OP-TEE is an open-source project that uses security concepts and cryptography to create a Trusted Execution Environment (TEE) based on software isolation. Although being open-source and one of the main TEE for Android smartphones, it lacks an in-depth performance/security analysis of available algorithms, especially digital signatures. Therefore, in order to support next-generation of security applications, this work faces the challenge of improving the security of this trusted computing environment by (I) surveying and analyzing the security of the natively implemented digital signature algorithms on OP-TEE; (II) embedding and suggesting modern/secure alternatives as expansion; and (III) conducting experiments to check the performance of each these digital signature algorithms. As a result, users who are interested in adopting OP-TEE will be able to evaluate the security and functionality of various digital signature algorithms. Furthermore, our analysis confirms the necessity to include new algorithms, particularly post-quantum.