1 files changed, 130 insertions, 0 deletions
diff --git a/scripts/chitu_crypt.py b/scripts/chitu_crypt.py
new file mode 100755
index 00000000..080b9f47
--- /dev/null
+++ b/scripts/chitu_crypt.py
@@ -0,0 +1,130 @@
+#!/usr/bin/env python2
+# Encrypts STM32 firmwares to be flashable from SD card by Chitu motherboards.
+# Relocate firmware to 0x08008800!
+
+# Copied from Marlin and modified.
+# Licensed under GPL-3.0
+
+import os
+import random
+import struct
+import uuid
+import sys
+
+def calculate_crc(contents, seed):
+    accumulating_xor_value = seed;
+
+    for i in range(0, len(contents), 4):
+        value = struct.unpack('<I', contents[ i : i + 4])[0]
+        accumulating_xor_value = accumulating_xor_value ^ value
+    return accumulating_xor_value
+
+def xor_block(r0, r1, block_number, block_size, file_key):
+    # This is the loop counter
+    loop_counter = 0x0
+
+    # This is the key length
+    key_length = 0x18
+
+    # This is an initial seed
+    xor_seed = 0x4bad
+
+    # This is the block counter
+    block_number = xor_seed * block_number
+
+    #load the xor key from the file
+    r7 =  file_key
+
+    for loop_counter in range(0, block_size):
+        # meant to make sure different bits of the key are used.
+        xor_seed = int(loop_counter/key_length)
+
+        # IP is a scratch register / R12
+        ip = loop_counter - (key_length * xor_seed)
+
+        # xor_seed = (loop_counter * loop_counter) + block_number
+        xor_seed = (loop_counter * loop_counter) + block_number
+
+        # shift the xor_seed left by the bits in IP.
+        xor_seed = xor_seed >> ip
+
+        # load a byte into IP
+        ip = r0[loop_counter]
+
+        # XOR the seed with r7
+        xor_seed = xor_seed ^ r7
+
+        # and then with IP
+        xor_seed = xor_seed ^ ip
+
+        #Now store the byte back
+        r1[loop_counter] = xor_seed & 0xFF
+
+        #increment the loop_counter
+        loop_counter = loop_counter + 1
+
+
+def encrypt_file(input, output_file, file_length):
+    input_file = bytearray(input.read())
+    block_size = 0x800
+    key_length = 0x18
+
+    uid_value = uuid.uuid4()
+    file_key = int(uid_value.hex[0:8], 16)
+
+    xor_crc = 0xef3d4323;
+
+    # the input file is exepcted to be in chunks of 0x800
+    # so round the size
+    while len(input_file) % block_size != 0:
+        input_file.extend(b'0x0')
+
+    # write the file header
+    output_file.write(struct.pack(">I", 0x443D2D3F))
+    # encrypt the contents using a known file header key
+
+    # write the file_key
+    output_file.write(struct.pack("<I", file_key))
+
+    #TODO - how to enforce that the firmware aligns to block boundaries?
+    block_count = int(len(input_file) / block_size)
+    print("Block Count is ", block_count)
+    for block_number in range(0, block_count):
+        block_offset = (block_number * block_size)
+        block_end = block_offset + block_size
+        block_array = bytearray(input_file[block_offset: block_end])
+        xor_block(block_array, block_array, block_number, block_size, file_key)
+        for n in range (0, block_size):
+            input_file[block_offset + n] = block_array[n]
+
+        # update the expected CRC value.
+        xor_crc = calculate_crc(block_array, xor_crc)
+
+    # write CRC
+    output_file.write(struct.pack("<I", xor_crc))
+
+    # finally, append the encrypted results.
+    output_file.write(input_file)
+    return
+
+if len(sys.argv) == 1:
+    print("Usage: chitu_crypt [firmware.bin]")
+    exit(1)
+
+fw = sys.argv[-1]
+
+if not os.path.isfile(fw):
+    print("Usage: chitu_crypt [firmware.bin]")
+    print("Firmware file", fw, "does not exist")
+    exit(1)
+
+firmware = open(fw, "rb")
+update = open('./update.cbd', "wb")
+length = os.path.getsize(fw)
+
+encrypt_file(firmware, update, length)
+
+firmware.close()
+update.close()
+
+print("Encryption complete. Firmware is written to update.cbd.")