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Internet-Checksum

Internet checksum algorithm (RFC 1071) used in IPv4, TCP, UDP protocols. Uses 16-bit one’s complement arithmetic for network packet header integrity verification.

Properties

Property	Value
Category	Checksums
Sub-category	Network Protocol Checksum
Security status	🎓 Educational Only
Complexity	Intermediate
Inventor	Internet Engineering Task Force (IETF)
Year	1988
Origin	🇺🇸 United States
Source	algorithms/checksum/internet-checksum.js

Security

Status: 🎓 Educational Only

Known vulnerabilities

Issue	Description	Mitigation
Not Cryptographically Secure	Designed for error detection only, not security - can be easily forged	—
Collision Prone	16-bit checksum provides limited collision resistance	—
No Protection Against Reordering	Cannot detect packet reordering or replay attacks	—

Documentation

• RFC 1071 - Computing the Internet Checksum
• Internet Protocol Specification
• TCP Specification

References

• IPv4 Header Format
• TCP Header Format
• UDP Header Format

Test vectors

4 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Empty data

Source: RFC 1071 - empty data gives all 1s checksum

Field	Value
input	(empty)
expected	ffff

Vector 2 — IPv4 header example

Source: RFC 1071 style IPv4 header checksum

Field	Value
input	4500003044224000800600008c7053548c70545f
expected	f611

Vector 3 — Sequential bytes 1-4

Source: Educational test vector

Field	Value
input	0001000200030004
expected	fff5

Vector 4 — Partial IPv4 header

Source: Educational test vector

Field	Value
input	45000020000040004006
expected	3ad9

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