Thunder Tables Kill Microsoft 40-bit Encryption

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According to Russian forensic security experts and 'password recovery' specialists ElcomSoft, the days of protecting documents and files with 40-bit encryption are now officially over.

It has now released a product which uses Thunder Tables technology to unlock password-protected documents that have been created using Microsoft Word. In fact, it guarantees that it can provide "near-instant recovery" of any such documents protected with 40-bit encryption. That compares with the days it would have taken using a straightforward brute-force approach.

Apparently the secret is the Thunder Tables technology, something that ElcomSoft claims is a result of "scientific research in cryptography" which ensures all 40-bit encryption keys are unlocked in seconds. These seem to be somewhat similar to Rainbow Tables, which come shipped on a DVD containing pre-computed hash tables. Rainbow Tables are well known in the security field, and can be sued to 'unlock' around 99 percent of encrypted documents in just a few minutes.

However, unlike Rainbow Tables the new Thunder Tables promise 100 percent 'password recovery' and in seconds rather than minutes.

They seem to work in a similar fashion though, pre-computing decryption information to speed up the password cracking process. With 40-bit encryption providing for a trillion possible keys, the Thunder Tables simply accounts for all of these possibilities as incredible as that may sound.

The news comes hot off the heels of ElcomSoft also revealing it has found a way of cracking WiFi WPA and WPA2 encryption by employing the use of Nvidia graphics cards.

Dani AI

Generated

— useful catch. A brief, practical update and what to do if this affects files in the wild.

The vendor technique described in the thread is a classic time–memory trade‑off: precomputed tables covering the small 40‑bit keyspace let an attacker (or a forensic tool) map an encrypted file to its key much faster than brute force. That approach specifically targets legacy 40‑bit protections used by older Office/PDF binaries; it does not apply to modern AES‑based Office encryption. (elcomsoft.com)

Why this matters: Office binary formats and old CryptoAPI providers historically used RC4/40‑bit keys or other weak options for backward compatibility, so documents saved in “compatibility” modes or as .doc/.xls can be vulnerable. Newer OOXML (.docx/.xlsx) uses PBKDF2/Agile encryption with AES (128+ bits) and far stronger key derivation, so migrating files stops this class of attack. If you must protect legacy files, re-save them in the modern format and re‑apply encryption using a long, unique passphrase. See Microsoft’s Office cryptography docs for the format differences. ()

Actionable checklist (quick):

  • Treat any .doc/.xls created before Office 2007 as potentially weak; convert to .docx/.xlsx and re‑encrypt.
  • Use long, unique passphrases (NIST recommends long memorized secrets / passphrases rather than short complex passwords). Consider a password manager. (pages.nist.gov)
  • For wireless concerns mentioned in the thread: GPU acceleration speeds up brute‑force testing of WPA/WPA2 but does not magically break strong passphrases — length and randomness still win. If you need auditing tools, use them in a controlled, legal context. (arstechnica.com)

This keeps the practical takeaways front and center: legacy 40‑bit protections are no longer adequate; migrate formats and use long passphrases.

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