National ID numbers (or similar personal identification numbers) usually have a unique structure and generation algorithm to ensure the uniqueness and validity of each number. The following are some specific examples of national ID numbers and their related algorithms: --- ### **1. Chinese Resident ID Number** **Structure:** - **Total length**: 18 digits. - **Components**: - **First 6 digits**: Address code, indicating the province, city, and county of the household registration place. - **Middle 8 digits**: Date of birth, in the format of YYYYMMDD. - **Last 3 digits**: Sequential code, where the 17th digit (the second to last digit) indicates gender (odd numbers are male, even numbers are female). - **18th digit**: Check code, calculated based on the first 17 digits through a specific algorithm, which can be a number 0-9 or the letter X. **Checksum algorithm (ISO 7064:1983.MOD 11-2):** 1. **Weight distribution**: Multiply each digit (from left to right) by the corresponding weight coefficient, and the weight coefficients are: 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2. 2. **Summation**: Add all the products. 3. **Modulus**: Divide the sum by 11 and take the remainder. 4. **Checksum determination**: Determine the checksum based on the correspondence between the remainders: - Remainder → Checksum: 0→1, 1→0, 2→X, 3→9, 4→8, 5→7, 6→6, 7→5, 8→4, 9→3, 10→2. **Example** (not a real number, just for illustration): ``` 11010519491231002X ``` --- ### **2. US Social Security Number (SSN)** **Structure:** - **Total length**: 9 digits. - **Format**: AAA-GG-SSSS - **AAA**: Area number, originally representing the region where the number was issued. - **GG**: Group number, indicating a group within a specific region. - **SSSS**: Sequential number, an individual unique number. **Generation rules:** - The number combination follows specific allocation rules to avoid using some specific number combinations (such as all zeros, 666, etc.). - In recent years, the allocation of SSN has shifted to randomization to improve security and expand the number pool. **Note**: SSN is highly sensitive personal information and should be handled and protected with care. --- ### **3. Canadian Social Insurance Number (SIN)** **Structure:** - **Total length**: 9 digits. - **Format**: ###-###-### (e.g., 123-456-789). **Checksum algorithm (Luhn algorithm):** 1. **Steps**: - Number the first digit from right to left. - Double all even-numbered digits (second, fourth, sixth, eighth). - If the result is greater than 9, subtract 9. - Add all digits together. 2. **Validity check**: The sum must be a multiple of 10. **Example** (not a real number, just for illustration): ``` 046 454 286 ``` --- ### **4. German ID card number (Personalausweisnummer)** **Structure:** - **Total length**: 9 characters, including letters and numbers. - **Components**: - **First letter**: Usually indicates the first letter of a surname. - **Middle characters**: A combination of letters and numbers that encodes personal information. - **Last character**: Check digit, used to verify the validity of the number. **Checksum algorithm**: - Use a weighted method to calculate the checksum, often using a modulus algorithm (such as modulo 10 or modulo 11) to ensure the correctness of the number. **Example** (not a real number, just for illustration): ``` C01X00T47 ``` --- ### **5. Swiss ID number (AHV number)** **Structure:** - **Total length**: 13 digits. - **Format**: 756.XXXX.XXXX.XX - **First 3 digits**: country code (756 for Switzerland). - **Last 10 digits**: personal unique number. **Checksum algorithm (modulo 10 incremental algorithm)**: 1. **Steps**: - Remove all non-numeric characters. - Weight each digit from right to left, with the weights being 1, 3, and so on. - Calculate the sum. 2. **Checksum**: The sum must be a multiple of 10. **Example** (not a real number, just for illustration): ``` 756.1234.5678.95 ``` --- ### **6. Australian Tax File Number (TFN)** **Structure:** - **Total length**: 9 digits. **Verification algorithm**: - Use the modulo 10 algorithm for simple verification. - Multiply each digit by the corresponding weight, which is usually 1 and increases from left to right. - The sum is divided by 10, and the remainder is 0 to be valid. **Example** (not a real number, just for illustration): ``` 123 456 789 ``` --- ### **Introduction to common verification algorithms** **1. Luhn algorithm (Mod 10 algorithm)**: - **Purpose**: Widely used in credit card numbers, Canadian SIN, etc. - **Principle**: - From right to left, multiply every other digit by 2. - If the result is greater than 9, subtract 9. - Sum all digits. - The sum must be a multiple of 10. **2. Modulo 11 algorithm**: - **Purpose**: Such as the calculation of the check digit of the Chinese ID card. - **Principle**: - Multiply each digit by the corresponding weight. - Take the modulo 11 after summing. - Determine the check digit based on the remainder. **3. Custom weighted algorithm**: - Different countries may use different weight allocation and calculation methods to ensure the uniqueness and anti-counterfeiting of the number. --- ### **Note** - **Privacy protection**: The ID card number is sensitive personal information. Do not disclose or use other people's numbers without permission. - **Legal use**: Make sure to use the ID card number in legal and authorized circumstances, such as identity verification, legal document filling, etc. - **Fraud prevention**: Understanding the structure of ID card numbers in different countries can help identify and prevent identity fraud. If you have a deeper interest in the ID card number system of a particular country, it is recommended to refer to the official documents released by the government or relevant agencies of that country to obtain the most accurate and detailed information.