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Home / Glossary / GCM
Glossary · Security

GCM

Galois Counter Mode

In plain language

A way of scrambling data that also detects if anyone has tampered with it.

The metaphor

Like a locked box with a tamper seal: opening or altering it is obvious to the person receiving it.

Going deeper

How it works

  • It encrypts data and adds a check that the data is unchanged.
  • It is fast, so it suits busy websites and VPNs.
  • It is used with the AES cipher in modern HTTPS connections.
  • If data is altered in transit, the check fails and the data is rejected.
In practice
  • A secure website connection uses it between your browser and the server.
  • A VPN uses it to protect traffic between two offices.
  • A security scan lists it among the strong settings.

A question owners ask

Is this a setting I choose?

No. Your browser and the server agree on it automatically when you connect.

Related terms
AAAAuthentication, Authorization, and AccountingAccount takeoverACLAccess Control ListAdmin accountAESAdvanced Encryption StandardAES-256Advanced Encryption Standards 256-bitAISAutomated Indicator SharingAPTAdvanced Persistent Threat

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