How can I share files with other individuals in the cloud in a secure way?

Question

I would like to us a dropbox because it is easy and convenient. But I want to encrypt the files with the public key of the intended recipient, so he will be the only one who can access the data in the file. I have not found an easy mechanism to encrypt the data before it is stored in the dropbox. Is there an easy way to do so or is there aleady a service that supports my wish?

Answer 1

If you are already settled on using DropBox, then your only choice at the moment is to use a 3rd party program such as PGP (or free/open GPG) to first encrypt the file and place it into your drop box. I know you said you wanted to use public/private keys, but as an alternative, you could also use 7-zip to create secure archives with AES encryption based on a pre-shared key (password).

If you have not yet decided on DropBox, you can look at similar online storage systems such as SpiderOak, Cryptoheaven, Mozy, etc. which perform client-side encryption of the files prior to uploading them into the cloud. You control the encryption key, and therefore the storage providers cannot access the data. I am not sure whether you can import existing private or public keys into those solutions or not, however.

Answer 2

True Crypt may suit your needs. It offers the ability to use keyfiles to encrypt your files which can then be stored in your drop box and shared. It also offers the ability to use tokens and smart cards to secure your files. This lets your key be passed in an out of band manner.

In my opinion the best feature of true crypt is the ability to create hidden volumes. This creates what the creators of true crypt call plausible deniability. This basically means that there is a second encrypted volume that appears to be comprised of nothing more than random data. This is created inside of your encrypted file using using the free space at the end of the first volume. It is also worth noting that several different encryption algorithms are available.

Answer 3

Give Wuala a shot. Data is encryted on the users device before uploaded to the cloud. It does not come with key-files but passwords. Maybe this is sufficient for you?