improve documentation, fixes https://github.com/PrivateBin/PrivateBin/issues/141

API.md

@@ -39,3 +39,21 @@ Error on any of the above           | N/A | N/A | N/A | `{"status":1, "message":
 * **formatID:** format key as defined in the [configuration file](https://github.com/PrivateBin/PrivateBin/blob/master/cfg/conf.ini#L69) of the service
 * **metadata:** various properties of the [paste](https://raw.githubusercontent.com/PrivateBin/PrivateBin/master/js/pastemeta.jsonld) or the [comment](https://raw.githubusercontent.com/PrivateBin/PrivateBin/master/js/commentmeta.jsonld).
 * **deletetoken:** the delete token is returned only on creation of a paste and can be used to delete it and its comments
+
+## Encryption
+
+PrivateBin [uses](https://github.com/PrivateBin/PrivateBin/blob/master/lib/Sjcl.php) the [SJCL library](https://github.com/bitwiseshiftleft/sjcl) for de- and encryption. If you do not want to use it, you can find all properties for the JSON encryption result it below.
+The validation logic can be found [in the Sjcl.php file](https://github.com/PrivateBin/PrivateBin/blob/master/lib/Sjcl.php#L31-L102) and some examples for valid requests can be found in the [unit tests](https://github.com/PrivateBin/PrivateBin/blob/master/tst/SjclTest.php) 
+
+## JSON object properties
+
+* **iv**: random initialization vector, encoded as base64 string
+* **v**: version number of the SJCL data format, currently always 1
+* **iter**: number of iterations, by default 1000
+* **ks**: key size in bits, should ideally be 256, but SJCL also supports 128 bit keys
+* **ts**: authentication strength in bits, should ideally be 128, but SJCL also supports 64
+* **mode**: encryption mode, we just switched to gcm by default, but before v1.0 it was ccm
+* **adata**: optional clear text authentication data (of which we currently make no use)
+* **cipher**: cipher algorithm, only aes is supported by SJCL for symmetric encryption
+* **salt**: the salt, encoded as base64 string
+* **ct**: cipher text, encoded as base64 string