Prefilling user input fields inside the subscription flow

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "JSON schema for pre-populating user input fields during subscription flow for fee-based smallcase",
    "type": "object",
    "properties": {
        "pan": {
            "type": "string",
            "description": "PAN number"
        },
        "name": {
            "type": "string",
            "description": "Investor name as per PAN"
        },
        "dob": {
            "type": "string",
            "description": "Date of birth as per PAN (YYYY-MM-DD format)"
        },
        "mobile": {
            "type": "object",
            "properties": {
                "countryCode": {
                    "type": "string",
                    "description": "Country code with plus sign. Eg. +91, +1, +44"
                },
                "number": {
                    "type": "string",
                    "description": "Mobile number without country code. Eg. 9876543210"
                }
            },
            "description": "mobile number with country code"
        },
        "email": {
            "type": "string",
            "description": "Email address"
        },
        "subscriptionOfferCode": {
            "type": "string",
            "description": "Offer code to be auto-applied during subscription flow"
        },
        "subsriptionPlanDuration": {
            "type": "string",
            "description": "Duration for which the offer code is applied. This is required for the offer code to be applied"
        },
        "state": {
            "type": "string",
            "description": "State name if in India, otherwise `Outside India`",
            "enum": ["Andaman and Nicobar Islands", "Andhra Pradesh", "Arunachal Pradesh", "Assam", "Bihar", "Chandigarh", "Chhattisgarh", "Dadra and Nagar Haveli", "Daman and Diu", "Delhi", "Goa", "Gujarat", "Haryana", "Himachal Pradesh", "Jammu and Kashmir", "Jharkhand", "Karnataka", "Kerala", "Lakshadweep", "Madhya Pradesh", "Maharashtra", "Manipur", "Meghalaya", "Mizoram", "Nagaland", "Odisha", "Puducherry", "Punjab", "Rajasthan", "Sikkim", "Tamil Nadu", "Telangana", "Tripura", "Uttar Pradesh", "Uttarakhand", "West Bengal", "Outside India"]
        }
    },
    "required": []
}

{
    "pan": "ABCPE123F",
    "name": "John Doe",
    "dob": "1990-12-31",
    "mobile": {
        "countryCode": "+91",
        "number": "9876543210"
    },
    "email": "[email protected]",
    "subscriptionOfferCode": "FLAT50",
    "subsriptionPlanDuration": "1Y",
    "state": "Gujarat"
}

const crypto = require("crypto");

const ALGORITHM = 'aes-256-cbc';
const IV_LENGTH = 16; // Must be 16 bytes for AES-256-CBC
const SHARED_GW_SECRET = 'gateway-name_blah65678aaa426d5djskjsdkjksd3232sa'; // Use the gateway secret key corresponding to the gateway used on SDK

// This function encrypts the utf-8 encoded string
// It returns the IV & Encrypted data as hex strings
function encrypt(text) {
    const key = crypto.createHash('sha256').update(SHARED_GW_SECRET).digest(); // Must be 32 bytes for AES-256
    const iv = crypto.randomBytes(IV_LENGTH);  // Must be 16 bytes for AES-256

    const cipher = crypto.createCipheriv(ALGORITHM, key, iv);
    let encryptedData = cipher.update(text, 'utf8', 'hex');
    encryptedData += cipher.final('hex');

    return { iv: iv.toString('hex'), encryptedData };
}

// This function decrypts the encrypted data (hex) & IV (hex)
// It returns the utf-8 encoded string
function decrypt(encryptedData, _iv) {
    const key = crypto.createHash('sha256').update(SHARED_GW_SECRET).digest(); // Must be 32 bytes for AES-256
    const iv = Buffer.from(_iv, 'hex'); // Convert hex string to buffer

    const decipher = crypto.createDecipheriv(ALGORITHM, key, iv);
    let decryptedData = decipher.update(encryptedData, 'hex', 'utf8');
    decryptedData += decipher.final('utf8');
    return decryptedData;
}


// Partner will encrypted the data before passing that as query param to smallcase SDK's openSmallplug method
function GetEnryptedDataWithIV(text) {
    const { iv, encryptedData } = encrypt(text);

    // Append IV to the encrypted data, so that we can decrypt the data at our end.
    // The first 16 bytes of the encrypted data will be the IV, and the rest will be the actual encrypted data
    return iv + encryptedData;
}

// Decryption is not required at your end. Below method is just for testing purposes.
// In production, the partner does not have any usecase to decrypt the data. It will just send the encrypted data to the smallcase SDK.
function GetDecryptedDataFromEnryptedDataWithIV(encryptedDataWithIv) {
    // first 16 bytes are IV
    encryptedDataWithIv = Buffer.from(encryptedDataWithIv, 'hex');
    const iv = Buffer.from(encryptedDataWithIv, 'hex').subarray(0, IV_LENGTH).toString('hex');
    const data = Buffer.from(encryptedDataWithIv, 'hex').subarray(IV_LENGTH).toString('hex');
    console.log('*'.repeat(20));
    console.log({ iv, data });
    console.log('*'.repeat(20));
    return decrypt(data, iv);
}

// Sample execution -
const data = {
    "pan": "ABCPE123F",
    "name": "John Doe",
    "dob": "31/12/1900",
    "mobile": {
        "countryCode": "+91",
        "number": "9876543210"
    },
    "email": "[email protected]",
    "subscriptionOfferCode": "FLAT50",
    "subsriptionPlanDuration": "1Y",
    "state": "Gujarat"
};
const enc = GetEnryptedDataWithIV(JSON.stringify(data));
console.log('Encrypted data that the partner will share as `ssed` query param:', enc);

const decString = GetDecryptedDataFromEnryptedDataWithIV(enc);
console.log('Gateway will read the encrypted data from URL query param and decrypt at its backend using the shared secret:', decString);