diff --git a/linked_data_sig.py b/linked_data_sig.py
index f36cc288f..abe4a9348 100644
--- a/linked_data_sig.py
+++ b/linked_data_sig.py
@@ -24,47 +24,65 @@ except ImportError:
 from pyjsonld import normalize
 
 
-def _options_hash(doc):
-    doc = dict(doc["signature"])
+def _options_hash(doc: {}) -> str:
+    """Returns a hash of the signature, with a few fields removed
+    """
+    docSig = dict(doc["signature"])
+
+    # remove fields from signature
     for k in ["type", "id", "signatureValue"]:
-        if k in doc:
-            del doc[k]
-    doc["@context"] = "https://w3id.org/identity/v1"
+        if k in docSig:
+            del docSig[k]
+
+    docSig["@context"] = "https://w3id.org/identity/v1"
     options = {
         "algorithm": "URDNA2015",
         "format": "application/nquads"
     }
-    normalized = normalize(doc, options)
+
+    normalized = normalize(docSig, options)
     h = hashlib.new("sha256")
     h.update(normalized.encode("utf-8"))
     return h.hexdigest()
 
 
-def _doc_hash(doc):
+def _doc_hash(doc: {}) -> str:
+    """Returns a hash of the ActivityPub post
+    """
     doc = dict(doc)
+
+    # remove the signature
     if "signature" in doc:
         del doc["signature"]
+
     options = {
         "algorithm": "URDNA2015",
         "format": "application/nquads"
     }
+
     normalized = normalize(doc, options)
     h = hashlib.new("sha256")
     h.update(normalized.encode("utf-8"))
     return h.hexdigest()
 
 
-def verifyJsonSignature(doc: {}, publicKeyPem: str):
+def verifyJsonSignature(doc: {}, publicKeyPem: str) -> bool:
+    """Returns True if the given ActivityPub post was sent
+    by an actor having the given public key
+    """
     key = RSA.importKey(publicKeyPem)
     to_be_signed = _options_hash(doc) + _doc_hash(doc)
     signature = doc["signature"]["signatureValue"]
     signer = PKCS1_v1_5.new(key)  # type: ignore
     digest = SHA256.new()
     digest.update(to_be_signed.encode("utf-8"))
-    return signer.verify(digest, base64.b64decode(signature))  # type: ignore
+    base64sig = base64.b64decode(signature)
+    return signer.verify(digest, base64sig)  # type: ignore
 
 
-def generateJsonSignature(doc: {}, privateKeyPem: str):
+def generateJsonSignature(doc: {}, privateKeyPem: str) -> None:
+    """Adds a json signature to the given ActivityPub post
+    """
     if not doc.get('actor'):
         return