90 lines
3.4 KiB
Markdown
90 lines
3.4 KiB
Markdown
# macaroons
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This is a more detailed, technical description of how macaroons work and how
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authentication and authorization is implemented in `lnd`.
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For a more high-level overview see
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[macaroons.md in the docs](../docs/macaroons.md).
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## Root key
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At startup, if the option `--no-macaroons` is **not** used, a Bolt DB key/value
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store named `data/macaroons.db` is created with a bucket named `macrootkeys`.
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In this DB the following two key/value pairs are stored:
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* Key `0`: the encrypted root key (32 bytes).
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* If the root key does not exist yet, 32 bytes of pseudo-random data is
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generated and used.
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* Key `enckey`: the parameters used to derive a secret encryption key from a
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passphrase.
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* The following parameters are stored: `<salt><digest><N><R><P>`
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* `salt`: 32 byte of random data used as salt for the `scrypt` key
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derivation.
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* `digest`: sha256 hashed key derived from the `scrypt` operation. Is used
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to verify if the password is correct.
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* `N`, `P`, `R`: Parameters used for the `scrypt` operation.
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* The root key is symmetrically encrypted with the derived secret key, using
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the `secretbox` method of the library
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[btcsuite/golangcrypto](https://github.com/btcsuite/golangcrypto).
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* If the option `--noseedbackup` is used, then the default passphrase
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`hello` is used to encrypt the root key.
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## Generated macaroons
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With the root key set up, `lnd` continues with creating three macaroon files:
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* `invoice.macaroon`: Grants read and write access to all invoice related gRPC
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commands (like generating an address or adding an invoice). Can be used for a
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web shop application for example. Paying an invoice is not possible, even if
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the name might suggest it. The permission `offchain` is needed to pay an
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invoice which is currently only granted in the admin macaroon.
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* `readonly.macaroon`: Grants read-only access to all gRPC commands. Could be
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given to a monitoring application for example.
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* `admin.macaroon`: Grants full read and write access to all gRPC commands.
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This is used by the `lncli` client.
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These three macaroons all have the location field set to `lnd` and have no
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conditions/first party caveats or third party caveats set.
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The access restrictions are implemented with a list of entity/action pairs that
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is mapped to the gRPC functions by the `rpcserver.go`.
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For example, the permissions for the `invoice.macaroon` looks like this:
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```go
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// invoicePermissions is a slice of all the entities that allows a user
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// to only access calls that are related to invoices, so: streaming
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// RPCs, generating, and listening invoices.
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invoicePermissions = []bakery.Op{
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{
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Entity: "invoices",
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Action: "read",
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},
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{
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Entity: "invoices",
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Action: "write",
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},
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{
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Entity: "address",
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Action: "read",
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},
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{
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Entity: "address",
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Action: "write",
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},
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}
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```
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## Constraints / First party caveats
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There are currently two constraints implemented that can be used by `lncli` to
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restrict the macaroon it uses to communicate with the gRPC interface. These can
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be found in `constraints.go`:
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* `TimeoutConstraint`: Set a timeout in seconds after which the macaroon is no
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longer valid.
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This constraint can be set by adding the parameter `--macaroontimeout xy` to
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the `lncli` command.
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* `IPLockConstraint`: Locks the macaroon to a specific IP address.
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This constraint can be set by adding the parameter `--macaroonip a.b.c.d` to
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the `lncli` command.
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