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CertifiedData

The Internet Computer allows canister smart contracts to store a small amount of data during update method processing so that during query call processing, the canister can obtain a certificate about that data.

[Intended audience]

This module provides a low-level interface to this API, aimed at advanced users and library implementors. See the Internet Computer interface specification and corresponding documentation for how to use this to make query calls to your canister tamperproof.

Function set​

func set(data : Blob) : ()

Set the certified data.

[Usage constraints]

Must be called from an update method, else traps. Must be passed a blob of at most 32 bytes, else traps.

Example:

import CertifiedData "mo:base/CertifiedData";
import Blob "mo:base/Blob";

// Must be in an update call

let array : [Nat8] = [1, 2, 3];
let blob = Blob.fromArray(array);
CertifiedData.set(blob);

See a full example on how to use certified variables.

Function getCertificate​

func getCertificate() : ?Blob

Gets a certificate.

[When available]

Returns null if no certificate is available, e.g. when processing an update call or inter-canister call. This returns a non-null value only when processing a query call.

Example:

import CertifiedData "mo:base/CertifiedData";
// Must be in a query call

CertifiedData.getCertificate();

See a full example on how to use certified variables.