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How To Build A Private Messenger App Like Signal

By 

Maulik Kotak

app like signal

Elon Musk’s Tweet:

It is early 2021 months, WhatsApp has rolled out its new terms of service. As a result, there was a lot of confusion among users about their data safety and privacy. Consequently, Tesla CEO Elon Musk suggested his 42.5 million Twitter followers switch to Signal from WhatsApp.

The incident has drawn the attention of a broad audience who uses instant messengers on various devices mainly from smartphones. However, Signal was not a much-known player in the IMs niche but its unbeatable security aspects have won it unprecedented fame in the global market.

Business Confidentiality:

Before the internet era, CEOs and managers have to travel often for various meetings. One-on-one and group meetings were common. The most significant thing of such meetings was privacy. Confidentiality always remains a priority in the business world and these meetings were assured as well.

Days have gone by with the arrival of messenger applications working across the globe using the internet. Now, it is time for virtual meetings. Unfortunately, keeping privacy and safety of data is still today a concern despite our advancements in data safety and security technologies.

If you wish to understand where and how security lapses occur in the usage of modern instant messenger apps, you need to know their revenue models first.

Messenger App Revenue Models:

We are talking about WhatsApp vs. Signal messengers and their revenue models. If I talk simply and straightforwardly, WhatsApp is a commercial product and it uses an in-app advertising model to generate income. 

Whereas, Signal is an open-source developed by Russian government institutions/developers and available on GitHub with special requests & permissions.

Now, one thing is obvious that Facebook is a vast advertisement platform and needs tons of user info/Metadata for its user targeting mechanism. Facebook owns WhatsApp now and it uses the selected info for its revenue generation through ads.

An app like Signal doesn't need anything to generate revenue as its development has been funded by the Russian government’s institutions.

Messenger App Value Proposition:

With this background, let's understand the value proposition of an encrypted messaging application or what is essential to make it the most secure app. There is four main value proposition for an app like Signal.

  • E2EE or End-to-End Encryption.
  • Power of message deletion. Either automatically or manually.
  • No Metadata retention. An app like Signal stores only data of login of the last connection; nothing else can threaten the security of app users at all.
  • Sheer privacy policy. An app like Signal does it holistically.

How Does An App Like Signal Work?

To understand how modern secure messenger apps are working, you need to know end-to-end encryption technology in simple words.

E2EE
  • User-A sends a message
  • The encryption process takes place on User-A's device. It generates two keys: 
    • one public key that goes to the server, (A separate process)
    • one private key that goes to user-B's device along with encrypted texts/messages. (A separate process)
  • The server identifies user-B's ID and sends the public key along with the message.
  • User-B's device decrypts the message using both keys. Done!

How Does Encrypted Message Hack by MITM (Man-in-the-Middle)?

It’s a vital question, indeed!

MITM obtains a public key from the server and turns the message to its device by compromising the server for the same. 

How Does App Like Signal Assure Security from MITM Hackers?

Signal has an advanced protocol with Double Ratchet Algorithm. It generates session keys besides public and private keys during the encryption process. The most important characteristic of the session key is that it is self-destructive. 

It means it is being automatically destroyed as soon as the session is completed (message read) and session keys go with an encrypted message directly to the recipient instead of via server process.

Signal's Cryptographic Protocol:

Here is Signal's cryptographic protocol to know. 

  1. X3DH (Extended Triple Diffie-Hellman)
  2. Double Ratchet algorithm, Curve25519
  3. AES-256
  4. HMAC-SHA256

Source Code Availability of Signal App:

Developers can access documents from GitHub and know from various resources on the web. Russian developers have made it an open-source project and provided excellent service to the community. Bravo!

App Development Estimation:

I hope everyone reading this post at least knows the app development process right from ideation to design and coding to uploading on the app store. So, I simply narrate the app estimation process here.

The following are features and functions those need to address in the form of modules you create for an app. A brief list is presented:

  • User onboarding module
  • User registration module
  • App security module with two-step authentication
  • User profile module
  • App setting module
  • App notification module
  • App text chat module
  • App voice chat module
  • App secrete chat module
  • Icons and Gyphy integration module
  • App message deletion module - automatic or manual
  • App sync module

Technologies You Have to Apply:

Erlang is a basic technology used in the creation of apps like Signal. Besides this, you can use Elixir programming technology for app creation, which also is based on Erlang. Databases and other matters are almost similar to app development.

The time estimation you can do in hours for each module and place your hourly rate to get the final estimation. For example:

  • UI & UX designing need - 170+ hours
  • Backend development - 500+ hours
  • Listed modules development - 450+ hours
  • Testing on different platforms - 200+ hours

If you count on an average rate of $15-20 per hour, the estimation goes in between $15 to $30K for both kinds of platforms-iOS & Android. 

For an accurate quote or estimation, you can contact our sales team where our business development officers will give you a fair estimation based on your bespoke requirements.

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