Resources

The Requests for Comments (RFC) document series is a set of technical and organizational notes about the Internet (originally the ARPANET), beginning in 1969. Memos in the RFC series discuss many aspects of computer networking, including protocols, procedures, programs, and concepts, as well as meeting notes, opinions, and sometimes humor. (from www.rfc-editor.org.

The list below is a small subset of RFC documents (get the entire set here) that may be useful in the context of port knocking.

cryptography

• Cryptographic Message Syntax (CMS)
• Determining Strengths for Public Keys Used For Exchanging Symmetric Keys
• Internet X.509 Public Key Infrastructure Certificate Management Protocols
• MD5 Message-Digest Algorithm
• Randomness Recommendations for Security

firewalls

• Behavior of and Requirements for Internet Firewalls
• Benchmarking Methodology for Firewall Performance
• Benchmarking Terminology for Firewall Performance
• Firewall Enhancement Protocol (FEP)

security

• Guidelines for the Secure Operation of the Internet
• Internet Security Glossary
• IP Authentication Header
• On Internet Authentication
• One Time Password System
• Security Architecture for the Internet Protocol
• Security Mechanisms for the Internet
• Site Security Handbook
• The S/Key One-Time Password System
• Strong Security Requirements for Internet Engineering Task Force Standard Protocols
• Users' Security Handbook

protocols

• Common Port Numbers (multiple RFCs)
• IANA port assignments
• Special-Use IPv4 Addresses
• Transmission Control Protocl (TCP)
• User Datagram Protocl (UDP)