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Day 1: SSL/TLS History and Threat Model

Phase 1 · May 14, 2026

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Agenda (2–3 hours)

  • Read (45 min): RFC 8446 §1 Introduction; skim the Wikipedia SSL/TLS history timeline
  • Study (45 min): Key protocol versions and their fatal flaws
  • Practice (45 min): openssl s_client exploration
  • Challenge (30 min): Written exercise
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Protocol Lineage

Version Year Status Fatal Flaw
SSL 2.0 1995 Broken DROWN, weak MAC
SSL 3.0 1996 Broken POODLE (CBC padding)
TLS 1.0 1999 Deprecated BEAST, POODLE
TLS 1.1 2006 Deprecated Superseded
TLS 1.2 2008 Allowed Misuse-prone cipher negotiation
TLS 1.3 2018 Current —

RFC 8996 (2021) formally deprecates TLS 1.0 and 1.1.

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TLS Threat Model

TLS is designed to defend against a network adversary who can:

  • Read all packets (passive eavesdropping)
  • Modify packets in transit (active MITM)
  • Inject new packets
  • Replay captured packets

TLS provides:

  • Confidentiality — traffic is encrypted
  • Integrity — tampering is detected
  • Authentication — at minimum, server identity is verified
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What TLS 1.3 Fixed

  • Eliminated static RSA key exchange (no forward secrecy)
  • Eliminated CBC mode ciphers (padding oracle attacks)
  • Eliminated MD5/SHA-1 in signatures
  • Eliminated compression (CRIME attack)
  • Eliminated renegotiation (complex, attack surface)
  • Reduced handshake to 1-RTT (was 2-RTT)
  • Encrypted more of the handshake (ServerHello extensions are encrypted)
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Practice Exercise

# Inspect a TLS 1.3 connection
openssl s_client -connect google.com:443 -tls1_3

# Compare with TLS 1.2
openssl s_client -connect google.com:443 -tls1_2

# Show full handshake trace
openssl s_client -connect google.com:443 -msg 2>&1 | head -60

Look for: Protocol: TLSv1.3, cipher suite, certificate chain depth.

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Challenge Assignment

Find 3 websites using TLS 1.2 and 3 using TLS 1.3 using openssl s_client.

For each, record:

  1. Exact protocol version
  2. Cipher suite selected
  3. Certificate chain depth
  4. Server's certificate CN / SAN

Write 2–3 sentences on what you observe about which servers are still on TLS 1.2 and what types of organizations they tend to be.

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Resources