SERVICE-DECLARATION-PROTOCOL

Timeline

• 2026-09-11 — 7c2ec59 — [RFC] The Last Served Epoch Is Rewardable (#435)
• 2026-09-03 — e2e9e0f — [RFC] The Epochs active and withdraw_at Record (#422)
• 2026-09-01 — 74f6f93 — [RFC] Per-Service zk_id Uniqueness Is Normative for Reward Distribution (#406)
• 2026-08-31 — 3cac48f — docs(blockchain): rename locked notes to service notes (#423)
• 2026-08-26 — 5e42374 — docs(blockchain): specify uint32 for epoch number (#420)
• 2026-08-24 — 8b6f4f4 — docs(blockchain): use one canonical encoding for ServiceType and Locator (#402)
• 2026-07-30 — 87d9ae5 — docs(blockchain): length-prefix the locators in the declaration_id preimage (#386)
• 2026-07-13 — d064449 — RFC-Bedrock-SDP: Per-Service Uniqueness of provider_id and zk_id (#371)
• 2026-07-03 — 709cf7f — Bedrock-RFC: Remove Concept of a Session (#365)
• 2026-05-28 — d45eed2 — Chore: mirror blochain specs into github/mdbook (#347)
• 2026-05-18 — 58b5698 — chore(blockchain): migrate contributor emails to @logos.co (#338)
• 2026-01-19 — f24e567 — Chore/updates mdbook (#262)
• 2026-01-16 — 89f2ea8 — Chore/mdbook updates (#258)

Revision History

Introduction

This document defines a mechanism enabling validators to declare their participation in specific protocols that require a known and agreed-upon list of participants. One example of this is the Blend Network. We create a single repository of identifiers which is used to establish secure communication between validators and provide services. Before being admitted to the repository, the validator proves that it locked at least a minimum stake through a service note.

Requirements

The requirements for the protocol are defined as follows:

• A declaration must be backed by a confirmation that the sender of the declaration owns a certain value of the stake.
• A declaration is valid until it is withdrawn or is not actively used for a service-specific amount of time.

Overview

The SDP enables nodes to declare their eligibility to provide a specific service in the system, and withdraw their declarations.

Protocol

The protocol defines the following actions:

• Declare: A node sends a declaration that confirms its willingness to provide a specific service, which is confirmed by locking a stake above a certain threshold in a service note.
• Active: A node marks that its participation in the protocol is active according to the service-specific activity logic. This action enables the protocol to monitor the node’s activity. We utilize this as a non-intrusive differentiator of node activity. It is crucial to exclude inactive nodes from the set of active nodes, as it enhances the stability of services.
• Withdraw: A node withdraws its declaration and stops providing a service.

The logic of the protocol is straightforward.

1. A node sends a declaration message for a specific service and proves it has a minimum stake.
2. The declaration is registered on the Ledger, and the node can commence its service according to the service-specific service logic.
3. After a service-specific service-providing time, the node confirms its activity.
4. The node must confirm its activity with a service-specific minimum frequency; otherwise, its declaration is inactive.
5. After the service-specific locking period, the node can send a withdrawal message, and its declaration is removed from the Ledger, which means that the node will no longer provide the service.

The protocol messages are subject to a finality that means messages become part of the immutable ledger after a delay. The delay at which it happens is defined by the consensus. Therefore, the protocol’s progress must be tracked from the perspective of the latest finalized block, not the tip of the chain. Otherwise, the protocol and services using it would need to handle chain reorganizations, which we must avoid due to their potential to break services. Hence, the services must use a snapshot from a fully finalized epoch: finalized_epoch = current_epoch - 2. For more details about finalization, refer to Cryptarchia Protocol.

Construction

In this section, we present the main constructions of the protocol. First, we start with data definitions. Second, we describe the protocol actions. Finally, we present part of the Bedrock Mantle design responsible for storing and processing SDP-related messages and data.

Data

In this section, we discuss and define data types, messages, and their storage.

Service Types

We define the following service type:

• BN: for Blend Network service.

class ServiceType(Enum):
    BN=0 # Blend Network

A declaration can be generated for any of the services above. Any declaration that is not one of the above must be rejected. The number of services might grow in the future.

Each service type is assigned a one-byte discriminant, given by the enum value above. This byte is the canonical encoding of a ServiceType and is used wherever a ServiceType is serialized or hashed: the transaction wire form (Mantle Transaction Encoding), the declaration_id preimage (Declaration Storage), and the reward op_id preimage (Service Reward Distribution).

Minimum Stake

The minimum stake is a global value that defines the minimum stake a node must have to perform any service.

The MinStake is a structure that holds the value of the stake stake_threshold and the epoch, which is an epoch number at which the threshold was set; it is an EpochNumber.

class MinStake:
    stake_threshold: StakeThreshold
    epoch: EpochNumber

The stake_thresholds is a structure aggregating all defined MinStake values.

stake_thresholds: list[MinStake]

For more information on how the minimum stake is calculated, please refer to the [Analysis] Static Minimum Stake Estimation for Service Declaration Protocol.

Service Parameters

The service parameters structure defines the parameters set necessary for correctly handling interaction between the protocol and services. Each of the service types defined above must be mapped to a set of the following parameters:

• inactivity_period defines the number of epochs after the epoch recorded in active for which the declaration remains active; after that, it is inactive and excluded from the service's participant set in the same way as a withdrawn declaration (Withdraw). A value of 2 + k tolerates k consecutive missed reports (Message Timing). Any value below 2 excludes every declaration.
• epoch defines the epoch number at which the parameter was set; it is an EpochNumber.

class ServiceParameters:
    inactivity_period: NumberOfEpochs
    epoch: EpochNumber

The parameters is a structure aggregating all defined ServiceParameters values.

parameters: list[ServiceParameters]

Snapshots

At the start of epoch , each node takes a snapshot of the SDP registry at the last block from the finalized epoch. Each snapshot updates the common view of the registry. Changes to the declaration registry take effect with up to a two-epoch delay: messages sent during epoch n are included in the next snapshot (for epoch n+2).

Epochs 0 and 1 read the snapshot at the genesis block, because the chain has not yet progressed far enough to provide a later finalized block. While at epoch 2, the last block of epoch 0 is read, and so forth according to the above logic.

Message Timing

The tables below trace each SDP message from the epoch e of the block that contained it. Reward timing follows the Service Reward Distribution Protocol.

Declaration message

Active message

At any epoch n, the most recent report a snapshot can contain was included in epoch n-2 and attests to epoch n-3.

Withdraw message

Identifiers

We define the following set of identifiers which are used for service-specific cryptographic operations:

• provider_id: used to sign the SDP messages and to establish secure links between validators; it is Ed25519PublicKey.
• zk_id: used for zero-knowledge operations by the validator that includes rewarding (Zero Knowledge Signature Scheme (ZkSignature)).

Locators

A Locator is the address of a validator which is used to establish secure communication between validators. It follows the multiaddr addressing scheme from libp2p, but it must contain only the location part and must not contain the node identity (peer_id).

The provider_id must be used as the node identity. Therefore, the Locator must be completed by adding the provider_id at the end of it, which makes the Locator usable in the context of libp2p.

The canonical form of a Locator is the multiaddr binary (byte) form. Wherever a Locator is serialized or hashed — the transaction wire form (Mantle Transaction Encoding) and the declaration_id preimage (Declaration Storage) — its binary form is used. The human-readable string form (e.g. /ip4/203.0.113.10/tcp/4001) is presentational only and must never appear in an encoding.

The length of the binary form of a Locator is restricted to 329 bytes.

The canonical form makes deterministic ID generation work consistently. The binary form carries no letter case and no textual shorthand, so two equal multiaddrs always share one byte representation; the string-form ambiguities (case, implicit defaults) cannot arise. Implementations that accept the string form as input must parse it into the binary form before any serialization or hashing, and every part of the address must be explicit (no implicit defaults).

The canonical form makes a single Locator unambiguous, but it does not make a list of them unambiguous. The byte form of a multiaddr is self-describing, so concatenating two Locators yields the byte form of a single longer one: [/ip4/203.0.113.10/tcp/4001] and [/ip4/203.0.113.10, /tcp/4001] are the same byte string. Wherever a list of Locators is hashed it must therefore be serialized as the Locators production of the Mantle Transaction Encoding: prefixed with its element count and with each element prefixed by its byte length.

Declaration Message

The construction of the declaration message is as follows.

class DeclarationMessage:
    service_type: ServiceType
    locators: list[Locator]
    provider_id: Ed25519PublicKey
    service_note_id: NoteId
    zk_id: ZkPublicKey

The locators list must be non-empty and its length must be limited to reduce the potential for abuse. Therefore, the length of the list cannot be longer than 8.

The message must be signed by the provider_id key to prove ownership of the key that is used for network-level authentication of the validator.

The service_note_id points to a service note used for minimum stake threshold verification purposes.

The message is also signed by the zk_id key.

Declaration Storage

Only valid declaration messages can be stored on the ledger. We define the DeclarationInfo as follows:

class DeclarationInfo:
    service: ServiceType
    provider_id: Ed25519PublicKey
    service_note_id: NoteId
    zk_id: ZkPublicKey
    locators: list[Locator]
    created: EpochNumber
    active: EpochNumber
    withdraw_at: EpochNumber | None
    nonce: Nonce

Where:

• service defines the service type of the declaration;
• provider_id is an Ed25519PublicKey used to sign the message by the validator;
• service_note_id is a NoteId used for minimum stake threshold verification purposes;
• zk_id is used for zero-knowledge operations by the validator that includes rewarding;
• locators is a copy of the locators from the DeclarationMessage;
• created refers to the epoch number of the block that contained the declaration;
• active refers to the epoch of the block that contained the latest accepted active message; it is initialised to created + 2 (Message Timing);
• withdraw_at refers to the epoch at which the node stops providing the service (Withdraw); it is set to None by default;
• The nonce must be set to 0 for the declaration message and must increase monotonically by every message sent for the declaration_id.

We also define the declaration_id (of a DeclarationId type) that is the unique identifier of DeclarationInfo calculated as a hash of the concatenation of service, provider_id, zk_id and locators. The implementation of the hash function is blake2b using 256 bits of the output.

declaration_id = Hash(service||provider_id||zk_id||locators)

Each component of the preimage is serialized in its canonical encoding, as defined by the Mantle Transaction Encoding for the SDP_DECLARE operation: service as the one-byte ServiceType discriminant (Service Types), and locators as the Locators production, its element count followed by each Locator's binary form prefixed with its byte length (Locators). Concatenating the locators without those lengths would leave the declaration_id not binding the locator list, for the reason given in Locators.

The declaration_id is not stored as part of the DeclarationInfo but it is used to index it.

All DeclarationInfo references are stored in the declarations and are indexed by declaration_id.

declarations: list[declaration_id]

Identifier Uniqueness

The SDP is responsible for enforcing the uniqueness of the provider_id and the zk_id in the context of a service. This means that, for a given service, each provider_id and each zk_id must be bound to at most one DeclarationInfo in declarations, whether or not its active field is set.

The declaration_id uniqueness alone is insufficient to guarantee this property. Because declaration_id = Hash(service||provider_id||zk_id||locators), two declarations for the same service that reuse the same provider_id (or the same zk_id) but differ in any other component would produce distinct declaration_ids and would therefore not collide. This holds only because each component is committed under an encoding that determines it uniquely: without the length prefixing defined above, two declarations differing only in how the same locator bytes are split across the list would share a declaration_id. The SDP must reject such declarations regardless.

Consequently, within a single service:

• A provider_id must not be bound to more than one DeclarationInfo.
• A zk_id must not be bound to more than one DeclarationInfo.

The uniqueness is scoped per-service: the same provider_id or zk_id may be reused across different services, but never more than once within the same service. A provider_id or zk_id becomes available for reuse in a service only once its previous DeclarationInfo for that service has been withdrawn and removed (see Withdraw).

Active Message

The construction of the active message is as follows:

class ActiveMessage:
    declaration_id: DeclarationId
    nonce: Nonce
    metadata: Metadata

where metadata is service-specific node activeness metadata.

The message must be signed by the zk_id key associated with the declaration_id.

The nonce must increase monotonically by every message sent for the declaration_id.

An active message attests to a single past epoch during which the node provided the service. The service defines when the message may be sent (see Active Message for the Blend Network).

The metadata layout is service-defined; the SDP does not parse it.

Withdraw Message

The construction of the withdraw message is as follows:

class WithdrawMessage:
    declaration_id: DeclarationId
    service_note_id: NoteId
    nonce: Nonce

The message must be signed by the zk_id key from the declaration_id.

The service_note_id is a NoteId that was used for minimum stake threshold verification purposes and will be unlocked after withdrawal.

The nonce must increase monotonically by every message sent for the declaration_id.

Indexing

Every event must be correctly indexed to enable lighter synchronization of the changes. Therefore, we index every declaration_id according to EventType, ServiceType, and Epoch. Where EventType = { "created", "active", "withdrawn" } follows the type of the message.

The Epoch key is the epoch of the block that contained the message, for all three event types.

events = {
    event_type: {
        service_type: {
            epoch: {
                declarations: list[declaration_id]
            }
        }
    }
}

Protocol

Declare

The Declare action associates a validator with a service it wants to provide. It requires sending a valid DeclarationMessage (as defined in Declaration Message), which is then processed (as defined below) and stored (as defined in Declaration Storage).

The declaration message is considered valid when all of the following are met:

• The sender meets the stake requirements and its service_note_id is valid.
• The declaration_id is unique.
• The provider_id and the zk_id are each unique in the context of the service (as defined in Identifier Uniqueness).
• The sender knows the secret behind the provider_id identifier.
• The length of the locators list must not be longer than 8.
• The nonce increases monotonically.

If all of the above conditions are fulfilled, then the message is stored on the ledger; otherwise, the message is discarded.

Active

The Active action enables marking the provider as actively providing a service. It requires sending a valid ActiveMessage (as defined in Active Message), which is relayed to the service-specific node activity logic (as indicated by the service type in Common SDP Structures).

The Active action updates the active value of the DeclarationInfo. A declaration considered inactive is not removed from the registry, and an accepted active message makes it active again. A declaration is removed only by withdrawal (Withdraw); a removed declaration cannot become active again.

The SDP active action logic is:

1. A node sends an ActiveMessage transaction.
2. The ActiveMessage is verified by the SDP logic:
   1. The declaration_id returns an existing DeclarationInfo.
   2. The transaction containing ActiveMessage is signed by the zk_id.
   3. The nonce increases monotonically.
3. If any of these conditions fail, discard the message and stop processing.
4. The message is processed by the service-specific activity logic, together with the epoch of the block that contained the message.
5. If the service-specific activity logic rejects the message, discard the message and stop processing.
6. The active field of the DeclarationInfo is set to that epoch.

An active message is valid only while the current epoch is at most withdraw_at (see Withdraw).

Withdraw

The withdraw action enables a withdrawal of a service declaration. It requires sending a valid WithdrawMessage (as defined in Withdraw Message). The withdrawal marks the intent to stop providing the service.

Let e be the epoch of the block that contained the WithdrawMessage; withdraw_at records e+2 (Snapshots).

A service deriving its participant set from a snapshot must exclude every declaration for which withdraw_at is not None and n >= withdraw_at, where n is the epoch the set is derived for.

The node provides the service through epoch withdraw_at - 1, its last rewardable epoch. The declaration is removed and the service note unlocked at epoch withdraw_at + 1 (SDP Epoch Finalization).

The logic of the withdraw action is:

1. A node sends a WithdrawMessage transaction.
2. The WithdrawMessage is verified by the SDP logic.
   1. The declaration_id returns an existing DeclarationInfo.
   2. The transaction containing WithdrawMessage is signed by the zk_id.
   3. The withdraw_at from DeclarationInfo is set to None.
   4. The nonce increases monotonically.
3. If any of the above is not correct, then discard the message and stop.
4. Set the withdraw_at from the DeclarationInfo to the current epoch number plus two.
5. The DeclarationInfo is removed and the stake unlocked (releasing the service_note_id) at epoch withdraw_at + 1 (SDP Epoch Finalization).

Query

The protocol must enable querying the ledger in at least the following manner:

• GetAllProviderId(epoch), returns all provider_ids associated with the epoch.
• GetAllProviderIdSince(epoch), returns all provider_ids since the epoch.
• GetAllDeclarationInfo(epoch), returns all DeclarationInfo entries associated with the epoch.
• GetAllDeclarationInfoSince(epoch), returns all DeclarationInfo entries since the epoch.
• GetDeclarationInfo(provider_id), returns the DeclarationInfo entry identified by the provider_id.
• GetDeclarationInfo(declaration_id), returns the DeclarationInfo entry identified by the declaration_id.
• GetAllServiceParameters(epoch), returns all entries of the ServiceParameters store for the requested epoch.
• GetAllServiceParametersSince(epoch), returns all entries of the ServiceParameters store since the requested epoch.
• GetServiceParameters(service_type, epoch), returns the service parameter entry from the ServiceParameters store of a service_type for a specified epoch.
• GetMinStake(epoch), returns the MinStake structure at the requested epoch.
• GetMinStakeSince(epoch), returns a set of MinStake structures since the requested epoch.

The query must return an error if the requested information is not available.

The list of queries may be extended.

Every query must return information for a finalized state only.

Mantle and ZK Proofs

For more information about Mantle and ZK proofs, please refer to Mantle.

Default Service Parameters

Blend Network

class BlendNetworkServiceParameters:
    inactivity_period: 2
    epoch: 0