Hands-On Machine Learning for Cybersecurity

Using the cosine similarity to quantify bad passwords

In this section, we will turn to some purely mathematical reasoning to judge password strength. We will use tools from scikit-learn to learn and understand password strength by comparing them to past passwords using vector similarities.

Cosine similarity is a quantitative measure [-1,1] of how similar two vectors are in a Vector Space. The closer they are to each other, the smaller the angle between them. The smaller the angle between them, the larger the cosine of that angle is; for example:

• If two vectors are opposites of each other, their angle is 180, and cos(0) = -1.
• If two vectors are the same, their angle is 0, and cos(0) = 1.
• If two vectors are perpendicular, their angle is 90, ...