gpg: New commands --add-recipients and --change-recipients.

* g10/gpg.c (aAddRecipients, aChangeRecipients): New consts.
(opts): Add --add-recipients and --change-recipients.
(main): Handle them.
* g10/gpg.h (struct server_control_s): Add fields modify_recipients,
clear_recipients, and last_read_ctb.
* g10/armor.c (was_armored): New.
* g10/decrypt.c (decrypt_message): Add optional arg 'remusr'.  Handle
re-encryption if desired.
* g10/encrypt.c (write_pubkey_enc): Factor info printing out to ...
(show_encrypted_for_user_info): new.
(reencrypt_to_new_recipients): New.
* g10/packet.h (struct parse_packet_ctx_s): Add fields only_fookey_enc
and last_ctb.
(init_parse_packet): Clear them.
* g10/parse-packet.c (parse): Store CTB in the context.  Early return
on pubkey_enc and symkey_enc packets if requested.
* g10/mainproc.c (proc_encrypted): Allow for PKT being NULL.  Return
early in modify-recipients mode.
(proc_encryption_packets): Add two optional args 'r_dek' and 'r_list'.
Adjust callers.  Call do_proc_packets in modify-recipients mode
depending on the optional args.
(do_proc_packets): Add arg 'keep_dek_and_list'.  Adjust callers.  Save
the last read CTB in CTRL and return after the last fooenc_enc
packets.
--

This basically works but does not yet handle symmetric encrypted
packets (symkey_enc).

GnuPG-bug-id: 1825
(Yes, this is an at least 9 year old feature request)

1 files changed, 78 insertions, 17 deletions

diff --git a/g10/mainproc.c b/g10/mainproc.c
index 3bb46b574..2429e1006 100644
--- a/g10/mainproc.c
+++ b/g10/mainproc.c
@@ -116,7 +116,7 @@ static int literals_seen;
 
 
 /*** Local prototypes.  ***/
-static int do_proc_packets (CTX c, iobuf_t a);
+static int do_proc_packets (CTX c, iobuf_t a, int keep_dek_and_list);
 static void list_node (CTX c, kbnode_t node);
 static void proc_tree (CTX c, kbnode_t node);
 
@@ -580,10 +580,15 @@ proc_encrypted (CTX c, PACKET *pkt)
   int early_plaintext = literals_seen;
   unsigned int compliance_de_vs = 0;
 
-  if (pkt->pkttype == PKT_ENCRYPTED_AEAD)
-    c->seen_pkt_encrypted_aead = 1;
-  if (pkt->pkttype == PKT_ENCRYPTED_MDC)
-    c->seen_pkt_encrypted_mdc = 1;
+  if (pkt)
+    {
+      if (pkt->pkttype == PKT_ENCRYPTED_AEAD)
+        c->seen_pkt_encrypted_aead = 1;
+      if (pkt->pkttype == PKT_ENCRYPTED_MDC)
+        c->seen_pkt_encrypted_mdc = 1;
+    }
+  else /* No PKT indicates the the add-recipients mode.  */
+    log_assert (c->ctrl->modify_recipients);
 
   if (early_plaintext)
     {
@@ -650,6 +655,22 @@ proc_encrypted (CTX c, PACKET *pkt)
   if (c->dek && opt.verbose > 1)
     log_info (_("public key encrypted data: good DEK\n"));
 
+  if (c->ctrl->modify_recipients)
+    {
+      if (c->anchor)
+        {
+          log_error ("command not possible with nested data\n");
+          write_status_errcode ("decryption.mod_recp", GPG_ERR_BAD_DATA);
+          xfree (c->dek);
+          c->dek = NULL;
+          return;
+        }
+      literals_seen++;
+      /* Simply return here.  Our caller will then test for DEK and
+       * the PK_list to decide whether decryption worked.  */
+      return;
+    }
+
   if (!opt.show_only_session_key)
     write_status (STATUS_BEGIN_DECRYPTION);
 
@@ -1112,7 +1133,7 @@ static int
 proc_encrypt_cb (iobuf_t a, void *info )
 {
   CTX c = info;
-  return proc_encryption_packets (c->ctrl, info, a );
+  return proc_encryption_packets (c->ctrl, info, a, NULL, NULL);
 }
 
 
@@ -1502,7 +1523,7 @@ proc_packets (ctrl_t ctrl, void *anchor, iobuf_t a )
 
   c->ctrl = ctrl;
   c->anchor = anchor;
-  rc = do_proc_packets (c, a);
+  rc = do_proc_packets (c, a, 0);
   xfree (c);
 
   return rc;
@@ -1525,7 +1546,7 @@ proc_signature_packets (ctrl_t ctrl, void *anchor, iobuf_t a,
   c->signed_data.used = !!signedfiles;
 
   c->sigfilename = sigfilename;
-  rc = do_proc_packets (c, a);
+  rc = do_proc_packets (c, a, 0);
 
   /* If we have not encountered any signature we print an error
      messages, send a NODATA status back and return an error code.
@@ -1568,7 +1589,7 @@ proc_signature_packets_by_fd (ctrl_t ctrl, void *anchor, iobuf_t a,
   c->signed_data.data_names = NULL;
   c->signed_data.used = (signed_data_fd != GNUPG_INVALID_FD);
 
-  rc = do_proc_packets (c, a);
+  rc = do_proc_packets (c, a, 0);
 
   /* If we have not encountered any signature we print an error
      messages, send a NODATA status back and return an error code.
@@ -1592,8 +1613,13 @@ proc_signature_packets_by_fd (ctrl_t ctrl, void *anchor, iobuf_t a,
 }
 
 
-int
-proc_encryption_packets (ctrl_t ctrl, void *anchor, iobuf_t a )
+/* Handle encryption packets.  If called recursively the caller's CTX
+ * should be given for ANCHOR.  If R_DEK and R_LIST are not NULL the
+ * DEK (or NULL) is returned there and the list at R_LIST; the caller
+ * needs to release them; even if the function returns an error. */
+gpg_error_t
+proc_encryption_packets (ctrl_t ctrl, void *anchor, iobuf_t a,
+                         DEK **r_dek, struct pubkey_enc_list **r_list)
 {
   CTX c = xmalloc_clear (sizeof *c);
   int rc;
@@ -1601,7 +1627,16 @@ proc_encryption_packets (ctrl_t ctrl, void *anchor, iobuf_t a )
   c->ctrl = ctrl;
   c->anchor = anchor;
   c->encrypt_only = 1;
-  rc = do_proc_packets (c, a);
+  if (r_dek && r_list)
+    {
+      rc = do_proc_packets (c, a, 1);
+      *r_dek = c->dek;
+      c->dek = NULL;
+      *r_list = c->pkenc_list;
+      c->pkenc_list = NULL;
+    }
+  else
+    rc = do_proc_packets (c, a, 0);
   xfree (c);
   return rc;
 }
@@ -1626,8 +1661,11 @@ check_nesting (CTX c)
 }
 
 
+/* Main processing loop.  If KEEP_DEK_AND_LIST is set the DEK and
+ * PKENC_LIST of the context C are not released at the end of the
+ * function.  The caller is then required to do this.  */
 static int
-do_proc_packets (CTX c, iobuf_t a)
+do_proc_packets (CTX c, iobuf_t a, int keep_dek_and_list)
 {
   PACKET *pkt;
   struct parse_packet_ctx_s parsectx;
@@ -1648,6 +1686,18 @@ do_proc_packets (CTX c, iobuf_t a)
       any_data = 1;
       if (rc)
         {
+          if (c->ctrl->modify_recipients && gpg_err_code (rc) == GPG_ERR_TRUE)
+            {
+              /* Save the last read CTB (which was the last byte
+               * actually read from the input) and get out of the
+               * loop.  */
+              c->ctrl->last_read_ctb = parsectx.last_ctb;
+              /* We need to call the first part of the encrypted data
+               * handler to get the DEK.  */
+              proc_encrypted (c, NULL);
+              rc = -1;
+              break;
+            }
           free_packet (pkt, &parsectx);
           /* Stop processing when an invalid packet has been encountered
            * but don't do so when we are doing a --list-packets.  */
@@ -1706,8 +1756,19 @@ do_proc_packets (CTX c, iobuf_t a)
               goto leave;
 
             case PKT_SIGNATURE:   newpkt = add_signature (c, pkt); break;
-            case PKT_SYMKEY_ENC:  proc_symkey_enc (c, pkt); break;
-            case PKT_PUBKEY_ENC:  proc_pubkey_enc (c, pkt); break;
+
+            case PKT_SYMKEY_ENC:
+            case PKT_PUBKEY_ENC:
+              /* In --add-recipients mode set the stop flag as soon as
+               * we see the first of these packets.  */
+              if (c->ctrl->modify_recipients)
+                parsectx.only_fookey_enc = 1;
+              if (pkt->pkttype == PKT_SYMKEY_ENC)
+                proc_symkey_enc (c, pkt);
+              else
+                proc_pubkey_enc (c, pkt);
+              break;
+
             case PKT_ENCRYPTED:
             case PKT_ENCRYPTED_MDC:
             case PKT_ENCRYPTED_AEAD: proc_encrypted (c, pkt); break;
@@ -1783,8 +1844,8 @@ do_proc_packets (CTX c, iobuf_t a)
 
 
  leave:
-  release_list (c);
-  xfree(c->dek);
+  if (!keep_dek_and_list)
+    release_list (c);
   free_packet (pkt, &parsectx);
   deinit_parse_packet (&parsectx);
   xfree (pkt);