What is a trapdoor function? @internet-class
What is a trapdoor function?  @internet-class
Uploaded October 2016 | Updated September 2026, 2 hours ago
Modern cryptography depends on the existence of several special kinds of mathematical functions. One important kind is a trapdoor function. Trapdoor functions are somewhat similar to hash functions in that they are easy to compute but hard to invert…​ except if you know a secret piece of information. So if someone does not have the secret or key, they cannot invert the function. If they do, they can open the trapdoor and invert the function. Trapdoor functions form the basis of modern cryptographic techniques that are widely-used online.

Credits: Talking: Geoffrey Challen (Assistant Professor, Computer Science and Engineering, University at Buffalo). Producing: Greg Bunyea (Undergraduate, Computer Science and Engineering, University at Buffalo).

Part of the internet-class.org online internet course. A blue Systems Research Group (https://blue.cse.buffalo.edu) production.
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What is a trapdoor function?

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