A trapdoor function is a function that is easy to compute in one direction but hard in the opposite direction. Just like a trapdoor; it is easy to fall in, but hard to get out. The easy direction is used for [[Encryption|encryption]] and decryption with the [[Encryption Key| encryption key]]. If you don't have the key, you will have to invert the function and compute the hard direction. ![[trapdoor_function.excalidraw.light.svg]] A typical example for a trapdoor function is the [[Discrete Logarithm Problem]]. Since that problem is slightly technical, we can use a related example here. It is easy for computers to multiply two arbitrary numbers (top row). However, it is much harder to find out which [[Prime Number|prime factors]] you can decompose a number into (bottom row). This computational problem is also used in the [[Discrete Logarithm Problem]]. >[!read]- Further Reading >- [[Encryption]] >[!ref]- References