Military transparency comes with trust
When China published its defense white paper, The Diversified Employment of China's Armed Forces in April, some Western critics lauded the efforts but claimed that China hadn't put much meat on the bone and the paper was short on details.
This raises the question: To what extent does a country need to be transparent about its military in order to build trust with other countries?
The answer to this is: It depends on whom you are dealing with.
Transparency is based on trust. You are unlikely to make a "confession" when you are not sure the listeners are your friends or, in the worst case, if they are adversaries or even potential enemies. While the West holds that information such as weapons systems, the break-down of military expenditure and listing of R&D efforts are essential for transparency, China stresses that there is no absolute transparency - as Prism whistleblower Edward Snowden seems to have proven. Otherwise why would the US monitor even its allies? Transparency only comes as a result of trust.
Transparency also has a lot to do with military strength. Underdeveloped countries keep more things as military secrets, while the militarily strong ones are not shy about showing off their muscles. While the West believes that China is strong enough not to be attacked by anyone, China is still concerned about a number of worst-case scenarios where external forces could be involved in either China's internal affairs such as Taiwan, or its maritime territorial disputes with other countries. China believes that there is still a gap between its strength and that of the US-led Western powers. Its objective, as laid out in the defense white paper, is to achieve military modernization by mid-century.
Transparency is also dependent on strategic equilibrium. During the Cold War, strategic arms reduction talks took place between the United States and the Soviet Union, only because both sides believed that their nuclear warheads were more than enough and their strategic equilibrium would not be jeopardized if they reduced the number of warheads. But China doesn't have such a strategic equilibrium with the US.