# Secure and Privacy-Aware Blockchain Design: Requirements, Challenges and Solutions
## 5 Evaluation and Discussion
### Current Recommendations and Research Directions
#### 5.2.1 Current Recommendations  
Some features are the top priority when designing new data privacy and security mechanisms for blockchain. Based on our previous analysis, these features are unlinkability, low cost, scalability, reliability, and efficiency, low overhead and low computational cost. In the following, we present the most appropriate privacy and security mechanisms and explain their relevance for blockchain. 1. **Ring signature** we consider ring signature to be efficient for identity protection, because of its lower complexity than zero-knowledge proof. However, it is not as scalable as other mechanisms. While scalability can be moderated by creating several rings with a manageable number of participants, key management remains a central problem for ring signature. 2. **Zero-knowledge proof** has higher memory cost and complexity as compared to ring signature. It is mostly considered as a solution to identity management where identity attributes need to be proven without revealing the actual identity. In such a case, it is considered relevant to prevent identity/transaction data disclosure. Despite their higher cost, zero-knowledge-proof constructions are currently the most suitable to address both privacy, and scalability. We conclude that ZKPs can be used to provide anonymous transactions such as Monero [39]. However, they can also be used as a scaling mechanism, where transactions can be batched off-chain, and verified on-chain in blockchain platforms with Turing-complete smart contracts. Presently, the use of ZKPs is limited by the time complexity of constructing proofs, and the lack of protocols that enable trust-less setup [138] with the exception of STARKs [40]. 3. **Mix network** is efficient to randomize the order of input data and it is scalable as compared to other available solutions. However, mixed networks require TTPs to shuffle transaction data [1] which is a major drawback in our context. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Privacy and** **Security Mechanisms** & **Advantages** & **Limitations** & **Attack Risks** \\ \hline \multirow{3}{*}{l-Diversity} & \multirow{3}{*}{Ensure privacy of user attributes.} & Does not prevent data against the attacks; In-efficient, Attribute disclosure can be possible. & \multirow{3}{*}{Sleewnness attack; Similarity attack.} \\ \cline{3-3} \cline{5-5}  & & Difficult to identify the closeness between the knowledge gained and t-value by using Earth Mover’s Distance(EMD) & & Linkability risk is possible to link external data to the equivalence areas \\ \hline \multirow{3}{*}{Symmetric Key Cryptography} & Re-identification of message is not possible; Authorized user has access to data; Fast; Easy to use. & Difficult to manage multiple keys; Require secure platform to share secret keys. & Re-identification of key from plain text; Recover plain text from cipher text. \\ \hline \multirow{3}{*}{Asymmetric Key Cryptography} & \multirow{3}{*}{Ensures data confidentiality.} & Slow; Does not provide data integrity. & Possible to crack private keys; Brute force attack. \\ \hline \multirow{3}{*}{Hash Function} & \multirow{3}{*}{Flexible; Easy to use.} & Not effective on small scale dataset; High computation cost; In-efficient. & Collision attack; Brute force attack. \\ \hline \multirow{3}{*}{Homomorphic Encryption} & No one can read or modify data; Prevention of active and passive attacks. & Slow. & Heuristic attack. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._4. **Identity-based encryption** is better to prevent users' identity disclosure because of its low complexity and computation overhead as compared to attribute-based encryption. However, it is not scalable and has a higher memory overhead than other available solutions. 5. **Attribute-based encryption mechanism** is good to enforce confidentiality on data and fulfills transaction data protection requirements without latency.