ssh-key: fix certificate::OptionsMap encoding (#207)

The values in an `OptionsMap` are encoded with a nested length prefix.

https://bugzilla.mindrot.org/show_bug.cgi?id=2389

ssh-key/src/certificate/options_map.rs

@@ -42,7 +42,13 @@ impl Decode for OptionsMap {
 
             while !reader.is_finished() {
                 let name = String::decode(reader)?;
-                let data = String::decode(reader)?;
+                let data = reader.read_prefixed(|reader| {
+                    if reader.remaining_len() > 0 {
+                        String::decode(reader)
+                    } else {
+                        Ok(String::default())
+                    }
+                })?;
 
                 // Options must be lexically ordered by "name" if they appear in
                 // the sequence. Each named option may only appear once in a
@@ -65,7 +71,16 @@ impl Encode for OptionsMap {
     fn encoded_len(&self) -> encoding::Result<usize> {
         self.iter()
             .try_fold(4, |acc, (name, data)| {
-                [acc, 4, name.len(), 4, data.len()].checked_sum()
+                [
+                    acc,
+                    name.encoded_len()?,
+                    if data.is_empty() {
+                        4
+                    } else {
+                        data.encoded_len_prefixed()?
+                    },
+                ]
+                .checked_sum()
             })
             .map_err(Into::into)
     }
@@ -78,7 +93,11 @@ impl Encode for OptionsMap {
 
         for (name, data) in self.iter() {
             name.encode(writer)?;
-            data.encode(writer)?;
+            if data.is_empty() {
+                0usize.encode(writer)?;
+            } else {
+                data.encode_prefixed(writer)?
+            }
         }
 
         Ok(())

ssh-key/tests/certificate.rs

@@ -139,6 +139,26 @@ fn decode_ed25519_openssh() {
     assert_eq!(cert.valid_principals()[0], "host.example.com");
 }
 
+#[test]
+fn decode_ed25519_openssh_with_crit_options() {
+    let src = "ssh-ed25519-cert-v01@openssh.com AAAAIHNzaC1lZDI1NTE5LWNlcnQtdjAxQG9wZW5zc2guY29tAAAAIBW/4zLqXWROWmN1sPgdySnH1GUsEFBjFrRwKKw71BoBAAAAIH1MFwI1oRdEifXgBQvWQfCBBtA/Pi8YCUE/I3wXFJo2AAAAAAAAAAAAAAABAAAAA2ZvbwAAAAAAAAAAAAAAAH//////////AAAAIwAAABFoZWxsb0BleGFtcGxlLmNvbQAAAAoAAAAGZm9vYmFyAAAAAAAAAAAAAAAzAAAAC3NzaC1lZDI1NTE5AAAAIH1MFwI1oRdEifXgBQvWQfCBBtA/Pi8YCUE/I3wXFJo2AAAAUwAAAAtzc2gtZWQyNTUxOQAAAEDRoPdI48KyoaLgaDZsSGs80qBeYQOXBd84CX8GYzFt/L21rxF1EeuPOkgsx7Q39WllXp+FgMMojsHftK/DJHEN";
+    let cert = Certificate::from_str(src).unwrap();
+
+    assert_eq!(Algorithm::Ed25519, cert.public_key().algorithm());
+
+    assert_eq!(cert.critical_options().len(), 1);
+    assert_eq!(
+        cert.critical_options().get("hello@example.com").unwrap(),
+        "foobar"
+    );
+
+    let openssh = cert.to_openssh().unwrap();
+
+    assert_eq!(openssh, src);
+
+    assert_eq!(cert, Certificate::from_str(&openssh).unwrap());
+}
+
 #[test]
 fn decode_rsa_4096_openssh() {
     let cert = Certificate::from_str(RSA_4096_CERT_EXAMPLE).unwrap();