Identity and Package Management¶
Since Daml ledgers enable parties to automate the management of their rights and obligations through smart contract code, they also have to provide party and code management functions. Hence, this document addresses:
- Management of parties’ digital identifiers in a Daml ledger.
- Distribution of smart contract code between the parties connected to the same Daml ledger.
The access to this functionality is usually more restricted compared to the other Ledger API services, as they are part of the administrative API. This document is intended for the users and implementers of this API.
The administrative part of the Ledger API provides both a party management service and a package service. Any implementation of the party and package services is guaranteed to accept inputs and provide outputs of the format specified by these services. However, the services’ behavior – the relationship between the inputs and outputs that the various parties observe – is largely implementation dependent. The remainder of the document will present:
- The minimal behavioral guarantees for identity and package services across all ledger implementations. The service users can rely on these guarantees, and the implementers must ensure that they hold.
- Guidelines for service users, explaining how different ledgers handle the unspecified part of the behavior.
A Daml ledger may freely define its own format of party and participant node identifiers, with some minor constraints on the identifiers’ serialized form. For example, a ledger may use human-readable strings as identifiers, such as “Alice” or “Alice’s Bank”. A different ledger might use public keys as identifiers, or the keys’ fingerprints. The applications should thus not rely on the format of the identifier – even a software upgrade of a Daml ledger may introduce a new format.
By definition, identifiers identify parties, and are thus unique for a ledger. They do not, however, have to be unique across different ledgers. That is, two identical identifiers in two different ledgers do not necessarily identify the same real-world party. Moreover, a real-world entity can have multiple identifiers (and thus parties) within the same ledger.
Since the identifiers might be difficult to interpret and manage for humans, the ledger may also accompany each identifier with a user-friendly display name. Unlike the identifier, the display name is not guaranteed to be unique, and two different participant nodes might return different display names for the same party identifier. Furthermore, a display name is in general not guaranteed to have any link to real world identities. For example, a party with a display name “Attorney of Nigerian Prince” might well be controlled by a real-world entity without a bar exam. However, particular ledger deployments might make stronger guarantees about this link. Finally, the association of identifiers to display names may change over time. For example, a party might change its display name from “Bruce” to “Caitlyn” – as long as the identifier remains the same, so does the party.
The set of parties of any Daml ledger is dynamic: new parties may always be added to the system.
The first step in adding a new party to the ledger is to provision a new identifier for the party.
The Ledger API provides an AllocateParty method for this purpose.
The method, if successful, returns an new party identifier.
AllocateParty call can take the desired identifier and display name as optional parameters, but these are merely hints and the ledger implementation may completely ignore them.
If the call returns a new identifier, the participant node serving this call is ready to host the party with this identifier.
For some ledgers (Daml for VMware Blockchain in particular), the returned identifier is guaranteed to be unique in the ledger; namely, no other call of the
AllocateParty method at this or any other ledger participant may return the same identifier.
On Canton ledgers, the identifier is also unique as long as the participant node is configured correctly (in particular, it does not share its private key with other participant nodes).
After an identifier is returned, the ledger is set up in such a way that the participant node serving the call is allowed to issue commands and receive transactions on behalf of the party.
However, the newly provisioned identifier need not be visible to the other participant nodes.
For example, consider the setup with two participants
P2, where the party
Alice_123 is hosted on
Assume that a new party
Bob_456 is next successfully allocated on
As long as
P2 are connected to the same Canton domain or Daml ledger,
Alice_123 can now submit a command with
Bob_456 as an informee.
For diagnostics, the ledger provides a ListKnownParties method which lists parties known to the participant node. The parties can be local (i.e., hosted by the participant) or not.
Identifiers and Authorization¶
To issue commands or receive transactions on behalf of a newly provisioned party, an application must provide a proof to the party’s hosting participant that they are authorized to represent the party. Before the newly provisioned party can be used, the application will have to obtain a token for this party. The issuance of tokens is specific to each ledger and independent of the Ledger API. The same is true for the policy which the participants use to decide whether to accept a token.
To learn more about Ledger API security model, please read the Authorization documentation.
Identifiers and the Real World¶
The “substrate” on which Daml workflows are built are the real-world obligations of the parties in the workflow. To give value to these obligations, they must be connected to parties in the real world. However, the process of linking party identifiers to real-world entities is left to the ledger implementation.
In centralized deployments, one can simplify the process by trusting the operator of the writer node(s) with providing the link to the real world. For example, if the operator is a stock exchange, it might guarantee that a real-world exchange participant whose legal name is “Bank Inc.” is represented by a ledger party with the identifier “Bank Inc.”. Alternatively, it might use a random identifier, but guarantee that the display name is “Bank Inc.”. In general, a ledger might not have such a single store of identities. The solutions for linking the identifiers to real-world identities could rely on certificate chains, verifiable credentials, or other mechanisms. The mechanisms can be implemented off-ledger, using Daml workflows (for instance, a “know your customer” workflow), or a combination of these.
All Daml ledgers implement endpoints that allow for provisioning new Daml code to the ledger. The vetting process for this code, however, depends on the particular ledger implementation and its configuration. The remainder of this section describes the endpoints and general principles behind the vetting process. The details of the process are ledger-dependent.
Package Formats and Identifiers¶
Any code – i.e., Daml templates – to be uploaded must compiled down to the Daml-LF language.
The unit of packaging for Daml-LF is the .dalf file.
.dalf file is uniquely identified by its package identifier, which is the hash of its contents.
Templates in a
.dalf file can reference templates from other
.dalf files, i.e.,
.dalf files can depend on other
A .dar file is a simple archive containing multiple
.dalf files, and has no identifier of its own.
The archive provides a convenient way to package
.dalf files together with their dependencies.
The Ledger API supports only
.dar file uploads.
Internally, the ledger implementation need not (and often will not) store the uploaded
.dar files, but only the contained
Package Management API¶
The package management API supports two methods:
- UploadDarFile for uploading
.darfiles. The ledger implementation is, however, free to reject any and all packages and return an error. Furthermore, even if the method call succeeds, the ledger’s vetting process might restrict the usability of the template. For example, assume that Alice successfully uploads a
.darfile to her participant containing a
NewTemplatetemplate. It may happen that she can now issue commands that create
NewTemplateinstances with Bob as a stakeholder, but that all commands that create
NewTemplateinstances with Charlie as a stakeholder fail.
- ListKnownPackages that lists the
.dalfpackage vetted for usage at the participant node. Like with the previous method, the usability of the listed templates depends on the ledger’s vetting process.
Using a Daml package entails running its Daml code. The Daml interpreter ensures that the Daml code cannot interact with the environment of the system on which it is executing. However, the operators of the ledger infrastructure nodes may still wish to review and vet any Daml code before allowing it to execute. One reason for this is that the Daml interpreter currently lacks a notion of reproducible resource limits, and executing a Daml contract might result in high memory or CPU usage.
Thus, Daml ledgers generally allow some form of vetting a package before running its code on a node. Not all nodes in a Daml ledger must vet all packages, as it is possible that some of them will not execute the code. The exact vetting mechanism is ledger-dependent. For example, in the Daml Sandbox, the vetting is implicit: uploading a package through the Ledger API already vets the package, since it’s assumed that only the system administrator has access to these API facilities. The vetting process can be manual, where an administrator inspects each package, or it can be automated, for example, by accepting only packages with a digital signature from a trusted package issuer.
In Canton, participant nodes also only need to vet code for the contracts of the parties they host.
As only participants execute contract code, only they need to vet it.
The vetting results may also differ at different participants.
For example, participants
P2 might vet a package containing a
NewTemplate template, whereas
P3 might reject it.
In that case, if Alice is hosted at
P1, she can create
NewTemplate instances with stakeholder Bob who is hosted at
P2, but not with stakeholder Charlie if he’s hosted at
The Ledger API does not have any special support for package upgrades. A new version of an existing package is treated the same as a completely new package, and undergoes the same vetting process. Upgrades to active contracts can be done by the Daml code of the new package version, by archiving the old contracts and creating new ones.