1 files changed, 128 insertions, 0 deletions
diff --git a/agent/sexp-secret.c b/agent/sexp-secret.c
new file mode 100644
index 000000000..5f0bdfa2e
--- /dev/null
+++ b/agent/sexp-secret.c
@@ -0,0 +1,128 @@
+/* sexp-secret.c - SEXP handling of the secret key
+ * Copyright (C) 2020 g10 Code GmbH.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include "agent.h"
+#include "../common/sexp-parse.h"
+
+/*
+ * When it's for ECC, fixup private key part in the cannonical SEXP
+ * representation in BUF.  If not ECC, do nothing.
+ */
+gpg_error_t
+fixup_when_ecc_private_key (unsigned char *buf, size_t *buflen_p)
+{
+  const unsigned char *s;
+  size_t n;
+  size_t buflen = *buflen_p;
+
+  s = buf;
+  if (*s != '(')
+    return gpg_error (GPG_ERR_INV_SEXP);
+  s++;
+  n = snext (&s);
+  if (!n)
+    return gpg_error (GPG_ERR_INV_SEXP);
+  if (!smatch (&s, n, "private-key"))
+    return gpg_error (GPG_ERR_UNKNOWN_SEXP);
+  if (*s != '(')
+    return gpg_error (GPG_ERR_UNKNOWN_SEXP);
+  s++;
+  n = snext (&s);
+  if (!smatch (&s, n, "ecc"))
+    return 0;
+
+  /* It's ECC */
+  while (*s == '(')
+    {
+      s++;
+      n = snext (&s);
+      if (!n)
+        return gpg_error (GPG_ERR_INV_SEXP);
+      if (n == 1 && *s == 'd')
+        {
+          unsigned char *s0;
+          size_t n0;
+
+          s += n;
+          s0 = (unsigned char *)s;
+          n = snext (&s);
+          n0 = s - s0;
+
+          if (!n)
+            return gpg_error (GPG_ERR_INV_SEXP);
+          else if ((n & 1) && !*s)
+            /* Detect wrongly added 0x00.  */
+            /* For all existing curves in libgcrypt-1.9 (so far), the
+               size of private part should be even.  */
+            {
+              size_t numsize;
+
+              n--;
+              buflen--;
+              numsize = snprintf (s0, s-s0+1, "%u:", (unsigned int)n);
+              memmove (s0+numsize, s+1, buflen - (s - buf));
+              memset (s0+numsize+buflen - (s - buf), 0, (n0 - numsize) + 1);
+              buflen -= (n0 - numsize);
+              s = s0+numsize+n;
+              *buflen_p = buflen;
+            }
+          else
+            s += n;
+        }
+      else
+        {
+          s += n;
+          n = snext (&s);
+          if (!n)
+            return gpg_error (GPG_ERR_INV_SEXP);
+          s += n;
+        }
+      if ( *s != ')' )
+        return gpg_error (GPG_ERR_INV_SEXP);
+      s++;
+    }
+  if (*s != ')')
+    return gpg_error (GPG_ERR_INV_SEXP);
+  s++;
+
+  return 0;
+}
+
+/*
+ * Scan BUF to get SEXP, put into RESULT.  Error offset will be in the
+ * pointer at R_ERROFF.  For ECC, the private part 'd' will be fixed
+ * up; That part may have 0x00 prefix of signed MPI encoding, which is
+ * incompatible to opaque MPI handling.
+ */
+gpg_error_t
+sexp_sscan_private_key (gcry_sexp_t *result, size_t *r_erroff,
+                        unsigned char *buf)
+{
+  gpg_error_t err;
+  size_t buflen, buflen0;
+
+  buflen = buflen0 = gcry_sexp_canon_len (buf, 0, NULL, NULL);
+  err = fixup_when_ecc_private_key (buf, &buflen);
+  if (!err)
+    err = gcry_sexp_sscan (result, r_erroff, (char*)buf, buflen0);
+  wipememory (buf, buflen0);
+
+  return err;
+}