I've recently been looking into the same issue. I need a way to encrypt data before inserting it into a database in such a way that the person inserting the record can read it, their supervisor can read, but their colleague can't. It needs to survive a password reset and I don't want to store any keys on the server unencrypted.
This lead me to attribute based encryption and the libbswabe library. The idea is you generate a master keypair and from these you generate private keys for each of your users. Your user's private keys can only decrypt data that was encrypted with attributes that were also applied to their key.
For example, let's say we have 2 users Alice and Bob. Alice is a supervisor for the IT department. Her key was generated with the attributes "alice" (her username) and "itdepartment". Bob is a normal employee in the IT department, the only attribute applied to his private key was his username "bob"
Now lets say we use the master public key to encrypt each of the fields in the user table (Firstname, Lastname, Email, etc). If each field for a user record is encrypted with the attributes: [current_username] and "itdepartment", then Bob can decrypt his fields because they are tagged with "bob" and "bob" is an attribute in his key and Alice can decrypt her record through the same logic AND every record whose fields were encrypted with the attribute "itdeparment".
If users private keys are encrypted with their password and stored in the database, then the only way you can get Bob's key is to break his password. An attacker now has access to the data that Bob's key can decrypt, but importantly, not everything. If Bob forgets his password (and therefore can't access his private key) then a new one can be generated and all it needs to do is have the "bob" attribute in order for him to have access to all his old data.
Now this is by no means a complete description of a solution, you have to securely store the master private key (you only need this to generate private keys for your users though, not for every put/get request), there's issues around key revocation and lots of gaps in my description, but these issues are present for any crypto system. Attribute based encryption though seems to me like it overcomes a lot of the issues that plague other solutions, the biggest single one being that other solutions require the master private key to either be on disk, or in memory at all times, this solution doesn't need that.
This lead me to attribute based encryption and the libbswabe library. The idea is you generate a master keypair and from these you generate private keys for each of your users. Your user's private keys can only decrypt data that was encrypted with attributes that were also applied to their key.
For example, let's say we have 2 users Alice and Bob. Alice is a supervisor for the IT department. Her key was generated with the attributes "alice" (her username) and "itdepartment". Bob is a normal employee in the IT department, the only attribute applied to his private key was his username "bob"
Now lets say we use the master public key to encrypt each of the fields in the user table (Firstname, Lastname, Email, etc). If each field for a user record is encrypted with the attributes: [current_username] and "itdepartment", then Bob can decrypt his fields because they are tagged with "bob" and "bob" is an attribute in his key and Alice can decrypt her record through the same logic AND every record whose fields were encrypted with the attribute "itdeparment".
If users private keys are encrypted with their password and stored in the database, then the only way you can get Bob's key is to break his password. An attacker now has access to the data that Bob's key can decrypt, but importantly, not everything. If Bob forgets his password (and therefore can't access his private key) then a new one can be generated and all it needs to do is have the "bob" attribute in order for him to have access to all his old data.
Now this is by no means a complete description of a solution, you have to securely store the master private key (you only need this to generate private keys for your users though, not for every put/get request), there's issues around key revocation and lots of gaps in my description, but these issues are present for any crypto system. Attribute based encryption though seems to me like it overcomes a lot of the issues that plague other solutions, the biggest single one being that other solutions require the master private key to either be on disk, or in memory at all times, this solution doesn't need that.