openpgp: Fix parsing and serializing keys on 32-bit time_t systems.

  - Previously, during parsing and serialization, OpenPGP's unsigned
    32-bit timestamps were converted to Rust's SystemTime, which uses
    time_t.  On platforms where that is a signed 32-bit value, the time
    was truncated.  See #668.

  - One way to fix that is to make Rust's SystemTime independent of
    time_t.  See https://github.com/rust-lang/rust/issues/44394.

  - The other way is not to convert to SystemTime at the API
    boundary.  See
    https://gitlab.com/sequoia-pgp/sequoia/-/issues/806.

  - This fixes handling during parsing and serialization, but doesn't
    address the API issue.

  - Fixes #802.

4 files changed, 55 insertions, 5 deletions

diff --git a/openpgp/src/packet/key.rs b/openpgp/src/packet/key.rs
index 4ddb1aeb..dd5c9c7c 100644
--- a/openpgp/src/packet/key.rs
+++ b/openpgp/src/packet/key.rs
@@ -915,6 +915,35 @@ impl<P, R> Key4<P, R>
     }
 }
 
+impl<P, R> Key4<P, R>
+where
+    P: key::KeyParts,
+    R: key::KeyRole,
+{
+    /// Creates an OpenPGP public key from the specified key material.
+    ///
+    /// This is an internal version for parse.rs that avoids going
+    /// through SystemTime.
+    pub(crate) fn make<T>(creation_time: T,
+                          pk_algo: PublicKeyAlgorithm,
+                          mpis: mpi::PublicKey,
+                          secret: Option<SecretKeyMaterial>)
+                          -> Result<Self>
+    where
+        T: Into<Timestamp>,
+    {
+        Ok(Key4 {
+            common: Default::default(),
+            creation_time: creation_time.into(),
+            pk_algo,
+            mpis,
+            secret,
+            p: std::marker::PhantomData,
+            r: std::marker::PhantomData,
+        })
+    }
+}
+
 impl<R> Key4<key::PublicParts, R>
     where R: key::KeyRole,
 {
@@ -1035,6 +1064,14 @@ impl<P, R> Key4<P, R>
         self.creation_time.into()
     }
 
+    /// Gets the `Key`'s creation time without converting it to a
+    /// system time.
+    ///
+    /// This conversion may truncate the time to signed 32-bit time_t.
+    pub(crate) fn creation_time_raw(&self) -> Timestamp {
+        self.creation_time
+    }
+
     /// Sets the `Key`'s creation time.
     ///
     /// `timestamp` is converted to OpenPGP's internal format,
diff --git a/openpgp/src/packet/mod.rs b/openpgp/src/packet/mod.rs
index e33ee469..edae051f 100644
--- a/openpgp/src/packet/mod.rs
+++ b/openpgp/src/packet/mod.rs
@@ -2010,4 +2010,19 @@ mod test {
             }
         }
     }
+
+    /// Problem on systems with 32-bit time_t.
+    #[test]
+    fn issue_802() -> Result<()> {
+        let pp = crate::PacketPile::from_bytes(b"-----BEGIN PGP ARMORED FILE-----
+
+xiEE/////xIJKyQDAwIIAQENAFYp8M2JngCfc04tIwMBCuU=
+-----END PGP ARMORED FILE-----
+")?;
+        let p = pp.path_ref(&[0]).unwrap();
+        let buf = p.to_vec().expect("Failed to serialize packet");
+        let q = Packet::from_bytes(&buf).unwrap();
+        assert_eq!(p, &q);
+        Ok(())
+    }
 }
diff --git a/openpgp/src/parse.rs b/openpgp/src/parse.rs
index 3afc077c..d1b5a440 100644
--- a/openpgp/src/parse.rs
+++ b/openpgp/src/parse.rs
@@ -2229,8 +2229,7 @@ impl Key4<key::UnspecifiedParts, key::UnspecifiedRole>
             -> Result<Key4<key::PublicParts, R>>
             where R: key::KeyRole
         {
-            Key4::new(Timestamp::from(creation_time),
-                      pk_algo, mpis)
+            Key4::make(creation_time, pk_algo, mpis, None)
         }
         fn s<R>(creation_time: u32,
                 pk_algo: PublicKeyAlgorithm,
@@ -2239,8 +2238,7 @@ impl Key4<key::UnspecifiedParts, key::UnspecifiedRole>
             -> Result<Key4<key::SecretParts, R>>
             where R: key::KeyRole
         {
-            Key4::with_secret(Timestamp::from(creation_time),
-                              pk_algo, mpis, secret)
+            Key4::make(creation_time, pk_algo, mpis, Some(secret))
         }
 
         let tag = php.header.ctb().tag();
diff --git a/openpgp/src/serialize.rs b/openpgp/src/serialize.rs
index 08b9cc40..6656e439 100644
--- a/openpgp/src/serialize.rs
+++ b/openpgp/src/serialize.rs
@@ -1807,7 +1807,7 @@ impl<P, R> Marshal for Key4<P, R>
         let have_secret_key = P::significant_secrets() && self.has_secret();
 
         write_byte(o, 4)?; // Version.
-        write_be_u32(o, Timestamp::try_from(self.creation_time())?.into())?;
+        write_be_u32(o, self.creation_time_raw().into())?;
         write_byte(o, self.pk_algo().into())?;
         self.mpis().serialize(o)?;