Elliptic curve discrete logarithm problem (ECDLP) is the basis of security of elliptic curve cryptography (ECC). The security evaluation of ECC has been studied by solving an ECDLP. We need a large amount of computational resources for the evaluation. This paper proposes a new system collecting computational resources with Web-based volunteer computing (Web-based VC). In the system, web applications are allocated to volunteer participants (workers) as jobs. Web applications are built by utilizing technologies called Native Client (NaCl) and Portable NaCl (PNaCl). This paper evaluates the performance of the system and solves 70-bit ECDLP with Web-based VC. The performance of the web application utilizing NaCl is approximately 6.4 times higher than that of the web application written in JavaScript. Also, the performance of the web application utilizing PNaCl is approximately 4.2 times higher. In the case of NaCl, 70-bit ECDLP is solved in only 1389 seconds.If we collect 100,000 PCs by Web-based VC, 114-bit ECDLP will be solved in only approximately 1 day.