# kimci86/bkcrack

Crack legacy zip encryption with Biham and Kocher's known plaintext attack.

Repository: https://github.com/kimci86/bkcrack
Canonical: https://ross.abutalabs.com/products/bkcrack
Language: C++
License: Zlib
License Family: permissive
Topics: crack, zip, multithread, attack, plaintext-attack, ciphertext, zipcrypto, pkzip, cracking, password, zipcracker
Last push: 2026-08-09T22:13:57+00:00

## Health v2 (maintenance only)
Score: 73/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 96, release rhythm 29, longevity 100
- inputs: {"age_days": 3611, "days_push": 24, "days_rel": 312, "gap_med": 153.5, "n_releases_24m": 3}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2176, forks 189 (observed 2026-08-28T04:06:22.177720+00:00)

## What it is
bkcrack is a command-line tool that cracks legacy ZIP encryption (ZipCrypto/PKWARE) using Biham and Kocher's known plaintext attack. Given ciphertext and at least 12 bytes of known plaintext, it recovers the keystream generator's internal state, can decrypt entries, remove or change passwords, and optionally brute-force the original password.

## Use cases
- recover password from encrypted zip file
- decrypt legacy zipcrypto archive with known plaintext
- remove password protection from a zip archive
- change the password of an encrypted zip file
- crack pkzip traditional encryption
- unlock old zip file when I know part of its contents

## When to choose
- you have at least 12 bytes of known plaintext for an encrypted entry
- the archive uses legacy ZipCrypto encryption rather than AES
- you want a fast, multithreaded, cross-platform CLI with prebuilt binaries

## When to avoid
- the zip uses AES or other modern strong encryption instead of ZipCrypto
- you have no known plaintext and the password is long or complex
- you need a GUI-based recovery tool

## Facets
- artifact type: cli-tool
- maturity: active
- function: security, cryptography, penetration-testing
- domain: security, files, privacy
- platform: windows, cli, cross-platform
- tags: zipcrypto, known-plaintext-attack, password-recovery, zip, cracking, linux, macos

## Member repositories
- kimci86/bkcrack (main) score 73

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:22.177720+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:48:53.083401+00:00, confidence not recorded.
  - readme: https://github.com/kimci86/bkcrack (fetched 2026-08-28T04:06:22.177720+00:00, sha e56b813d8776)
- Data as of 2026-08-30T08:39:29.467469+00:00.