crypto/new_caesar

crypto/new_caesar/code.txt

@@ -0,0 +1 @@
+mlnklfnknljflfjljnjijjmmjkmljnjhmhjgjnjjjmmkjjmijhmkjhjpmkmkmljkjijnjpmhmjjgjj

crypto/new_caesar/new_caesar.py

@@ -0,0 +1,28 @@
+import string
+
+LOWERCASE_OFFSET = ord("a")
+ALPHABET = string.ascii_lowercase[:16]
+
+def b16_encode(plain):
+	enc = ""
+	for c in plain:
+		binary = "{0:08b}".format(ord(c))
+		enc += ALPHABET[int(binary[:4], 2)]
+		enc += ALPHABET[int(binary[4:], 2)]
+	return enc
+
+def shift(c, k):
+	t1 = ord(c) - LOWERCASE_OFFSET
+	t2 = ord(k) - LOWERCASE_OFFSET
+	return ALPHABET[(t1 + t2) % len(ALPHABET)]
+
+flag = "redacted"
+key = "redacted"
+assert all([k in ALPHABET for k in key])
+assert len(key) == 1
+
+b16 = b16_encode(flag)
+enc = ""
+for i, c in enumerate(b16):
+	enc += shift(c, key[i % len(key)])
+print(enc)

crypto/new_caesar/solve.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+import string
+
+LOWERCASE_OFFSET = ord("a")
+ALPHABET = string.ascii_lowercase[:16]
+
+flag = "mlnklfnknljflfjljnjijjmmjkmljnjhmhjgjnjjjmmkjjmijhmkjhjpmkmkmljkjijnjpmhmjjgjj"
+
+def b16_decode(enc):
+    dec = ""
+    for i in range(0, len(enc), 2):
+        first = "{0:04b}".format(ALPHABET.index(enc[i]))
+        second = "{0:04b}".format(ALPHABET.index(enc[i + 1]))
+        dec += chr(int(first + second, 2))
+    return dec
+
+def unshift(c, k):
+    t1 = ord(c) - LOWERCASE_OFFSET
+    t2 = ord(k) - LOWERCASE_OFFSET
+    return ALPHABET[(t1 - t2) % len(ALPHABET)]
+
+
+def main():
+    for key in ALPHABET:
+        unenc = ""
+        for i, c in enumerate(flag):
+            unenc += unshift(c, key[i % len(key)])
+        unshifted = ''.join(unshift(c, key) for c in flag)
+
+        # NOTE: key is 'g', "et tu?" is a caesar reference.
+        #       Remove the if statement to see all outpus for all keys
+        if key == 'g':
+            print(f'picoCTF{{{b16_decode(unenc)}}}')
+
+if __name__ == "__main__":
+    main()