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 <[email protected]>

1 files changed, 12 insertions, 0 deletions

diff --git a/agent/agent.h b/agent/agent.h
index b3d3c0407..af040b63f 100644
--- a/agent/agent.h
+++ b/agent/agent.h
@@ -560,6 +560,18 @@ gpg_error_t agent_pkdecrypt (ctrl_t ctrl, const char *desc_text,
                              const unsigned char *ciphertext, size_t ciphertextlen,
                              membuf_t *outbuf, int *r_padding);
 
+enum kemid
+  {
+    KEM_PQC_PGP,
+    KEM_PGP,
+    KEM_CMS,
+  };
+
+gpg_error_t agent_kem_decrypt (ctrl_t ctrl, const char *desc_text, int kemid,
+                               const unsigned char *ct, size_t ctlen,
+                               const unsigned char *option, size_t optionlen,
+                               membuf_t *outbuf);
+
 /*-- genkey.c --*/
 #define CHECK_CONSTRAINTS_NOT_EMPTY  1
 #define CHECK_CONSTRAINTS_NEW_SYMKEY 2