x0-guard

Program ID: 2uYGW3fQUGfhrwVbkupdasXBpRPfGYBGTLUdaPTXU9vP x0-guard is the protocol’s policy enforcement layer. It implements the SPL Transfer Hook interface, meaning every Token-2022 transfer is intercepted and validated against the sender’s AgentPolicy before the transfer can settle.

How It Works

When a Token-2022 TransferChecked instruction executes on a mint configured with x0-guard as its transfer hook, Solana automatically invokes x0-guard’s validate_transfer handler. The guard loads the agent’s policy PDA and checks:

Policy is active — is_active must be true
Amount within single-transaction limit — If max_single_transaction is set, the amount must not exceed it
Rolling window budget — The cumulative spend in the last 24 hours plus this amount must not exceed daily_limit
Whitelist membership — If a whitelist is configured, the recipient must pass verification
Minimum transfer amount — Amount must be ≥ 100 micro-units (anti-dust)

If any check fails, the transfer is rejected at the runtime level — the entire transaction reverts.

Instructions

`initialize_policy`

Creates a new AgentPolicy PDA for an owner-agent pair.

initialize_policy(
    daily_limit: u64,
    whitelist_mode: WhitelistMode,
    whitelist_data: Option<Vec<u8>>,
    privacy_level: PrivacyLevel
)

Parameter	Type	Description
`daily_limit`	`u64`	Maximum spend in a 24-hour rolling window (micro-units)
`whitelist_mode`	`WhitelistMode`	`None`, `Merkle`, `Bloom`, or `Domain`
`whitelist_data`	`Option<Vec<u8>>`	Merkle root (32 bytes), Bloom filter (4096 bytes), or domain prefixes
`privacy_level`	`PrivacyLevel`	`Public` or `Confidential { auditor: Option<Pubkey> }`

`update_policy`

Updates an existing policy. Rate-limited to one update per ~5 minutes (POLICY_UPDATE_COOLDOWN_SLOTS = 750).

update_policy(
    new_daily_limit: Option<u64>,
    new_whitelist_mode: Option<WhitelistMode>,
    new_whitelist_data: Option<Vec<u8>>,
    new_privacy_level: Option<PrivacyLevel>,
    new_auditor_key: Option<Pubkey>,
    new_max_single_transaction: Option<u64>
)

`update_agent_signer`

Rotates the agent’s signing key. The old key is immediately invalidated.

update_agent_signer(new_agent_signer: Pubkey)

`revoke_agent_authority`

Emergency revocation — immediately invalidates the agent’s key and sets is_active = false. Only the policy owner can call this.

`set_policy_active`

Pauses or unpauses an agent policy without destroying it.

set_policy_active(is_active: bool)

`validate_transfer`

The Transfer Hook entry point. Called automatically by Token-2022 on every transfer. Not callable directly by users.

validate_transfer(amount: u64, merkle_proof: Option<Vec<[u8; 32]>>)

`record_blink`

Records a Blink (human-approval request) generation event. Rate-limited to MAX_BLINKS_PER_HOUR = 3.

record_blink(amount: u64, recipient: Pubkey, reason: String)

`get_current_spend`

View instruction — returns the current rolling window spend, remaining allowance, and oldest entry expiry.

State Accounts

AgentPolicy

pub struct AgentPolicy {
    pub version: u8,
    pub owner: Pubkey,              // Wallet that created the policy
    pub agent_signer: Pubkey,       // Delegated agent hot-key
    pub daily_limit: u64,           // Max 24h rolling window spend
    pub max_single_transaction: Option<u64>,
    pub rolling_window: Vec<SpendingEntry>,
    pub privacy_level: PrivacyLevel,
    pub whitelist_mode: WhitelistMode,
    pub whitelist_data: Vec<u8>,
    pub auditor_key: Option<Pubkey>,
    pub blinks_this_hour: u8,
    pub blink_hour_start: i64,
    pub is_active: bool,
    pub bump: u8,
    pub require_delegation: bool,
    pub bound_token_account: Option<Pubkey>,
    pub last_update_slot: u64,      // Rate-limiting
}

PDA Seeds: ["agent_policy", owner, agent_signer]

SpendingEntry

Each entry in the rolling window tracks one transfer:

pub struct SpendingEntry {
    pub amount: u64,      // Transfer amount in micro-units
    pub timestamp: i64,   // Unix timestamp of transfer
}

Rolling Window Algorithm

The spend limit uses a sliding 24-hour window rather than a fixed daily reset:

On each transfer, expired entries (older than ROLLING_WINDOW_SECONDS = 86,400) are pruned
The sum of remaining entries is computed as current_spend
If current_spend + amount > daily_limit, the transfer is rejected
On success, a new SpendingEntry is appended
Maximum entries capped at MAX_ROLLING_WINDOW_ENTRIES = 144 (~one per 10 minutes)

This prevents the “midnight boundary” attack where an agent spends the daily limit at 23:59 and again at 00:01.

Whitelist Modes

None
Merkle
Bloom
Domain

No whitelist — the agent can transfer to any recipient.

A Merkle root (32 bytes) is stored on-chain. Each transfer must include a Merkle proof (up to 14 levels deep) proving the recipient’s address is a leaf in the tree. Supports up to 10,000 addresses.

const root = buildMerkleRoot(allowedAddresses);
const proof = generateMerkleProof(allowedAddresses, recipientIndex);

A Bloom filter (4,096 bytes, 7 hash functions) is stored on-chain. Provides probabilistic membership testing with ~1% false positive rate for ~1,000 items. No false negatives.

const filter = createBloomFilter(allowedAddresses);
// On-chain: checkBloomFilter(filter, recipient)

Privacy Levels

Level	Behavior
`Public`	Standard Token-2022 transfer. Amount and parties are visible on-chain.
`Confidential`	Uses Token-2022 ConfidentialTransfer extension. Amounts are encrypted with Twisted ElGamal. Optional `auditor` pubkey can decrypt for compliance.

Events Emitted

Event	When
`PolicyCreated`	New policy initialized
`PolicyUpdated`	Policy parameters changed
`AgentRevoked`	Agent authority revoked
`TransferValidated`	Transfer passed policy check
`TransferRejected`	Transfer failed policy check
`BlinkGenerated`	Blink approval request recorded
`WhitelistUpdated`	Whitelist data changed

Overview

Core Programs

Zero-Knowledge

Application Layer

Reference

How It Works

Instructions

`initialize_policy`

`update_policy`

`update_agent_signer`

`revoke_agent_authority`

`set_policy_active`

`validate_transfer`

`record_blink`

`get_current_spend`

State Accounts

AgentPolicy

SpendingEntry

Rolling Window Algorithm

Whitelist Modes

Privacy Levels

Events Emitted

​How It Works

​Instructions

​initialize_policy

​update_policy

​update_agent_signer

​revoke_agent_authority

​set_policy_active

​validate_transfer

​record_blink

​get_current_spend

​State Accounts

​AgentPolicy

​SpendingEntry

​Rolling Window Algorithm

​Whitelist Modes

​Privacy Levels

​Events Emitted

How It Works

Instructions

`initialize_policy`

`update_policy`

`update_agent_signer`

`revoke_agent_authority`

`set_policy_active`

`validate_transfer`

`record_blink`

`get_current_spend`

State Accounts

AgentPolicy

SpendingEntry

Rolling Window Algorithm

Whitelist Modes

Privacy Levels

Events Emitted