diff --git a/plume-common/src/activity_pub/sign.rs b/plume-common/src/activity_pub/sign.rs
index fa9252e..427f50f 100644
--- a/plume-common/src/activity_pub/sign.rs
+++ b/plume-common/src/activity_pub/sign.rs
@@ -97,46 +97,47 @@ impl SignatureValidity {
 }
 
 pub fn verify_http_headers<S: Signer+::std::fmt::Debug>(sender: &S, all_headers: HeaderMap, data: String) -> SignatureValidity{
-    if let Some(sig_header) = all_headers.get_one("Signature") {
-        let mut _key_id = None;
-        let mut _algorithm = None;
-        let mut headers = None;
-        let mut signature = None;
-        for part in sig_header.split(',') {
-            match part {
-                part if part.starts_with("keyId=") => _key_id = Some(&part[7..part.len()-1]),
-                part if part.starts_with("algorithm=") => _algorithm = Some(&part[11..part.len()-1]),
-                part if part.starts_with("headers=") => headers = Some(&part[9..part.len()-1]),
-                part if part.starts_with("signature=") => signature = Some(&part[11..part.len()-1]),
-                _ => {},
-            }
-        }
-        if signature.is_some() && headers.is_some() {
-            let headers = headers.unwrap().split_whitespace().collect::<Vec<_>>();
-            let signature = signature.unwrap();
-            let h = headers.iter()
-                .map(|header| (header,all_headers.get_one(header)))
-                .map(|(header, value)| format!("{}: {}", header.to_lowercase(), value.unwrap_or("")))
-                .collect::<Vec<_>>().join("\n");
-            if sender.verify(h, base64::decode(signature).unwrap_or(Vec::new())) {
-                if headers.contains(&"digest") {
-                    let digest = all_headers.get_one("digest").unwrap_or("");
-                    let digest = request::Digest::from_header(digest);
-                    if digest.map(|d| d.verify(data)).unwrap_or(false) {
-                        SignatureValidity::Valid
-                    } else {
-                        SignatureValidity::Invalid
-                    }
-                } else {
-                    SignatureValidity::ValidNoDigest
-                }
-            } else {
-                SignatureValidity::Invalid
-            }
-        } else {
-            SignatureValidity::Invalid
+    let sig_header = all_headers.get_one("Signature");
+    if sig_header.is_none() {
+        return SignatureValidity::Absent
+    }
+    let sig_header = sig_header.unwrap();
+
+    let mut _key_id = None;
+    let mut _algorithm = None;
+    let mut headers = None;
+    let mut signature = None;
+    for part in sig_header.split(',') {
+        match part {
+            part if part.starts_with("keyId=") => _key_id = Some(&part[7..part.len()-1]),
+            part if part.starts_with("algorithm=") => _algorithm = Some(&part[11..part.len()-1]),
+            part if part.starts_with("headers=") => headers = Some(&part[9..part.len()-1]),
+            part if part.starts_with("signature=") => signature = Some(&part[11..part.len()-1]),
+            _ => {},
         }
+    }
+
+    if signature.is_none() || headers.is_none() {//missing part of the header
+        return SignatureValidity::Invalid
+    }
+    let headers = headers.unwrap().split_whitespace().collect::<Vec<_>>();
+    let signature = signature.unwrap();
+    let h = headers.iter()
+        .map(|header| (header,all_headers.get_one(header)))
+        .map(|(header, value)| format!("{}: {}", header.to_lowercase(), value.unwrap_or("")))
+        .collect::<Vec<_>>().join("\n");
+
+    if !sender.verify(h, base64::decode(signature).unwrap_or(Vec::new())) {
+        return SignatureValidity::Invalid
+    }
+    if !headers.contains(&"digest") {// signature is valid, but body content is not verified
+        return SignatureValidity::ValidNoDigest
+    }
+    let digest = all_headers.get_one("digest").unwrap_or("");
+    let digest = request::Digest::from_header(digest);
+    if !digest.map(|d| d.verify(data)).unwrap_or(false) {// signature was valid, but body content does not match its digest
+        SignatureValidity::Invalid
     } else {
-        SignatureValidity::Absent
+	    SignatureValidity::Valid// all check passed
     }
 }