CIA is a common security model. It stands for: 

• Confidentiality – the information can not be intercepted
• Integrity- the information is correct and not modified
• Authenticity - the sender and receiver are confirmed who they are

Encryption makes the information impossible to understand for an outsider, nor can it be modified during the transport. By choosing well known and proven cipher algorithms a very good security can be achieved. Most common ciphers today are probably 3DES and AES, even if there are several other good ciphers. The key length is also important and for every bit the key is extended, the possible number of combinations will double. With a key exchange method where the keys are changed frequently the communication with the right sender/receiver can be assured.