# Quiz 9 **Let's apply what you have learned so far to a specific scenario. Choose the correct response.** You are designing a system that uses hash functions to store user data securely. A colleague suggests using an older hash function, MD5, for this purpose. What should you do? **Type all answers and select the correct one** * [x] Explain that MD5 is no longer considered secure due to its vulnerability to collision attacks and recommend using SHA-256 instead. * [ ] Agree to use MD5 since it is faster and widely known. * [ ] Suggest using MD5 but double-hashing the data to improve security. * [ ] Use MD5 for now and plan to upgrade to a more secure hash function later. **Note to learners** MD5 is cryptographically broken and unsuitable for secure applications due to its vulnerability to collision attacks. Using MD5, even with double hashing, does not mitigate its inherent weaknesses. It is best to use a secure hash function like SHA-256, which is resistant to collisions and widely used in modern systems. To learn more about it, you can follow the course [What are Hash functions?](https://bsvblockchain.360learning.com/course/play/68b55339580a65662452b269) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://hub.bsvblockchain.org/higher-learning/bsv-academy/bitcoin-primitives-hash-functions/quiz-bitcoin-hash-functions/quiz-9.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.