computer science

Hashcat

Hashcat is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hashcat rather than just read about it. In short: Hashcat is a password recovery tool. It had a proprietary code base until 2015, but was then released as open source software.

Key takeaways

Hashcat belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hashcat to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hashcat from memory before moving on to harder problems.

Reference excerpt

Hashcat is a password recovery tool. It had a proprietary code base until 2015, but was then released as open source software. Versions are available for Linux, macOS, and Windows. Examples of hashcat-supported hashing algorithms are LM hashes, MD4, MD5, SHA-family and Unix Crypt formats as well as algorithms used in MySQL and Cisco PIX. Hashcat has received publicity because it is partly based on flaws in other software discovered by its creator. An example was a flaw in 1Password's password manager hashing scheme. It has also been compared to similar software in a Usenix publication and been described on Ars Technica.

Variants Previously, two variants of hashcat existed:

hashcat - CPU-based password recovery tool oclHashcat/cudaHashcat - GPU-accelerated tool (OpenCL or CUDA) With the release of hashcat v3.00, the GPU and CPU tools were merged into a single tool called hashcat. The CPU-only version became hashcat-legacy. Both CPU and GPU now require OpenCL. Many of the algorithms supported by hashcat-legacy (such as MD5, SHA1, and others) can be cracked in a shorter time with the GPU-based hashcat. However, not all algorithms can be accelerated by GPUs. Bcrypt is an example of this. Due to factors such as data-dependent branching, serialization, and memory (and more), oclHashcat/cudaHashcat weren't catchall replacements for hashcat-legacy. hashcat-legacy is available for Linux, OSX and Windows. hashcat is available for macOS, Windows, and Linux with GPU, CPU and generic OpenCL support which allows for FPGAs and other accelerator cards.

Sample output

Attack types Hashcat offers multiple attack modes for obtaining effective and complex coverage over a hash's keyspace. These modes are:

Brute-force attack Combinator attack Dictionary attack Fingerprint attack Hybrid attack Mask attack Permutation attack Rule-based attack Table-Lookup attack (CPU only) Toggle-Case attack PRINCE attack (in CPU version 0.48 and higher only) The traditional bruteforce attack is considered outdated, and the Hashcat core team recommends the Mask-Attack as a full replacement.

Competitions Team Hashcat (the official team of the Hashcat software composed of core Hashcat members) won first place in the KoreLogic "Crack Me If you Can" Competitions at DefCon in 2010, 2012, 2014, 2015, and 2018, and at DerbyCon in 2017.

Worked examples

Example 1 — a first encounter with Hashcat

Start with the simplest possible case. Write down what Hashcat claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hashcat before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hashcat ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hashcat

In research: Hashcat appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hashcat in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hashcat is common in secondary-school and first-year university syllabi. It links to neighbouring topics Formerly proprietary software, Free security software, Password cracking software, so understanding it makes those chapters shorter.
In everyday life: Look for Hashcat outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hashcat in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hashcat means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hashcat out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hashcat in simple terms?

Hashcat is a password recovery tool. It had a proprietary code base until 2015, but was then released as open source software.

Why does Hashcat matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hashcat?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hashcat.