Encrypted SMS

استخدام RSA المفتاح العمومي / مفتاح خاص لتأمين كل الرسالة التي أرسلت!

Do you think your SMS messages are safe?

No, absolutely not. Hackers are listening to the signals, criminals are stealing data, employees in the carrier may sell the data, and, devices may break. In China, criminals even can hijack the traffic and pretend to be your friend to converse with you with SMS.

So what can you do?

To secure the messages, first we need to encrypt the messages at the beginning, so no plain text is sent to the network. Second, we shouldn't send to anybody else, s themselves are not secure.

This is what Encrypted SMS app is doing:

- encrypting with RSA + AES algorithm, no plain text is sent out

- RSA keys are generated by you on your device, they are only known to your device

- only public key is sent to your s, it is used to encrypt messages, but can not be used to decrypt messages

- private key is only on your device and never sent out, this ensures the confidentiality

- if your message is too long for RSA to encrypt, it will be encrypted with a randomly generated AES key using AES algorithm. The AES key will be encrypted with RSA public key and sent together with the message. This ensures efficiency.

What does it mean for public key and private key?

Usual way of encrypting: (the way NOT used in this app)

Sender: Hello, this is the message I want to share with you, I've locked it in the box and here is the key to unlock it!

(locked box) + (key)

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|<-thief: oh this is key to the lock, let me check if money is inside!

|<-courier: I am just interested in what is inside? I have a locked box but I have the key too!

|<-hacker: a locked box with a key? Let me tell you hackers are powerful!

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v

Receiver: Ok this key to unlock the box. (but I don't know it is already unlocked many times!)

Public key / private key encrypting: (the way this app is using)

Receiver: Hello, if you have message for me, please use this locker! I will keep the key with myself!

(open locker)

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|<-thief: a locker without key? useless. It is sold at convenience store at only 30 cents! plus the key!

|<-courier: a locker without key? I should do my work so I get salary.

|<-hacker: a locker without key? not interested

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v

Sender: Ok got the locker

~~~~~

Sender: Hello, I have a message for you, locked with the key you sent me!

(locked box)

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|<-thief: a locked box without key??? Damm it! Where is key?

|<-courier: a locked box without key??? I am honest person

|<-hacker: a locked box without key??? I can show my power somewhere else

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v

Receiver: Great! I have the key to unlock it!

(find the key to unlock it)

Being cautious is the only way to deal with the security problem we are having today.