From 96577e2e46e4c5b66a2685cb605e07be0a6a09a5 Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Thu, 29 Apr 2021 16:05:19 +0200
Subject: [PATCH] scd: Rewrite READKEY to allow for compressed points.

* scd/app-help.c (app_help_pubkey_from_cert): New.  Taken from 2.3.
* scd/command.c (cmd_readkey): Rewrite using new helper.
--

Actually the readkey functions needs to return the uncompressed points
but if there is no readkey function, like in app-p15.c, readcert is
used and here we need to extract and the key and uncompress the point.

Noet that the --advanced flag did not and still does not work if the
key is fetched via readcert.

Signed-off-by: Werner Koch <wk@gnupg.org>
---
 scd/app-common.h |  2 ++
 scd/app-help.c   | 54 +++++++++++++++++++++++++++++++++++++++++
 scd/command.c    | 62 +++++++++++++++---------------------------------
 3 files changed, 75 insertions(+), 43 deletions(-)

diff --git a/scd/app-common.h b/scd/app-common.h
index 299465023..0265604c5 100644
--- a/scd/app-common.h
+++ b/scd/app-common.h
@@ -211,6 +211,8 @@ gpg_error_t app_help_get_keygrip_string_pk (const void *pk, size_t pklen,
                                             int *r_algo);
 gpg_error_t app_help_get_keygrip_string (ksba_cert_t cert, char *hexkeygrip,
                                          gcry_sexp_t *r_pkey, int *r_algo);
+gpg_error_t app_help_pubkey_from_cert (const void *cert, size_t certlen,
+                                       unsigned char **r_pk, size_t *r_pklen);
 size_t app_help_read_length_of_cert (int slot, int fid, size_t *r_certoff);
 
 
diff --git a/scd/app-help.c b/scd/app-help.c
index 476eecf2f..f95928675 100644
--- a/scd/app-help.c
+++ b/scd/app-help.c
@@ -122,6 +122,60 @@ app_help_get_keygrip_string (ksba_cert_t cert, char *hexkeygrip,
 }
 
 
+/* Get the public key from the binary encoded (CERT,CERTLEN).  */
+gpg_error_t
+app_help_pubkey_from_cert (const void *cert, size_t certlen,
+                           unsigned char **r_pk, size_t *r_pklen)
+{
+  gpg_error_t err;
+  ksba_cert_t kc;
+  unsigned char *pk, *fixed_pk;
+  size_t pklen, fixed_pklen;
+
+  *r_pk = NULL;
+  *r_pklen = 0;
+
+  pk = NULL; /*(avoid cc warning)*/
+
+  err = ksba_cert_new (&kc);
+  if (err)
+    return err;
+
+  err = ksba_cert_init_from_mem (kc, cert, certlen);
+  if (err)
+    goto leave;
+
+  pk = ksba_cert_get_public_key (kc);
+  if (!pk)
+    {
+      err = gpg_error (GPG_ERR_NO_PUBKEY);
+      goto leave;
+    }
+  pklen = gcry_sexp_canon_len (pk, 0, NULL, &err);
+
+  err = uncompress_ecc_q_in_canon_sexp (pk, pklen, &fixed_pk, &fixed_pklen);
+  if (err)
+    goto leave;
+  if (fixed_pk)
+    {
+      ksba_free (pk); pk = NULL;
+      pk = fixed_pk;
+      pklen = fixed_pklen;
+    }
+
+ leave:
+  if (!err)
+    {
+      *r_pk = pk;
+      *r_pklen = pklen;
+    }
+  else
+    ksba_free (pk);
+  ksba_cert_release (kc);
+  return err;
+}
+
+
 /* Given the SLOT and the File ID FID, return the length of the
    certificate contained in that file. Returns 0 if the file does not
    exists or does not contain a certificate.  If R_CERTOFF is not
diff --git a/scd/command.c b/scd/command.c
index e1895c6e3..dd965a31b 100644
--- a/scd/command.c
+++ b/scd/command.c
@@ -513,9 +513,7 @@ cmd_readkey (assuan_context_t ctx, char *line)
   int rc;
   int advanced = 0;
   unsigned char *cert = NULL;
-  size_t ncert, n;
-  ksba_cert_t kc = NULL;
-  ksba_sexp_t p;
+  size_t ncert;
   unsigned char *pk;
   size_t pklen;
 
@@ -526,60 +524,38 @@ cmd_readkey (assuan_context_t ctx, char *line)
     advanced = 1;
 
   line = skip_options (line);
-
   line = xstrdup (line); /* Need a copy of the line. */
+
   /* If the application supports the READKEY function we use that.
      Otherwise we use the old way by extracting it from the
      certificate.  */
   rc = app_readkey (ctrl->app_ctx, ctrl, advanced, line, &pk, &pklen);
   if (!rc)
-    { /* Yeah, got that key - send it back.  */
-      rc = assuan_send_data (ctx, pk, pklen);
-      xfree (pk);
-      xfree (line);
-      line = NULL;
-      goto leave;
-    }
-
-  if (gpg_err_code (rc) != GPG_ERR_UNSUPPORTED_OPERATION)
-    log_error ("app_readkey failed: %s\n", gpg_strerror (rc));
-  else
+    ; /* Yeah, got that key - send it back.  */
+  else if (gpg_err_code (rc) == GPG_ERR_UNSUPPORTED_OPERATION
+           || gpg_err_code (rc) == GPG_ERR_NOT_FOUND)
     {
+      /* Fall back to certificate reading.  */
       rc = app_readcert (ctrl->app_ctx, ctrl, line, &cert, &ncert);
       if (rc)
         log_error ("app_readcert failed: %s\n", gpg_strerror (rc));
+      else
+        {
+          rc = app_help_pubkey_from_cert (cert, ncert, &pk, &pklen);
+          if (rc)
+            log_error ("failed to parse the certificate: %s\n",
+                       gpg_strerror (rc));
+        }
     }
-  xfree (line);
-  line = NULL;
-  if (rc)
-    goto leave;
+  else
+    log_error ("app_readkey failed: %s\n", gpg_strerror (rc));
 
-  rc = ksba_cert_new (&kc);
-  if (rc)
-    goto leave;
+  if (!rc && pk && pklen)
+    rc = assuan_send_data (ctx, pk, pklen);
 
-  rc = ksba_cert_init_from_mem (kc, cert, ncert);
-  if (rc)
-    {
-      log_error ("failed to parse the certificate: %s\n", gpg_strerror (rc));
-      goto leave;
-    }
-
-  p = ksba_cert_get_public_key (kc);
-  if (!p)
-    {
-      rc = gpg_error (GPG_ERR_NO_PUBKEY);
-      goto leave;
-    }
-
-  n = gcry_sexp_canon_len (p, 0, NULL, NULL);
-  rc = assuan_send_data (ctx, p, n);
-  xfree (p);
-
-
- leave:
-  ksba_cert_release (kc);
   xfree (cert);
+  xfree (pk);
+  xfree (line);
   return rc;
 }