Thursday, September 20, 2012

Ecrypting sensitive information in database

Recently for PCI complaince, we needed to encrypt credit card information (PAN) before storing it in the database. We decided to use AES 256 bit encryption for the same and developed a .NET component in the middle tier for the encryption/decryption.

After this, we faced the chicken-n-egg problem of storing the encryption key :)
In the past, we had used techniques such as storing the key in the windows registry and using RBAC to control access. Other option was to split the key into multiple files and use file-based OS permissions to control access.

But in the lastest version of .NET, you have another good option - i.e. DPAPI (Data Protection API). Using DPAPI, we can delegate key management to the operating system.
We do not provide a key with which to encrypt the data. Rather, the data is encrypted with a key derived from the logged-in user or system credentials. Thus we can pass any "sensitive" information to DPAPI and it would encrypt it using the "password" of the logged-in user or machine level authentication credentials.

The following MSDN links give detailed information on how to achieve this for connection strings - a common requirement scenario.

In our case, we placed our encryption key in a configuration section and encrypted that section using the methods described in the above link.
Because we were using a web farm scenario with two servers, we had 2 options- either use DPAPI on each server to encrypt the data using the machine specific key or use a separate key store/container and use RSA for encryption. In the first option, we would end up with different 'cipher-value' for the same input data. In the second option, the 'cipher-value' would be the same, but we would need to import the RSA keys on each server in the farm.

More information at this link: 

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