From 3cd27dab04a2b8841196b9ce8f6f69b89e032c76 Mon Sep 17 00:00:00 2001
From: PlexSheep <PlexSheep@protonmail.com>
Date: Sat, 22 Apr 2023 09:50:40 +0200
Subject: [PATCH] moved basic-decrypt.py to this repo

---
 src/basic-decrypt.py | 122 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100755 src/basic-decrypt.py

diff --git a/src/basic-decrypt.py b/src/basic-decrypt.py
new file mode 100755
index 0000000..715df79
--- /dev/null
+++ b/src/basic-decrypt.py
@@ -0,0 +1,122 @@
+#!/usr/bin/env python3
+
+MAX_IN_LINE = 16
+DE_MOST_COMMON = ['E', 'N', 'I', 'R', 'A']
+EN_MOST_COMMON = ['E', 'T', 'A', 'O', 'I']
+
+def main():
+    with open("chiffrat.txt", "r") as file:
+        text = file.read().split(" ")
+        intarr = []
+        chars_in_text: int = len(text)
+        for item in text:
+            intarr.append(int(item, 16))
+        print('=' * 80)
+        print("dumping cyphertext (%d chars)" % chars_in_text)
+        print('=' * 80)
+        print(dump_intarr(intarr))
+        freq = freq_analysis(intarr)
+        print('=' * 80)
+        print("Top 5 occurences:")
+        print('=' * 80)
+        dump_frequencies(freq, chars_in_text)
+        print('=' * 80)
+        print("Trying to find key from frequencies")
+        print('=' * 80)
+        key = find_key(freq, DE_MOST_COMMON)
+        if not key:
+            print("The key could not be determined.")
+        if key:
+            print('=' * 80)
+            print("decrypt (key %d):" % key)
+            print('=' * 80)
+            decry = shift_intarr(intarr, key)
+            print(dump_intarr(decry))
+
+def freq_analysis(intarr: list):
+    freql: dict = {}
+    for i in range(0, 255):
+        freql[i] = 0
+    # list of tuples with all possible values and their frequency
+    for item in intarr:
+        freql[item] += 1
+    return dict(sorted(freql.items(), key=lambda item: item[1], reverse=True))
+
+def find_key(freq: dict, language_reference: list):
+    # caesar
+    caesar_keys = [0] * len(language_reference)
+    for index, common_char in enumerate(language_reference):
+        # this is probably garbage
+        caesar_keys[index] = list(freq.values())[index] - ord(common_char) - 64
+
+    all_same = False
+    for i in range(1, len(caesar_keys)):
+        if all_same:
+            all_same = caesar_keys[i-1] == caesar_keys[i]
+        else: break
+    if all_same:
+        print("found a perfect match in the caesar checks: %s" % caesar_keys)
+        return caesar_keys[0]
+    else:
+        print("Caesar keys ambiguos: %s" % caesar_keys)
+    # was not caesar encrypted, continue with XOR checks
+    # XOR
+    xor_keys = [0] * len(language_reference)
+    for index, common_char in enumerate(language_reference):
+        # this is probably garbage
+        item = list(freq.values())[index]
+        xor_keys[index] = item ^ ord(common_char)
+
+    all_same = False
+    for i in range(1, len(xor_keys)):
+        if all_same:
+            all_same = xor_keys[i-1] == xor_keys[i]
+        else: break
+    if all_same:
+        print("found a perfect match in the caesar checks: %s" % xor_keys)
+        return xor_keys[0]
+    else:
+        # ????????
+        print("xor keys ambiguos: %s" % xor_keys)
+    
+
+def dump_frequencies(frequencies, chars_in_text: int = -1, print_top_x = 5):
+    for i in range(print_top_x):
+        print("Top %s:\t'%s' with %s\toccurences (%s%%)" % (
+            i+1, 
+            hex(list(frequencies.keys())[i]), 
+            list(frequencies.values())[i],
+            (list(frequencies.values())[i] / chars_in_text) * 100,
+            ))
+
+def shift_intarr(cypher_text_arr, key: int = 0):
+    decrypt = [0] * len(cypher_text_arr)
+    for index, item in enumerate(cypher_text_arr):
+        decrypt[index] = item + key
+    return decrypt
+
+def dump_intarr(intarr) -> str:
+    output = ""
+    for index, item in enumerate(intarr) :
+        if index % MAX_IN_LINE == 0:
+            output += ("%02x\t| %02x " % (index,item))
+        elif index % MAX_IN_LINE == MAX_IN_LINE - 1:
+            output += ("%02x\n" %item)
+        else:
+            output += ("%02x " %item)
+    # now dump as chars
+    output += ("\n" + '=' * 80 + "\n")
+    output += ("Char Representation\n")
+    output += ('=' * 80 + "\n")
+    char_max = MAX_IN_LINE * 4
+    for index, item in enumerate(intarr) :
+        if index % char_max == 0:
+            output += ("%s\t| %c " % (hex(index),item))
+        elif index % char_max == char_max - 1:
+            output += ("%c\n" %item)
+        else:
+            output += ("%c " %item)
+    return output
+
+if __name__ == "__main__":
+    main()