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Cryptology Academy · Lesson

TLS Record Layer & Cipher Suites

Understand record fragmentation, AEAD encryption, and cipher selection.

Record Layer Overview

The TLS Record Layer is the transport sublayer of TLS. It fragments data into records of up to 16 KB, optionally compresses (TLS 1.2 only), encrypts with AEAD, and adds a 5-byte header.

Record Header Fields

Bytes 0: ContentType (20=ChangeCipherSpec, 21=Alert, 22=Handshake, 23=ApplicationData). Bytes 1-2: Legacy version (0x0303 for TLS 1.2 compat). Bytes 3-4: Length of the following payload.

All lessons in this course

  1. TLS 1.3 Handshake Step by Step
  2. TLS Record Layer & Cipher Suites
  3. Certificate Validation in TLS
  4. TLS Attacks: BEAST, POODLE & Downgrade
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