From 0173b249cfb7f02f94911ec759630d81f312e0bd Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Wed, 27 Feb 2019 10:37:26 +0900
Subject: [PATCH] agent: PKSIGN should return signature in same format for
 card.

* agent/pksign.c (agent_pksign_do):

--

It's best to keep same data format by libgcrypt.

For card (due to historical reasons), gpg-agent or scdaemon used to
prefix 0x00 when it starts 0x80, so that it can be parsed signed MPI
as well as unsigned MPI.  It used to do nothing for preceding zeros.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 agent/pksign.c | 84 ++++++++++++++++++++++----------------------------
 1 file changed, 37 insertions(+), 47 deletions(-)

diff --git a/agent/pksign.c b/agent/pksign.c
index f54af0817..828e63f58 100644
--- a/agent/pksign.c
+++ b/agent/pksign.c
@@ -367,20 +367,29 @@ agent_pksign_do (ctrl_t ctrl, const char *cache_nonce,
 
       if (is_RSA)
         {
-          check_signature = 1;
-          if (*buf & 0x80)
-            {
-              len++;
-              buf = xtryrealloc (buf, len);
-              if (!buf)
-                goto leave;
+          unsigned char *p = buf;
 
-              memmove (buf + 1, buf, len - 1);
-              *buf = 0;
+          check_signature = 1;
+
+          /*
+           * Smartcard returns fixed-size data, which is good for
+           * PKCS1.  If variable-size unsigned MPI is needed, remove
+           * zeros.
+           */
+          if (ctrl->digest.algo == MD_USER_TLS_MD5SHA1
+              || ctrl->digest.raw_value)
+            {
+              int i;
+
+              for (i = 0; i < len - 1; i++)
+                if (p[i])
+                  break;
+              p += i;
+              len -= i;
             }
 
           err = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%b)))",
-                                 (int)len, buf);
+                                 (int)len, p);
         }
       else if (is_EdDSA)
         {
@@ -389,53 +398,34 @@ agent_pksign_do (ctrl_t ctrl, const char *cache_nonce,
         }
       else if (is_ECDSA)
         {
-          unsigned char *r_buf_allocated = NULL;
-          unsigned char *s_buf_allocated = NULL;
           unsigned char *r_buf, *s_buf;
           int r_buflen, s_buflen;
+          int i;
 
           r_buflen = s_buflen = len/2;
 
-          if (*buf & 0x80)
-            {
-              r_buflen++;
-              r_buf_allocated = xtrymalloc (r_buflen);
-              if (!r_buf_allocated)
-                {
-                  err = gpg_error_from_syserror ();
-                  goto leave;
-                }
+          /*
+           * Smartcard returns fixed-size data.  For ECDSA signature,
+           * variable-size unsigned MPI is assumed, thus, remove
+           * zeros.
+           */
+          r_buf = buf;
+          for (i = 0; i < r_buflen - 1; i++)
+            if (r_buf[i])
+              break;
+          r_buf += i;
+          r_buflen -= i;
 
-              r_buf = r_buf_allocated;
-              memcpy (r_buf + 1, buf, len/2);
-              *r_buf = 0;
-            }
-          else
-            r_buf = buf;
-
-          if (*(buf + len/2) & 0x80)
-            {
-              s_buflen++;
-              s_buf_allocated = xtrymalloc (s_buflen);
-              if (!s_buf_allocated)
-                {
-                  err = gpg_error_from_syserror ();
-                  xfree (r_buf_allocated);
-                  goto leave;
-                }
-
-              s_buf = s_buf_allocated;
-              memcpy (s_buf + 1, buf + len/2, len/2);
-              *s_buf = 0;
-            }
-          else
-            s_buf = buf + len/2;
+          s_buf = buf + len/2;
+          for (i = 0; i < s_buflen - 1; i++)
+            if (s_buf[i])
+              break;
+          s_buf += i;
+          s_buflen -= i;
 
           err = gcry_sexp_build (&s_sig, NULL, "(sig-val(ecdsa(r%b)(s%b)))",
                                  r_buflen, r_buf,
                                  s_buflen, s_buf);
-          xfree (r_buf_allocated);
-          xfree (s_buf_allocated);
         }
       else
         err = gpg_error (GPG_ERR_NOT_IMPLEMENTED);