I am looking for a desktop application that is easy to use and can run without Administrator privileges for Windows 10/8/7/Visa/XP etc. I should be able to encrypt files using a public key and then decrypt them using a private key. We have some sensitive data that we would like to share over the internet and hence maximum security is our target. Both options of paid and free software are OK. Thanks
I would recommend gpa4win. It is a free encryption program that has pretty good encryption. It uses asymmetric encryption so you will have a public and private key. I have not tested the program on XP or vista but I think it will work on those platforms. I have however tested the program on windows 10 and windows 8.1 and it works perfectly on those platforms. It does not need to run with admin rights so it should work for your purposes. Here is a download link. As far as I can tell this program meets all of your needs.
use gpg4usb it works great....has upto 4096 key asymmetric encryption......only drawback is that both private key and public key are generated in a single file. Manually you can copy public key part to another file and use that file as public key file to encrypt. For decryption either you can use the same combined keyfile OR if you seperate private key part you can use that.