Password cracking
Initial steps
Steps required for password cracking software:
- Identify which columns contain the username and the password (hashed or otherwise). May be easier to convert to a standard internal representation before processing.
- Identify the algorithm used.
- Identify whether a salt is used.
From these there are multiple stages:
- If no salt is used (e.g. plain MD5), consult a pre-computed lookup table.
Identifying an algorithm
- Length: 32 characters (16 bytes) is likely to be MD5.
- Characters: 0-9a-fA-F is likely to be MD5.
Lookup tables
- How should these be delivered? Plain text file, SQLite database, Lightning Memory-Mapped Database (LMDB), something else?
- What options does the chosen language support?
- Which options are the most efficient?
- Can lookup tables be built entirely in memory and then flushed to disk? Regular flushing as used by SQLite prevents data loss but may take longer due to regular I/O. (answer: Yes, just put the whole thing in a huge transaction and commit at the end).
Contents of lookup tables:
- Dictionary words
- Common words not in dictionary (e.g. TV shows)
- Simple combinations, such as dictionary word concatenated with '1', '123' etc.
- Every possible combination of case and 0-9a-z from 6-12 characters in length.
Libraries
Ultimately most crypto libraries end up being a wrapper around OpenSSL.
Python
- hashlib is the Python wrapper around OpenSSL and appears to be in the standard library.
- Python bindings to LMDB