Which of the following provides cryptographic security services for electronic messaging applications?

A.
POP3

B.
EFS

C.
S/MIME

D.
SMTP

Explanation:
S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of e-mail encapsulated in MIME. S/MIME provides the following cryptographic security services for electronic messaging applications: authentication, message integrity, non-repudiation of origin (using digital signatures), privacy, and data security {using encryption). Answer option A is incorrect. Post Office Protocol version 3 (POP3) is a protocol used to retrieve e-mails from a mail server. It is designed to work with other applications that provide theability to send e-mails. POP3 is mostly supported by the commercially available mail servers. It does not support retrieval of encrypted e-mails. POP3 uses port 110.

Answer option D is incorrect. Simple Mail Transfer Protocol (SMTP) is a protocol for sending e- mail messages between servers. E-mailing systems use this protocol to send mails over the Internet. SMTP works on the application layer of the TCP/IP or OSI reference model. The SMTP client typically initiates a Transmission Control Protocol (TCP) connection to the SMTP server on the well-known port designated for SMTP, port number 25. However, e-mail clients require POP or IMAP to retrieve mails from e-mail servers.

Answer option B is incorrect. The Encrypting File System (EFS) is a component of the NTFS file system that is used to encrypt files stored in the file system of Windows 2000, Windows XP Professional, and Windows Server 2003 computers. EFS uses advanced and standard cryptographic algorithms to enable transparent encryption and decryption of files. The encrypted data cannot be read by an individual or program without the appropriate cryptographic key.

Encrypted files can be protected even from those who have physical possession of the computer where the encrypted files are stored. Even authorized persons who are able to access the computer and its file system cannot view the data. EFS is the built-in file encryption tool for windows file systems.