K Anonymity

Segments are fetched from the server using a k-anonymity system originally proposed by Girst and implemented by Zegnat and Joe-Dowd.

Every time you watch a video, it takes the videoID and hashes it, producing a value that looks like 5f6b0b4e201f2a7e66927abb5cadeec81624dcc8efe6644b78aa182213f653a2. Instead of sending the videoID to the server, it sends only the first 4 characters of that hash, 5f6b.

https://sponsor.ajay.app/api/skipSegments/5f6b?categories=["sponsor","intro","outro","selfpromo","music_offtopic","preview"]

The client then gets a list of possible videos that have that prefix. This list may or may not contain the videoID

Click to see the result

[
   {
      "videoID":"ifI_fwg55k8",
      "hash":"5f6b9697b907622242a43ac766a0735840efe62a93249dd00e4cd2bd3e29c6c2",
      "segments":[
         {
            "category":"intro",
            "segment":[
               0,
               2.811777
            ],
            "UUID":"1db91efbce60d754d1cc86687202701741c8f31ee239f75d88979e29ecd9be03",
            "videoDuration":1163
         },
         {
            "category":"intro",
            "segment":[
               24.182026,
               39.86125
            ],
            "UUID":"966d6ee4f37811e790bc902eff1650c912e6e148e85a150730c15a22bffa8878",
            "videoDuration":1163
         }
      ]
   },
   {
      "videoID":"rPA_nqPHjXo",
      "hash":"5f6b2a774993bd13c38ea79d53d341f9246e1fc564d2e33c08014262690746de",
      "segments":[
         {
            "category":"outro",
            "segment":[
               0,
               145
            ],
            "UUID":"5d5184386913bd10021f5bccff54c26441cc88479caf33c087710b12fcc887a7",
            "videoDuration":1828
         },
         {
            "category":"outro",
            "segment":[
               1705.593,
               1827.661
            ],
            "UUID":"1829807614e13b0cb81e8aa9ac9ed23892ce66dd300c64c40e2b4f77f5a14070",
            "videoDuration":1828
         }
      ]
   },
   {
      "videoID":"6qc2GsH_ii4",
      "hash":"5f6b3279fbf3a40cd1eefe71aa9e1812a3957b44d0d88f6f23b8bb7d8db857a0",
      "segments":[
         {
            "category":"intro",
            "segment":[
               0,
               27.439728
            ],
            "UUID":"9ee28368f6f450d14fd9cede79dcf6b6ceff04ddb7eb48ca6f12120e19304139",
            "videoDuration":1790
         }
      ]
   },
   {
      "videoID":"dQw4w9WgXcQ",
      "hash":"5f6b0b4e201f2a7e66927abb5cadeec81624dcc8efe6644b78aa182213f653a2",
      "segments":[
         
      ]
   },
   {
      "videoID":"auBq3fZ-WAM",
      "hash":"5f6b5627fa138974690be4333b8f53fb3e76e2dc70dd661e9d82c7c5854aaceb",
      "segments":[
         {
            "category":"intro",
            "segment":[
               0,
               6.9
            ],
            "UUID":"e0a750b81efc389b2a69f8a4a62926f4f8d2cb7acc37aff110b5b43370706b11",
            "videoDuration":0
         }
      ]
   },
   {
      "videoID":"YRQuvRjXXPc",
      "hash":"5f6b3d10cc6f79f099014ac4dc4aad4a43f648f25397a1a481ccae9a37cca644",
      "segments":[
         {
            "category":"intro",
            "segment":[
               0,
               12
            ],
            "UUID":"7b590105e87bfcecfb3c9524c7ec889bde92a1486b7fafd08309531bec408460",
            "videoDuration":0
         }
      ]
   },
   {
      "videoID":"5GKIUKsrnKo",
      "hash":"5f6bbb7cc756d761ab675469743142c0b27d0e1b2436309410201cc3c86ba2c9",
      "segments":[
         {
            "category":"intro",
            "segment":[
               0,
               4.177
            ],
            "UUID":"975f0840028e7ce21e9608a9dcc2a2a529a079b68eca636da87259d7e3cba80a",
            "videoDuration":0
         },
         {
            "category":"sponsor",
            "segment":[
               80.93964,
               145.15292
            ],
            "UUID":"6bb6d1cbf85c7fa65ad5c08acdceb6c4ebb7720f2f794e51e38caf20fad83853",
            "videoDuration":0
         }
      ]
   },
   {
      "videoID":"aQp-iM0bCs4",
      "hash":"5f6bcdd946838ebf572b0526cb29dc557918674e7ff650e33d8a78893f4aabb2",
      "segments":[
         {
            "category":"sponsor",
            "segment":[
               0,
               31.861
            ],
            "UUID":"b772d4b75ca73ce63940fa982d051c031964160941efd93bd6ed1bbe9327a46e",
            "videoDuration":361
         }
      ]
   },
   {
      "videoID":"thODYqd9G9U",
      "hash":"5f6bb87827fd5c93e44650defe57247c5965fac3c2d26068c3aae770436b83a7",
      "segments":[
         {
            "category":"sponsor",
            "segment":[
               0.332106,
               22.484015
            ],
            "UUID":"5f498eade41a1fbb46aee46d94fdc6fff5ad3b1d9f5046720c75ad6a28bdfd8b",
            "videoDuration":0
         }
      ]
   },
   {
      "videoID":"5t6saOlOTZE",
      "hash":"5f6bb71ba929d4395f0c25f964f010e103de517f3adb269b22d0cb939bd06550",
      "segments":[
         {
            "category":"sponsor",
            "segment":[
               171.933,
               255.06
            ],
            "UUID":"33ef5c921624914930ffb0b37e1182abe938f2ff44a7fdeeafd7e8e5ba6f608b",
            "videoDuration":0
         },
         {
            "category":"selfpromo",
            "segment":[
               438.051,
               476.568
            ],
            "UUID":"e0f8c2416494211200774f74dea45e0dcad62eead20217a7582fbb3ece395f3d",
            "videoDuration":0
         }
      ]
   },
   {
      "videoID":"HXzMwe8PZBA",
      "hash":"5f6b33fd117ef95e62f7fe07c9fa1a7667147994081a70cb933941a8622d589f",
      "segments":[
         {
            "category":"outro",
            "segment":[
               449.84006,
               459.581
            ],
            "UUID":"cbd9fd2701548277e43cbb83fc839b5679a525a30ee794282958ef3036a8741e",
            "videoDuration":460
         }
      ]
   }
]

The client then gets back these 11 videos (in this case) and checks to see if the video it is looking for is in the list. If it is not, it treats it as not found. Since the list may, or may not contain the video, this makes it even more secure than a 1 / 11 chance.

This system allows the client to be lightweight and always get the latest segments on every video while still ensuring the server cannot predict which videos they are watching.