# BioShare: An Open Framework for Trusted Biometric Authentication under User Control
## 6 Discussion and Future Work  
This paper makes the case for biometric authentication as a trusted service under users' full control, and demonstrates how we addressed several challenges in making this service secure, practical, and efficient. Our solution reconciles the demand for open services and the requirement for privacy security, and shows comparative advantages over the currently available solutions. Table 12 lists the details of the comparisons. When compared to terminal local-processing solutions, such as Apple Touch ID and Windows Hello, as shown in Section 2.1, our solution extends open biometric authentication services from local mobile apps to remote network applications with high security levels. When compared to centralized-processing solutions such as facial recognition payment systems, as listed in Section 2.3, BioShare can avoid both unintentional leakages and the intentional abuse of biometric data by keeping private data in an encrypted format within secure storage, and running trusted code in isolated secure environments. Based on our test results, the BioShare implementation meets the performance requirements of most human-interactive businesses and fulfills the security requirements of recommended standards for business systems. We now discuss important challenges that are outside the focus of this paper. **TEE Fragmentation:** BioShare relies on terminal TEEs and server enclaves to handle service requests; however, the TEE market as a whole is currently fragmented. In both terminal and server markets, different manufacturers offer different TEE solutions that are incompatible with each other, such as QSEE/iTrustee on the terminal side and SGX/TrustZone on the server side, and therefore, we have to develop native code for each manufacturer, and even for each system model. This tremendously increases the development costs and implementation complexity for large-scale applications of BioShare, and we need a universal standard and interface protocol for terminal TEEs as well as server enclaves. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline \multirow{2}{*}{**Category**} & \multirow{2}{*}{**Algorithms**} & \multicolumn{2}{c}{**NIST Recommendations**} & \multicolumn{2}{c}{**Algorithms of BioShare**} \\ \cline{3-6}  & & **(Key Length)** & **Algorithm** & **Key Length** & **Security Strength** \\ \hline \multirow{2}{*}{Symmetric encryption} & \multirow{2}{*}{AES} & \multirow{2}{*}{128+} & AES-128 & 128 & 128 \\ \cline{3-6}  & & & AES-192 & 192 & 192 \\ \hline \multirow{4}{*}{Asymmetric encryption} & \multirow{2}{*}{RSA} & \multirow{2}{*}{2048+} & RSA & 3072 & 128 \\ \cline{3-6}  & & & RSA & 7680 & 192 \\ \cline{3-6}  & & & ECC & 256 & 128 \\ \cline{3-6}  & & & ECC & 384 & 192 \\ \hline Hash & SHA & 224+ & SHA-256 & 256 & 256 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Security Strength of Cryptographic Algorithms of BioShare. \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Security Properties**} & \multicolumn{2}{c}{**Terminal TEE**} & **Server Enclave** \\  & **(ARM Trustzone)** & **(Intel SGX)** \\ \hline Isolated Execution & Yes & Yes \\ \hline Encrypted RAM & No & Yes \\ \hline Secure Storage & Yes & Yes \\ \hline Remote Attestation & Yes & Yes \\ \hline Secure provisioning & Yes & Yes \\ \hline Privileged software attack defense & Yes & Yes \\ \hline Trusted Path & Yes & No \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Security Properties of Terminal TEE and Server Enclave. **Network Attacks:** BioShare opens up terminal capabilities to network applications, meaning that the terminals are faced with various network attacks, such as replay attacks and man-in-the-middle attacks. In addition, the server connects to numerous terminals through TCP/IP connections, and therefore is put at risk of cyber-attacks such as impersonation attacks and distributed denial of service attacks. We need to design defense technology and systems against various network attacks on user terminals, as well as the BioShare server.