<p>Elliptic curves over finite fields have been extensively used to build public key cryptography (a.k.a. Elliptic Curve Cryptography (ECC)). The choice of elliptic curves significantly affects the security and performance of the relevant cryptosystem. At present, standardized curves in ECC are all defined over finite fields of characteristic 2 or large prime characteristic, while those of characteristic 3 have drawn little attention mainly due to their lower efficiency in implementation. In this work, the authors primarily study ordinary elliptic curves defined over the quadratic extension field of characteristic 3 equipped with the Frobenius endomorphism. All relevant operations of finite field and elliptic curves, implemented by the AVX2 instructions and 256-bit wide SIMD operands, are developed and optimized to ensure both efficient and constant-time execution. At the 128-bit security level, the proposed implementation is approximately 1.8 times faster than the previous work for scalar multiplication on ordinary curves of characteristic 3. To the best of our knowledge, this is the first scalar multiplication implementation on elliptic curves of characteristic 3 which outperforms those on standard curves such as NIST P-256 and SM2.</p>