agent: Add initial support for hybrid ECC+PQC decryption with KEM.

* agent/agent.h (enum kemid): New.
(agent_kem_decrypt): New.
* agent/command.c (cmd_pkdecrypt): Support --kem option to call
agent_kem_decrypt.
* agent/pkdecrypt.c (reverse_buffer): New.
(agent_hybrid_pgp_kem_decrypt): New.
(agent_kem_decrypt): New.

--

Now, it only supports X25519 + ML-KEM.

GnuPG-bug-id: 7014
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

1 files changed, 39 insertions, 6 deletions

diff --git a/agent/command.c b/agent/command.c
index 5e74381ed..fd050ee6b 100644
--- a/agent/command.c
+++ b/agent/command.c
@@ -1049,10 +1049,14 @@ cmd_pksign (assuan_context_t ctx, char *line)
 
 
 static const char hlp_pkdecrypt[] =
-  "PKDECRYPT [<options>]\n"
+  "PKDECRYPT [--kem[=<kemid>] [<options>]\n"
   "\n"
   "Perform the actual decrypt operation.  Input is not\n"
-  "sensitive to eavesdropping.";
+  "sensitive to eavesdropping.\n"
+  "If the --kem option is used, decryption is done with the KEM,\n"
+  "inquiring upper-layer option, when needed.  KEMID can be\n"
+  "specified with --kem option;  Valid value is: PQC-PGP, PGP, or CMS.\n"
+  "Default is PQC-PGP.";
 static gpg_error_t
 cmd_pkdecrypt (assuan_context_t ctx, char *line)
 {
@@ -1061,22 +1065,51 @@ cmd_pkdecrypt (assuan_context_t ctx, char *line)
   unsigned char *value;
   size_t valuelen;
   membuf_t outbuf;
-  int padding;
+  int padding = -1;
+  unsigned char *option = NULL;
+  size_t optionlen = 0;
+  const char *p;
+  int kemid = -1;
 
-  (void)line;
+  p = has_option_name (line, "--kem");
+  if (p)
+    {
+      kemid = KEM_PQC_PGP;
+      if (*p++ == '=')
+        {
+          if (strcmp (p, "PQC-PGP"))
+            kemid = KEM_PQC_PGP;
+          else if (strcmp (p, "PGP"))
+            kemid = KEM_PGP;
+          else if (strcmp (p, "CMS"))
+            kemid = KEM_CMS;
+          else
+            return set_error (GPG_ERR_ASS_PARAMETER, "invalid KEM algorithm");
+        }
+    }
 
   /* First inquire the data to decrypt */
   rc = print_assuan_status (ctx, "INQUIRE_MAXLEN", "%u", MAXLEN_CIPHERTEXT);
   if (!rc)
     rc = assuan_inquire (ctx, "CIPHERTEXT",
 			&value, &valuelen, MAXLEN_CIPHERTEXT);
+  if (!rc && kemid > KEM_PQC_PGP)
+    rc = assuan_inquire (ctx, "OPTION",
+                         &option, &optionlen, MAXLEN_CIPHERTEXT);
   if (rc)
     return rc;
 
   init_membuf (&outbuf, 512);
 
-  rc = agent_pkdecrypt (ctrl, ctrl->server_local->keydesc,
-                        value, valuelen, &outbuf, &padding);
+  if (kemid < 0)
+    rc = agent_pkdecrypt (ctrl, ctrl->server_local->keydesc,
+                          value, valuelen, &outbuf, &padding);
+  else
+    {
+      rc = agent_kem_decrypt (ctrl, ctrl->server_local->keydesc, kemid,
+                              value, valuelen, option, optionlen, &outbuf);
+      xfree (option);
+    }
   xfree (value);
   if (rc)
     clear_outbuf (&outbuf);