（Ecns.cn）--The four great Chinese inventions are the compass, gunpowder, paper and printing, all internationally recognized symbols of ancient China's advanced science and technology. The wise early Chinese also invented other great stuff, including gadgets used by intelligence-gathering circles.
Four clever devices stand out as tools of the spy trade, and were the forerunners of modern technology developed for the very same purposes, according to Yangcheng Evening Paper on December 21.
Jar - the earliest wiretap
The earthen jar, in the shape of a big belly and small mouth, was used by spies to eavesdrop on conversations. It was invented by the Chinese about 2,500 years ago, according to a book written by Mozi and his followers during the last stage of the Warring States period.
Rather than being pressed up against a wall however, the lower part of the crude "bug" was buried underground and the upper part including its mouth was remained on the ground. Its mouth was covered by a thin piece of leather. Intelligence would put one ear on the leather to hear.
To minimize the chances conversations would be misheard the blind were often chosen to complete the eavesdropping task, as disabled people, when trained, could hear and distinguish sounds from dozens of miles away.
The earthen jar was improved over time and remained the most effective audio detection technology in China before the appearance of wiretapping and modern bugging devices.
Invisible writing
Invisible writing is another technique often used by spies to spread secret information undetected. Ancient intelligence agents wrote with a special ink to prevent messages from being read by those they were not intended to reach.
The ink was made of ingredients quite common today: water blended with alum. When this ink dries, the handwriting becomes invisible. Just sink the paper into water though, and the words reappear.
Water left over from boiling rice was another kind of invisible ink.
Zhiyuan - the simplest signal flare
The ancient Chinese tried many methods to pass on intelligence. Trained pigeons made good messengers but were not available in every kind of circumstance.
Zhiyuan, literally meaning paper bird, is the ancient Chinese for kite, and this was a simple and convenient method to signal people at a distance.
The Han Dynasty marquis Han Xin was the first person in recorded history to send information via kite, and this was over 2,000 years ago. The marquis Chen Xi was conspiring against the Han emperor Liu Bang. Han Xin, was a minister of the emperor's government and Chen Xi's man on the inside. When the time was right in the capital Han Xin flew a kite as a signal to Chen Xi to take action.
Zhiyuan were widely used in military and spy activities. A kite can fly very high, and while an enemy may see it, it remains out of reach. General Tian Yue of the Tang Dynasty once saw a kite flying over the city his army was besieging. Tian recognized it as the population's distress call and directed a sharp shooter to take the kite out, but failed.
Ciphers and decoding
Modern spies can't work without codes. Neither did the ancient spies.
Yinfu is probably the earliest army code used in ancient China and was used to mark a tally. Yinfu encoded tallies were composed of two halves, each held by a different person. When the two meet, they check whether the two halves match, and this is the way they verify each other's identity, a more sophisticated version of a code word and its matching response.
Different materials and lengths of tallies symbolized different kinds of intelligence. But no words appear in a tally, so even if it falls into enemy hands, they are unable to make any sense of it.
In the middle of the 16th century, the famous general Qi Jiguang, also a military talent, created a cryptographic technique named Fanqie Code. Fanqie used Chinese characters in complicated combinations as phonetic symbols. Qi Jiguang made full use of Fanqie to encode and decode military information.
To help with the memorization of Fanqie Code, Qi even wrote two poems that describe the complicated system.
The first Chinese spy
Yi Yin was the first spy of record in the country's history. In 16th Century BC, Jie was the last ruler of the Xia Dynasty, living in extremely luxurious conditions and famous for his cruel streak. Neighboring states wanted to seize control of his territory, so they planted in his household a Shang State official and spy called Yi Yin. While pretending to be a cook he gathered military and other relevant information from Jie's staff and guests. Based on an insider's information, Xia was eventually taken down by Yi Yin and his Shang rulers.
