Hackvent 2019: Day 5

Challenge

HV19.05 Santa Parcel Tracking

Introduction
To handle the huge load of parcels Santa introduced this year a parcel tracking system. He didn't like the black and white barcode, so he invented a more solemn barcode. Unfortunately the common barcode readers can't read it anymore, it only works with the pimped models santa owns. Can you read the barcode

Resources

Solution

Initially we try scanning the barcode as it looks like a Code 128 barcode. It works but gives us the string Not a solution which is unfortunately a dead end. After a lot of experimentation, we manually note down the hexadecimal values for each colour in sequence. We decided to use Photoshop's colour picker but in hindsight should have done this pragmatically using MATLAB.

This gives us the following list of 64 hex codes:

735058
745938
6c5059
6d4549
72314f
793346
735030
65515a
673850
7a3934
754c53
685438
654748
7a3056
615831
673039
6c4f7b
744f44
6c4a31
674a66
784966
7a4969
675563
6a5375
69486c
695174
76365f
763074
734d6f
73495f
615167
694933
653474
77535f
623961
74455f
754753
683450
613854
6c4e5f
715652
635633
6c5061
663664
713565
724772
634f7d
775853
664c31
713030
765639
655730
6e4a4f
67574d
78325a
653345
6b3230
6f3345
615333
6c524e
745546
793850
764236
654245

After more experimentation, we discover that the blue channel of each hex code is significant! We discard all data but the blue channel and run our sequence of hex codes through an online hex to ascii converter.

This gives us the following string which has our flag surrounded by what appears to be noise:

X8YIOF0ZP4S8HV19{D1fficult_to_g3t_a_SPT_R3ader}S1090OMZE0E3NFP6E

Flag:

HV19{D1fficult_to_g3t_a_SPT_R3ader}