Many applications need to handle sensitive data either in memory or on disk. If this sensitive data is not protected properly, it might lead to loss of secrecy or integrity of the data. It is very difficult (or expensive) to completely secure all the sensitive data. Users tend to use the same passwords everywhere. So even if your program is a simple game that stores the user's profile information and requires the user to enter a password, the user might choose the same password he or she uses for an online bank account for your game program. Now the user's bank account is only as secure as your program enables it to be.
There are simple steps you can take to secure sensitive data in your programs.
Prefer the system's authentication dialog (or any other mechanism provided by the OS) for authentication to privileged services.
If you are accessing some privileged service already installed on the system, most likely that service will have some mechanism to take a password from the user. Before asking the user for a user name and password from your application, check if the service itself authenticates the user in some way. If so, let the service handle the authentication because doing so would at least not increase the footprint of the sensitive data.
Do not hard code sensitive data in programs.
See MSC41-C. Never hard code sensitive information for details.
Disable memory dumps.
Memory dumps are automatically created when your program crashes. They can contain information stored in any part of program memory. Therefore, memory dumps should be disabled before an application is shipped to users. See MEM06-C. Ensure that sensitive data is not written out to disk for details.
Do not store sensitive data beyond its time of use in a program.
Sensitive data that is stored in memory can get written to disk when a page is swapped out of the physical memory. (See next point for details about keeping sensitive data on disk.) You may be able to "lock" your data to keep it from swapping out. Your program will generally need administrative privileges to do so successfully, but it never hurts to try. See MEM06-C. Ensure that sensitive data is not written out to disk for details.
Do not store sensitive data in plaintext (either on disk or in memory).
While using a password, consider storing its hash instead of plaintext. Use the hash for comparisons and other purposes. The following code [Viega 2001] illustrates:
If you must store sensitive data, encrypt it first.
- If encrypting or hashing sensitive data, do not implement your own encryption functions (or library). Use proven secure crypto libraries, which have been extensively tested for security.
- If using standard crypto libraries, be aware that they have certain requirements (documented with the library) for the key sizes and other properties. Choose keys that satisfy these conditions.
- Do not store the encryption keys (you can derive the key from the hash of the user's password or any other cryptographic mechanism, provided the above condition holds). If the key is to be stored, store it securely.
Securely erase sensitive data from disk and memory.
- Be aware of compiler optimization when erasing memory. (See MSC06-C. Beware of compiler optimizations.)
- Use secure erase methods specified in U.S. Department of Defense Standard 5220 [DOD 5220] or Peter Gutmann's paper [Gutmann 1996].
If sensitive data is not handled correctly in a program, an attacker can gain access to it.
Hardcoded Crypto Key
Hardcoded Crypto Salt
Encryption without Padding
Plaintext Storage of Password
|Polyspace Bug Finder|
Sensitive data not cleared or released by memory routine
Variable in stack is not cleared and contains sensitive data
Function is not reentrant or uses a risky encryption algorithm
Encryption or decryption key is constant instead of randomized or generated from a weak random number generator
Initialization vector is constant instead of randomized
Encryption or decryption key is generated from a weak random number generator
Initialization vector is generated from a weak random number generator
|CERT Oracle Secure Coding Standard for Java||MSC03-J. Never hard code sensitive information|
|SEI CERT C Coding Standard||MSC41-C. Never hard code sensitive information|
|MITRE CWE||CWE-259, Use of Hard-coded Password|
CWE-261, Weak Cryptography for Passwords
CWE-311, Missing encryption of sensitive data
CWE-319, Cleartext Transmission of Sensitive Information
CWE-321, Use of Hard-coded Cryptographic Key
CWE-326, Inadequate encryption strength
CWE-798, Use of hard-coded credentials
|[DOD 5220]||Standard 5220|
|[Gutmann 1996]||"Secure Deletion of Data from Magnetic and Solid-State Memory"|
|[Lewis 2006]||"Security Considerations when Handling Sensitive Data"|
|[Viega 2001]||"Protecting Sensitive Data in Memory"|