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Toy Hash Function

Let's build a toy hash function!

Our goal will be to build a function that:

  • Is hard to reverse
  • Has a fixed output size
  • Is deterministic

Our function will not be suitable for production use, but will be useful for the Passly marketing team to explain how our security systems work from a high level.

Shifting Bits in Go

To shift a byte left by numBits:

numBits := 3
// original = 11110000
shifted := original << numBits
// shifted = 10000000

XOR in Go

 
result := a ^ b

Assignment

Complete the hash() function. It takes an arbitrarily sized []byte and returns a fixed size [4]byte.

It should do the following:

  1. Rotate the bits in each byte left 3 bits, do this one byte at a time
  2. Shift the bits in each byte left 2 bits, do this one byte at a time
  3. Create a new empty "final" array of exactly 4 bytes
  4. XOR each byte with its corresponding byte in the final array, and save the result back to the final array. Do this one byte at a time for each byte in the rotated/shifted input. The "corresponding" byte in the final array is at index i%4, where i is the index of the byte in the input.