Chinese scientists have found a way to hide secret messages in the sound pulses that sperm whales emit to keep enemy reconnaissance systems from deciphering them – a breakthrough that could help military submarines avoid scrutiny, researchers said.
With this technique, whale sounds are edited and a coding system is built around it. Messages are emitted in the form of these edited whale sound bites, indistinguishable from regular whale sound, which are deciphered by the receivers following the code.
Jiang Jiajia, a Tianjin University precision-measurement professor who led the research, said the method camouflages undersea signals, making them harder to detect.
The team took its cue from sperm whales and long-finned pilot whales that use sound waves and echoes to locate and identify objects near them – a process known as echolocation.
Since they inhabit all the world’s oceans and their sounds typically get filtered out when undersea reconnaissance systems sweep an area for submarine signals, the giant mammals were seen as candidates to help military submarines avoid scrutiny, according to the researchers.
According to a study published last month in IEEE Communication Magazine, the journal of the New York-based Institute of Electrical and Electronics Engineers, civil or military submarines typically have two ways to keep acoustic signals carrying secret messages off the radar: they can either tweak the characteristics of man-made signals to make them harder to crack if picked up by an enemy, or they can send weaker signals to make them harder to discover.
Both methods have their drawbacks, Jiang said in an email.
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The first one – changing the traits of signals – is based on a process similar to encryption, which makes information harder to decipher by converting data into a code.
But the technique tends to alert the enemy because it stands out from natural waveforms.
The second approach – sending a weakened signal – is more effective at keeping messages from being detected but is hampered when the message has to travel a long distance, Jiang said.
Since underwater reconnaissance systems generally filter out “ocean noise” such as a whale’s sounds, Jiang and his team began to investigate the possibilities of building a system for hiding signals around the camouflage approach, known in the field as steganography, or hiding a file, image or audio signal within another one, the researcher said.
While steganography has roots in ancient warfare, and is behind the camouflage pattern featured on modern-day army fatigues, applying the technique in securing underwater communications is a new concept, Han Guangjie, a computer scientist at northwestern China’s Dalian University of Technology, said in an interview.
“The advantage of steganography over encryption and other conventional methods is that the intended secret message does not attract attention to itself, avoiding scrutiny,” said Han, who was not involved in the study. “Plainly visible encrypted messages, no matter how unbreakable they are, arouse interest.”
Han said the new technology would make underwater communication more secure, even if the signals were detected by an enemy’s reconnaissance system.
“It is hard for the enemy to crack the signals, mainly because in steganography, a hidden message looks more like a part of others,” he said.
“For example, the real message may look like noise in sperm whales’ sound pulses.”
Although an enemy could still possibly decipher the signals, doing so would be very challenging and require greater resources than would be needed to decode a conventionally encrypted message, Jiang said.
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