Support sending DigestSign request to management client

To receive undigested message for signing, indicate support
for handling message digesting in the client using an argument
"digest" to --management-external-key.

For example, to announce pkcs1 padding and digesting support use:

--management-external-key pkcs1 pss digest

In PK_SIGN, the algorithm string will get data=message
in addition to other relevant options.

Note that it is not guaranteed that the client will be prompted
with undigested message. This is possible only when OpenSSL
calls our provider for DigestSign() as opposed to Sign(). In
practice, signature operation always appears to result in
a DigestSign() call through the provider interface.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20211214165928.30676-12-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23435.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/manage.h b/src/openvpn/manage.h
index 5ed27c0c5430224d403dc1826f08fafb23098131..9621f479d7d01620e20e8d00fd344091a178d767 100644 (file)
--- a/src/openvpn/manage.h
+++ b/src/openvpn/manage.h
@@ -340,6 +340,7 @@ struct management *management_init(void);
 #define MF_QUERY_PROXY              (1<<14)
 #define MF_EXTERNAL_CERT            (1<<15)
 #define MF_EXTERNAL_KEY_PSSPAD      (1<<16)
+#define MF_EXTERNAL_KEY_DIGEST      (1<<17)
 
 bool management_open(struct management *man,
                      const char *addr,

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 42ea3baea82b8ed217bc6e00b9a12a8e69e1aef2..eeb745473d821021e9661067cdd1d02c5dade5d9 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -5525,6 +5525,10 @@ add_option(struct options *options,
             {
                 options->management_flags |= MF_EXTERNAL_KEY_PSSPAD;
             }
+            else if (streq(p[j], "digest"))
+            {
+                options->management_flags |= MF_EXTERNAL_KEY_DIGEST;
+            }
             else
             {
                 msg(msglevel, "Unknown management-external-key flag: %s", p[j]);

diff --git a/src/openvpn/xkey_helper.c b/src/openvpn/xkey_helper.c
index 8a42c249551b8e10e97abae8dfd9fe770276b2a4..56e6c4708c22893356683c38a2988227ef3dc3d2 100644 (file)
--- a/src/openvpn/xkey_helper.c
+++ b/src/openvpn/xkey_helper.c
@@ -138,17 +138,22 @@ int
 xkey_management_sign(void *unused, unsigned char *sig, size_t *siglen,
                      const unsigned char *tbs, size_t tbslen, XKEY_SIGALG alg)
 {
+    dmsg(D_LOW, "In xkey_management_sign with keytype = %s, op = %s",
+         alg.keytype, alg.op);
+
     (void) unused;
     char alg_str[128];
     unsigned char buf[EVP_MAX_MD_SIZE]; /* for computing digest if required */
     size_t buflen = sizeof(buf);
 
-    unsigned char enc[EVP_MAX_MD_SIZE + 32]; /* 32 bytes enough for digest inf structure */
+    unsigned char enc[EVP_MAX_MD_SIZE + 32]; /* 32 bytes enough for digest info structure */
     size_t enc_len = sizeof(enc);
 
     unsigned int flags = management->settings.flags;
+    bool is_message = !strcmp(alg.op, "DigestSign"); /* tbs is message, not digest */
 
-    if (!strcmp(alg.op, "DigestSign"))
+    /* if management client cannot do digest -- we do it here */
+    if (!strcmp(alg.op, "DigestSign") && !(flags & MF_EXTERNAL_KEY_DIGEST))
     {
         dmsg(D_LOW, "xkey_management_sign: computing digest");
         if (xkey_digest(tbs, tbslen, buf, &buflen, alg.mdname))
@@ -156,6 +161,7 @@ xkey_management_sign(void *unused, unsigned char *sig, size_t *siglen,
             tbs = buf;
             tbslen = buflen;
             alg.op = "Sign";
+            is_message = false;
         }
         else
         {
@@ -165,22 +171,38 @@ xkey_management_sign(void *unused, unsigned char *sig, size_t *siglen,
 
     if (!strcmp(alg.keytype, "EC"))
     {
-        strncpynt(alg_str, "ECDSA", sizeof(alg_str));
+        if (!strcmp(alg.op, "Sign"))
+        {
+            strncpynt(alg_str, "ECDSA", sizeof(alg_str));
+        }
+        else
+        {
+            openvpn_snprintf(alg_str, sizeof(alg_str), "ECDSA,hashalg=%s", alg.mdname);
+        }
     }
     /* else assume RSA key */
     else if (!strcmp(alg.padmode, "pkcs1") && (flags & MF_EXTERNAL_KEY_PKCS1PAD))
     {
-        /* management interface expects a pkcs1 encoded digest -- add it */
-        if (!encode_pkcs1(enc, &enc_len, alg.mdname, tbs, tbslen))
+        /* For Sign, management interface expects a pkcs1 encoded digest -- add it */
+        if (!strcmp(alg.op, "Sign"))
         {
-            return 0;
+            if (!encode_pkcs1(enc, &enc_len, alg.mdname, tbs, tbslen))
+            {
+                return 0;
+            }
+            tbs = enc;
+            tbslen = enc_len;
+            strncpynt(alg_str, "RSA_PKCS1_PADDING", sizeof(alg_str));
+        }
+        /* For undigested message, add hashalg=digest parameter */
+        else
+        {
+            openvpn_snprintf(alg_str, sizeof(alg_str), "%s,hashalg=%s",
+                            "RSA_PKCS1_PADDING", alg.mdname);
         }
-        tbs = enc;
-        tbslen = enc_len;
-
-        strncpynt(alg_str, "RSA_PKCS1_PADDING", sizeof(alg_str));
     }
-    else if (!strcmp(alg.padmode, "none") && (flags & MF_EXTERNAL_KEY_NOPADDING))
+    else if (!strcmp(alg.padmode, "none") && (flags & MF_EXTERNAL_KEY_NOPADDING)
+             &&!strcmp(alg.op, "Sign")) /* NO_PADDING requires digested data */
     {
         strncpynt(alg_str, "RSA_NO_PADDING", sizeof(alg_str));
     }
@@ -190,10 +212,16 @@ xkey_management_sign(void *unused, unsigned char *sig, size_t *siglen,
                        "RSA_PKCS1_PSS_PADDING", alg.mdname,alg.saltlen);
     }
     else {
-        msg(M_NONFATAL, "RSA padding mode unknown or not supported by management-client <%s>",
+        msg(M_NONFATAL, "RSA padding mode not supported by management-client <%s>",
             alg.padmode);
         return 0;
     }
+
+    if (is_message)
+    {
+        strncat(alg_str, ",data=message", sizeof(alg_str) - strlen(alg_str) - 1);
+    }
+
     dmsg(D_LOW, "xkey management_sign: requesting sig with algorithm <%s>", alg_str);
 
     char *in_b64 = NULL;