# Advent of Code 2020 Day 25

The final day! Of course it hase to be public-key cryptography…

## Part 1

Well the first part is pretty straightforward, just implement the algorithm described to find the secret key (a.k.a. the number of loops):

```
transform(n, subj) = (n*subj)%20201227
function loops(key, subject=7)
n = subject
i = 1
while n != key
n = transform(n, subject)
i += 1
end
return i
end
```

And then to calculate the encryption key:

```
function encrypt(key, loops)
n = 1
for i in 1:loops
n = transform(n, key)
end
return n
end
```

## Part 2

**Merry Christmas and Happy New Year!**