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Geffe Generator

Classical stream cipher using three Linear Feedback Shift Registers (LFSRs) and a Boolean combining function. Uses correlation between output bits for keystream generation.

Properties

Property	Value
Category	Stream Ciphers
Sub-category	LFSR Stream Cipher
Security status	Not classified
Complexity	Not specified
Inventor	Harold Geffe
Year	1973
Origin	🇺🇸 United States
Source	algorithms/stream/geffe.js

Parameters

Parameter	Supported values
Key sizes	16 bytes (128 bits)
Nonce sizes	8 bytes (64 bits)

Security

Status: not classified — treat as unverified.

Known vulnerabilities

Issue	Description	Mitigation
Correlation Attack	The Geffe generator is vulnerable to correlation attacks due to statistical bias in the combining function - educational purposes only	—

Documentation

• Stream Cipher Design
• LFSR-based Stream Ciphers
• Correlation Attacks on Stream Ciphers

References

• Geffe Generator Analysis
• LFSR Theory
• Stream Cipher Cryptanalysis

Test vectors

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

Vector 1 — Geffe Generator Test Vector 1 (Educational)

Source: Educational implementation test

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	0001020304050607
input	000102030405060708090a0b0c0d0e0f
expected	0c0502030405060708090a0b0c0d0e0f

Vector 2 — Geffe Generator Test Vector 2 (Shorter input)

Source: Educational implementation test

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	0001020304050607
input	00010203040506070809
expected	0c050203040506070809

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