crypto: add a few more challenges

crypto/substitution2/message.txt

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+nafyffoxenefufytpqnafymfppfentkpxeafbaxraezaqqpzqgswnfyefzwyxnhzqgsfnxnxqlexlzpwbxlrzhkfystnyxqntlbwezhkfyzatppflrfnafefzqgsfnxnxqlevqzwesyxgtyxphqlehenfgetbgxlxenytnxqlvwlbtgflntpemaxzatyfufyhwefvwptlbgtycfntkpfecxppeaqmfufymfkfpxfufnafsyqsfyswysqefqvtaxraezaqqpzqgswnfyefzwyxnhzqgsfnxnxqlxelqnqlphnqnftzautpwtkpfecxppekwntpeqnqrfnenwbflnexlnfyfenfbxltlbfozxnfbtkqwnzqgswnfyezxflzfbfvflexufzqgsfnxnxqletyfqvnflptkqyxqwetvvtxyetlbzqgfbqmlnqywllxlrzafzcpxenetlbfofzwnxlrzqlvxrezyxsneqvvflefqlnafqnafyatlbxeaftuxphvqzwefbqlfospqytnxqltlbxgsyquxetnxqltlbqvnflatefpfgflneqvspthmfkfpxfuftzqgsfnxnxqlnqwzaxlrqlnafqvvflexuffpfgflneqvzqgswnfyefzwyxnhxenafyfvqyftkfnnfyufaxzpfvqynfzafutlrfpxegnqenwbflnexltgfyxztlaxraezaqqpevwynafymfkfpxfufnatntlwlbfyentlbxlrqvqvvflexufnfzalxiwfexefeeflnxtpvqygqwlnxlrtlfvvfznxufbfvfleftlbnatnnafnqqpetlbzqlvxrwytnxqlvqzweflzqwlnfyfbxlbfvflexufzqgsfnxnxqlebqfelqnpftbenwbflnenqclqmnafxyflfghtefvvfznxufphtenftzaxlrnafgnqtznxufphnaxlcpxcftltnntzcfysxzqznvxetlqvvflexufphqyxflnfbaxraezaqqpzqgswnfyefzwyxnhzqgsfnxnxqlnatneffcenqrflfytnfxlnfyfenxlzqgswnfyezxflzftgqlraxraezaqqpfyenftzaxlrnafgflqwratkqwnzqgswnfyefzwyxnhnqsxiwfnafxyzwyxqexnhgqnxutnxlrnafgnqfospqyfqlnafxyqmltlbfltkpxlrnafgnqkfnnfybfvflbnafxygtzaxlfenafvptrxesxzqZNV{L6Y4G_4L41H515_15_73B10W5_8F1KV808}

crypto/substitution2/solve.py

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+#!/usr/bin/env nix-shell
+#!nix-shell -i python -p python3
+
+# NOTE: the colors are used to keep track of which letters have been
+#       already substituted, and which are still unknown.
+
+def green(s):
+    return f"\033[42m{s}\033[0m"
+
+def red(s):
+    return f"\033[41m{s}\033[0m"
+
+def substitute(cipher_text, substitution_map):
+    for letter in cipher_text:
+        if letter.lower() in substitution_map:
+            if letter.isupper():
+                x = substitution_map[letter.lower()].upper()
+            else:
+                x = substitution_map[letter]
+            print(green(x), end="")
+        else:
+            print(red(letter), end="")
+
+with open('message.txt', 'r') as file:
+    enc = file.read()
+
+# Here, I will be slowly substituting the letters in the ciphertext
+# based on what I believe the words to be. I have commented out the
+# invocations of substitute, and commented the newly found letters
+# after each invocation.
+
+# Starting off, "sxzqZNV{...}" looks like "picoCTF{...}"
+
+substitution_map = {
+    '0': '0',
+    '1': '1',
+    '2': '2',
+    '3': '3',
+    '4': '4',
+    '5': '5',
+    '6': '6',
+    '7': '7',
+    '8': '8',
+    '9': '9',
+    '_': '_',
+    '{': '{',
+    '}': '}',
+    's': 'p',
+    'x': 'i',
+    'z': 'c',
+    'q': 'o',
+    'n': 't',
+    'v': 'f',
+}
+
+# substitute(enc, substitution_map)
+
+# Using frequency analysis (https://www.dcode.fr/frequency-analysis), we find that:
+
+# F	175×	13.87%
+# N	125×	9.9%
+# X	103×	8.16%
+# Q	102×	8.08%
+# L	98×	7.77%
+# E	83×	6.58%
+# T	68×	5.39%
+# Z	63×	4.99%
+# Y	61×	4.83%
+# A	56×	4.44%
+# P	46×	3.65%
+# W	42×	3.33%
+# V	39×	3.09%
+# G	35×	2.77%
+# B	34×	2.69%
+# S	28×	2.22%
+# R	24×	1.9%
+# U	20×	1.58%
+# H	19×	1.51%
+# K	16×	1.27%
+# M	9×	0.71%
+# C	9×	0.71%
+# O	5×	0.4%
+# I	2×	0.16%
+
+# Based on this, and the frequency of letters in the english alphabet, we can guess for 'e'
+
+substitution_map['f'] = 'e' # 13.87% ~= 12.7%
+
+# 'petitiol' -> 'petition'
+
+substitution_map['l'] = 'n'
+
+# 'incpwbinr' -> 'including'
+# 'effectiue' -> 'effective'
+
+substitution_map['p'] = 'l'
+substitution_map['w'] = 'u'
+substitution_map['b'] = 'd'
+substitution_map['r'] = 'g'
+
+# 'encountey' -> 'encounter'
+
+substitution_map['y'] = 'r'
+
+# 'eecurith' -> 'security'
+
+substitution_map['e'] = 's'
+substitution_map['h'] = 'y'
+
+# 'effectiuely' -> 'effectively'
+
+substitution_map['u'] = 'v'
+
+# 'cogputer' -> 'computer'
+
+substitution_map['g'] = 'm'
+
+# 'catllenge' -> 'challenge'
+
+substitution_map['a'] = 'h'
+substitution_map['t'] = 'a'
+
+# 'thinc' -> 'think'
+
+substitution_map['c'] = 'k'
+
+# 'valuakle' -> 'valuable'
+
+substitution_map['k'] = 'b'
+
+# 'thereeoists' -> 'there exists'
+
+substitution_map['o'] = 'x'
+
+# 'homever' -> 'however'
+
+substitution_map['m'] = 'w'
+
+# 'techniiue' -b 'technique'
+
+substitution_map['i'] = 'q'
+
+substitute(enc, substitution_map)
+