You should not write business logic inside the model/{model}.js files.
For these purposes you can use functions:
https://strapi.io/documentation/developer-docs/latest/concepts/configurations.html#functions
Create a file under ./config/functions/encryption.js
With the content:
const Hashids = require("hashids/cjs");
const hashids = new Hashids("RandomSalt", 10);
module.exports = {
async decrypt(id) {
id = hashids.decode(id);
if (id.length === 0) return 0;
else if (id.length === 1) return Number(id[0]);
return id;
},
async decryptId(params) {
if (params.id) params.id = decrypt(params.id);
return params;
}
}
Now these functions are accessible from anywhere as follows:
await strapi.config.functions['encryption'].decrypt(id)
await strapi.config.functions['encryption'].decryptId(params)