▁area ▁of ▁research ▁that ▁is ▁known ▁as ▁physical ▁layer ▁encryption . ▁ ▁It ▁explo its ▁the ▁physical ▁wireless ▁channel ▁for ▁its ▁security ▁by ▁communic ations , ▁signal ▁processing , ▁and ▁coding ▁techniques . ▁The ▁security ▁is ▁prov able , ▁un break able , ▁and ▁quant ifiable ▁( in ▁bits / second / h ert z ). ▁ ▁W yn er ' s ▁initial ▁physical ▁layer ▁encryption ▁work ▁in ▁the ▁ 1 9 7 0 s ▁pos ed ▁the ▁Alice – Bob – E ve ▁problem ▁in ▁which ▁Alice ▁wants ▁to ▁send ▁a ▁message ▁to ▁Bob ▁without ▁E ve ▁dec oding ▁it . ▁If ▁the ▁channel ▁from ▁Alice ▁to ▁Bob ▁is ▁statist ically ▁better ▁than ▁the ▁channel ▁from ▁Alice ▁to ▁E ve , ▁it ▁had ▁been ▁shown ▁that ▁secure ▁communication ▁is ▁possible . ▁That ▁is ▁intuit ive , ▁but ▁W yn er ▁measured ▁the ▁secre cy ▁in ▁information ▁the or etic ▁terms ▁defining ▁secre cy ▁capacity , ▁which ▁essentially ▁is ▁the ▁rate ▁at ▁which ▁Alice ▁can ▁transmit ▁secret ▁information ▁to ▁Bob . ▁ ▁Short ly ▁after ward , ▁Im re ▁Cs isz ár ▁and ▁Kör ner ▁showed ▁that ▁secret ▁communication ▁was ▁possible ▁even ▁if ▁E ve ▁had ▁a ▁statist ically ▁better ▁channel ▁to ▁Alice ▁than ▁Bob ▁did . ▁The ▁basic ▁idea ▁of ▁the ▁information ▁the or etic ▁approach ▁to ▁secure ly ▁transmit ▁confident ial ▁messages ▁( without ▁using ▁an ▁encryption ▁key ) ▁to ▁a ▁legit imate ▁receiver ▁is ▁to ▁use ▁the ▁inher ent ▁random ness ▁of ▁the ▁physical ▁medium ▁( including ▁no ises ▁and