mfa

The concatenation of the authentication device's serial number, a space, and the value that is displayed on your authentication device. The serial number is the number that uniquely identifies the MFA device. For physical MFA devices, this is the unique serial number that's provided with the device. For virtual MFA devices, the serial number is the device ARN. For more information, see Enabling versioning on buckets and Configuring MFA delete in the Amazon Simple Storage Service User Guide.