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Glossary · Security

CTM

Counter Mode

In plain language

A method of scrambling data that turns a block cipher into a stream using a running counter.

The metaphor

Like numbering a roll of tickets and scrambling each one by its number, so no two come out alike.

Going deeper

How it works

  • A counter value is combined with the key.
  • Each block is processed independently.
  • Fast and parallel.
  • The counter must never repeat.
In practice
  • A secure connection uses it.
  • Disk encryption lists it.
  • A tool lists it as the mode.

A question owners ask

Does it matter to me?

Rarely. It is a setting inside the software.

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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