Cryptography

Most applications use cryptography to protect data and to ensure it remains private and unaltered. Top threats surrounding your application's use of cryptography include:

• Poor key generation or key management

• Weak or custom encryption

• Checksum spoofing

Poor Key Generation or Key Management

Attackers can decrypt encrypted data if they have access to the encryption key or can derive the encryption key. Attackers can discover a key if keys are managed poorly or if they were generated in a non-random fashion.

Countermeasures to address the threat of poor key generation and key management include:

• Use built-in encryption routines that include secure key management. Data Protection application programming interface (DPAPI) is an example of an encryption service provided on Windows 2000 and later operating systems where the operating system manages the key.

• Use strong random key generation functions and store the key in a restricted location for example, in a registry key secured with a restricted ACL if you use an encryption mechanism that requires you to generate or manage the key.

• Encrypt the encryption key using DPAPI for added security.

• Expire keys regularly.

Weak or Custom Encryption

An encryption algorithm provides no security if the encryption is cracked or is vulnerable to brute force cracking. Custom algorithms are particularly vulnerable if they have not been tested . Instead, use published, well-known encryption algorithms that have withstood years of rigorous attacks and scrutiny.

Countermeasures that address the vulnerabilities of weak or custom encryption include:

• Do not develop your own custom algorithms.

• Use the proven cryptographic services provided by the platform.

• Stay informed about cracked algorithms and the techniques used to crack them.

Checksum Spoofing

Do not rely on hashes to provide data integrity for messages sent over networks. Hashes such as Safe Hash Algorithm (SHA1) and Message Digest compression algorithm (MD5) can be intercepted and changed. Consider the following base 64 encoding UTF-8 message with an appended Message Authentication Code (MAC).

 Plaintext: Place 10 orders. Hash: T0mUNdEQh13IO9oTcaP4FYDX6pU= 

If an attacker intercepts the message by monitoring the network, the attacker could update the message and recompute the hash (guessing the algorithm that you used). For example, the message could be changed to:

 Plaintext: Place 100 orders. Hash: oEDuJpv/ZtIU7BXDDNv17EAHeAU= 

When recipients process the message, and they run the plaintext ("Place 100 orders") through the hashing algorithm, and then recompute the hash, the hash they calculate will be equal to whatever the attacker computed.

To counter this attack, use a MAC or HMAC. The Message Authentication Code Triple Data Encryption Standard (MACTripleDES) algorithm computes a MAC, and HMACSHA1 computes an HMAC. Both use a key to produce a checksum. With these algorithms, an attacker needs to know the key to generate a checksum that would compute correctly at the receiver.