nbulischeck · March 11, 2019 19:07 · Mar 11, 2019 · Mar 11, 2019
diff --git a/rubikstega.py b/rubikstega.py
@@ -1,7 +1,9 @@
+# Values from the white paper
 EXAMPLE_PHDR = 'L2 F\' B2 U D2 B U D\' F2 L\' F U2 R U\' L\' R\' U\' B F D U\''.split(" ")
 EXAMPLE_LHDR = 'B U2 D2 R\' F U2 B R L\' B L\' B L\' D F\' L U\' B2 R F2 L\' F2'.split(" ")
 EXAMPLE_MSG = 'F L U2 L2 F\' B D\' B2 L\' B\' U L2 F\' R2 D\' B\' U\' L\' B R D2 L2 R\' B F2 D\' U R B D2 U2 R2 U\' F2 R2 F D F2 B2 D\' R\' D R\' U\' F\' B2 U F2 D R U L F U2 L2 D R B D\' B\' U L U\''.split(" ")
 
+# Values from the challenge
 CHALL_PHDR = 'B2 R U F\' R\' L\' B B2 L F D D\' R\' F2 D\' R R D2 B\' L R'.split(" ")
 CHALL_LHDR = 'L\' L B F2 R2 F2 R\' L F\' B\' R D\' D\' F U2 B\' U U D\' U2 F\''.split(" ")
 CHALL_MSG = 'L F\' F2 R B R R F2 F\' R2 D F\' U L U\' U\' U F D F2 U R U\' F U B2 B U2 D B F2 D2 L2 L2 B\' F\' D\' L2 D U2 U2 D2 U B\' F D R2 U2 R\' B\' F2 D\' D B\' U B\' D B\' F\' U\' R U U\' L\' L\' U2 F2 R R F L2 B2 L2 B B\' D R R\' U L'.split(" ")

diff --git a/rubikstega.py b/rubikstega.py
@@ -0,0 +1,110 @@
+EXAMPLE_PHDR = 'L2 F\' B2 U D2 B U D\' F2 L\' F U2 R U\' L\' R\' U\' B F D U\''.split(" ")
+EXAMPLE_LHDR = 'B U2 D2 R\' F U2 B R L\' B L\' B L\' D F\' L U\' B2 R F2 L\' F2'.split(" ")
+EXAMPLE_MSG = 'F L U2 L2 F\' B D\' B2 L\' B\' U L2 F\' R2 D\' B\' U\' L\' B R D2 L2 R\' B F2 D\' U R B D2 U2 R2 U\' F2 R2 F D F2 B2 D\' R\' D R\' U\' F\' B2 U F2 D R U L F U2 L2 D R B D\' B\' U L U\''.split(" ")
+
+CHALL_PHDR = 'B2 R U F\' R\' L\' B B2 L F D D\' R\' F2 D\' R R D2 B\' L R'.split(" ")
+CHALL_LHDR = 'L\' L B F2 R2 F2 R\' L F\' B\' R D\' D\' F U2 B\' U U D\' U2 F\''.split(" ")
+CHALL_MSG = 'L F\' F2 R B R R F2 F\' R2 D F\' U L U\' U\' U F D F2 U R U\' F U B2 B U2 D B F2 D2 L2 L2 B\' F\' D\' L2 D U2 U2 D2 U B\' F D R2 U2 R\' B\' F2 D\' D B\' U B\' D B\' F\' U\' R U U\' L\' L\' U2 F2 R R F L2 B2 L2 B B\' D R R\' U L'.split(" ")
+
+notation1 = ["D", "B'", "L", "R'", "R", "L'", "F2", "U", "B2"]
+notation2 = ["R2", "D'", "F", "U'", "B", "F'", "U2", "L2", "D2"]
+
+default_table = [
+    [0, "L", "F"],
+    [1, "R", "B"],
+    [2, "U", "L2"],
+    [3, "D", "R2"],
+    [4, "F2", "U2"],
+    [5, "B2", "D2"],
+    [6, "L'", "F'"],
+    [7, "R'", "U'"],
+    [8, "B'", "D'"],
+]
+
+def find_encoded(i, seq):
+    if i in notation1:
+        f = lambda x: x[2] == i
+    elif i in notation2:
+        f = lambda x: x[3] == i
+    else:
+        quit(0)
+
+    for item in seq:
+        if f(item): 
+            return item[1]
+
+def find_default(i, seq):
+    if i in notation1:
+        f = lambda x: x[1] == i
+    elif i in notation2:
+        f = lambda x: x[2] == i
+    else:
+        quit(0)
+
+    for item in seq:
+        if f(item): 
+            return item[0]
+
+def get_enc_table(HEADER):
+    # Step 1: Map header to default table in base-9
+    ENCODED_P = ''.join([str(find_default(i, default_table)) for i in HEADER])
+
+    # Step 2: Convert first scramble into decimal
+    ENCODED_P = str(int(ENCODED_P, 9))
+
+    # Reverse engineering of 2.1.1 Embedding the permutation information
+    i = int(ENCODED_P[0])
+    sub1 = ENCODED_P[1:i+1]
+    P = ENCODED_P[i+1:i+10]
+    sub2 = ENCODED_P[i+10:]
+
+    # Use P to permute the default encoding table
+    enc_table = [default_table[int(x)] for x in P]
+
+    # Insert the "After" indexes
+    for idx, item in enumerate(enc_table):
+        item.insert(1, idx)
+
+    return enc_table
+
+def get_length(enc_table, HEADER):
+    # Step 1: Map header to encoded table in base-9
+    HEADER_LENGTH = ''.join([str(find_encoded(i, enc_table)) for i in HEADER])
+
+    # Step 2: Convert first scramble into decimal
+    HEADER_LENGTH = str(int(HEADER_LENGTH, 9))
+
+    # Reverse engineering of 2.1.3 Embedding the length information
+    j = int(HEADER_LENGTH[0])
+    k = int(HEADER_LENGTH[1])
+    sub3 = HEADER_LENGTH[2:j+2]
+    length = int(HEADER_LENGTH[j+2:j+2+k])
+    sub4 = HEADER_LENGTH[j+2+k:]
+
+    return length
+
+def decrypt_message(length, enc_table, MESSAGE):
+    # Step 1: Get m by taking length notations starting from third scramble
+    MESSAGE_PIECE = MESSAGE[0:length]
+
+    # Step 2: Map header to encoded table in base-9
+    MAPPED_MESSAGE = ''.join([str(find_encoded(i, enc_table)) for i in MESSAGE_PIECE])
+
+    # Step 2: Convert first scramble into decimal, then binary
+    MAPPED_MESSAGE = int(MAPPED_MESSAGE, 9)
+    BINARY_MESSAGE = f"{MAPPED_MESSAGE:b}"
+
+    # Step N: Pad
+    PADDED_MESSAGE = '0' * (8 - (151 % 8)) + BINARY_MESSAGE
+
+    # Step N: Chunk
+    CHUNKED_MESSAGE = [PADDED_MESSAGE[i:i+8] for i in range(0, len(PADDED_MESSAGE), 8)]
+
+    # Step N: Join
+    DECRYPTED_MESSAGE = ''.join([chr(int(x, 2)) for x in CHUNKED_MESSAGE])
+
+    print(DECRYPTED_MESSAGE)
+
+enc_table = get_enc_table(CHALL_PHDR)
+length = get_length(enc_table, CHALL_LHDR)
+decrypt_message(length, enc_table, CHALL_MSG)
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