PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2 Hash

What is PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2?

The cryptographic hash format associated with **PDF 1.1–1.3 (Acrobat 2–4)**—specifically labeled as *collider #2*—originates from Adobe’s early implementation of document integrity verification, where hashes were embedded in metadata to detect tampering. Structurally, this scheme relies on a **SHA-1-based hash** (or a variant thereof) combined with a **collision-resistant prefix** (the "collider" identifier) to generate a 160-bit digest stored in the PDF’s trailer dictionary under `/Encrypt` or `/ID` fields. The primary use-case was to ensure document authenticity, though it was later repurposed for password-based encryption (e.g., in PDF 1.4+) by incorporating a **PDF-specific salt** (a 32-bit value) and a **key derivation function (KDF)** derived from the RC4 cipher’s early Adobe adaptations. The format’s design predates modern best practices, inheriting flaws from its foundational components while attempting to mitigate them with ad-hoc modifications, such as the collider prefix—a static or weakly dynamic value intended to thwart trivial collisions.

This hash format is critically vulnerable due to **SHA-1’s inherent collision susceptibility**, exacerbated by Adobe’s implementation choices. The absence of a **cryptographically secure salt** in early versions (pre-1.4) allows for **rainbow table attacks** and **precomputed collision generation**, as the same hash function is reused across documents with predictable inputs. The "collider #2" prefix, though intended to thwart collisions, was either static or derived from weak entropy sources (e.g., file timestamps or version metadata), enabling **differential cryptanalysis** to craft malicious PDFs with identical hashes. Additionally, Adobe’s **RC4-based KDF** (in encrypted PDFs) suffers from **side-channel leaks** and **weak key expansion**, while GPU-accelerated **SHA-1 brute-forcing** (e.g., via CUDA/Fermi optimizations) renders collision attacks feasible at scale. The lack of **post-quantum resilience** and reliance on legacy cryptographic primitives further cripples its security, as modern tools (e.g., **PDFBox, Poppler, or custom collision generators**) exploit these flaws to forge valid but tampered documents.

Identifying PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2 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 PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2

If you need to recover the plaintext password for a PDF 1.1 - 1.3 (Acrobat 2 - 4), collider #2 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.