openpgp: Change the `decrypt` proxy in the decryption helper.

  - Returning rich errors from this function may compromise secret key
    material due to Bleichenbacher-style attacks.  Change the API to
    prevent this.

  - Hat tip to Hanno Böck.

  - Fixes #507.

1 files changed, 4 insertions, 3 deletions

diff --git a/ipc/examples/gpg-agent-decrypt.rs b/ipc/examples/gpg-agent-decrypt.rs
index b580b353..76be71db 100644
--- a/ipc/examples/gpg-agent-decrypt.rs
+++ b/ipc/examples/gpg-agent-decrypt.rs
@@ -100,14 +100,15 @@ impl<'a> DecryptionHelper for Helper<'a> {
                   sym_algo: Option<SymmetricAlgorithm>,
                   mut decrypt: D)
                   -> openpgp::Result<Option<openpgp::Fingerprint>>
-        where D: FnMut(SymmetricAlgorithm, &SessionKey) -> openpgp::Result<()>
+        where D: FnMut(SymmetricAlgorithm, &SessionKey) -> bool
     {
         // Try each PKESK until we succeed.
         for pkesk in pkesks {
             if let Some(key) = self.keys.get(pkesk.recipient()) {
                 let mut pair = KeyPair::new(self.ctx, key)?;
-                if let Some(_) = pkesk.decrypt(&mut pair, sym_algo)
-                    .and_then(|(algo, session_key)| decrypt(algo, &session_key).ok())
+                if pkesk.decrypt(&mut pair, sym_algo)
+                    .map(|(algo, session_key)| decrypt(algo, &session_key))
+                    .unwrap_or(false)
                 {
                     break;
                 }