# Gatekeeper and Sturdy-references

 - [`[syndicate-protocols]/schemas/gatekeeper.prs`](https://git.syndicate-lang.org/syndicate-lang/syndicate-protocols/src/branch/main/schemas/gatekeeper.prs)
 - [`[syndicate-protocols]/schemas/sturdy.prs`](https://git.syndicate-lang.org/syndicate-lang/syndicate-protocols/src/branch/main/schemas/sturdy.prs)

## Gatekeeper protocol

The Gatekeeper protocol allows a peer to "upgrade" a `SturdyRef` to a live reference to an
entity. For details of the use of `Resolve` and `Bind` assertions, see the [guide to the
built-in gatekeeper entity](../../operation/builtin/gatekeeper.md).

**Implementation.** The protocol is implemented within the
[`syndicate-server`](../../operation/system-bus.md) program.

```
Resolve = <resolve @sturdyref sturdy.SturdyRef @observer #!#!any>.
Bind = <bind @oid any @key bytes @target #!any>.
```

## Sturdy-reference structures

A "sturdyref" is a long-lived certificate including a cryptographic signature that can be
upgraded by a gatekeeper entity to a live reference to the entity named in the sturdyref. For
an overview of `SturdyRef`s, see the [guide to the built-in gatekeeper
entity](../../operation/builtin/gatekeeper.md#sturdyrefs).

```
SturdyRef = <ref @oid any @caveatChain [Attenuation ...] @sig bytes>.
```

For detail of the interpretation of `Attenuation`s, `Caveat`s, `Pattern`s, and `Template`s, see
the [Syndicate protocol specification](../../protocol.md#capabilities-on-the-wire).

```
Attenuation = [Caveat ...].
Caveat = Rewrite / Alts .
Rewrite = <rewrite @pattern Pattern @template Template>.
Alts = <or @alternatives [Rewrite ...]>.

Lit = <lit @value any>.

Pattern = PDiscard / PAtom / PEmbedded / PBind / PAnd / PNot / Lit / PCompound .
PDiscard = <_>.
PAtom = =Boolean / =Float / =Double / =SignedInteger / =String / =ByteString / =Symbol .
PEmbedded = =Embedded .
PBind = <bind @pattern Pattern>.
PAnd = <and @patterns [Pattern ...]>.
PNot = <not @pattern Pattern>.
PCompound =
    / @rec <rec @label any @fields [Pattern ...]>
    / @arr <arr @items [Pattern ...]>
    / @dict <dict @entries { any: Pattern ...:... }> .

Template = TAttenuate / TRef / Lit / TCompound .
TAttenuate = <attenuate @template Template @attenuation Attenuation>.
TRef = <ref @binding int>.
TCompound =
    / @rec <rec @label any @fields [Template ...]>
    / @arr <arr @items [Template ...]>
    / @dict <dict @entries { any: Template ...:... }> .
```