On ARM64 and RISC-V platforms, the SM2 curve utilizes a scalar multiplication implementation that is not constant-time. Because conditional branches and table lookups are determined by the bits of the secret scalar, the execution time and cache-access patterns depend on the long-term private key during decryption or the per-signature nonce during signature generation. This creates a timing and cache side-channel that allows an attacker to learn information about the secret scalar.