Fear of security breaches has been a major reason for the business world's reluctance to embrace the Internet as a viable means of communication. A widely adopted solution consists of physically separating private networks from the rest of Internet using firewalls. This paper discusses the current cryptographic security measures available for the Internet infrastructure as an alternative to physical segregation. First the IPsec architecture including security protocols in the Internet Layer and the related key management proposals are introduced. The transport layer security protocol and security issues in the network control and management are then presented. The paper is addressed to readers with a basic understanding of common security mechanisms including encryption, authentication and key exchange techniques.