Use of a Broken or Risky Cryptographic Algorithm

What is CWE-327?

Step-by-step attacker path

1. 1

   These code examples use the Data Encryption Standard (DES).

2. 2

   Once considered a strong algorithm, DES now regarded as insufficient for many applications. It has been replaced by Advanced Encryption Standard (AES).

3. 3

   Suppose a chip manufacturer decides to implement a hashing scheme for verifying integrity property of certain bitstream, and it chooses to implement a SHA1 hardware accelerator for to implement the scheme.

4. 4

   However, SHA1 was theoretically broken in 2005 and practically broken in 2017 at a cost of $110K. This means an attacker with access to cloud-rented computing power will now be able to provide a malicious bitstream with the same hash value, thereby defeating the purpose for which the hash was used.

5. 5

   This issue could have been avoided with better design.

How to prevent CWE-327

• Architecture and Design When there is a need to store or transmit sensitive data, use strong, up-to-date cryptographic algorithms to encrypt that data. Select a well-vetted algorithm that is currently considered to be strong by experts in the field, and use well-tested implementations. As with all cryptographic mechanisms, the source code should be available for analysis. For example, US government systems require FIPS 140-2 certification [REF-1192]. Do not develop custom or private cryptographic algorithms. They will likely be exposed to attacks that are well-understood by cryptographers. Reverse engineering techniques are mature. If the algorithm can be compromised if attackers find out how it works, then it is especially weak. Periodically ensure that the cryptography has not become obsolete. Some older algorithms, once thought to require a billion years of computing time, can now be broken in days or hours. This includes MD4, MD5, SHA1, DES, and other algorithms that were once regarded as strong. [REF-267]
• Architecture and Design Ensure that the design allows one cryptographic algorithm to be replaced with another in the next generation or version. Where possible, use wrappers to make the interfaces uniform. This will make it easier to upgrade to stronger algorithms. With hardware, design the product at the Intellectual Property (IP) level so that one cryptographic algorithm can be replaced with another in the next generation of the hardware product.
• Architecture and Design Carefully manage and protect cryptographic keys (see CWE-320). If the keys can be guessed or stolen, then the strength of the cryptography itself is irrelevant.
• Architecture and Design Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Industry-standard implementations will save development time and may be more likely to avoid errors that can occur during implementation of cryptographic algorithms. Consider the ESAPI Encryption feature.
• Implementation / Architecture and Design When using industry-approved techniques, use them correctly. Don't cut corners by skipping resource-intensive steps (CWE-325). These steps are often essential for preventing common attacks.

Frequently asked questions

Further reading

• MITRE — official CWE-327 https://cwe.mitre.org/data/definitions/327.html
• Applied Cryptography https://www.schneier.com/books/applied-cryptography
• Handbook of Applied Cryptography https://cacr.uwaterloo.ca/hac/
• Avoiding bogus encryption products: Snake Oil FAQ http://www.faqs.org/faqs/cryptography-faq/snake-oil/
• FIPS PUB 140-2: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES https://csrc.nist.gov/files/pubs/fips/140-2/upd2/final/docs/fips1402.pdf
• Microsoft Scraps Old Encryption in New Code https://www.eweek.com/security/microsoft-scraps-old-encryption-in-new-code/
• Writing Secure Code https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223