# Analysis of Usability for the Dice CAPTCHA

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## Abstract

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## 1. Introduction

- A traditional statistical analysis as in [2] makes preliminary assumptions on the data. By contrast, the association rule mining does not need any initial assumption on the data, and is able to capture dependences of multiple user’s factors on the Dice CAPTCHA solution time.
- The set of the adopted user’s features is different from the set in [2]. It includes age, education level, Internet use, device type on which Dice CAPTCHA is solved and number of attempts for obtaining a correct solution. Gender is omitted since it has no influence in both association rule mining and artificial neural network analysis.

## 2. Related Work

## 3. The Dice CAPTCHA

## 4. Materials and Methods

#### 4.1. Participants

#### 4.2. Materials

#### 4.3. Methods

#### 4.3.1. Modeling Features Dependence by Association Rule Mining

- support
- confidence
- lift
- conviction

- FP-tree creation
- Extraction of the frequent itemsets by FP-tree traversal

#### 4.3.2. Modeling Features Dependence by Artificial Neural Network

## 5. Results

#### 5.1. Association Rule Mining Results

#### 5.2. Artificial Neural Network Results

## 6. Discussion

## 7. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**Distribution of: (

**a**) users’ age; (

**b**) Internet experience in number of years; and (

**c**) daily Internet usage in number of hours.

**Figure 5.**Scatter plot of the ARs given: (i) support; (ii) confidence; and (iii) lift, for Dice 1 and 2. Each coloured point represents an AR identified by its numerical ID (see Table 1 and Table 2). The position $x-y$ of each point depends on the support and confidence values of the corresponding AR. The colour of each point represents the lift value of the corresponding AR.

**Figure 7.**Pearson’s correlation coefficient R between the target and predicted solution time for one training, validation, and test part of the Dice 1 dataset and for the whole dataset varying the number of neurons (${N}_{h}$) in the hidden layer of the ANN model.

**Figure 8.**Pearson’s correlation coefficient R between the target and predicted solution time for one training, validation, and test part of the Dice 2 dataset and for the whole dataset varying the number of neurons (${N}_{h}$) in the hidden layer of the ANN model.

**Figure 9.**(

**a**) Histogram of the error (target—predicted solution time) for one training, validation, and test part of the Dice 1 dataset (${N}_{h}$ = 45); (

**b**) trend of the target vs. predicted solution times for the Dice 1 dataset; (

**c**) histogram of the error (target—predicted solution time) for one training, validation, and test part of the Dice 2 dataset (${N}_{h}$ = 20); and (

**d**) trend of the target vs. predicted solution times for the Dice 2 dataset.

**Figure 11.**Regression results (target vs. predicted solution time) for one training, validation, test part of the Dice 1 dataset and for the whole dataset (${N}_{h}$ = 45).

**Figure 12.**Regression results (target vs. predicted solution time) for one training, validation, test part of the Dice 2 dataset and for the whole dataset (${N}_{h}$ = 20).

**Table 1.**The set of the extracted association rules for Dice 1 CAPTCHA. The number of attempts in the consequent is 1 for all ARs (consequently, it is omitted).

Id. | Ant. | Cons. | S | C | L | $\mathit{C}\mathit{v}$ |
---|---|---|---|---|---|---|

1 | > 35, Tablet, High Int. experience | Interm. | 0.06 | 0.44 | 1.99 | 1.40 |

2 | Middle Int. experience | Quick | 0.24 | 0.45 | 1.34 | 1.21 |

3 | Middle Int. experience, Middle Int. daily usage | Quick | 0.13 | 0.52 | 1.55 | 1.39 |

4 | < 35 | Quick | 0.11 | 0.44 | 1.31 | 1.19 |

5 | Middle Int. experience, < 35 | Quick | 0.08 | 0.53 | 1.60 | 1.43 |

6 | Tablet, < 35 | Quick | 0.08 | 0.42 | 1.26 | 1.15 |

7 | > 35, Middle Int. experience | Quick | 0.17 | 0.42 | 1.25 | 1.14 |

8 | Middle Int. experience, Low Int. daily usage | Quick | 0.09 | 0.45 | 1.34 | 1.21 |

9 | > 35, Middle Int. experience, Low Int. daily usage | Quick | 0.06 | 0.43 | 1.29 | 1.17 |

10 | > 35, Middle Int. experience, Middle Int. daily usage | Quick | 0.10 | 0.49 | 1.45 | 1.30 |

11 | Laptop | Quick | 0.20 | 0.40 | 1.20 | 1.11 |

12 | Middle Int. experience, Laptop | Quick | 0.17 | 0.51 | 1.54 | 1.37 |

13 | > 35, Middle Int. experience, Laptop | Quick | 0.14 | 0.48 | 1.44 | 1.28 |

14 | Middle Int. experience, Laptop, Low Int. daily usage | Quick | 0.06 | 0.50 | 1.49 | 1.33 |

15 | > 35, Middle Int. experience, Laptop, Low Int. daily usage | Quick | 0.05 | 0.46 | 1.37 | 1.23 |

16 | > 35, Laptop | Very quick | 0.18 | 0.42 | 1.94 | 1.36 |

17 | > 35, Laptop, Low Int. daily usage | Very quick | 0.08 | 0.40 | 1.83 | 1.30 |

18 | > 35, Middle Int. experience, Laptop, Low Int. daily usage | Very quick | 0.05 | 0.42 | 1.91 | 1.34 |

19 | Laptop, Middle Int. daily usage | Quick | 0.10 | 0.45 | 1.36 | 1.22 |

20 | Middle Int. experience, Laptop, Middle Int. daily usage | Quick | 0.10 | 0.58 | 1.72 | 1.57 |

21 | Laptop, High Int. experience | Very quick | 0.08 | 0.64 | 2.93 | 2.17 |

22 | > 35, Laptop, High Int. experience | Very quick | 0.07 | 0.67 | 3.05 | 2.34 |

23 | > 35, Laptop, Middle Int. daily usage | Quick | 0.09 | 0.47 | 1.41 | 1.26 |

24 | > 35, Middle Int. experience, Laptop, Middle Int. daily usage | Quick | 0.09 | 0.57 | 1.69 | 1.53 |

**Table 2.**The set of the extracted association rules for Dice 2 CAPTCHA. The number of attempts in the consequent is 1 for all ARs (consequently, it is omitted).

Id. | Ant. | Cons. | S | C | L | $\mathit{C}\mathit{v}$ |
---|---|---|---|---|---|---|

1 | Middle Int. experience | Quick | 0.22 | 0.41 | 1.11 | 1.07 |

2 | Middle Int. experience, Tablet | Quick | 0.09 | 0.44 | 1.18 | 1.12 |

3 | Tablet, Middle Int. daily usage | Quick | 0.07 | 0.41 | 1.11 | 1.07 |

4 | < 35 | Quick | 0.11 | 0.44 | 1.19 | 1.12 |

5 | Middle Int. experience, < 35 | Quick | 0.06 | 0.46 | 1.25 | 1.17 |

6 | Tablet, < 35 | Quick | 0.08 | 0.42 | 1.14 | 1.09 |

7 | > 35 | Very quick | 0.32 | 0.43 | 1.16 | 1.10 |

8 | > 35, Low Int. daily usage | Very quick | 0.15 | 0.45 | 1.21 | 1.14 |

9 | > 35, High Int. experience | Very quick | 0.10 | 0.42 | 1.11 | 1.07 |

10 | Low Int. daily usage, High Int. experience | Very quick | 0.05 | 0.40 | 1.06 | 1.04 |

11 | > 35, Middle Int. experience, Middle Int. daily usage | Quick | 0.08 | 0.41 | 1.11 | 1.07 |

12 | > 35, Tablet, Middle Int. daily usage | Quick | 0.05 | 0.42 | 1.12 | 1.08 |

13 | Middle Int. experience | Very quick | 0.22 | 0.41 | 1.09 | 1.06 |

14 | Middle Int. daily usage | Very quick | 0.16 | 0.41 | 1.09 | 1.06 |

15 | Middle Int. experience, Middle Int. daily usage | Very quick | 0.11 | 0.44 | 1.16 | 1.11 |

16 | > 35, Middle Int. experience | Very quick | 0.20 | 0.51 | 1.35 | 1.26 |

17 | Middle Int. experience, Low Int. daily usage | Very quick | 0.10 | 0.47 | 1.26 | 1.19 |

18 | > 35, Middle Int. experience, Low Int. daily usage | Very quick | 0.10 | 0.63 | 1.69 | 1.70 |

19 | High Int. daily usage | Quick | 0.08 | 0.42 | 1.14 | 1.09 |

20 | Middle Int. experience, High Int. daily usage | Quick | 0.05 | 0.58 | 1.56 | 1.49 |

21 | Tablet, High Int. daily usage | Quick | 0.06 | 0.43 | 1.16 | 1.10 |

22 | > 35, Middle Int. daily usage | Very quick | 0.14 | 0.45 | 1.20 | 1.14 |

23 | > 35, Middle Int. experience, Middle Int. daily usage | Very quick | 0.09 | 0.46 | 1.23 | 1.16 |

24 | Laptop | Very quick | 0.27 | 0.55 | 1.45 | 1.38 |

25 | Middle Int. experience, Laptop | Very quick | 0.18 | 0.54 | 1.45 | 1.37 |

26 | > 35, Laptop | Very quick | 0.26 | 0.60 | 1.60 | 1.56 |

27 | > 35, Middle Int. experience, Laptop | Very quick | 0.17 | 0.59 | 1.56 | 1.51 |

28 | Laptop, Low Int. daily usage | Very quick | 0.12 | 0.53 | 1.42 | 1.34 |

29 | > 35, Laptop, Low Int. daily usage | Very quick | 0.12 | 0.57 | 1.53 | 1.47 |

30 | Middle Int. experience, Laptop, Low Int. daily usage | Very quick | 0.08 | 0.58 | 1.53 | 1.47 |

31 | > 35, Middle Int. experience, Laptop, Low Int. daily usage | Very quick | 0.08 | 0.62 | 1.66 | 1.66 |

32 | Laptop, Middle Int. daily usage | Very quick | 0.13 | 0.57 | 1.51 | 1.44 |

33 | > 35, Laptop, Middle Int. daily usage | Very quick | 0.12 | 0.63 | 1.68 | 1.69 |

34 | Middle Int. experience, Laptop, Middle Int. daily usage | Very quick | 0.09 | 0.54 | 1.45 | 1.37 |

35 | > 35, Middle Int. experience, Laptop, Middle Int. daily usage | Very quick | 0.09 | 0.57 | 1.51 | 1.44 |

36 | Laptop, High Int. experience | Very quick | 0.08 | 0.60 | 1.60 | 1.56 |

37 | > 35, Laptop, High Int. experience | Very quick | 0.08 | 0.71 | 1.90 | 2.18 |

**Table 3.**Pearson’s correlation coefficient for the whole dataset from Dice 1 and Dice 2. The best values are marked.

R | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 |

Dice 1 | 0.733 | 0.675 | 0.728 | 0.724 | 0.777 | 0.553 | 0.723 | 0.774 | 0.789 | 0.553 |

Dice 2 | 0.796 | 0.752 | 0.657 | 0.803 | 0.795 | 0.560 | 0.300 | 0.569 | 0.321 | 0.726 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Amelio, A.; Draganov, I.R.; Janković, R.; Tanikić, D. Analysis of Usability for the Dice CAPTCHA. *Information* **2019**, *10*, 221.
https://doi.org/10.3390/info10070221

**AMA Style**

Amelio A, Draganov IR, Janković R, Tanikić D. Analysis of Usability for the Dice CAPTCHA. *Information*. 2019; 10(7):221.
https://doi.org/10.3390/info10070221

**Chicago/Turabian Style**

Amelio, Alessia, Ivo Rumenov Draganov, Radmila Janković, and Dejan Tanikić. 2019. "Analysis of Usability for the Dice CAPTCHA" *Information* 10, no. 7: 221.
https://doi.org/10.3390/info10070221