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Transaction authentication number
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<p>A transaction authentication number (TAN) is used by some <a href="/facts/Online_banking/lYdBsukr">online banking</a> services as a form of <i>single use</i> <a href="/facts/One-time_password/4u0a4vgk">one-time passwords</a> (OTPs) to authorize <a href="/facts/Financial_transaction/boHRc8mw">financial transactions</a>. TANs are a second layer of security above and beyond the traditional single-password <a href="/facts/Authentication_protocol/pcX97lnA">authentication</a>. </p><p>TANs provide additional security because they act as a form of <i>two-factor authentication</i> (2FA). If the physical document or token containing the TANs is stolen, it will be useless without the password. Conversely, if the login data are obtained, no transactions can be performed without a valid TAN. </p>