Public-Key Cryptography, created in the 1970s, is a matched-pair encryption/decryption standard. Using this method, the sender and recipient share public encryption keys, thereby establishing a relationship of trust. After that occurs, files can be encrypted by one and decrypted by the other without using passwords. While Public-Key Cryptography can use a variety of levels of security, DropKey uses the 256-bit method, a well-established industry standard.
I talked to DropKey’s CEO Ian Schray, and what impresses me about the app is that it only takes one extra click to encrypt a file and send it in an email, than it does if you didn’t encrypt the file. I’ve tried file encryption software in the past and it was a real pain, but this looks really good.
Update: 5/8/2015 This product is no longer available.