A.
Social Security Number(SSN), like the resident registration number in Korea, is the most commonly used method for administrative purposes required by all U.S administrative agencies.
It serves as a basic code and is necessary for opening a bank account, obtaining a driver's license, renting an apartment and etc.
In principle, SSN is issued for ONLY foreigners who hold green cards(entitled to work in the U.S) or any equivalent visas that allow them to work lawfully in the U.S.
To apply for SSN, visit the Social Security Office near your residence, fill out the application form
(Form SS-5) and submit it for further qualification process.
*NOTE: You must carry your passport and relevant documents proving your employment entitlement or qualification when you visit the office for the application.
Individual Taxpayer Identification Number(ITTN) is a tax processing number issued by the IRS to individuals. It is not replaceable SSN completely, however, it is used to enable individuals who do not have a SSN to file tax returns and comply with federal and state tax laws.