Cryptographic hash

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If you've never encountered a hash in this context before, this usage may be confusing at first. Searching the Internet for "hash" probably reveals more pages about cannabis than computer security at first, but adding "computer" to your searches will get you many, many, many more relevant results. Another tip for beginners, especially if you've found the regular Wikipedia article impenetrable, is to check if there is a "simple" version of the Wikipedia page. In this case, you're in luck: the Simple Wikipedia article for "Cryptographic hash function" is relatively straightforward by comparison.

In the end, a "hash" in the context of computer security is simply a value that ("cryptographically") represents some other value. The idea, in theory, is that two different original values will never be represented by the same two ultimate values after they have been "hashed," and that it is infeasible to recover the original value from the hashed value. (Watch these few minutes from "Crypto 101" for a further explanation and some pictures depicting this.) In practice, however, weaknesses in cryptographic hash functions (whether by design due to flaws in their algorithm, or by mistakes introduced through their actual implementation) sometimes result in two different values being hashed to the same value. When this happens, the hash function is said to be "cryptographically broken," because if you can hash two different values and get the same resulting value, then there is little point to the hash from a security perspective in the first place.

Read next: Hash algorithms ➡️