started to implements the encryption process

doc/fileformat.md

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+
+### public key
+Note that any private key are a public key.
+
+~~~
+
+~~~
+
+### private key
+
+
+
+
+### cypher format
+
+We use the `.cyp` file extension for the encrypted file.  A .cyp is nothing
+else than a zip file containing the following shit.
+
+1.  a `data.encrypted` containing the encrypted data
+2.  a `meta_data.yml` file containing the meta data of the encrypted file
+    *  symetric encryption algorithm
+    *  mode
+    *  encrypted symetric key
+    *  hash of the encrypted data (always use full for validation)
+3.  a 'signature' file with the signature of the `meta_data.yml` file