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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.

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
admin.macaroon
permissions: all
chainnotifier.macaroon
onchain: read
invoices.macaroon
invoices: read & write
invoice.macaroon
address, invoice: read & write; onchain: read
readonly.macaroon
address, info, invoices, macaroon, message, offchain, onchain, peers, signer: read
router.macaroon
offchain: read & write
signer.macaroon
signer: generate & read
walletkit.macaroon
address, onchain: read & write

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
{
"version": 2,
"location": "lnd",
"root_key_id": "0",
"permissions": [
"address:read",
"address:write",
"info:read",
"info:write",
"invoices:read",
"invoices:write",
"macaroon:generate",
"macaroon:read",
"macaroon:write",
"message:read",
"message:write",
"offchain:read",
"offchain:write",
"onchain:read",
"onchain:write",
"peers:read",
"peers:write",
"signer:generate",
"signer:read"
],
"caveats": [
"ipaddr 127.0.0.1",
"lnd-custom onchain read"
]
}
​

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:
GET https://localhost:8080/v1/getinfo
Grpc-Metadata-macaroon: <macaroon>
Where <macaroon> is the hex encoded binary data from the macaroon file itself.
A very simple example using curl may look something like this:
⛰ curl --insecure --header "Grpc-Metadata-macaroon: $(xxd -ps -u -c 1000 $HOME/.lnd/data/chain/bitcoin/simnet/admin.macaroon)" https://localhost:8080/v1/getinfo
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 and changepassword of lncli
    all have a flag called --stateless_init that instructs the daemon not
    to create *.macaroon files.
  • The two operations create and changepassword that actually create/update
    the macaroon database will return the admin macaroon in the RPC call.
    Assuming the daemon and the lncli are not used on the same machine, this
    will leave no unencrypted information on the machine where lnd runs on.
    • To be more precise: By default, when using the changepassword command, the
      macaroon 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 to
      invalidate all previously created macaroons, the --new_mac_root_key flag
      of the changepassword command should be used!
  • An user of lncli will see the returned admin macaroon printed to the screen
    or saved to a file if the parameter --save_to=some_file.macaroon is used.
  • Important: By default, lnd will create the macaroon files during the
    unlock phase, if the --stateless_init flag is not used. So to avoid
    leakage 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):
    ⛰ lncli create --stateless_init --save_to=/safe/location/admin.macaroon
  • Unlock a wallet that has previously been initialized stateless:
    ⛰ lncli unlock --stateless_init
  • Use the created macaroon:
    ⛰ lncli --macaroonpath=/safe/location/admin.macaroon getinfo
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Last modified 5mo ago