Principal
A principal is an identifier for an entity on the IC such as a user, a canister (dapps/smart contracts), or a subnet.
Motoko’s shared functions support a simple form of caller identification that allows to inspect the Internet Computer principal associated with the caller of a function. The principal associated with a call is a value that identifies a unique user or canister. Using the principal associated with the caller of a function allows to implement a basic form of access-control in a program.
Types of principals
There are several types of principals.
Management principal
The management principal is used to reference the management canister.
Opaque principal
An opaque principal is chosen by the protocol. This kind of principal is used to reference any canister that is not the management canister.
Self-Authenticating principal
A self-authenticating principal is a hash of a public signature key. This kind of principal is for instance used to reference a subnet or user.
Derived principal
The principal is derived from a registering principal. This type of principal is currently not used.
Anonymous principal
The anonymous principal is used to reference an anonymous user.
Representation
Binary
A principal consists of a variable-length byte array of up to 29 bytes. The last byte is used to indicate the type. The table below gives the type inferred from the last byte.
| Byte | Type |
| none | Management |
0x01
|
Opaque |
0x02
|
Self-Authenticating |
0x03
|
Derived |
0x04
|
Anonymous |
0x05
|
Unassigned |
Textual
A principal is shown in textual format by prepending it with its CRC-32 value in big-endian byte order, applying Base32 encoding without padding, grouping characters by length five, and separating them by a hyphen. The maximal length of the encoding, including hyphens, is 63 characters. The table below gives some common principals.
| Principal | Description |
|---|---|
aaaaa-aa
|
management canister |
rrkah-fqaaa-aaaaa-aaaaq-cai
|
governance canister |
ryjl3-tyaaa-aaaaa-aaaba-cai
|
ledger canister |
tdb26-jop6k-aogll-7ltgs-eruif-6kk7m-qpktf-gdiqx-mxtrf-vb5e6-eqe
|
network nervous system |
2vxsx-fae
|
anonymous user |
Further Information
- Check the Motoko Base Library to see how to use principal functions.
- See the principals and caller identification documentation for a more in-depth guide to the uses of principals on the IC.
- See the access-control with identity tutorial to add extra functionality to a dapp.