PDF 1.7 Level 3 (Acrobat 9) Hash

Technical details, regex signatures, and cracking commands for the PDF 1.7 Level 3 (Acrobat 9) algorithm.

Regex Identification Signature:

                        \$pdf\$5\*[5|6]\*[0-9]{3}\*[-0-9]{1,6}\*[0-9]\*[0-9]{1,4}\*[a-f0-9]{0,1024}\*[0-9]{1,4}\*[a-f0-9]{0,1024}\*[0-9]{1,4}\*[a-f0-9]{0,1024}\*[0-9]{1,4}\*[a-f0-9]{0,1024}\*[0-9]{1,4}\*[a-f0-9]{0,1024}
                    

Hashcat Command (Mode: 10600):

John the Ripper Command:

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What is PDF 1.7 Level 3 (Acrobat 9)?

The cryptographic hash format used in **PDF 1.7 Level 3 (Acrobat 9)**—specifically for document integrity and authentication—relies on the **SHA-1** (Secure Hash Algorithm 1) hash function, standardized in Adobe’s PDF specification (ISO 32000-1) for digital signatures and encryption metadata. Introduced in 2007 with Acrobat 9, this format embeds a **PDF object dictionary** (`/Filter /Standard` or `/Filter /LZW` for compression) alongside the SHA-1 hash of the document’s byte stream, along with a **certificate chain** and **signature container** (e.g., `/SigFlags` with `1` for basic signing). The primary use-case is ensuring document tamper-evidence via **CMS (Cryptographic Message Syntax) PKCS#7** or **PAdES (PDF Advanced Electronic Signature)** compliance, where the hash serves as a fixed-length (160-bit) fingerprint of the signed content. However, the implementation deviates from pure PKCS#7 by incorporating Adobe’s proprietary **Cryptographic Dictionary** (`/Crypt` and `/V`), which may include additional metadata (e.g., `/Reason`, `/Location`) but does not alter the core SHA-1 hashing mechanism.

SHA-1’s vulnerability in this context stems from its **collision resistance weakness**, exacerbated by **GPU/ASIC optimizations** and **lack of salting** in Adobe’s implementation. While SHA-1 was never designed for long-term security, its 160-bit output became crackable via **birthday attack algorithms** (e.g., **SHA1crack** or **SHA-1 collision attacks** like those demonstrated by Chloé-Arguin et al. in 2017). Adobe’s PDF 1.7 format further compounds risks by **reusing hashes for document metadata** (e.g., `/Length`, `/Filter` flags) without cryptographic binding, enabling **preimage attacks** via brute-force or **rainbow table** techniques. Additionally, the **compression filters** (e.g., `/Filter /FlateDecode`) can alter byte sequences before hashing, introducing **length-extension vulnerabilities** if not properly padded. Finally, the **lack of HMAC or keyed hashing** in the signature container means adversaries can exploit **length-extension attacks** to forge valid-looking hashes, while GPU-accelerated tools (e.g., **OpenCL/SHA1 optimizations**) enable parallel cracking of weak passwords or certificate chains in the `/Crypt` dictionary.

Identifying PDF 1.7 Level 3 (Acrobat 9) 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 1.7 Level 3 (Acrobat 9), security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack PDF 1.7 Level 3 (Acrobat 9)

If you need to recover the plaintext password for a PDF 1.7 Level 3 (Acrobat 9) 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.