We developed security function modules based DICOM standard, including Secure Connection of TLS, Digital Signature, and Media Security of CMS. Using DICOM standard security functions, medical equipment, modality, and PACS software are able to communicate and exchange information safely without sacrifice for the compatibility. TLS enables secure connection between modality. Digital Signature guarantees data integrity and authentication based on PKI technology. Lastly, CMS algorithm provides how to encrypt DICOM File based on Media Storage Security. Signed and encrypted images are only to be decrypted by patient or who has authority, and it is to be proved that those images are not changed.