Hawkynt

F-FCSR (DarkCrypt)

Feedback-with-Carry Shift Register (Galois FCSR) filter generator from the DarkCrypt Total Commander plugin. Non-standard 256-bit register variant with a custom feedback polynomial, 128-bit key and 128-bit IV.

Properties

Property	Value
Category	Stream Ciphers
Sub-category	FCSR Stream Cipher
Security status	Not classified
Complexity	Intermediate
Inventor	François Arnault, Thierry Berger, Cédric Lauradoux (base F-FCSR); DarkCrypt variant by Alexander Myasnikov
Year	2005
Origin	🇷🇺 Russia
Source	algorithms/stream/darkcrypt-ffcsr.js

Parameters

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

Security

Status: not classified — treat as unverified.

Known vulnerabilities

Issue	Description	Mitigation
Broken family	The F-FCSR family was cryptanalytically broken; this non-standard variant is unanalyzed.	Use a modern vetted stream cipher.

Documentation

• DarkCrypt plugin (Total Commander PlugRing)
• F-FCSR Specification (base algorithm)

Test vectors

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

Vector 1 — DarkCrypt Ffcsr — keystream (zero input)

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	00000000000000000000000000000000
input	00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000
expected	76ca63bf052e9a95075561334c58b548 f7fd37f3d211bcbcdef9179ada8227db 98454d5385979d0c2870dab8060ebfdb e1867588ffccc9103e9eba78e4e25e54 753831b76e78b0b5f80263c43b57efe6 18c838c23176f5cb3e87ecf323fa802a 6b91ccfba84d26d1052ed0c923ae3068 de16643f9934e513c232f6b99ae17363

Vector 2 — DarkCrypt Ffcsr — encryption of incrementing bytes 00..3f

Field	Value
key	000102030405060708090a0b0c0d0e0f
iv	00000000000000000000000000000000
input	000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f
expected	76cb61bc012b9c920f5c6b384055bb47 e7ec25e0c604aaabc6e00d81c69f39c4 b8646f70a1b2bb2b0059f0932a2391f4 d1b747bbcbf9ff2706a78043d8df606b

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