Re: more on read_s2k() for GnuTLS 2.4.1 (including "GNU dummy S2K")

[Daniel Kahn Gillmor]

On Thu 2008-08-14 04:19:01 -0400, Simon Josefsson wrote:

> Ouch.  

I know!  One day i'll be a better programmer, i hope :/

> FWIW, I think your goal is fine and it should be supported
> eventually.

Thanks, that's good to hear.

> I'm not sure this can go into 2.4.x, it seems like a somewhat large
> addition, although I'll let Nikos comment as well.  Maybe it could
> go in.

Hrm.  I don't think it's that big of a change (and it only affects a
people using GnuTLS for OpenPGP), but of course i'll defer to you and
Nikos.

> However, this certainly seems appropriate for 2.5.  Please create a
> patch for it, and I'll apply it.

The patch to enable parsing (but not decrypting) of locked secret keys
(including the "gnu-dummy" S2K option) against GnuTLS 2.5.3 is
attached, and seems to work for me.  Please let me know if you have
any problems or concerns with it.

> Btw, I want to get the 2.6.x release process started, I think we
> have enough new features in 2.5.x to be ready for a new stable
> release.  So maybe it isn't that important to get into 2.4.x if
> 2.6.x is release relatively soon.

I was hoping for 2.4.x because i'd love to see support for this in
debian lenny, but we likely won't be able to get a new version of
2.4.x into lenny at this point in debian's release cycle anyway.
Regardless of its status in 2.4.x, i'd certainly like to see this
behavior in 2.6.

Regards,

        --dkg

diff --git a/lib/opencdk/opencdk.h b/lib/opencdk/opencdk.h
index 9df17ff..d4717b1 100644
--- a/lib/opencdk/opencdk.h
+++ b/lib/opencdk/opencdk.h
@@ -185,7 +185,8 @@ enum cdk_pubkey_algo_t {
 enum cdk_s2k_type_t {
     CDK_S2K_SIMPLE     = 0,
     CDK_S2K_SALTED     = 1,
-    CDK_S2K_ITERSALTED = 3
+    CDK_S2K_ITERSALTED = 3,
+    CDK_S2K_GNU_DUMMY = 101 /* look for --export-secret-subkeys in gpg(1) */
 };
 
 /* The different kind of user ID preferences. */
diff --git a/lib/opencdk/read-packet.c b/lib/opencdk/read-packet.c
index 9e40903..78e5605 100644
--- a/lib/opencdk/read-packet.c
+++ b/lib/opencdk/read-packet.c
@@ -78,10 +78,35 @@ read_16 (cdk_stream_t s)
 }
 
 
-static int
+/* read about S2K at http://tools.ietf.org/html/rfc4880#section-3.7.1 */
+static cdk_error_t
 read_s2k (cdk_stream_t inp, cdk_s2k_t s2k)
 {
-  return CDK_Not_Implemented;
+  size_t nread;
+
+  s2k->mode = cdk_stream_getc (inp);
+  s2k->hash_algo = cdk_stream_getc (inp);
+  if (s2k->mode == CDK_S2K_SIMPLE) 
+      return 0;
+  else if (s2k->mode == CDK_S2K_SALTED || s2k->mode == CDK_S2K_ITERSALTED)
+    {
+      if (stream_read (inp, s2k->salt, DIM (s2k->salt), &nread))
+       return CDK_Inv_Packet;
+      if (nread != DIM (s2k->salt))
+       return CDK_Inv_Packet;
+      
+      if (s2k->mode == CDK_S2K_ITERSALTED)
+       s2k->count = cdk_stream_getc (inp);
+    }
+  else if (s2k->mode == CDK_S2K_GNU_DUMMY)
+    {
+      /* look for --export-secret-subkeys in gpg(1) */
+      return 0;
+    }
+  else
+    return CDK_Not_Implemented;
+
+  return 0;
 }
 
 
@@ -330,14 +355,19 @@ read_secret_key (cdk_stream_t inp, size_t pktlen, 
cdk_pkt_seckey_t sk)
       rc = read_s2k (inp, sk->protect.s2k);
       if (rc)
        return rc;
-      sk->protect.ivlen = _gnutls_cipher_get_block_size (sk->protect.algo);
-      if (sk->protect.ivlen <= 0)
-       return CDK_Inv_Packet;
-      rc = stream_read (inp, sk->protect.iv, sk->protect.ivlen, &nread);
-      if (rc)
-       return rc;
-      if (nread != sk->protect.ivlen)
-       return CDK_Inv_Packet;
+       /* refer to --export-secret-subkeys in gpg(1) */
+      if (sk->protect.s2k->mode == CDK_S2K_GNU_DUMMY) 
+       sk->protect.ivlen = 0;
+      else {
+       sk->protect.ivlen = gcry_cipher_get_algo_blklen (sk->protect.algo);
+       if (!sk->protect.ivlen)
+         return CDK_Inv_Packet;
+       rc = stream_read (inp, sk->protect.iv, sk->protect.ivlen, &nread);
+       if (rc)
+         return rc;
+       if (nread != sk->protect.ivlen)
+         return CDK_Inv_Packet;
+      }
     }
   else
     sk->protect.algo = _pgp_cipher_to_gnutls (sk->s2k_usage);
@@ -391,6 +421,11 @@ read_secret_key (cdk_stream_t inp, size_t pktlen, 
cdk_pkt_seckey_t sk)
        return CDK_Out_Of_Core;
       if (stream_read (inp, sk->encdata, sk->enclen, &nread))
        return CDK_Inv_Packet;
+      /* checking that this is supposed to be a GNU Dummy S2K, which we know: 
*/
+      if ((sk->protect.s2k->mode == CDK_S2K_GNU_DUMMY) && 
+         ((sk->enclen != strlen("GNU\01")) ||
+          (0 != memcmp("GNU\01", sk->encdata, strlen("GNU\01")))))
+       return CDK_Inv_Packet;
       nskey = cdk_pk_get_nskey (sk->pk->pubkey_algo);
       if (!nskey)
        {

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