first commit

6.txt

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b64.py

@@ -0,0 +1,14 @@
+import base64
+
+def b64_to_bytes(b64_str):
+    ascii_bytes = b64_str.encode("ascii")
+    return base64.b64decode(ascii_bytes)
+
+
+def bytes_to_b64(bytearr):
+    return base64.b64encode(bytearr).decode("ascii")
+
+
+if __name__ == "__main__":
+    b = b64_to_bytes("BAAA")
+    print(b)

challenge_1_b64.py

@@ -0,0 +1,37 @@
+
+
+# Convert hexadecimal string to base 64 string
+def hex_to_b64(hexstr):
+    hextable = "0123456789abcdef"
+
+    pad = len(hexstr) % 3
+    if pad == 1:
+        hexstr = "00" + hexstr
+    elif pad == 2:
+        hexstr = "0" + hexstr
+
+
+    b64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+    b64str = ""
+
+    for i in range(0, len(hexstr), 3):
+        n = 0
+        mul = 1
+        for j in range(2, -1, -1):
+            single_hex = hextable.index(hexstr[i + j])
+            n += single_hex*mul
+            mul = mul << 4
+        # now that we have 3 hex characters together, that is 2 base64 characters
+        char2 = b64_table[n % 64]
+        n = n // 64
+        char1 = b64_table[n % 64] 
+        b64str += char1 + char2
+    return b64str
+
+
+def test_hex_to_b64():
+    hex = "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d"
+    ans = "SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t"
+    val = hex_to_b64(hex)
+    assert val == ans, f"{val=}"
+

challenge_2_xor.py

@@ -0,0 +1,4 @@
+n1 = 0x1c0111001f010100061a024b53535009181c
+n2 = 0x686974207468652062756c6c277320657965
+
+print(hex(n1 ^ n2))

challenge_3_xor_cipher.py

@@ -0,0 +1,64 @@
+
+with open("letter_frequency.csv") as f:
+    freqs = f.readlines()
+
+english_freqs = {line.split(",")[0]:float(line.strip().split(",")[1]) for line in freqs[1:]}
+
+cipher = 0x1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736
+
+
+def to_ascii(hex_num):
+    ascii = ""
+    while hex_num > 0:
+
+        ascii += chr(hex_num % 2**8)
+
+        hex_num = hex_num >> 8
+    return ascii[::-1]
+
+def list_to_num(lst, bits):
+    num = 0
+    mul = 1
+    for item in lst[::-1]:
+
+        num += item*mul
+        mul = mul << bits
+
+    return num
+
+def letter_freq_score(text):
+    score = 0
+    text = text.lower()
+    my_freqs = {}
+    for character in text:
+        my_freqs[character] = my_freqs.get(character, 0) + 1
+
+    for key in my_freqs.keys():
+        my_freqs[key] /= len(text)
+
+    for key in my_freqs.keys():
+        if key in english_freqs:
+            score += my_freqs[key]*english_freqs[key]
+
+    return score
+
+output = []
+
+for i in range(26*2 + 6):
+    letter = ord("A") + i
+    letters = [letter] * 34
+
+    key = list_to_num(letters, 8)
+
+    text = to_ascii(cipher^key)
+    score = letter_freq_score(text)
+    output.append((chr(letter), text, score))
+
+output = sorted(output, key=lambda x: x[2], reverse=True)
+for o in output[:5]:
+    print(o)
+
+
+
+
+

challenge_4_detect_xor.py

@@ -0,0 +1,73 @@
+
+
+with open("letter_frequency.csv") as f:
+    freqs = f.readlines()
+
+english_freqs = {line.split(",")[0]:float(line.strip().split(",")[1]) for line in freqs[1:]}
+
+
+with open("challenge_4_encrypted.txt") as f:
+    ciphers = f.read().splitlines() 
+
+def to_ascii(num):
+    ascii = ""
+    while num > 0:
+
+        ascii += chr(num % 2**8)
+
+        num = num >> 8
+    return ascii[::-1]
+
+def list_to_num(lst, bits):
+    num = 0
+    mul = 1
+    for item in lst[::-1]:
+
+        num += item*mul
+        mul = mul << bits
+
+    return num
+
+def letter_freq_score(text):
+
+
+    score = 0
+    text = text.lower()
+    my_freqs = {}
+    for character in text:
+        my_freqs[character] = my_freqs.get(character, 0) + 1
+
+    for key in my_freqs.keys():
+        my_freqs[key] /= len(text)
+
+    for key in my_freqs.keys():
+        if key in english_freqs:
+            score += my_freqs[key]*english_freqs[key]
+
+    return score
+
+output = []
+for cipher in ciphers:
+    n_chars = len(cipher)//2
+    n_cipher = int(cipher, 16)
+
+    for i in range(256):
+        letter = i
+        letters = [letter] * n_chars
+
+        key = list_to_num(letters, 8)
+
+        text = to_ascii(n_cipher^key)
+        score = letter_freq_score(text)
+        output.append((cipher, chr(letter), text, score))
+
+output = sorted(output, key=lambda x: x[3], reverse=True)
+for o in output[:5]:
+    print(o)
+
+# Answer: 
+# ('7b5a4215415d544115415d5015455447414c155c46155f4058455c5b523f', '5', 'Now that the party is jumping\n', 0.066741)
+
+
+
+