This content originally appeared on DEV Community and was authored by Rijul Rajesh
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When you connect to Wi-Fi, you probably think the main job of security is to keep your data hidden so no one else can read it. That is true, but there is another important job that often gets less attention: making sure no one changes your data while it is on the way.
That is what MIC does. MIC stands for Message Integrity Code. It is like a seal of trust on every packet of data that goes over Wi-Fi.
Imagine this with a letter
Think about sending a letter through the post. You write your message, put it in an envelope, and then place a unique stamp or seal on it. When the person receives it, they look at the seal. If the seal is broken or fake, they know someone tampered with the letter.
MIC works the same way for Wi-Fi. It makes sure the message you sent is exactly the same message that was received.
Why Wi-Fi needs MIC
Unlike cables, Wi-Fi signals are everywhere in the air. Anyone nearby can try to catch them. This makes it possible for an attacker to:
- Capture a packet of data
- Change a few bits inside it
- Send it along as if nothing happened
Without MIC, the receiver would not notice the tampering. With MIC, the receiver checks the “seal” and rejects any data that looks suspicious.
How MIC actually works
- Before sending data, the sender creates a small digital tag called a MIC. This tag is created using the contents of the data and a secret key that both sender and receiver know.
- The tag is attached to the data packet.
- When the receiver gets the packet, it recalculates the tag using the same method.
- If the tag matches the one in the packet, all is good. If it does not match, the packet is thrown away.
So, MIC is basically a trust check for every piece of Wi-Fi data.
WPA vs WPA2
- In WPA (the older version), the MIC method used was called Michael. It was light enough to work on older hardware, but it was not very strong against attacks.
- In WPA2 (the improved version), MIC is part of a stronger system called CCMP. This version is far more reliable and resistant to tampering.
What happens if the MIC check fails
If the MIC says something is wrong, the packet is dropped. To stop attackers from repeatedly messing with packets, WPA added an extra rule: if too many MIC failures happen in a short time, the Wi-Fi access point can temporarily block traffic. This slows attackers down.
Why you should care
You might not directly work with MIC in daily life, but knowing about it gives you a better picture of how Wi-Fi keeps you safe. Encryption hides your data, while MIC makes sure no one changes it along the way. Both together give you the security you expect when you log in to your favorite café’s Wi-Fi or connect at home.
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This content originally appeared on DEV Community and was authored by Rijul Rajesh