encrypted vs impenetrable

encrypted

adj
  • Being in code; having been encrypted. 

impenetrable

adj
  • Incomprehensible; fathomless; inscrutable. 

  • Opaque; obscure; not translucent or transparent. 

  • Not penetrable. 

noun
  • A person not openly given to friendship. 

How often have the words encrypted and impenetrable occurred in a corpus of books? (source: Google Ngram Viewer )