Merge pull request #2 from HbHbNr/layer3

Layer3

ascii85.py

@@ -1,3 +1,5 @@
+import fileinput
+
 # GNU General Public License Version 3
 
 def decode(a):
@@ -40,3 +42,14 @@ def decodeTuple(tuple5):
     #print(tuple5)
     #print(decoded)
     return decoded
+
+def loadpayload(inputfile):
+    payloadmarkerfound = False
+    payload = []
+    for line in fileinput.input(inputfile):
+        if not payloadmarkerfound and line.startswith('<~'):
+            payloadmarkerfound = True
+        if payloadmarkerfound:
+            line = line.strip()
+            payload.append(line)
+    return ''.join(payload)

ascii85_test.py

@@ -6,6 +6,7 @@
 
 leviathan_encoded = '''<~9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,O<DJ+*.@<*K0@<6L(Df-\\0Ec5e;DffZ(EZee.Bl.9pF"AGXBPCsi+DGm>@3BB/F*&OCAfu2/AKYi(DIb:@FD,*)+C]U=@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIal(DId<j@<?3r@:F%a+D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G>uD.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c~>'''
 leviathan_plain = 'Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.'
+leviathan_file = 'tests/leviathan.txt'
 
 tuples = [('t', 'F8'), ('td', 'FCY'), ('tdo', 'FC]:'), ('tdo!', 'FC];5')]
 
@@ -24,3 +25,7 @@ def test_decodeTuple():
             assert bytearray(plain, 'utf-8') == ascii85.decodeTuple(encoded.ljust(5, 'u'))[0:len(plain)]
         else:
             assert False == ascii85.decodeTuple(encoded)
+
+def test_loadpayload():
+    payload = ascii85.loadpayload(leviathan_file)
+    assert leviathan_encoded == payload

layer3.py

@@ -0,0 +1,39 @@
+# GNU General Public License Version 3
+
+def decrypt(decoded):
+    # beginning of the text is known, leading to the first bytes of the key
+    expectedstart = bytearray('==[ Layer 4/6: ', 'utf-8')
+    xor = bytearray()
+
+    for i in range(len(expectedstart)):
+        x = expectedstart[i] ^ decoded[i]
+        xor.append(x)
+
+    # a) 15 * '=' must be in the encrypted text, because the line "==[ Payload ]==" contains 47 * '='.
+    # b) Multiple occurences are possible, but hopefully in at least one case 17 more '=' will follow.
+    # c) The last occurence is tried first, because that should be the "Payload"-line.
+    tattletale = bytearray()
+    for x in xor:
+        tattletale.append(x ^ ord('='))
+    xorfullstart = decoded.rfind(tattletale)
+
+    # assumption/hope: the next 32 bytes are all encoded '='
+    xorfull = bytearray()
+    for d in decoded[xorfullstart:xorfullstart+32]:
+        xorfull.append(d ^ ord('='))
+
+    # decrypt the bytes with the assumed key
+    decrypted = bytearray()
+    for i in range(len(decoded)):
+        decrypted.append(decoded[i] ^ xorfull[i % 32])
+
+    return decrypted
+
+
+if __name__ == '__main__':
+    import ascii85
+
+    payload = ascii85.loadpayload('layers/layer3.txt')
+    decoded = ascii85.decode(payload)
+    decoded = decrypt(decoded)
+    print(decoded.decode()[0:500])

solve.py

@@ -1,19 +1,7 @@
-import fileinput
-import ascii85
+import ascii85, layer3
 
 # GNU General Public License Version 3
 
-def loadpayload(inputfile):
-    payloadmarkerfound = False
-    payload = []
-    for line in fileinput.input(inputfile):
-        if not payloadmarkerfound and line.startswith('<~'):
-            payloadmarkerfound = True
-        if payloadmarkerfound:
-            line = line.strip()
-            payload.append(line)
-    return ''.join(payload)
-
 def dumpexcerpt(fulltext, frombegin, fromend):
     fulltextlength = len(fulltext)
     print(str(fulltextlength) + ' characters of fulltext found')
@@ -65,17 +53,19 @@ def layer2filtervalid(payload):
             divided.append((i >> ((6 - ii) * 8)) & 255)
     return divided
 
-for layer in [2]:
+for layer in [3]:
     inputfile = 'layers/layer' + str(layer) + '.txt'
     outputfile = 'layers/layer' + str(layer + 1) + '.txt'
 
-    payload = loadpayload(inputfile)
+    payload = ascii85.loadpayload(inputfile)
     dumpexcerpt(payload, 20, 20)
     decoded = ascii85.decode(payload)
     if layer == 1:
         decoded = layer1bitmod(decoded)
     elif layer == 2:
         decoded = layer2filtervalid(decoded)
+    elif layer == 3:
+        decoded = layer3.decrypt(decoded)
     #print(decoded[0:100].decode())
     #quit()
     dumpexcerpt(decoded.decode(), 200, 200)

tests/leviathan.txt

@@ -0,0 +1,10 @@
+Example from https://en.wikipedia.org/wiki/Ascii85#Example_for_Ascii85
+
+Clear text contains no newlines and reads:
+Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.
+
+<~9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,
+O<DJ+*.@<*K0@<6L(Df-\0Ec5e;DffZ(EZee.Bl.9pF"AGXBPCsi+DGm>@3BB/F*&OCAfu2/AKY
+i(DIb:@FD,*)+C]U=@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIa
+l(DId<j@<?3r@:F%a+D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G
+>uD.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c~>