选出入下面一段英语中______内的正确答案。 Public Key Infrastructure (PKI) service providers offer organizations fully integrated PKI-managed services designed to secure Intranet, Extranet, Virtual Private Network (VPN), and e-commerce applications. PKI solutions can enable a number of security services, including strong authentication and non-repudiation oftransaction. eToken enables the users of PKI systems to generate and store (1) and digital certifications inside the token, creating a secure environment and allowing full portability and maximum ease of use. eToken Pro can also perfonn sensitive on-chip (2) operations, ensuring that users' keys are never exposed to PC environment, eToken eliminates the need to store (3) and keys on a hard disk or browser file, or to transmit them across the Internet/Extranet, assuring peace-of-mind and confidence during online communications. A digital signature is created using the private key of an individual to ensure the validity of his request. This technology can be used to guarantee (4) of various transactions. The strength of either the authentication level or the digital signature relies on the level of protection offered to the private key. eToken PRO offers the maximum level of security, since it enables the use of the private key for signing and authenticating inside the eToken. The most secure use of authentication involves enclosing at least one certificate with every signed message. The message (5) verifies the certificate using the CA's public key. If the sender's public key is legitimate, the recipient verifies the message's signature. Digital signatures created with a private key are verified with the digital certificate containing the public key.