CTB file format: encrypted CTB

Newer printers take a second CTB layout with the magic number 0x12FD0107 (07 01 FD 12), still with the extension .ctb. Its settings are encrypted with AES, and the file ends with an encrypted signature that printers check. The key and initialisation vector are not published by CBD-Tech; they were recovered by reverse engineering and are built into UVtools (CTBEncryptedFile.cs), which this page follows. They are not reproduced here. All numbers are little-endian.

Order of blocks

File header (48 bytes)
Settings, 288 bytes, AES-256 in CBC mode without padding
Large and small previews, as in the older layout
Machine name, copyright notice (320 bytes), then resin parameters (version 5)
Layer pointer table
For each layer: an 88-byte layer record, then its image data
In version 5, 8 bytes of unknown purpose
Signature, 32 bytes

File header

Offset	Size	Type	Name	Meaning
0	4	uint32	Magic	0x12FD0107
4	4	uint32	SettingsSize	288
8	4	uint32	SettingsOffset	48
12	4	uint32	Unknown	0
16	4	uint32	Version	4 or 5
20	4	uint32	SignatureSize	32
24	4	uint32	SignatureOffset	Offset of the signature at the end
28	4	uint32	Unknown	0
32	2	uint16	Unknown	1
34	2	uint16	Unknown	1
36	4	uint32	Unknown	0
40	4	uint32	Unknown	42 (0x2A)
44	4	uint32	Unknown	0 or 1

Settings (after decryption)

Offset	Size	Type	Name	Meaning
0	8	uint64	ChecksumValue	Value whose hash forms the signature (UVtools writes 0xCAFEBABE)
8	4	uint32	LayerPointersOffset	Offset of the layer pointer table
12	4	float	DisplayWidth	Screen width, mm
16	4	float	DisplayHeight	Screen height, mm
20	4	float	MachineZ	Build height, mm
24	8	uint32 × 2	Unknown
32	4	float	TotalHeight	Model height, mm
36	4	float	LayerHeight	mm
40	4	float	ExposureTime	Normal layers, s
44	4	float	BottomExposureTime	Bottom layers, s
48	4	float	LightOffDelay	s
52	4	uint32	BottomLayerCount
56	4	uint32	ResolutionX	pixels
60	4	uint32	ResolutionY	pixels
64	4	uint32	LayerCount
68	4	uint32	LargePreviewOffset
72	4	uint32	SmallPreviewOffset
76	4	uint32	PrintTime	s
80	4	uint32	ProjectorType	0 normal, 1 mirrored
84	4	float	BottomLiftHeight	mm
88	4	float	BottomLiftSpeed	mm/min
92	4	float	LiftHeight	mm
96	4	float	LiftSpeed	mm/min
100	4	float	RetractSpeed	mm/min
104	4	float	MaterialMilliliters	ml
108	4	float	MaterialGrams	g
112	4	float	MaterialCost
116	4	float	BottomLightOffDelay	s
120	4	uint32	Unknown	1
124	2	uint16	LightPWM	0 to 255
126	2	uint16	BottomLightPWM	0 to 255
128	4	uint32	LayerXorKey	Seed for the layer XOR, as in the older layout; 0 for none
132	4	float	BottomLiftHeight2	mm
136	4	float	BottomLiftSpeed2	mm/min
140	4	float	LiftHeight2	mm
144	4	float	LiftSpeed2	mm/min
148	4	float	RetractHeight2	mm
152	4	float	RetractSpeed2	mm/min
156	4	float	RestTimeAfterLift	s
160	4	uint32	MachineNameOffset
164	4	uint32	MachineNameSize
168	1	uint8	AntiAliasFlag	7 without, 15 with antialiasing
169	2	uint16	Padding
171	1	uint8	PerLayerSettings	0 not allowed, 0x40 to 0x50 allowed
172	4	uint32	ModifiedMinutes	Minutes since 1970 UTC
176	4	uint32	AntiAliasLevel	1 or 8
180	4	float	RestTimeAfterRetract	s
184	4	float	RestTimeAfterLift2	s
188	4	uint32	TransitionLayerCount
192	4	float	BottomRetractSpeed	mm/min
196	4	float	BottomRetractSpeed2	mm/min
200	16	mixed	Unknown	Padding, 4.0, padding, 4.0 (as in version 4 parameters)
216	4	float	RestTimeAfterRetract2	s
220	4	float	RestTimeAfterLift3	s
224	4	float	RestTimeBeforeLift	s
228	4	float	BottomRetractHeight2	mm
232	12	uint32 × 3	Unknown	The last usually 4
244	4	uint32	LastLayerIndex	LayerCount − 1
248	16	uint32 × 4	Padding
264	4	uint32	DisclaimerOffset
268	4	uint32	DisclaimerSize	320
272	4	uint32	Padding
276	4	uint32	ResinParametersOffset	Resin parameters, laid out as in the older layout
280	8	uint32 × 2	Padding

Layer pointers (16 bytes each)

Offset	Size	Type	Name	Meaning
0	4	uint32	LayerOffset	Offset of the layer record within its 4 GiB page
4	4	uint32	PageNumber	Page; real offset is PageNumber × 2³² + LayerOffset
8	4	uint32	LayerTableSize	88
12	4	uint32	Padding	0

Layer record (88 bytes)

Offset	Size	Type	Name	Meaning
0	4	uint32	TableSize	88
4	4	float	PositionZ	mm
8	4	float	ExposureTime	s
12	4	float	LightOffDelay	s
16	4	uint32	LayerDataOffset	Offset of the image data
20	4	uint32	PageNumber	Its 4 GiB page
24	4	uint32	DataLength	Length of the image data
28	4	uint32	Unknown
32	4	uint32	EncryptedDataOffset	Start, within the image data, of a part that is also AES-encrypted
36	4	uint32	EncryptedDataLength	Length of that part; 0 if none
40	4	float	LiftHeight	mm
44	4	float	LiftSpeed	mm/min
48	4	float	LiftHeight2	mm
52	4	float	LiftSpeed2	mm/min
56	4	float	RetractSpeed	mm/min
60	4	float	RetractHeight2	mm
64	4	float	RetractSpeed2	mm/min
68	4	float	RestTimeBeforeLift	s
72	4	float	RestTimeAfterLift	s
76	4	float	RestTimeAfterRetract	s
80	4	float	LightPWM	0 to 255
84	4	uint32	Unknown

The image data uses the CTB 7-bit run-length code (Image encoding). To read it, first AES-decrypt the part given by EncryptedDataOffset and EncryptedDataLength, if any, then undo the XOR with LayerXorKey and the layer number. Decoded black runs may run past the end of the image as padding.

Signature

The last 32 bytes, at SignatureOffset: the SHA-256 hash of the settings’ 8-byte ChecksumValue, encrypted with the same AES key and initialisation vector. A reader can check it by recomputing the hash.