The most easy and handy way is to zip files and encrypt them with a password. To that end you can use B1 Free Archiver — a free multiplatform compression tool. When creating the archive check the "Protect with a password" option, type in the password (keeping in mind the no. 3 rule) and only after that you can move it to the cloud. If you want to share it with someone just give the password to that person. Note that B1 Free Archiver zips files only in B1 format which makes the overall protection of your info more reliable.
The only software that opens B1 files is B1 Free Archiver, therefore you won't be able to open any B1 archive, even one that isn't password-protected, without this utility. B1 encrypted archives appear to be more safe and secure than the usual zip files.
In case you have more time and energy or want to provide an even higher level of protection for your files you can use TrueCrypt encryption software. It's an open source encryption program with which you can create an encrypted file (the so called "virtual disk") and keep all of your private files protected with a password.
TrueCrypt is a bit harder to use than B1 Free Archiver, but it gives you the choice of encryption algorithms (in addition to AES it also offers Serpent, Twofish, etc) some of which deliver a higher level of reliability. But at the same time it also has its drawback as compared to encrypted zip files.
In TrueCrypt you preset a precise volume of your encrypted file from the very beginning so a lot of space may be wasted before you fill it with data. The size of an encrypted zip file depends only on the data volume contained in it.
5. Use an encrypted cloud service.
There are some cloud services that provide local encryption and decryption of your files in addition to storage and backup. It means that the service takes care of both encrypting your files on your own computer and storing them safely on the cloud. Therefore, there is a bigger chance that this time no one — including service providers or server administrators — will have access to your files (the so called "zero-knowledge" privacy). Among such services are Spideroak and Wuala.
Spideroak provides 2GB space for full featured backup, sync, share, access and storage for free. However, you'll have to upgrade to Plus Plan for $10/monthly if you need more space. Wuala offers 5GB for free and paid accounts with the price depending on the amount of space you need.
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