void PBKDF2_SHA256(const uint8_t *passwd, size_t passwdlen, const uint8_t *salt, size_t saltlen, uint64_t c, uint8_t *buf, size_t dkLen)
PBKDF2_SHA256(passwd, passwdlen, salt, saltlen, c, buf, dkLen): Compute PBKDF2(passwd, salt, c, dkLen) using HMAC-SHA256 as the PRF, and write the output to buf.