crypto: add already solved challenges

crypto/caesar/ciphertext

@@ -0,0 +1 @@
+picoCTF{dspttjohuifsvcjdpoabrkttds}

crypto/caesar/solve.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i python3 -p python3
+
+def decrypt(ciphertext: str, key: int):
+    for letter in ciphertext:
+        shifted = chr(((ord(letter) - ord('a') + key + 26) % 26) + ord('a'))
+        print(shifted, end='')
+    print()
+
+if __name__ == "__main__":
+    with open('ciphertext') as file:
+        enc = file.read().strip()[len('picoCTF{'):-len('}')]
+
+    # Note: seems to be the last one, "crossing the rubicon"
+    for shift in range(26):
+        decrypt(enc, shift)