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.