Where Did China Get Its Stealth Technology?

China is reveling in the attention its new stealth aircraft is getting, even though it's not clear whether the J-20 is as technologically advanced as the country's leaders would like the world to believe.

Chinese officials are adamant that the aircraft was developed by engineers at home using their own designs, but analysts and aerospace experts presume the J-20 owes at least some credit to others. Here are the leading theories on where China may have copied -- or perhaps even stolen -- designs for its new aircraft.

1. From the U.S. F-117: One of the theories is that China was able to gain some insights into stealth technology thanks to the F-117 shot down over Serbia in 1999. A number of reports claim that Chinese agents bought up pieces of the radar-evading aircraft in order to reverse-engineer the technology. While China may indeed have studied pieces of the purloined aircraft, the J-20 doesn't resemble the distinctive-looking faceted stealth design of the F-117.

2. From a spy: It could be that China used good old-fashioned human intelligence to collect information on U.S. stealth designs. Earlier this week, a former Northrop Grumman engineer received a 32-year prison sentence for his role in passing on information about stealth designs to China. The court case did not accuse Noshir Gowadia, originally from India, of helping the J-20 aircraft, but he was convicted of passing on stealth information on missiles.

3. From the Joint Strike Fighter: Back in 2009, the Pentagon's computer systems were breached by hackers who made off with reams of information on the F-35 Joint Strike Fighter, a stealthy, multirole fighter under development. The Wall street Journal reported at the time that the "intruders were able to copy and siphon off several terabytes of data related to design and electronics systems, officials say, potentially making it easier to defend against the craft." Though the attacks were never linked to a specific foreign government, officials said they suspected China.

More recently, a Lockheed official told the Journal that the J-20's engine inlet looked similar to that of the Joint Strike Fighter.

4. From Russia: Russia has long been a leading arms seller to China, and some analysts believe that the Chinese stealth plane most closely resembles Russian aircraft, including a long--abandoned stealth project. "American intelligence believes that the tech behind the new Chinese J-20 stealth aircraft came from Russia," says StrategyPage.com website. "So far, not a lot of protests from Russia."

5. The Chinese made it themselves. China is denying that its new aircraft is anything other than a technological marvel of China's own engineering. "Different from previous fighters such as the J-7 and J-8, which drew on the merits of aircraft from other countries, the J-20 is a masterpiece of China's technological innovation," test pilot Xu Yongling was quoted as saying in one of China state-run newspapers, according to UPI.

While China may well have done much of its own engineering work, it's unlikely that all of it comes from China. Even the U.S. gives credit to others: The first stealth aircraft designs are traced back to a Russian-developed math model.