package
0.18.4-beta.rc2
Repository: https://github.com/lightningnetwork/lnd.git
Documentation: pkg.go.dev

# README

macaroons

This is a more detailed, technical description of how macaroons work and how authentication and authorization is implemented in lnd.

For a more high-level overview see macaroons.md in the docs.

Root key

At startup, if the option --no-macaroons is not used, a Bolt DB key/value store named data/macaroons.db is created with a bucket named macrootkeys. In this DB the following two key/value pairs are stored:

  • Key 0: the encrypted root key (32 bytes).
    • If the root key does not exist yet, 32 bytes of pseudo-random data is generated and used.
  • Key enckey: the parameters used to derive a secret encryption key from a passphrase.
    • The following parameters are stored: <salt><digest><N><R><P>
      • salt: 32 byte of random data used as salt for the scrypt key derivation.
      • digest: sha256 hashed key derived from the scrypt operation. Is used to verify if the password is correct.
      • N, P, R: Parameters used for the scrypt operation.
    • The root key is symmetrically encrypted with the derived secret key, using the secretbox method of the library btcsuite/golangcrypto.
    • If the option --noseedbackup is used, then the default passphrase hello is used to encrypt the root key.

Generated macaroons

With the root key set up, lnd continues with creating three macaroon files:

  • invoice.macaroon: Grants read and write access to all invoice related gRPC commands (like generating an address or adding an invoice). Can be used for a web shop application for example. Paying an invoice is not possible, even if the name might suggest it. The permission offchain is needed to pay an invoice which is currently only granted in the admin macaroon.
  • readonly.macaroon: Grants read-only access to all gRPC commands. Could be given to a monitoring application for example.
  • admin.macaroon: Grants full read and write access to all gRPC commands. This is used by the lncli client.

These three macaroons all have the location field set to lnd and have no conditions/first party caveats or third party caveats set.

The access restrictions are implemented with a list of entity/action pairs that is mapped to the gRPC functions by the rpcserver.go. For example, the permissions for the invoice.macaroon looks like this:

	// invoicePermissions is a slice of all the entities that allows a user
	// to only access calls that are related to invoices, so: streaming
	// RPCs, generating, and listening invoices.
	invoicePermissions = []bakery.Op{
		{
			Entity: "invoices",
			Action: "read",
		},
		{
			Entity: "invoices",
			Action: "write",
		},
		{
			Entity: "address",
			Action: "read",
		},
		{
			Entity: "address",
			Action: "write",
		},
	}

Constraints / First party caveats

There are currently two constraints implemented that can be used by lncli to restrict the macaroon it uses to communicate with the gRPC interface. These can be found in constraints.go:

  • TimeoutConstraint: Set a timeout in seconds after which the macaroon is no longer valid. This constraint can be set by adding the parameter --macaroontimeout xy to the lncli command.
  • IPLockConstraint: Locks the macaroon to a specific IP address. This constraint can be set by adding the parameter --macaroonip a.b.c.d to the lncli command.

Bakery

As of lnd v0.9.0-beta there is a macaroon bakery available through gRPC and command line. Users can create their own macaroons with custom permissions if the provided default macaroons (admin, invoice and readonly) are not sufficient.

For example, a macaroon that is only allowed to manage peers with a default root key 0 would be created with the following command:

$  lncli bakemacaroon peers:read peers:write

For even more fine-grained permission control, it is also possible to specify single RPC method URIs that are allowed to be accessed by a macaroon. This can be achieved by passing uri:<methodURI> pairs to bakemacaroon, for example:

$  lncli bakemacaroon uri:/lnrpc.Lightning/GetInfo uri:/verrpc.Versioner/GetVersion

The macaroon created by this call would only be allowed to call the GetInfo and GetVersion methods instead of all methods that have similar permissions (like info:read for example).

A full list of available entity/action pairs and RPC method URIs can be queried by using the lncli listpermissions command.

Upgrading from v0.8.0-beta or earlier

Users upgrading from a version prior to v0.9.0-beta might get a permission denied error when trying to use the lncli bakemacaroon command. This is because the bakery requires a new permission (macaroon/generate) to access. Users can obtain a new admin.macaroon that contains this permission by removing all three default macaroons (admin.macaroon, invoice.macaroon and readonly.macaroon, NOT the macaroons.db!) from their data/chain/<chain>/<network>/ directory inside the lnd data directory and restarting lnd.

Root key rotation

To manage the root keys used by macaroons, there are listmacaroonids and deletemacaroonid available through gPRC and command line. Users can view a list of all macaroon root key IDs that are in use using:

$  lncli listmacaroonids

And remove a specific macaroon root key ID using command:

$  lncli deletemacaroonid root_key_id

Be careful with the deletemacaroonid command as when a root key is deleted, all the macaroons created from it are invalidated.

# Functions

AddConstraints returns new derived macaroon by applying every passed constraint and tightening its restrictions.
ContextWithRootKeyID passes the root key ID value to context.
CustomChecker returns a Checker function that is used by the macaroon bakery library to check whether a custom caveat is supported by lnd in general or not.
CustomConstraint returns a function that adds a custom caveat condition to a macaroon.
GetCustomCaveatCondition returns the custom caveat condition for the given custom caveat name from the given macaroon.
HasCustomCaveat tests if the given macaroon has a custom caveat with the given custom caveat name.
IPLockChecker accepts client IP from the validation context and compares it with IP locked in the macaroon.
IPLockConstraint locks macaroon to a specific IP address.
NewMacaroonCredential returns a copy of the passed macaroon wrapped in a MacaroonCredential struct which implements PerRPCCredentials.
NewRootKeyStorage creates a RootKeyStorage instance.
NewService returns a service backed by the macaroon DB backend.
RawMacaroonFromContext is a helper function that extracts a raw macaroon from the given incoming gRPC request context.
RootKeyIDFromContext retrieves the root key ID from context using the key RootKeyIDContextKey.
SafeCopyMacaroon creates a copy of a macaroon that is safe to be used and modified.
TimeoutConstraint restricts the lifetime of the macaroon to the amount of seconds given.

# Constants

CondLndCustom is the first party caveat condition name that is used for all custom caveats in lnd.
RootKeyLen is the length of a root key.

# Variables

DefaultRootKeyID is the ID of the default root key.
ErrAlreadyUnlocked specifies that the store has already been unlocked.
ErrContextRootKeyID is used when the supplied context doesn't have a root key ID.
ErrDefaultRootKeyNotFound is returned when the default root key is not found in the DB when it is expected to be.
ErrDeletionForbidden is used when attempting to delete the DefaultRootKeyID or the encryptedKeyID.
ErrEncKeyNotFound specifies that there was no encryption key found even if one was expected to be generated.
ErrInvalidID is returned when a macaroon ID is invalid.
ErrKeyValueForbidden is used when the root key ID uses encryptedKeyID as its value.
ErrMissingRootKeyID specifies the root key ID is missing.
ErrPasswordRequired specifies that a nil password has been passed.
ErrRootKeyBucketNotFound specifies that there is no macaroon root key bucket yet which can/should only happen if the store has been corrupted or was initialized incorrectly.
ErrStoreLocked specifies that the store needs to be unlocked with a password.
ErrUnknownVersion is returned when a macaroon is of an unknown is presented.
PermissionEntityCustomURI is a special entity name for a permission that does not describe an entity:action pair but instead specifies a specific URI that needs to be granted access to.
RootKeyIDContextKey is the key to get rootKeyID from context.

# Structs

MacaroonCredential wraps a macaroon to implement the credentials.PerRPCCredentials interface.
RootKeyStorage implements the bakery.RootKeyStorage interface.
Service encapsulates bakery.Bakery and adds a Close() method that zeroes the root key service encryption keys, as well as utility methods to validate a macaroon against the bakery and gRPC middleware for macaroon-based auth.

# Interfaces

CustomCaveatAcceptor is an interface that contains a single method for checking whether a macaroon with the given custom caveat name should be accepted or not.
ExtendedRootKeyStore is an interface augments the existing macaroons.RootKeyStorage interface by adding a number of additional utility methods such as encrypting and decrypting the root key given a password.
MacaroonValidator is an interface type that can check if macaroons are valid.

# Type aliases

Checker type adds a layer of indirection over macaroon checkers.
Constraint type adds a layer of indirection over macaroon caveats.