PKZIP (Mixed Multi-File Checksum-Only) Hash

What is PKZIP (Mixed Multi-File Checksum-Only)?

The **PKZIP Mixed Multi-File Checksum-Only** hash format originates from the early PKZIP compression algorithm (developed by Phil Katz in the late 1980s), where checksums were initially used to verify file integrity during compression and decompression. This format specifically refers to the **16-bit CRC-16 (CRC-CCITT, polynomial 0x1021)** checksums stored in PKZIP archives for individual files, later supplemented by **32-bit CRC-32 (polynomial 0xEDB88320)** in newer versions. Structurally, these checksums are stored as raw 2-byte (CRC-16) or 4-byte (CRC-32) values in the local file header of PKZIP archives, concatenated with the file’s name and compression metadata. The primary use-case was lightweight integrity verification, enabling quick validation of decompressed files without full cryptographic security. While not designed for collision resistance, these checksums were sufficient for error detection in data transmission and archival scenarios where cryptographic hashing was unnecessary.

The **PKZIP Mixed Multi-File Checksum-Only** format is highly vulnerable to cracking due to fundamental design flaws inherent in CRC algorithms. CRC-16 and CRC-32 are **deterministic, non-cryptographic** checksums optimized for error detection, lacking properties like avalanche effect, salt, or keyed operations, making them susceptible to **birthday attacks** and **preimage attacks**. The absence of a salt or secret input allows attackers to exploit **rainbow tables** or **brute-force collisions** by leveraging the **linear nature of CRC polynomials**, where small input variations can produce predictable checksum outputs. Additionally, modern **GPU/FPGA acceleration** (e.g., via CUDA or OpenCL) enables parallelized brute-force attacks, drastically reducing the time complexity for finding collisions or forgeries. The **fixed-length output** (16/32 bits) further limits entropy, while the **lack of cryptographic padding or keying** renders these checksums trivial to manipulate, rendering them unsuitable for any security-critical application beyond basic data integrity checks.

Identifying PKZIP (Mixed Multi-File Checksum-Only) Hashes

Identifying a hash blindly is often difficult because multiple algorithms can output strings of the exact same length. For example, a standard 32-character hexadecimal string could be MD5, NTLM, MD4, or LM. To definitively identify PKZIP (Mixed Multi-File Checksum-Only), security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack PKZIP (Mixed Multi-File Checksum-Only)

If you need to recover the plaintext password for a PKZIP (Mixed Multi-File Checksum-Only) hash during a penetration test or forensics investigation, you must supply the correct module ID to your cracking software. Use the exact commands provided at the top of this page to target the hash successfully.