PaytmChecksum.js

"use strict";

var crypto = require("crypto");

class PaytmChecksum {
    static encrypt(input, key) {
        var cipher = crypto.createCipheriv(
            "AES-128-CBC",
            key,
            PaytmChecksum.iv
        );
        var encrypted = cipher.update(input, "binary", "base64");
        encrypted += cipher.final("base64");
        return encrypted;
    }
    static decrypt(encrypted, key) {
        var decipher = crypto.createDecipheriv(
            "AES-128-CBC",
            key,
            PaytmChecksum.iv
        );
        var decrypted = decipher.update(encrypted, "base64", "binary");
        try {
            decrypted += decipher.final("binary");
        } catch (e) {
            console.log(e);
        }
        return decrypted;
    }
    static generateSignature(params, key) {
        if (typeof params !== "object" && typeof params !== "string") {
            var error =
                "string or object expected, " + typeof params + " given.";
            return Promise.reject(error);
        }
        if (typeof params !== "string") {
            params = PaytmChecksum.getStringByParams(params);
        }
        return PaytmChecksum.generateSignatureByString(params, key);
    }

    static verifySignature(params, key, checksum) {
        if (typeof params !== "object" && typeof params !== "string") {
            var error =
                "string or object expected, " + typeof params + " given.";
            return Promise.reject(error);
        }
        if (params.hasOwnProperty("CHECKSUMHASH")) {
            delete params.CHECKSUMHASH;
        }
        if (typeof params !== "string") {
            params = PaytmChecksum.getStringByParams(params);
        }
        return PaytmChecksum.verifySignatureByString(params, key, checksum);
    }

    static async generateSignatureByString(params, key) {
        var salt = await PaytmChecksum.generateRandomString(4);
        return PaytmChecksum.calculateChecksum(params, key, salt);
    }

    static verifySignatureByString(params, key, checksum) {
        var paytm_hash = PaytmChecksum.decrypt(checksum, key);
        var salt = paytm_hash.substr(paytm_hash.length - 4);
        return paytm_hash === PaytmChecksum.calculateHash(params, salt);
    }

    static generateRandomString(length) {
        return new Promise(function (resolve, reject) {
            crypto.randomBytes((length * 3.0) / 4.0, function (err, buf) {
                if (!err) {
                    var salt = buf.toString("base64");
                    resolve(salt);
                } else {
                    console.log(
                        "error occurred in generateRandomString: " + err
                    );
                    reject(err);
                }
            });
        });
    }

    static getStringByParams(params) {
        var data = {};
        Object.keys(params)
            .sort()
            .forEach(function (key, value) {
                data[key] =
                    params[key] !== null && params[key].toLowerCase() !== "null"
                        ? params[key]
                        : "";
            });
        return Object.values(data).join("|");
    }

    static calculateHash(params, salt) {
        var finalString = params + "|" + salt;
        return (
            crypto.createHash("sha256").update(finalString).digest("hex") + salt
        );
    }
    static calculateChecksum(params, key, salt) {
        var hashString = PaytmChecksum.calculateHash(params, salt);
        return PaytmChecksum.encrypt(hashString, key);
    }
}
PaytmChecksum.iv = "@@@@&&&&####$$$$";
module.exports = PaytmChecksum;