A Document Signer Certificate (DSC) is a certificate issued by the Country Signing Certification Authority (CSCA). The Document Signer application uses the DSC to digitally sign the ePassport data on the chip. The chip of an ePassport also contains the public key portion of the DSC required to verify the digital signature on an ePassport. In contrast to CSCA certificates which remain relatively static due to the longer use period, a large number of DSC will be created over time. While there are no minimum or maximum use periods prescribed in Doc 9303, the DSC are changed regularly depending on the Certificate Policy of the issuing State (for example, a Certificate Policy may stipulate that the DS be changed every 3 months or after signing 150,000 travel documents, whichever is sooner). Border control in a receiving State validates the DSC associated with an ePassport against the CSCA certificate for the issuing State to confirm the document is authentic and has not been tampered with.