One way functions are easy to calculate the output from an input but are hard to reverse or calculate the input from the output. Examples of one way functions include prime factorization, discrete logarithm problems, and secure hash functions. Trapdoor functions are a special type of one way function that are easy to reverse if a secret piece of information called a trapdoor is known.

1. One way functions and trapdoor
functions

2. One way functions

3. One way functions
• Easy to have
output from
input
• Hard rather
impossible to
reverse or
inverse i.e.,
from out put
to input

4. One way function
Examples
Prime factorization
Discrete logarithm problems
Secure hash functions

5. One way functions
• Simple prime factorization example

6. Trapdoor Function