add strict IV validation to decryption handler

add strict IV validation to decryption handler

Optionally (on CLI, with the “-s” flag) check for additional IV
properties:

    - Accidental reuse: in GCM, the same IV used more than once
      means that the plaintext is compromised.

    - Unstructured archive: In the headers of a normal PDT
      encrypted archive, the variable parts of the IVs are
      consecutive unless the fixed part changes.