Social security numbers are usually issued by national or regional social security agencies to identify an individual's identity and social security rights. The social security number generation rules of different countries may be different. The following are some common social security number structures and generation rules: ### 1. **US Social Security Number (SSN)** - **Structure**: The format is XXX-XX-XXXX - First three digits (XXX): Geographic area code - Middle two digits (XX): Group number - Last four digits (XXXX): Serial number - **Example**: 123-45-6789 ### 2. **China Social Security Number (Social Security Number)** - **Structure**: The format is 18 digits. - First 6 digits: address code (usually the administrative division code of the place of residence) - Middle 8 digits: personal serial number - Last 4 digits: check code (generated by a specific algorithm) - **Example**: 410100200001011234 (where 410100 is the address code, and the following part is the personal serial number and check code) ### 3. **Canadian Social Insurance Number (SIN)** - **Structure**: The format is XXX-XXX-XXX - The entire number is only 9 digits - **Example**: 123-456-789 ### 4. **UK National Insurance Number (NIN)** - **Structure**: The format is AB123456C - The first two letters: distinguish the individual type - The next six digits: serial number - The last letter: check letter - **Example**: AB123456C ### 5. **Australian Tax File Number (TFN)** - **Structure**: The format is 9 digits - **Example**: 123 456 789 ### Summary The structure of social security numbers is generally designed to take into account a variety of functions, including unique personal identity, identification of regions, and other necessary information. Although the specific rules vary from country to country, most social security numbers contain some form of geocoding or identity coding to ensure accuracy and prevent forgery. When using social security numbers, pay special attention to privacy and security, as these numbers are often closely related to an individual's financial and social security rights.