Latest revision as of 02:01, 30 January 2014

Overview

Command 0x40 is a very versatile command that can make the Cricut move or cut to an absolute position. Four of them can also make the Cricut cut a curve. These commands are encrypted and each type of move/cut seems to use a different key.

Units

Unit appears to use fixed point units with between 400 and 405 ticks per inch. Resolution may be 404 x 400 dpi (roller x stylus).

Encryption

• XXTEA. Reference implementation from wikipedia works fine.
• Each command has its own keyset( TEAs require 4x32bit word keys )
• A separate key may be used to sign information headed back to the PC
• There is one word of random noise in the encrypted data, this makes sure that it is unlikely two commands sent to the same position will have the same *output to the cricut. The random noise must be between 10000 and 32767.
• It has become apparent that the command is not embedded in the ciphertext, but instead the command is found by decrypting the 12 byte sentence, with every key, until a result is found with valid arguments( noise > 10000, x < 10000, y < 10000 )
  • The x and y constraint combined with the 404 steps per inch would create a maximum working surface of 24.75"x24.75". In other words no banners larger than 24". Although modified or custom firmware could change this constraint.

Keys Used

• 0 - Cut Line
• 1 - Cut Curve (one Curve is made of 4 of these)
• 2 - Move to these coordinates (X,Y)
• 3 - Lower stylus and cut line to these coordinates (X,Y)
• 4 - Raise stylus and cut line
• 5 - Lower stylus and cut curve (4-command set)
• 6 - Raise stylus and cut curve (4-command set)
• 7 - Used for communicating back to PC

Grab the keys here.[keys.txt]

Commands 3-6 appear to be used to ensure a smoother cut. Using commands 3/4 or 5/6 for the first and last line/curve of a path, with the final segment being a duplicate of the first, a complete cut should leave no attached corners.