Macaroons
Macaroons are fancy cookies. You use LND to create custom macaroons that limit their permissions with great granularity, down to the exact RPC calls.
LND, Loop, Pool and litd all use macaroons to authenticate RPC calls. Macaroons are similar to cookies in that they are bearer instruments, but they can be more easily verified by the server using HMACs and a root key alone. They can also be attenuated, both by the server and by the user. This greatly simplifies how LND authenticates RPC calls while expanding the detail in which authority over specific RPC calls is permissioned.
Learn more about Macaroons here.
The default macaroons
By default, LND will generate eight macaroons, created for specific purposes. You can inspect the permissions of each macaroon with the command lncli printmacaroon --macaroon_file ~/path/to/macaroon
Baking custom macaroons
The process of creating a custom macaroon is called “baking.” For this process, LND includes the LND macaroon bakery that can be invoked with lncli bakemacaroon
For instance, a macaroon that is only allowed to manage peers could be created with the command:
lncli bakemacaroon peers:read peers:write
For even more granularity, it is possible to specify individual RPC calls.
lncli bakemacaroon uri:/lnrpc.Lightning/GetInfo uri:/verrpc.Versioner/GetVersion
To get a list of all available restrictions, run lncli listpermissions
By default, LND will generate new macaroons with the root key 0. You can specify another root key ID, even one that does not yet exist, using the flag --root_key_id
. To save your macaroon to a file rather than returning its hex value, use the --save_to flag
. Additionally, macaroons can be bound by IP address as well.
LND supports adding external permissions, even if LND does not understand these permissions, with the --allow_external_permissions
flag.
LND does not include a tool to convert a macaroon back to its hex value, but you may run the xxd
utility if it is installed on your system.
xxd -ps -u -c 1000 /path/to.macaroon
Restraining macaroons
Using the macaroon bakery, you can take any existing macaroon and restrain it further, even if the macaroon was not issued by you.
For example, we can limit our admin macaroon to only be valid for calls made from localhost, as well as take away its authority to perform on-chain actions:
lncli constrainmacaroon --ip_address 127.0.0.1 --custom_caveat_name onchain --custom_caveat_condition read admin.macaroon constrained.macaroon
We can now inspect the permissions of this new macaroon with:
lncli printmacaroon --macaroon_file constrained.macaroon
Revoking macaroons
To revoke a macaroon, it is not sufficient to delete the macaroon. Instead, its root key has to be deleted. Which root key is used for a macaroon can be found out using the lncli printmacaroon
command above.
lncli deletemacaroonid root_key_id
Using Macaroons with GRPC clients
When interacting with lnd
using the GRPC interface, the macaroons are encoded as a hex string over the wire and can be passed to lnd
by specifying the hex-encoded macaroon as GRPC metadata:
Where <macaroon>
is the hex encoded binary data from the macaroon file itself.
A very simple example using curl
may look something like this:
Have a look at the Java GRPC example for programmatic usage details.
Stateless initialization
As mentioned above, by default lnd
creates several macaroon files in its directory. These are unencrypted and in case of the admin.macaroon
provide full access to the daemon. This can be seen as quite a big security risk if the lnd
daemon runs in an environment that is not fully trusted.
The macaroon files are the only files with highly sensitive information that are not encrypted (unlike the wallet file and the macaroon database file that contains the root key, these are always encrypted, even if no password is used).
To avoid leaking the macaroon information, lnd
supports the so called stateless initialization
mode:
The three startup commands
create
,unlock
andchangepassword
oflncli
all have a flag called
--stateless_init
that instructs the daemon notto create
*.macaroon
files.The two operations
create
andchangepassword
that actually create/updatethe macaroon database will return the admin macaroon in the RPC call.
Assuming the daemon and the
lncli
are not used on the same machine, thiswill leave no unencrypted information on the machine where
lnd
runs on.To be more precise: By default, when using the
changepassword
command, themacaroon root key in the macaroon DB is just re-encrypted with the new
password. But the key remains the same and therefore the macaroons issued
before the
changepassword
command still remain valid. If a user wants toinvalidate all previously created macaroons, the
--new_mac_root_key
flagof the
changepassword
command should be used!
An user of
lncli
will see the returned admin macaroon printed to the screenor saved to a file if the parameter
--save_to=some_file.macaroon
is used.Important: By default,
lnd
will create the macaroon files during theunlock
phase, if the--stateless_init
flag is not used. So to avoidleakage of the macaroon information, use the stateless initialization flag
for all three startup commands of the wallet unlocker service!
Examples:
Create a new wallet stateless (first run):
Unlock a wallet that has previously been initialized stateless:
Use the created macaroon:
Actions and RPC permissions
Macaroons in LND may refer to one of seven actions: onchain
, address
, message
, peers
, offchain
, info
, invoices
and macaroon
. These actions encompass the following RPC services:
Onchain
/lnrpc.Lightning/SendCoins
/lnrpc.Lightning/ListUnspent
/lnrpc.Lightning/SendMany
/lnrpc.Lightning/OpenChannel
/lnrpc.Lightning/BatchOpenChannel
/lnrpc.Lightning/OpenChannelSync
/lnrpc.Lightning/CloseChannel
/lnrpc.Lightning/WalletBalance
/lnrpc.Lightning/EstimateFee
/lnrpc.Lightning/ChannelBalance
/lnrpc.Lightning/SubscribeTransactions
/lnrpc.Lightning/GetTransactions
/lnrpc.Lightning/ChannelAcceptor
/lnrpc.Lightning/FundingStateStep
Address
/lnrpc.Lightning/NewAddress
Message
/lnrpc.Lightning/SignMessage
/lnrpc.Lightning/VerifyMessage
Peers
/lnrpc.Lightning/ConnectPeer
/lnrpc.Lightning/DisconnectPeer
/lnrpc.Lightning/ListPeers
/lnrpc.Lightning/SubscribePeerEvents
Offchain
/lnrpc.Lightning/AbandonChannel
/lnrpc.Lightning/PendingChannels
/lnrpc.Lightning/ListChannels
/lnrpc.Lightning/SubscribeChannelEvents
/lnrpc.Lightning/ClosedChannels
/lnrpc.Lightning/SendPayment
/lnrpc.Lightning/SendPaymentSync
/lnrpc.Lightning/SendToRoute
/lnrpc.Lightning/SendToRouteSync
/lnrpc.Lightning/ListPayments
/lnrpc.Lightning/DeletePayment
/lnrpc.Lightning/DeleteAllPayments
/lnrpc.Lightning/DecodePayReq
/lnrpc.Lightning/UpdateChannelPolicy
/lnrpc.Lightning/ForwardingHistory
/lnrpc.Lightning/RestoreChannelBackups
/lnrpc.Lightning/ExportChannelBackup
/lnrpc.Lightning/VerifyChanBackup
/lnrpc.Lightning/ExportAllChannelBackups
/lnrpc.Lightning/SubscribeChannelBackups
/lnrpc.Lightning/SendCustomMessage
/lnrpc.Lightning/SubscribeCustomMessages
/lnrpc.Lightning/LookupHtlcResolution
/lnrpc.Lightning/ListAliases
Info
/lnrpc.Lightning/GetInfo
/lnrpc.Lightning/GetRecoveryInfo
/lnrpc.Lightning/DescribeGraph
/lnrpc.Lightning/GetNodeMetrics
/lnrpc.Lightning/GetChanInfo
/lnrpc.Lightning/GetNodeInfo
/lnrpc.Lightning/QueryRoutes
/lnrpc.Lightning/GetNetworkInfo
/lnrpc.Lightning/StopDaemon
/lnrpc.Lightning/SubscribeChannelGraph
/lnrpc.Lightning/DebugLevel
/lnrpc.Lightning/FeeReport
/lnrpc.Lightning/ListPermissions
Invoices
/lnrpc.Lightning/AddInvoice
/lnrpc.Lightning/LookupInvoice
/lnrpc.Lightning/ListInvoices
/lnrpc.Lightning/SubscribeInvoices
Macaroon
/lnrpc.Lightning/BakeMacaroon
/lnrpc.Lightning/ListMacaroonIDs
/lnrpc.Lightning/DeleteMacaroonID
/lnrpc.Lightning/CheckMacaroonPermissions
/lnrpc.RegisterRPCMiddlewareURI
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