ipfs/baf...).
- Implementations MUST include this value in both IpnsEntry.value and inside the DAG-CBOR document in IpnsEntry.data[Value].
Validity Type (uint64)
- Defines the conditions under which the record is valid.
- The only supported value is 0, which indicates the validity field contains the expiration date after which the IPNS record becomes invalid.
- Implementations MUST support validityType = 0 and include this value in both IpnsEntry.validityType and inside the DAG-CBOR document at IpnsEntry.data[ValidityType].
Validity (bytes)
- When validityType = 0
  - Expiration date of the record with nanoseconds precision. Expiration time should match the publishing medium's window.
    - For example, IPNS records published on the DHT should have an expiration time set to within 48 hours after publication. Setting the expiration time to longer than 48 hours will not have any effect, as DHT peers only keep records for up to 48 hours.
  - Represented as an ASCII string that follows notation from [rfc3339] (1970-01-01T00:00:00.000000001Z).
- Implementations MUST include this value in both IpnsEntry.validity and inside the DAG-CBOR document at IpnsEntry.data[Validity].
Sequence (uint64)
- Represents the current version of the record (starts at 0).
- Implementations MUST include this value in both IpnsEntry.sequence and inside the DAG-CBOR document at IpnsEntry.data[Sequence].
TTL (uint64)
- A hint for how long the record should be cached before going back to, for instance the DHT, in order to check if it has been updated.
- Implementations MUST include this value in both IpnsEntry.ttl and inside the DAG-CBOR document at IpnsEntry.data[TTL].
Public Key (bytes)
- Public key used to sign this record.
  - If public key is small enough to fit in IPNS name (e.g., Ed25519 keys inlined using identity multihash), IpnsEntry.pubKey field is redundant and MAY be skipped to save space.
  - The public key MUST be included if it cannot be extracted from the IPNS name (e.g., legacy RSA keys). Implementers MUST follow key serialization defined in PeerID specs.
Signature (bytes)
- Provides the cryptographic proof that the IPNS record was created by the owner of the private key.
- Implementations MUST include this value in IpnsEntry.signatureV2 and follow signature creation and verification as described in Record Creation and Record Verification.
Extensible Data (DAG-CBOR)
- Extensible record data in DAG-CBOR format.
- The default set of fields can be augmented with additional information.
  - Implementations are free to leverage this, or simply ignore unexpected fields.
  - A good practice is to:
    - prefix custom field names with _ to avoid collisions with any new mandatory fields that may be added in a future version of this specification.
    - and/or create own namespace by setting value to DAG-CBOR: IpnsEntry.data[_namespace][customfield].

IPNS records are stored locally, as well as spread across the network, in order to be accessible to everyone.

4.1 Record Serialization Format

For storing this structured data at rest and on the wire, we use IpnsEntry encoded as protobuf, which is a language-neutral, platform neutral extensible mechanism for serializing structured data. The extensible part of IPNS Record is placed in IpnsEntry.data field, which itself is encoded using a strict and deterministic subset of CBOR named DAG-CBOR.

message IpnsEntry {
 enum ValidityType {
  // setting an EOL says "this record is valid until..."
  EOL = 0;
 }

 // deserialized copy of data[Value]
 optional bytes value = 1;

 // legacy field, verify 'signatureV2' instead
 optional bytes signatureV1 = 2;

 // deserialized copies of data[ValidityType] and data[Validity]
 optional ValidityType validityType = 3;
 optional bytes validity = 4;

 // deserialized copy of data[Sequence]
 optional uint64 sequence = 5;

 // record TTL in nanoseconds, a deserialized copy of data[TTL]
 optional uint64 ttl = 6;

 // in order for nodes to properly validate a record upon receipt, they need the public
 // key associated with it. For old RSA keys, its easiest if we just send this as part of
 // the record itself. For newer Ed25519 keys, the public key can be embedded in the
 // IPNS Name itself, making this field unnecessary.
 optional bytes pubKey = 7;

 // the signature of the IPNS record
 optional bytes signatureV2 = 8;

 // extensible record data in DAG-CBOR format
 optional bytes data = 9;
}

Notes:

For legacy reasons, some values must be stored in both IpnsEntry protobuf and IpnsEntry.data CBOR. This should not be ignored, as it impacts interoperability with old software.

4.2 Record Size Limit

IPNS implementations MUST support sending and receiving a serialized IpnsEntry less than or equal to 10 KiB in size.

Records over the limit MAY be ignored. Handling records larger than the limit is not recommended so as to keep compatibility with implementations and transports that follow this specification.

4.3 Backward Compatibility

Implementations that want to interop with the public IPFS swarm MUST maintain backward compatibility for legacy consumers of IPNS records:

A legacy publisher MUST always be able to update to the latest implementation of this specification without breaking record resolution for legacy consumers.
A legacy consumer MUST always be able to resolve IPNS name, even when publisher updated to the latest implementation of this specification.

This means, for example, that changes made to the IpnsEntry protobuf, or validation logic should always be additive.

Future changes to this spec should include design decisions that allow legacy nodes to gracefully ignore new fields and verify compatible records using legacy logic.

5. Protocol

5.1 Overview

IPNS overview

Taking into consideration a p2p network, each peer should be able to publish IPNS records to the network, as well as to resolve the IPNS records published by other peers.

When a node intends to publish a record to the network, an IPNS record needs to be created first. The node needs to have a previously generated asymmetric key pair to create the record according to the data structure previously specified. It is important pointing out that the record needs to be uniquely identified in the network. As a result, the record identifier should be a hash of the public key used to sign the record.

As an IPNS record may be updated during its lifetime, a versioning related logic is needed during the publish process. As a consequence, the record must be stored locally, in order to enable the publisher to understand which is the most recent record published. Accordingly, before creating the record, the node must verify if a previous version of the record exists, and update the sequence value for the new record being created.

Once the record is created, it is ready to be spread through the network. This way, a peer can use whatever routing system it supports to make the record accessible to the remaining peers of the network.

The means of distribution are left unspecified. Implementations MAY choose to publish signed record using multiple routing systems, such as libp2p Kademlia DHT or [ipns-pubsub-router] (see Routing record).

On the other side, each peer must be able to get a record published by another node. It only needs to have the unique identifier used to publish the record to the network. Taking into account the routing system being used, we may obtain a set of occurrences of the record from the network. In this case, records can be compared using the sequence number, in order to obtain the most recent one.

As soon as the node has the most recent record, the signature and the validity must be verified, in order to conclude that the record is still valid and not compromised.

Finally, the network nodes may also republish their records, so that the records in the network continue to be valid to the other nodes.

5.2 Record Creation

IPNS record MUST be serialized as IpnsEntry protobuf, and IpnsEntry.data MUST be signed using the private key. Creating a new IPNS record MUST follow the below steps:

Create IpnsEntry and set value, validity, validityType, sequence, and ttl
- If you are updating an existing record, remember to increase values in sequence and validity
Create a DAG-CBOR document with the same values for Value, Validity, ValidityType, Sequence, and TTL
- This is paramount: this CBOR will be used for signing.
Store DAG-CBOR in IpnsEntry.data.
- If you want to store additional metadata in the record, add it under unique keys at IpnsEntry.data.
- The order of fields impacts signature verification. If you are using an alternative CBOR implementation, make sure the CBOR field order follows [rfc7049] sorting rules: length and then bytewise. The order of fields impacts signature verification.
If your public key can't be inlined inside the IPNS Name, include a serialized copy in IpnsEntry.pubKey
- This step SHOULD be skipped for Ed25519, and any other key types that are inlined inside of IPNS Name itself.
Create IpnsEntry.signatureV2
- Create bytes for signing by concatenating ipns-signature: prefix (bytes in hex: 69706e732d7369676e61747572653a) with raw CBOR bytes from IpnsEntry.data
- Sign concatenated bytes from the previous step using the private key, and store the signature in IpnsEntry.signatureV2
Create IpnsEntry.signatureV1 (backward compatibility, for legacy software)
- Create bytes for signing by concatenating IpnsEntry.value + IpnsEntry.validity + string(IpnsEntry.validityType)
- Sign concatenated bytes from the previous step using the private key, and store the legacy signature in IpnsEntry.signatureV1
Confirm that the serialized IpnsEntry bytes sum to less than or equal to the size limit.

5.3 Record Verification

Implementations MUST resolve IPNS Names using only verified records. Record's data and signature verification MUST be implemented as outlined below, and fail on the first error.

Before parsing the protobuf, confirm that the serialized IpnsEntry bytes sum to less than or equal to the size limit.
Confirm IpnsEntry.signatureV2 and IpnsEntry.data are present and are not empty
Extract public key
- Use IpnsEntry.pubKey or a cached entry in the local key store, if present.
- If public key is missing
  - Assume the public key is inlined in the IPNS Name itself (e.g., Ed25519 inlined using identity multihash)
  - Confirm Multihash type is identity
  - Unmarshall public key from Multihash digest
Deserialize IpnsEntry.data as a DAG-CBOR document
Confirm values in IpnsEntry protobuf match deserialized ones from IpnsEntry.data:
- IpnsEntry.value must match IpnsEntry.data[Value]
- IpnsEntry.validity must match IpnsEntry.data[Validity]
- IpnsEntry.validityType must match IpnsEntry.data[ValidityType]
- IpnsEntry.sequence must match IpnsEntry.data[Sequence]
- IpnsEntry.ttl must match IpnsEntry.data[TTL]
Create bytes for signature verification by concatenating ipns-signature: prefix (bytes in hex: 69706e732d7369676e61747572653a) with raw CBOR bytes from IpnsEntry.data
Verify signature in IpnsEntry.signatureV2 against concatenation result from the previous step.

Value in IpnsEntry.signatureV1 MUST be ignored.

6. Integration with IPFS

Below are additional notes for implementers, documenting how IPNS is integrated within IPFS ecosystem.

6.1 Local Record

This record is stored in the peer's repo datastore and contains the latest version of the IPNS record published by the provided key. This record is useful for republishing, as well as tracking the sequence number. A legacy convention that implementers MAY want to follow is to store serialized IpnsEntry under:

Key format: /ipns/base32(<HASH>)

Note: Base32 according to the [rfc4648].

6.2 Routing Record

The routing record is spread across the network according to the available routing systems. The two routing systems currently available in IPFS are the libp2p Kademlia DHT and [ipns-pubsub-router].

Key format: /ipns/BINARY_ID

/ipns/ is the ASCII prefix (bytes in hex: 2f69706e732f)
BINARY_ID is the binary representation of IPNS Name

As the pubsub topics must be utf-8 for interoperability among different implementations, IPNS over PubSub topics use additional wrapping /record/base64url-unpadded(key)