You can use a script Gmail Encrypt to add encryption to the emails you write in Gmail.
It uses public key encryption and is implemented in an RSA type scheme in Javascript.
Keys can be exchanged securely as you can safely place your public key anywhere.
A seperate public key is required for each person, because they are [...]
Any email messages that you send move across a vast array of servers around the internet and on each server the information gets copied. Anyone with access to those servers - or someone who is sniffing packets along the way - can read your email messages if they are sent in plain [...]
The process of encrypting data means to make it so that it is unreadable to anybody except the the person who is supposed to ge the data. When non-secured messages are sent over the Internet, it is virtually impossible to determine how many people may have access to the equipment being used, without physically securing [...]