code breaking

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Across
  1. 3. tashbar encoded with key=3
  2. 6. the name of the machine
  3. 7. the genius who helped break the code (4,6)
  4. 8. genius (4,6)
  5. 11. is surrounded by sea
  6. 12. the maths teacher (3,9)
  7. 13. wrote loads of books including one about a chocolate factory (5,4)
  8. 14. Mr Oakley's full first name
  9. 17. tallest building (3,5)
  10. 19. yellow and curved
  11. 20. missing for a long time (8,3,6)
Down
  1. 1. before nisan (7,4)
  2. 2. when the light stops shining
  3. 4. another name for the moon
  4. 5. the place in the English countryside where the code breaking took place (9,4)
  5. 9. always with tintin
  6. 10. had a mine (4,7)
  7. 12. she could move things with her eyes
  8. 15. it has dots and dashes (5,4)
  9. 16. a word meaning very hot
  10. 18. a word that means make a code