WhatsApp System Design
End-to-End Encryption
2 min read
End-to-End Encryption (E2EE) ensures that only the intended recipients can read a message.
Even the messaging server cannot decrypt the content.
Encryption Flow
The server only forwards encrypted data.
It never sees the plaintext.
What Does the Server Store?
Typically something like
Encrypted Payload
Message ID
Conversation ID
Timestamp
Notice
The payload is encrypted.
The metadata is not.
Metadata is still required for routing and delivery.
Why Metadata Matters
Without metadata,
the server wouldn't know
-
Who sent the message
-
Which conversation it belongs to
-
Who should receive it
Encryption protects content,
not routing information.
Temporary Storage
If the recipient is offline,
the encrypted message is temporarily stored until delivery.
Because the payload is encrypted,
the server still cannot read its contents.
Interview Notes
Interviewer
Can the messaging server read encrypted messages?
Answer
No.
The server stores and forwards encrypted payloads.
Only recipient devices can decrypt them.
Key Takeaways
✔ Content is encrypted before leaving the sender.
✔ Servers forward encrypted payloads.
✔ Metadata remains available for routing.
✔ Offline delivery still works using encrypted temporary storage.