This is a good example of how Tresorit employs multiple layers of protection around your valuable data, always backed up by strong cryptographic routines. Even if other users have access to the group key file, they still won't be able to access tresor contents, because they don't have the RSA private key to decrypt the tresor encryption key. Our servers won't allow non-tresor members to download this file. When a member downloads the contents of a tresor, their Tresorit application first downloads the group key file, decrypts the encryption keys with its own agreement private key, and uses it to decrypt the root folder and the tresor’s content. This file serves as the starting point when accessing a tresor. Group Key FileĮach tresor contains a special file in the cloud called the group key file, containing the encryption key protected by each member's agreement public key. Periodically and on certain operations, like password change, new secrets are generated into your roaming profile, including a new agreement key pair, which is updated in all your tresors to ensure cryptographic access revocation of your old password. The agreement private keys are stored securely in the users' roaming profile.Įvery user has multiple agreement keys (public/private pairs). This way all tresor members are able to decrypt the encryption key needed to access the tresor’s contents using their own agreement private key, but they don't employ any kind of common secret, only standard asymmetric encryption methods. The encryption key is is encrypted as many times as many members are in the tresor, using the personal agreement public key of each member. Tresorit also employs this scheme by encrypting the AES-256 tresor encryption key with RSA-4096 algorithm using the public key (called the agreement public key) of the tresor members. It is a common technique in cryptography to protect symmetric keys with asymmetric encryption, such as RSA. Integrity of all ciphertext is protected with HMAC-SHA-512. Folders, including file names, are encrypted the same way. Each version of a file has a random IV, so even if you change one bit in a large file, the encrypted form changes completely, ensuring that neither Tresorit, nor others have any information about your changes. All files have different, independent and freshly generated 256-bit encryption keys. I'm never one to turn down free storage, so while I may never share truly personal info there, I'll gladly make use of the 5GB of space.For encrypting the uploaded files and folders in your tresors, Tresorit uses a symmetric key encryption algorithm, more specifically AES-256, in OpenPGP CFB mode described in RFC2440. No one has succeeded despite attempts by over 900 'hackers' over the course of 498 days including those from MIT, Stanford, Caltech, and Harvard. the other options out there, but they initiated a bounty of $50,000 and invited leading Universities and hackers to breach the service. I can't speak on the validity of their claims about being more secure vs.
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