xome crypto challenges

CTFLearn/Cryptography/120.md

@@ -0,0 +1,20 @@
+# [RSA Noob](https://ctflearn.com/challenge/120)
+
+```text
+e: 1
+c: 9327565722767258308650643213344542404592011161659991421
+n: 245841236512478852752909734912575581815967630033049838269083
+```
+
+**RSA** Intro [here](https://ctf101.org/cryptography/what-is-rsa/)
+
+```text
+c = (m^e)%n
+e = 1 -> c = m%n -> m = k*n + c, where k>=0 is an integer
+```
+
+Starting from k=0, try to check which m gives a flag-like output. Luckily, here m = c works.
+
+```bash
+echo "obase=16; ibase=10; 9327565722767258308650643213344542404592011161659991421" | bc | xxd -r -p
+```

CTFLearn/Cryptography/121.md

@@ -0,0 +1,27 @@
+# [So many 64s](https://ctflearn.com/challenge/121)
+
+Repeatedly decode (b64) until the string is of small length, say 30
+Bash script:
+
+```bash
+if [ $# -eq 0 ]; then
+  echo "Usage: $0 <input_file>"
+  exit 1
+fi
+
+if [ ! -f "$1" ]; then
+  echo "Error: File '$1' does not exist."
+  exit 2
+fi
+
+input_text=$(cat "$1")
+
+while [ ${#input_text} -gt 30 ]; do
+  input_text=$(echo "$input_text" | base64 -d)
+
+  if [ $? -ne 0 ]; then
+    echo "$input_text"
+    exit 3
+  fi
+done
+```

CTFLearn/Cryptography/238.md

@@ -0,0 +1,33 @@
+# [Substitution Cipher](https://ctflearn.com/challenge/238)
+
+Python script:
+
+```python
+# Mapping defined by pure observation, intuition, manual substitution and repeated runs of code
+REVERSE_CIPHER_ALPHABET = {
+    'M': 'T', 'I': 'H', 'T': 'E', 'L': 'S', 'O': 'I', 'F': 'N', 'S':'L', 'B':'Y', 'K': 'R', 'W': 'U', 'Z': 'B', 'R':'D', 'E':'C', 'D': 'M', 'X': 'V', 'G':'O', 'C': 'W', 'U':'G', 'Q':'K','Y':'F', 'H':'P'
+}
+
+def decode_substitution_cipher(cipher_text):
+    decoded_message = ''.join(
+        REVERSE_CIPHER_ALPHABET.get(char, char) for char in cipher_text.upper()
+    )
+    return decoded_message
+
+def read_cipher_text(file_path):
+    try:
+        with open(file_path, 'r', encoding='utf-8') as file:
+            return file.read()
+    except FileNotFoundError:
+        print(f"Error: File '{file_path}' not found.")
+        return ""
+
+if __name__ == "__main__":
+    file_path = "Substitution.txt"
+    cipher_text = read_cipher_text(file_path)
+
+    if cipher_text:
+        decoded_message = decode_substitution_cipher(cipher_text)
+        print("Decoded Message:")
+        print(decoded_message)
+```

CTFLearn/Cryptography/263.md

@@ -0,0 +1,22 @@
+# [5x5 Crypto](https://ctflearn.com/challenge/263)
+
+Python script:
+
+```python
+grid5x5 = [
+    ['a','b','c','d','e'],
+    ['f','g','h','i','j'],
+    ['l','m','n','o','p'],
+    ['q','r','s','t','u'],
+    ['v','w','x','y','z']
+]
+
+text="1-3,4-4,2-1,{,4-4,2-3,4-5,3-2,1-2,4-3,_,4-5,3-5,}"
+text = text.split(',')
+for t in text:
+    if '-' in t:
+        x,y = t.split('-')
+        print(grid5x5[int(x)-1][int(y)-1],end='')
+    else:
+        print(t,end='')
+```

CTFLearn/Cryptography/443.md

@@ -0,0 +1,21 @@
+# [HyperStream Test #2](https://ctflearn.com/challenge/443)
+
+Use **Bacon Cipher** (original 24-letter variant):
+
+```python
+BACON_CIPHER_DICT = {
+    'AAAAA': 'A', 'AAAAB': 'B', 'AAABA': 'C', 'AAABB': 'D', 'AABAA': 'E',
+    'AABAB': 'F', 'AABBA': 'G', 'AABBB': 'H', 'ABAAA': 'I', 'ABAAB': 'K',
+    'ABABA': 'L', 'ABABB': 'M', 'ABBAA': 'N', 'ABBAB': 'O', 'ABBBA': 'P',
+    'ABBBB': 'Q', 'BAAAA': 'R', 'BAAAB': 'S', 'BAABA': 'T', 'BAABB': 'U',
+    'BABAA': 'W', 'BABAB': 'X', 'BABBA': 'Y', 'BABBB': 'Z'
+}
+
+def decode_bacon(bacon_input):
+    bacon_groups = [bacon_input[i:i+5] for i in range(0, len(bacon_input), 5)]
+    decoded_message = ''.join(BACON_CIPHER_DICT.get(group, '') for group in bacon_groups)
+    return decoded_message
+
+decoded_flag = decode_bacon(bacon_input)
+print(decoded_flag.lower())
+```