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Sometimes I buy in a online shop video files (mp4). The online shop forces it's customers to buy with verified real name. In case of leaking his content the shop can identity who leaked it. I don't know how he does it technically, I guess some sort of Digital watermarking.

Now I compared the SHA Checksum of a video I bought and one leaked on a forum. The same checksum.

shasum customer_a.mp4 customer_b.mp4   
195bb682e5cb4fzod75923321d0e9c82316b6952  customer_a.mp4                  
195bb682e5cb4fzod75923321d0e9c82316b6952  customer_b.mp4       

file customer_a.mp4 
customer_a.mp4: ISO Media, Apple iTunes Video (.M4V) Video

mediainfo customer_a.mp4 
General
Complete name                            : customer_a.mp4
Format                                   : MPEG-4
Codec ID                                 : M4V  (M4V /mp42/isom)
File size                                : 907 MiB
Duration                                 : 21 min 14 s
Overall bit rate mode                    : Variable
Overall bit rate                         : 4 193 kb/s
Encoded date                             : UTC 2017-07-31 14:29:26
Tagged date                              : UTC 2017-07-31 14:29:26
©TIM                                     : 00:00:00:00
©TSC                                     : 25
©TSZ                                     : 1

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Main@L3.2
Format settings, CABAC                   : No
Format settings, RefFrames               : 2 frames
Format settings, GOP                     : M=1, N=33
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 21 min 14 s
Bit rate                                 : 3 995 kb/s
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 25.000 FPS
Standard                                 : PAL
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.173
Stream size                              : 865 MiB (95%)
Language                                 : English
Encoded date                             : UTC 2017-07-31 14:49:20
Tagged date                              : UTC 2017-07-31 14:49:20
Color range                              : Limited

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 21 min 14 s
Source duration                          : 21 min 14 s
Bit rate mode                            : Variable
Bit rate                                 : 192 kb/s
Maximum bit rate                         : 245 kb/s
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 41.0 MiB (5%)
Source stream size                       : 41.0 MiB (5%)
Language                                 : English
Encoded date                             : UTC 2017-07-31 14:49:20
Tagged date                              : UTC 2017-07-31 14:49:20

Does this mean if I share this video he can't trace me back? Are there other methods I am unaware?

3

Does this mean if I share this video he can't trace me back?

If the hashes are the same, then you can conclude that the files are identical.1

This implies that the file doesn't contain a watermark tied to your identity. However, there might be a watermark that associates it with the shop where you bought it.

1 Note that shasum defaults to SHA-1 which is broken. Hence, you should start using another algorithm, e.g. shasum -a 256 (or sha256sum, respectively). However, that doesn't mean that it's trivially feasible for the company to generate different videos that produce the same SHA-1 hash. You can safely assume this is not the case here.

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