openpgp: Update backsig when changing expiration time.

  - When updating the expiration time of signing-capable subkeys, also
    create a new primary key binding signature.

  - Fixes #534.

2 files changed, 14 insertions, 1 deletions

diff --git a/openpgp-ffi/include/sequoia/openpgp.h b/openpgp-ffi/include/sequoia/openpgp.h
index 99510a81..074170d5 100644
--- a/openpgp-ffi/include/sequoia/openpgp.h
+++ b/openpgp-ffi/include/sequoia/openpgp.h
@@ -1187,12 +1187,17 @@ pgp_signature_t pgp_valid_key_amalgamation_binding_signature (pgp_valid_key_amal
 /// Creates one or more self-signatures that when merged with the
 /// certificate cause the key to expire at the specified time.
 ///
+/// `subkey_signer` must be `NULL` when updating the expiration of the
+/// primary key, or updating the expiration of a non-signing capable
+/// subkey.  Otherwise, a signer for the subkey must be given.
+///
 /// The returned buffer must be freed using libc's allocator.
 /*/
 pgp_status_t pgp_valid_key_amalgamation_set_expiration_time
   (pgp_error_t *errp,
    pgp_valid_key_amalgamation_t ka,
    pgp_signer_t signer,
+   pgp_signer_t subkey_signer,
    time_t time,
    pgp_signature_t **sigs,
    size_t *sig_count);
diff --git a/openpgp-ffi/src/key_amalgamation.rs b/openpgp-ffi/src/key_amalgamation.rs
index d25fb2bc..f44ad04f 100644
--- a/openpgp-ffi/src/key_amalgamation.rs
+++ b/openpgp-ffi/src/key_amalgamation.rs
@@ -99,12 +99,17 @@ pub extern "C" fn pgp_valid_key_amalgamation_binding_signature<'a>(ka: *const Va
 /// Creates one or more self-signatures that when merged with the
 /// certificate cause the key to expire at the specified time.
 ///
+/// `subkey_signer` must be `NULL` when updating the expiration of the
+/// primary key, or updating the expiration of a non-signing capable
+/// subkey.  Otherwise, a signer for the subkey must be given.
+///
 /// The returned buffer must be freed using libc's allocator.
 #[::sequoia_ffi_macros::extern_fn] #[no_mangle] pub extern "C"
 fn pgp_valid_key_amalgamation_set_expiration_time(
     errp: Option<&mut *mut crate::error::Error>,
     ka: *const ValidKeyAmalgamation,
     primary_signer: *mut Box<dyn crypto::Signer>,
+    subkey_signer: Option<&'static mut Box<dyn crypto::Signer + 'static>>,
     expiry: time_t,
     sigs: *mut *mut *mut Signature, sig_count: *mut size_t)
     -> Status
@@ -117,7 +122,10 @@ fn pgp_valid_key_amalgamation_set_expiration_time(
     let sigs = ffi_param_ref_mut!(sigs);
     let sig_count = ffi_param_ref_mut!(sig_count);
 
-    match ka.set_expiration_time(signer.as_mut(), expiry) {
+    match ka.set_expiration_time(signer.as_mut(),
+                                 subkey_signer.map(|s| s.as_mut()),
+                                 expiry)
+    {
         Ok(new_sigs) => {
             let buffer = unsafe {
                 libc::calloc(new_sigs.len(), std::mem::size_of::<*mut Signature>())