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WAN potentially, The Internet is a public network and a WAN (Wide Area Network) is usually private, either a leased line or a virtual private network (VPN) over the Internet.
The main advantage of internal email is that it does not leave the organization's private network and thus is considered more secure. Internal email is often delivered more quickly as well because it stays in the private network.
More secure
The questions is not really which key is more secure - rather it is a question of "can you determine the private key if you know the public key?" Public and private keys are associated with asymmetric cryptography. They are generated as a pair. The security comes from the difficulty in determining the private key if you already know the public key and have some cyphertext that the private key has been applied to or encrypting text with the public key and determining what key would be required to decrypt it. Since each key can be used to decrypt cyphertext encrypted with the other key using the same algorithm, there is not inherent reason to think that one key is more secure than the other. In reality, one of the keys will be numerically a better starting point than the other when it comes to executing an attack on the encryption and deriving the other key. In practical terms, however, an attacker is always trying to start with the public key and discover the private key, without which messages encrypted with the public key cannot be decrypted (or without which the attacker cannot impersonate the holder of the private key).
well, public and private is more PUBLIC but you get better People skills when you homeschool :)
extranet
Not everybody chooses private banks. People prefer public sector banks over private sector. The only reason for choosing private banks is the salary. If salary in private and government banks is same, everybody will choose government jobs as the job is more secure.
Virtual Private Network Advantages :Users working at home can use the VPN connections to connect to their company's private network. Organizations can use VPN connection to establish connections with geographically separate offices using the public network like internet. Communication over VPN connection is more secure because VPN uses the following two protocols for data encryption: Point-to-Point Tunneling Protocol (PPTP) Layer Two Tunneling Protocol (L2TP) with Internet Protocol security (IPSec)
A good way to keep your private data secure is GnuPG or PGP, which are encryption suites (google them to get more info)
Ethernet is more "physically secure", in that it is sometimes more difficult to gain unauthorized access to a network, since you need to be in close physical proximity to a network cable. However, it does not require any form of cryptographic authentication to connect to a network, which can be optionally provided by wireless.
United Intranet is like a social private internet for a company or group of people. United Airlines uses it for their employees. The benefit of it, is that it is more secure than a regular network.
Let's put it this way, the public sector is under WAY more scrutiny than the private sector is.