Hawkynt

F-FCSR

Feedback with Carry Shift Register stream cipher based on eSTREAM specification. Uses FCSR automaton with binary expansion of 2-adic numbers for keystream generation.

Properties

Property	Value
Category	Stream Ciphers
Sub-category	FCSR Stream Cipher
Security status	Not classified
Complexity	Intermediate
Inventor	François Arnault, Thierry Berger, Cédric Lauradoux
Year	2005
Origin	Not specified
Source	algorithms/stream/f-fcsr.js

Parameters

Parameter	Supported values
Key sizes	10 bytes (80 bits); 16 bytes (128 bits)
Nonce sizes	8 bytes (64 bits)

Security

Status: not classified — treat as unverified.

Known vulnerabilities

Issue	Description	Mitigation
Cryptographically Broken	F-FCSR has been cryptanalytically broken and should not be used for actual security - educational purposes only	—

Documentation

• eSTREAM Portfolio
• F-FCSR Specification
• FCSR Theory

References

• Cryptanalysis of F-FCSR
• FCSR Automata
• Academic Paper

Test vectors

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

Vector 1 — F-FCSR Test Vector 1 (Educational)

Source: Educational implementation test

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	0001020304050607
input	000102030405060708090a0b0c0d0e0f
expected	00ab0203aeafac07a2090aa1a6a70ea5

Vector 2 — F-FCSR Test Vector 2 (Shorter input)

Source: Educational implementation test

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	0001020304050607
input	00010203040506070809
expected	00ab0203aeafac07a209

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