Hawkynt

QCypher (DarkCrypt)

Autokey byte-feedback stream cipher from the DarkCrypt Total Commander plugin. A 256-entry table plus three running indices are updated on every byte using an S-box-driven transform in which the plaintext byte itself indexes the table, so encryption is not a plain independent-keystream XOR.

Properties

Property Value
Category Stream Ciphers
Sub-category Stream Cipher
Security status 🎓 Educational Only
Complexity Intermediate
Inventor DarkCrypt variant by Alexander Myasnikov
Year 2013
Origin 🇷🇺 Russia
Source algorithms/stream/darkcrypt-qcypher.js

Parameters

Parameter Supported values
Key sizes 64 bytes (512 bits)
Block sizes 1 byte (8 bits) to 65536 bytes (524288 bits)

Security

Status: 🎓 Educational Only

Known vulnerabilities

Issue Description Mitigation
Non-standard, unanalyzed construction Ad-hoc autokey S-box transform with no public design rationale or cryptanalysis; not recommended for real use. Use a vetted stream cipher.

Documentation

Test vectors

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

Vector 1 — DarkCrypt Qcypher — keystream from incrementing key, zero plaintext

Field Value
key 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f
input 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000
expected bfc942b0682ded41418464d6357e8dba 86af59fb971424fcd25b5827fe74dd43 7d12caa54d09e4d0c2a3d4db2b16f6c1 fece08767dcbe78442036d83b7d3acb9 2b57e4543371e0caca4810784571a8fe 7599cbaffe3c7e3e1a7810d3bd5a2330 972af0bda7ab74edb6e12b6a81557704 c01d8af10a9cf6cde1c016f5313e78ef

Vector 2 — DarkCrypt Qcypher — incrementing key/plaintext

Field Value
key 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f
input 000102030405060708090a0b0c0d0e0f 101112131415161718191a1b1c1d1e1f 202122232425262728292a2b2c2d2e2f 303132333435363738393a3b3c3d3e3f
expected bf3502c4af056921ca34a9b99e94c4eb 3872e9bf05d36fcc8d04bd78800e9b81 7d2984e03ba9c5f58f022631ef4111dd bd859b5fa4673acc7f9b7a6ebb0e589e

Vector 3 — DarkCrypt Qcypher — all-zero key, zero plaintext

Field Value
key 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000 00000000000000000000000000000000
input 00000000000000000000000000000000
expected f234bc5b14597fb310906d97aff87900

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