ArcBlock Technical Learning Series Presents an introduction to QRCodes. We scan QRCode for payment, links and basically everything. How do QRcodes work? Are QRcodes secure? Why can I put a logo in the middle of QRCode and it still works? In this talk, we will show you how the QRCode is being drawn. Also, we will talk about Reed-Solomon error correction inside QRCode that makes it fault tolerant. 二维码源于日本，如今世界各国都在使用。一张简单的二维码蕴藏了不简单的信息。二维码究竟是如何画出来的？二维码安全吗？为何在二维码中加个图标还能被扫出来？卫星通讯中用到的Reed-Solomon纠错码如何被用在了二维码中？本次讲座为您揭晓二维码的生成原理，听完保证可以get手绘二维码技能。 https://www.arcblock.io

1. QR Code
Brought to you by Boshan Sun
1

2. Why QR code? 2

3. Why QR code? 3

4. Why QR code? 4

5. Why QR code? 5

6. How QR code works?
.
"show me the money"
↓
+---+------------+---+
| | ## ## | |
+---+ # # # +---+
| # # # # |
| # # ## # |
| # # # # # # |
+---+ # ## # |
| | # # # # |
+--------------------+
↓
"show me the money"
6

7. Data structure
.
{{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0},
{0,0,0,0,0}}
7

8. QR code structure 8

9. Structure: nder patterns 9

10. Structure: seperators 10

11. Structure: alignment patterns 11

12. Structure: timing patterns 12

13. Structure: dark module 13

14. Structure: reserved format areas 14

15. Structure: reserved version areas 15

16. Structure: data & ecc 16

17. Structure: quite zone 17

18. Encoding mode
numeric 12345 9527
alphanumeric "hello world 123"
kanji "自動車車車"
byte "doughnut doughnut doughnut giraffe" "你好, 世界!”
18

19. Byte mode encoding
mode indicator 0100
count indicator 0001 0001
encoded data 0111 0011 ...
terminator 0000
padding byte 1110 1100 0001 0001
show me the money
0100 0001 0001 0111 0011 0110 1000 0110 1111 0111
0111 0010 0000 0110 1101 0110 0101 0010 0000 0111
0100 0110 1000 0110 0101 0010 0000 0110 1101 0110
1111 0110 1110 0110 0101 0111 1001 0000
19

20. Error correction coding
• Reed-Solomon
• Galois Field GF(256)
• Polynomial long division
20

21. Reed-Solomon 21

22. Galois Field 22

23. Polynomial long division
.
message polynomial
rs_ecc = --------------------
generator polynomial
0100 0001 0001 0111 0011 0110 1000 0110 1111 0111
0111 0010 0000 0110 1101 0110 0101 0010 0000 0111
0100 0110 1000 0110 0101 0010 0000 0110 1101 0110
1111 0110 1110 0110 0101 0111 1001 0000
65,24,54,134,247,114,6,214,82,7,70,134,82,6,214,246,230,87,144
--------------------------------------------------------------
0,87,229,146,149,238,102,21
87,3,122,77,183,109,202
0101 0111 0000 0011 0111 1010 0100 1101 1011 0111 0110 1101
1100 1010
23

24. Data + ecc
.
0100 0001 0001 0111 0011 0110 1000 0110 1111 0111
0111 0010 0000 0110 1101 0110 0101 0010 0000 0111
0100 0110 1000 0110 0101 0010 0000 0110 1101 0110
1111 0110 1110 0110 0101 0111 1001 0000 0101 0111
0000 0011 0111 1010 0100 1101 1011 0111 0110 1101
1100 1010
24

25. Matrix so far 25

26. Fill in the data 26

27. Data masking 27

28. Mask 0 28

29. Mask 1 29

30. Mask 2 30

31. Mask 3 31

32. Mask 4 32

33. Mask 5 33

34. Mask 6 34

35. Mask 7 35

36. Apply masks 36

37. Apply masks 37

38. Penalty rules 38

39. Rule 1 39

40. Rule 2 40

41. Rule 3 41

42. Rule 4 42

43. And the winnder is… 43

44. Mask 3 44

45. Format information 45

46. Format information 46

47. Format information 47

48. Almost done 48

49. Finished 49

50. Customize QR code 50

51. Customize QR code 51

52. Customize QR code 52

53. Customize QR code 53

54. Padding with 0 54

55. XOR the mask 55

56. XOR the mask 56

57. Draw the pattern bits 57

58. Some work 58

59. Some work 59

60. 60