Magic Lantern Firmware Wiki

Canon EOS DSLR .FIR fomat[]

v1.1. September 4th, 2010 by Arm.Indy,

based on a first version by Trammell Hudson

  • 550D/T2i update: the updater is now encrypted with AES like the payload, and new keys are used. The file format is the same.


The following fir file format is used by Canon It is used to update code and data of EOS DSLRs, since the 1D Mark III.

The vocabulary used in this document (I.E. updater and firmware) is as used by Canon in their code. The purpose of releasing information about this file format is to allow running your own code on your camera and nothing else.

Mainly a FIR (for firmware) file contains all needed to update the camera: code that is run (updater) on the camera to do the updates and the updates themselves (called firmware).

Previous FIR file format[]

  • 300D, 10D (fir v1)
  • 1D, 1Ds, 1D Mark II, 1Ds MarkII, 1D Mark II n (.bin)
  • 20D, 20Da, 350D. (fir v2)
  • 5D, 30D, 400D. (fir v3). See [400d file format], by ASalina (April 28th, 2008)
  • 40D, 50D, 450D, 500D, 1000D, 5D Mark II, WFT-E2, WFT-E3 (fir v4, DigicIII & Digic IV)
  • 1D Mark III, 1Ds Mark III, 7D, 1D Mark IV (fir v4, with hmac signature)
  • 550D (updater encrypted with AES, same format as 40D etc.)

Previous work[]


FIR file format[]

Offset Len Description
0x00 0x10

Model Id (5D Mark II=0x8000218, 7D=0x8000250). Filled with 0.

See Camera Model IDs from Phil Harvey ExifTool website:

0x10 0x10

Version (ASCII string). "1.1.0". filled with 0.

0x20 4 File checksum (literally the sum of all the bytes)
0x24 4 1st updater header offset (always 0xb0 or 0x100)
0x28 4 ciphered (xor) updater offset (always 0x120)
0x2c 4 Offset of second updater header, only with dual Digic models.

5D has 0xffffffff, 7D has 0x001c0970. Setting this to 0xFFFFFFF or any other value causes orange box on 7D. this value is noted 'updater2'

0x30 4 firmware header offset. this value is noted 'firmware'
0x34 4 3rd updater header offset on 1DX Mk II otherwise 0xffffffff
0x38 4 Length of FIR file in bytes
0x3c 4 0
0x40 4 sha1 seed value.
0x44 4 used for signature (always here, only verified by dual Digic Models, only tested on 7D)
0x5c 4 Flasher Header+Code length. Starts at 0xb0
0x64 4 firmware Header + firmware data section length. Starts from value at 0x30
0x68 20 flashers hmac-sha1 (hmac-sha1 is the final step)
0x88 20 firmware flasher hmac-sha1 (hmac-sha1 is the final step)
0xb0 0x70 updater1 header. Length of flasher program in bytes (orange box)
0xb4 4 Length of flasher program - 4
0xb8 4 MBZ
0xbc 4 IV for XOR decryptor. Used to compute initial offsets in 512/513 keys. (orange box)
0x70 0xb0-0x120 is not zero when AES encryption is used. Like payload + 0xc...
0x120 var encrypted 1st updater. Soldeersmurfje discovered how to decode it and the 512/513 bytes tables in dec 2007.
updater2 4 second updater header (only with dual digic models). model Id
updater2+0x10 4 version (ascii)
updater2+0x20 4 checksum. sum of bytes, but computed on cleartext version of the 2nd updater!
updater2+0x24 4 0xb0. relative offset, to updater header
updater2+0x28 4 0x120. relative offset, to ciphered updater
updater2+0x2c 12 12 bytes = 0xff
updater2+0x38 4 updater length (including header)
updater2+0xb0 4 updater length
updater2+0xbc 4 XOR deciphering seed
updater2+0x120 var updater2 xor ciphered
firmware 4 offset to decryption data = 0xc
firmware+4 4 offset to encrypted data = 0x7c. starts at 'firmware' offset
firmware+8 4 total firmware length (including header). starts at 'firmware' offset
firmware+0xc 4 firmware length (encrypted part). starts at 'firmware' offset
firmware+0x7c var encrypted firmware

Sample headers[]

produced using

  • 1D Mark IV 1.0.8

See also[]