Modes of Operation: CTR Mode

Learn about the counter mode of operation and how, unlike some of the other modes, it is able to benefit from parallelization.

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Counter mode

Counter mode

The last of the modes of operation we will describe in full is counter (CTR) mode.

Encryption using CTR mode

Counter mode can be considered a counter-based version of CFB mode without feedback. The main difference is that we assume both the sender and receiver have access to a reliable counter, which computes a new shared value each time a ciphertext block is exchanged. This shared counter is not necessarily a secret value, but both sides must synchronize the counter. Both encryption and decryption in CTR mode are depicted in the illustration below:

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Introduction

Basic Principles

Historical Cryptosystems

Theoretical versus Practical Security

Symmetric Encryption

Public-Key Encryption

Data Integrity

Digital Signature Schemes

Entity Authentication

Cryptographic Protocols

Key Management

Public-Key Management

Cryptographic Applications

Cryptography for Personal Devices

Control of Cryptography

Mathematics Appendix

Closing Remarks

Modes of Operation: CTR Mode

Counter mode

Encryption using CTR mode