Hawkynt

Achterbahn-128/80

NLFSR-based stream cipher from eSTREAM project. BROKEN - multiple cryptanalytic attacks exist. DO NOT USE in production. Supports 80-bit and 128-bit keys with 10-13 NLFSRs.

Properties

Property	Value
Category	Stream Ciphers
Sub-category	NLFSR Stream Cipher
Security status	❌ Broken
Complexity	Expert
Inventor	Berndt Gammel, Rainer Göttfert, Oliver Kniffler (Infineon Technologies)
Year	2005
Origin	🇩🇪 Germany
Source	algorithms/stream/achterbahn.js

Parameters

Parameter	Supported values
Key sizes	10 bytes (80 bits) to 16 bytes (128 bits)
Nonce sizes	0 bytes (0 bits) to 16 bytes (128 bits)

Security

Status: ❌ Broken

Known vulnerabilities

Issue	Description	Mitigation
Distinguishing Attack	Linear distinguishing attacks can distinguish keystream from random with practical complexity	DO NOT USE - cipher is cryptographically broken
Key Recovery Attack	Practical key recovery attacks demonstrated against both 80-bit and 128-bit variants	DO NOT USE - fundamental design flaws exist
Correlation Attack	NLFSR correlation attacks reduce effective security below key length	DO NOT USE - not suitable for any production use

Documentation

• eSTREAM Achterbahn Specification
• Achterbahn Official Site
• Wikipedia: Achterbahn

References

• Achterbahn-128/80 C Reference Implementation (Gammel, Göttfert, Kniffler)
• SUPERCOP Benchmarking Suite (includes eSTREAM submission sources)

Test vectors

1 vector ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Achterbahn-128 Functionality Test (BROKEN CIPHER - DO NOT USE)

Source: Research-derived for validation only

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	0011223344556677
input	48656c6c6f20576f726c64
expected	9bf6a4199a0c2911440125

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