alsp

README

Application Layer Spam Prevention (ALSP)

Overview

The Application Layer Spam Prevention (ALSP) is a module that provides a mechanism to prevent the malicious nodes from spamming the Flow nodes at the application layer (i.e., the engines). ALSP is not a multi-party protocol, i.e., it does not require the nodes to exchange any messages with each other for the purpose of spam prevention. Rather, it is a local mechanism that is implemented by each node to protect itself from malicious nodes. ALSP is not meant to replace the existing spam prevention mechanisms at the network layer (e.g., the Libp2p and GossipSub). Rather, it is meant to complement the existing mechanisms by providing an additional layer of protection. ALSP is concerned with the spamming of the application layer through messages that appear valid to the networking layer and hence are not filtered out by the existing mechanisms.

ALSP relies on the application layer to detect and report the misbehaviors that lead to spamming. It enforces a penalty system to penalize the misbehaving nodes that are reported by the application layer. ALSP also takes extra measures to protect the network from malicious nodes that attempt an active spamming attack. Once the penalty of a remote node reaches a certain threshold, the local node will disconnect from the remote node and no-longer accept any incoming connections from the remote node until the penalty is reduced to zero again through a decaying interval.

Features

• Spam prevention at the application layer.
• Penalizes misbehaving nodes based on their behavior.
• Configurable penalty values and decay intervals.
• Misbehavior reports with customizable penalty amplification.
• Thread-safe and non-blocking implementation.
• Maintains the safety and liveness of the Flow blockchain system by disallow-listing malicious nodes (i.e., application layer spammers).

Architectural Principles

• Non-intrusive: ALSP is a local mechanism that is implemented by each node to protect itself from malicious nodes. It is not a multi-party protocol, i.e., it does not require the nodes to exchange any messages with each other for the purpose of spam prevention.
• Non-blocking: ALSP is non-blocking and does not affect the performance of the networking layer. It is implemented in a way that does not require the networking layer to wait for the ALSP to complete its operations. Non-blocking behavior is mandatory for the networking layer to maintain its performance.
• Thread-safe: ALSP is thread-safe and can be used concurrently by multiple threads, e.g., concurrent engine calls on reporting misbehaviors.

Usage

ALSP is enabled by default through the networking layer. It is not necessary to explicitly enable it. One can disable it by setting the alsp-enable flag to false. The network.Conduit interface provides the following method to report misbehaviors:

• ReportMisbehavior(*MisbehaviorReport): Reports a misbehavior to the ALSP. The misbehavior report contains the misbehavior type and the penalty value. The penalty value is used to increase the penalty of the remote node. The penalty value is amplified by the penalty amplification factor before being applied to the remote node.

By default, the penalty amplification factor is set to 0.01 * disallow-listing threshold. The disallow-listing threshold is the penalty threshold at which the local node will disconnect from the remote node and no-longer accept any incoming connections from the remote node until the penalty is reduced to zero again through a decaying interval. Hence, by default, every time a misbehavior is reported, the penalty of the remote node is increased by 0.01 * disallow-listing threshold. This penalty value is configurable through an option function on the MisbehaviorReport struct. The example below shows how to create a misbehavior report with a penalty amplification factor of 10, i.e., the penalty value of the misbehavior report is amplified by 10 before being applied to the remote node. This is equal to increasing the penalty of the remote node by 10 * 0.01 * disallow-listing threshold. The misbehavingId is the Flow identifier of the remote node that is misbehaving. The misbehaviorType is the reason for reporting the misbehavior.

report, err := NewMisbehaviorReport(misbehavingId, misbehaviorType, WithPenaltyAmplification(10))
if err != nil {
    // handle the error
}

Once a misbehavior report is created, it can be reported to the ALSP by calling the ReportMisbehavior method on the network conduit. The example below shows how to report a misbehavior to the ALSP.

// let con be network.Conduit
err := con.ReportMisbehavior(report)
if err != nil {
    // handle the error
}

Misbehavior Types (MisbehaviorType)

ALSP package defines several constants that represent various types of misbehaviors that can be reported by engines. These misbehavior types help categorize node behavior and improve the accuracy of the penalty system.

Constants

The following constants represent misbehavior types that can be reported:

• StaleMessage: This misbehavior is reported when an engine receives a message that is deemed stale based on the local view of the engine. A stale message is one that is outdated, irrelevant, or already processed by the engine.
• ResourceIntensiveRequest: This misbehavior is reported when an engine receives a request that takes an unreasonable amount of resources for the engine to process, e.g., a request for a large number of blocks. The decision to consider a request heavy is up to the engine. Heavy requests can potentially slow down the engine, causing performance issues.
• RedundantMessage: This misbehavior is reported when an engine receives a message that is redundant, i.e., the message is already known to the engine. The decision to consider a message redundant is up to the engine. Redundant messages can increase network traffic and waste processing resources.
• UnsolicitedMessage: This misbehavior is reported when an engine receives a message that is not solicited by the engine. The decision to consider a message unsolicited is up to the engine. Unsolicited messages can be a sign of spamming or malicious behavior.
• InvalidMessage: This misbehavior is reported when an engine receives a message that is invalid and fails the validation logic as specified by the engine, i.e., the message is malformed or does not follow the protocol specification. The decision to consider a message invalid is up to the engine. Invalid messages can be a sign of spamming or malicious behavior.

Thresholds and Parameters

The ALSP provides various constants and options to customize the penalty system:

• misbehaviorDisallowListingThreshold: The threshold for concluding a node behavior is malicious and disallow-listing the node. Once the penalty of a remote node reaches this threshold, the local node will disconnect from the remote node and no-longer accept any incoming connections from the remote node until the penalty is reduced to zero again through a decaying interval.
• defaultPenaltyValue: The default penalty value for misbehaving nodes. This value is used when the penalty value is not specified in the misbehavior report. By default, the penalty value is set to 0.01 * misbehaviorDisallowListingThreshold. However, this value can be amplified by a positive integer in [1-100] using the WithPenaltyAmplification option function on the MisbehaviorReport struct. Note that amplifying at 100 means that a single misbehavior report will disallow-list the remote node.
• misbehaviorDecayHeartbeatInterval: The interval at which the penalty of the misbehaving nodes is decayed. Decaying is used to reduce the penalty of the misbehaving nodes over time. So that the penalty of the misbehaving nodes is reduced to zero after a certain period of time and the node is no-longer considered misbehaving. This is to avoid persisting the penalty of a node forever.
• defaultDecayValue: The default value that is deducted from the penalty of the misbehaving nodes at each decay interval.
• decayValueSpeedPenalty: The penalty for the decay speed. This is a multiplier that is applied to the defaultDecayValue at each decay interval. The purpose of this penalty is to slow down the decay process of the penalty of the nodes that make a habit of misbehaving.
• minimumDecayValue: The minimum decay value that is used to decay the penalty of the misbehaving nodes. The decay value is capped at this value.

Documentation

Index

• Constants
• func AllMisbehaviorTypes() []network.Misbehavior
• type MisbehaviorReport
  • func NewMisbehaviorReport(misbehavingId flow.Identifier, reason network.Misbehavior, ...) (*MisbehaviorReport, error)
  • func (r MisbehaviorReport) OriginId() flow.Identifier
  • func (r MisbehaviorReport) Penalty() float64
  • func (r MisbehaviorReport) Reason() network.Misbehavior
• type MisbehaviorReportOpt
  • func WithPenaltyAmplification(v float64) MisbehaviorReportOpt
• type SpamRecordCache

Constants

const (
	// StaleMessage is a misbehavior that is reported when an engine receives a message that is deemed stale based on the
	// local view of the engine. The decision to consider a message stale is up to the engine.
	StaleMessage network.Misbehavior = "misbehavior-stale-message"

	// ResourceIntensiveRequest is a misbehavior that is reported when an engine receives a request that takes an unreasonable amount
	// of resources by the engine to process, e.g., a request for a large number of blocks. The decision to consider a
	// request heavy is up to the engine.
	ResourceIntensiveRequest network.Misbehavior = "misbehavior-resource-intensive-request"

	// RedundantMessage is a misbehavior that is reported when an engine receives a message that is redundant, i.e., the
	// message is already known to the engine. The decision to consider a message redundant is up to the engine.
	RedundantMessage network.Misbehavior = "misbehavior-redundant-message"

	// UnsolicitedMessage is a misbehavior that is reported when an engine receives a message that is not solicited by the
	// engine. The decision to consider a message unsolicited is up to the engine.
	UnsolicitedMessage network.Misbehavior = "misbehavior-unsolicited-message"

	// InvalidMessage is a misbehavior that is reported when an engine receives a message that is invalid, i.e.,
	// the message is not valid according to the engine's validation logic. The decision to consider a message invalid
	// is up to the engine.
	InvalidMessage network.Misbehavior = "misbehavior-invalid-message"

	// UnExpectedValidationError is a misbehavior that is reported when a validation error is encountered during message validation before the message
	// is processed by an engine.
	UnExpectedValidationError network.Misbehavior = "unexpected-validation-error"

	// UnknownMsgType is a misbehavior that is reported when a message of unknown type is received from a peer.
	UnknownMsgType network.Misbehavior = "unknown-message-type"

	// SenderEjected is a misbehavior that is reported when a message is received from an ejected peer.
	SenderEjected network.Misbehavior = "sender-ejected"

	// UnauthorizedUnicastOnChannel is a misbehavior that is reported when a message not authorized to be sent via unicast is received via unicast.
	UnauthorizedUnicastOnChannel network.Misbehavior = "unauthorized-unicast-on-channel"

	// UnAuthorizedSender is a misbehavior that is reported when a message is sent by an unauthorized role.
	UnAuthorizedSender network.Misbehavior = "unauthorized-sender"

	// UnauthorizedPublishOnChannel is a misbehavior that is reported when a message not authorized to be sent via pubsub is received via pubsub.
	UnauthorizedPublishOnChannel network.Misbehavior = "unauthorized-pubsub-on-channel"
)

Functions

func AllMisbehaviorTypes

func AllMisbehaviorTypes() []network.Misbehavior

Types

type MisbehaviorReport

type MisbehaviorReport struct {
	// contains filtered or unexported fields
}

MisbehaviorReport is a report that is sent to the networking layer to penalize the misbehaving node. A MisbehaviorReport reports the misbehavior of a node on sending a message to the current node that appears valid based on the networking layer but is considered invalid by the current node based on the Flow protocol.

A MisbehaviorReport consists of a reason and a penalty. The reason is a string that describes the misbehavior. The penalty is a value that is deducted from the overall score of the misbehaving node. The score is decayed at each decay interval. If the overall penalty of the misbehaving node drops below the disallow-listing threshold, the node is reported to be disallow-listed by the networking layer, i.e., existing connections to the node are closed and the node is no longer allowed to connect till its penalty is decayed back to zero.

func NewMisbehaviorReport

func NewMisbehaviorReport(misbehavingId flow.Identifier, reason network.Misbehavior, opts ...MisbehaviorReportOpt) (*MisbehaviorReport, error)

NewMisbehaviorReport creates a new misbehavior report with the given reason and options. If no options are provided, the default penalty value is used. The returned error by this function indicates that the report is not created. In BFT setup, the returned error should be treated as a fatal error. The default penalty value is 0.01 * misbehaviorDisallowListingThreshold = -86.4

func (MisbehaviorReport) OriginId

func (r MisbehaviorReport) OriginId() flow.Identifier

OriginId returns the ID of the misbehaving node.

func (MisbehaviorReport) Penalty

func (r MisbehaviorReport) Penalty() float64

Penalty returns the penalty value of the misbehavior.

func (MisbehaviorReport) Reason

func (r MisbehaviorReport) Reason() network.Misbehavior

Reason returns the reason of the misbehavior.

type MisbehaviorReportOpt

type MisbehaviorReportOpt func(r *MisbehaviorReport) error

MisbehaviorReportOpt is an option that can be used to configure a misbehavior report.

func WithPenaltyAmplification

func WithPenaltyAmplification(v float64) MisbehaviorReportOpt

WithPenaltyAmplification returns an option that can be used to amplify the penalty value. The penalty value is multiplied by the given value. The value should be between 1-100. If the value is not in the range, an error is returned. The returned error by this option indicates that the option is not applied. In BFT setup, the returned error should be treated as a fatal error.

type SpamRecordCache

type SpamRecordCache interface {
	// Adjust applies the given adjust function to the spam record of the given origin id.
	// Returns the Penalty value of the record after the adjustment.
	// It returns an error if the adjustFunc returns an error or if the record does not exist.
	// Assuming that adjust is always called when the record exists, the error is irrecoverable and indicates a bug.
	AdjustWithInit(originId flow.Identifier, adjustFunc model.RecordAdjustFunc) (float64, error)

	// Identities returns the list of identities of the nodes that have a spam record in the cache.
	Identities() []flow.Identifier

	// Remove removes the spam record of the given origin id from the cache.
	// Returns true if the record is removed, false otherwise (i.e., the record does not exist).
	Remove(originId flow.Identifier) bool

	// Get returns the spam record of the given origin id.
	// Returns the record and true if the record exists, nil and false otherwise.
	// Args:
	// - originId: the origin id of the spam record.
	// Returns:
	// - the record and true if the record exists, nil and false otherwise.
	// Note that the returned record is a copy of the record in the cache (we do not want the caller to modify the record).
	Get(originId flow.Identifier) (*model.ProtocolSpamRecord, bool)

	// Size returns the number of records in the cache.
	Size() uint
}

SpamRecordCache is a cache of spam records for the ALSP module. It is used to keep track of the spam records of the nodes that have been reported for spamming.