Hashcat.

Hashcat is the most widely used password-recovery tool, written by Jens Steube (atom) and released as open source in 2015. It runs on CPUs and GPUs via OpenCL/CUDA/HIP, supports more than 300 hash modes (NTLM, bcrypt, scrypt, Kerberos AS-REP/TGS, WPA2, KeePass, etc.), and offers wordlist, rule-based, brute-force, mask, hybrid, and association attacks. Penetration testers and red teams use it to crack stolen hashes during engagements, while defenders use it to audit password strength and validate key-derivation-function (KDF) parameters.

The tool is the clearest practical demonstration of why the choice of hash matters. On a single RTX 4090, NTLM runs at roughly 288 billion guesses per second, so any 8-character password over that fast, unsalted hash falls almost instantly — the entire NTLM keyspace for short passwords is trivial. Feed the same GPU a bcrypt hash (mode 3200) and throughput collapses to a few thousand per second, dropping further as the cost factor rises (cost 12 is ~128× slower than the cost-5 benchmark). That five-to-six-order-of-magnitude gap is exactly the design goal of deliberately slow, salted KDFs like bcrypt, scrypt, and Argon2. Practical defences follow directly: store credentials with a modern memory-hard KDF and a high work factor, enforce long passphrases, and treat any dump of fast MD5/SHA-1/NTLM hashes as already compromised. Cracking hashes obtained without authorization may violate computer-misuse and privacy laws.

flowchart TD
  A[Hash dump] --> B{Hash mode -m}
  B --> C[Candidate generator]
  C --> D[Wordlist + rules]
  C --> E[Mask / brute-force]
  C --> F[Hybrid / association]
  D --> G[GPU hashing engine]
  E --> G
  F --> G
  G --> H{Match?}
  H -- yes --> I[Recovered password]
  H -- no --> C