1. Analyze the ciphertext
`Ypw'zj  tpmwfe ...`
```Y = Y + 0p = o + 1w = u + 2' = ' + 3z = v + 4j = e + 5  =   + 6t = s + 7p = o + 8m = l + 9w = v + 10f = e + 11e = d + 12...```
2. Decode for ROT-i
```file = open('challenge.txt').readline().strip()cipher = list(file)upper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'lower = upper.lower()i = 0for c in cipher:    if c in upper:        x = upper.index(c) - i        print(upper[x], end = '')    elif c in lower:        x = lower.index(c) - i        print(lower[x], end = '')    else:        print(c, end = '')    i = (i + 1) % 26```
3.  Here is the result
`You've solved the beginner crypto challenge! The flag is DUCTF{crypto_is_fun_kjqlptzy}. Now get out some pen and paper for the rest of them, they won't all be this easy :).`
4.  Here is the flag
`DUCTF{crypto_is_fun_kjqlptzy}`