The new Mega site, sucessor of Megaupload, claims that all information is encrypted with a symetric key that only the user has access.
The general terms are listed here:
All files stored on MEGA are encrypted. All data transfers from and to MEGA are encrypted. And while most cloud storage providers can and do claim the same, MEGA is different – unlike the industry norm where the cloud storage provider holds the decryption key, with MEGA, you control the encryption, you hold the keys, and you decide who you grant or deny access to your files, without requiring any risky software installs. It’s all happening in your web browser!
In the developers page there are some details about AES 128bits, 64 random bits as some initial value, and so on, but I can't find details on how the end-user will have that protection.
Does someone how their encryption / security really works? Is it really secure?