National identification number

Many countries issued such numbers for a singular purpose, but over time, they become a de facto national identification number. For example, the United States developed its Social Security number (SSN) system as a means of organizing disbursing of Social Security benefits. However, due to function creep, the number has become used for other purposes to the point where it is almost essential to have one to, among other things, open a bank account, obtain a credit card, or drive a car. Although some countries are required to collect Taxpayer Identification Number (TIN) information for overseas payment procedures, some countries, like the US, are not required to collect other nations' TIN if other requirements are met, such as date of birth. Authorities use databases and they need a unique identifier in order to be that data actually refer to the searched person. In countries where there is no established nationwide number, authorities need to create their own number for each person, though there is a risk of mismatching people.

Question: is it legal to use a social security number for identification
Answer: yes