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SWEET32 Attack on 64-bit Block Ciphers

SWEET32 Attack on 64-bit Block Ciphers

Description

This vulnerability indicates that the server is susceptible to SWEET32 attacks, which exploit the birthday paradox in 64-bit block ciphers like 3DES to recover plaintext from encrypted data after collecting approximately 32GB of traffic.

SWEET32 (Birthday attacks on 64-bit block ciphers) occurs when the same encryption key is used to encrypt large amounts of data. Due to the birthday paradox, identical ciphertext blocks are statistically guaranteed after ~2^32 blocks, revealing mathematical relationships that allow plaintext recovery.

How It Works:

  1. Attacker triggers millions of HTTPS requests containing victim's authentication cookies
  2. Network traffic is captured and analyzed for identical 8-byte encrypted blocks
  3. When collision occurs, CBC mathematics allows recovery of secret data through XOR operations
  4. Process repeats across multiple collisions to extract complete secrets

Requirements:

  • 3DES or other 64-bit block cipher in use
  • Long-lived TLS sessions (18+ hours)
  • High request volume capability (~2,900 requests/second)
  • Network-level traffic capture ability

Example Scenario: A banking application uses 3DES encryption with persistent HTTPS connections. An attacker injects JavaScript that makes millions of requests over 18 hours, capturing 700GB of encrypted traffic. Statistical analysis reveals block collisions that expose the victim's session cookie, allowing complete account takeover.

The attack demonstrates why 64-bit block ciphers are fundamentally unsafe for modern applications, leading to session hijacking, data exposure, and regulatory compliance violations.

Recommendation

To mitigate SWEET32 attacks:

Primary Defense - Disable 64-bit Ciphers:

# Nginx configuration
ssl_ciphers 'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:!3DES:!DES';
# Apache configuration  
SSLCipherSuite ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:!3DES:!DES

Additional Mitigations:

  • Upgrade to TLS 1.3 which removes 3DES entirely
  • Limit connection duration through aggressive rekeying (every 64MB for 3DES)
  • Restrict request volume per connection (Apache/Nginx default 100 requests)
  • Monitor for excessive traffic patterns indicating potential attacks
  • Prioritize AES ciphers over legacy 64-bit alternatives in cipher suite ordering

Testing Commands:

# Test server configuration
openssl s_client -connect example.com:443 -cipher '3DES'

# Verify 3DES is disabled (should fail)
nmap --script ssl-enum-ciphers -p 443 example.com

Standards

  • SOC2_CONTROLS:
    • CC_6_7
    • CC_7_1
  • CCPA:
    • CCPA_1798_150
  • GDPR:
    • ART_32
  • PCI_STANDARDS:
    • REQ_4_1
    • REQ_6_2
    • REQ_11_3