Teacher:Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Teacher: Now, understand the problem? Solve this instance: Context : SHACAL-1 (originally simply SHACAL) is a 160-bit block cipher based on SHA-1, and supports keys from 128-bit to 512-bit.
Answer : SHA-1
Student:
Which is the basis of SHACAL?