* parse-packet.c (parse_key): Support a SHA1 checksum as per

draft-rfc2440-bis04.
* packet.h (PKT_secret_key): Add field sha1chk.
* seckey-cert.c (do_check): Check the SHA1 checksum
(protect_secret_key): And create it.
* build-packet.c (do_secret_key): Mark it as sha-1 protected.
* g10.c, options.h: New option --simple-sk-checksum.

doc/gpg.sgml

@@ -581,6 +581,9 @@ The second form of the command has the special property to
 render the secret part of the primary key useless; this is
 a GNU extension to OpenPGP and other implementations can
 not be expected to successfully import such a key.
+
+See the option --simple-sk-checksum if you want to import such an
+exported key with an older OpenPGP implementation.
 </para></listitem></varlistentry>
 
 
@@ -1324,6 +1327,18 @@ for conventional encryption.
 </para></listitem></varlistentry>
 
 
+<varlistentry>
+<term>--simple-sk-checksum</term>
+<listitem><para>
+Secret keys are integrity protected by using a SHA-1 checksum.  This
+method will be part of an enhanced OpenPGP specification but GnuPG
+already uses it as a countermeasure against certain attacks.  Old
+applications don't understand this new format, so this option may be
+used to switch back to the old behaviour.  Using this this option
+bears a security risk.
+</para></listitem></varlistentry>
+
+
 <varlistentry>
 <term>--compress-algo &ParmN;</term>
 <listitem><para>

g10/ChangeLog

@@ -1,3 +1,16 @@
+2002-04-17  Werner Koch  <wk@gnupg.org>
+
+
+2002-04-16  Werner Koch  <wk@gnupg.org>
+
+	* parse-packet.c (parse_key): Support a SHA1 checksum as per
+	draft-rfc2440-bis04.
+	* packet.h (PKT_secret_key): Add field sha1chk.
+	* seckey-cert.c (do_check): Check the SHA1 checksum
+	(protect_secret_key): And create it.
+	* build-packet.c (do_secret_key): Mark it as sha-1 protected.
+	* g10.c, options.h: New option --simple-sk-checksum.
+
 2002-04-13  David Shaw  <dshaw@jabberwocky.com>
 
 	* parse-packet.c (parse_signature): Minor fix - signatures should

g10/build-packet.c

@@ -389,7 +389,7 @@ do_secret_key( IOBUF out, int ctb, PKT_secret_key *sk )
 	}
 	else {
           /* OpenPGP protection according to rfc2440 */
-	    iobuf_put(a, 0xff );
+	    iobuf_put(a, sk->protect.sha1chk? 0xfe : 0xff );
 	    iobuf_put(a, sk->protect.algo );
 	    if( sk->protect.s2k.mode >= 1000 ) {
                 /* These modes are not possible in OpenPGP, we use them

g10/g10.c

@@ -218,6 +218,7 @@ enum cmd_and_opt_values { aNull = 0,
     oS2KMode,
     oS2KDigest,
     oS2KCipher,
+    oSimpleSKChecksum,                          
     oCharset,
     oNotDashEscaped,
     oEscapeFrom,
@@ -412,6 +413,7 @@ static ARGPARSE_OPTS opts[] = {
 		N_("|NAME|use message digest algorithm NAME for passphrases")},
     { oS2KCipher, "s2k-cipher-algo",2,
 		N_("|NAME|use cipher algorithm NAME for passphrases")},
+    { oSimpleSKChecksum, "simple-sk-checksum", 0, "@"},
     { oCipherAlgo, "cipher-algo", 2 , N_("|NAME|use cipher algorithm NAME")},
     { oDigestAlgo, "digest-algo", 2 , N_("|NAME|use message digest algorithm NAME")},
     { oCompressAlgo, "compress-algo", 1 , N_("|N|use compress algorithm N")},
@@ -1132,7 +1134,7 @@ main( int argc, char **argv )
 	  case oS2KMode:   opt.s2k_mode = pargs.r.ret_int; break;
 	  case oS2KDigest: s2k_digest_string = m_strdup(pargs.r.ret_str); break;
 	  case oS2KCipher: s2k_cipher_string = m_strdup(pargs.r.ret_str); break;
-
+          case oSimpleSKChecksum: opt.simple_sk_checksum = 1; break;
 	  case oNoEncryptTo: opt.no_encrypt_to = 1; break;
 	  case oEncryptTo: /* store the recipient in the second list */
 	    sl = add_to_strlist2( &remusr, pargs.r.ret_str, utf8_strings );

g10/options.h

@@ -94,6 +94,8 @@ struct {
     int s2k_mode;
     int s2k_digest_algo;
     int s2k_cipher_algo;
+    int simple_sk_checksum; /* create the deprecated rfc2440 secret
+                               key protection*/
     int not_dash_escaped;
     int escape_from;
     int lock_once;

g10/packet.h

@@ -232,6 +232,7 @@ typedef struct {
 			/* and should never be passed to a mpi_xxx() */
     struct {
 	byte algo;  /* cipher used to protect the secret information*/
+        byte sha1chk;  /* SHA1 is used instead of a 16 bit checksum */ 
 	STRING2KEY s2k;
 	byte ivlen;  /* used length of the iv */
 	byte iv[16]; /* initialization vector for CFB mode */

g10/parse-packet.c

@@ -1494,14 +1494,16 @@ parse_key( IOBUF inp, int pkttype, unsigned long pktlen,
         if (rc) /* one of the MPIs were bad */
             goto leave;
 	sk->protect.algo = iobuf_get_noeof(inp); pktlen--;
+        sk->protect.sha1chk = 0;
 	if( sk->protect.algo ) {
 	    sk->is_protected = 1;
 	    sk->protect.s2k.count = 0;
-	    if( sk->protect.algo == 255 ) {
+	    if( sk->protect.algo == 254 || sk->protect.algo == 255 ) {
 		if( pktlen < 3 ) {
 		    rc = G10ERR_INVALID_PACKET;
 		    goto leave;
 		}
+                sk->protect.sha1chk = (sk->protect.algo == 254);
 		sk->protect.algo = iobuf_get_noeof(inp); pktlen--;
 		sk->protect.s2k.mode  = iobuf_get_noeof(inp); pktlen--;
 		sk->protect.s2k.hash_algo = iobuf_get_noeof(inp); pktlen--;
@@ -1550,8 +1552,10 @@ parse_key( IOBUF inp, int pkttype, unsigned long pktlen,
 		}
 
 		if( list_mode ) {
-		    printf(", algo: %d, hash: %d",
+		    printf(", algo: %d,%s hash: %d",
 				     sk->protect.algo,
+                                     sk->protect.sha1chk? ""
+                                                        :" simple checksum,",
 				     sk->protect.s2k.hash_algo );
 		    if( sk->protect.s2k.mode == 1
 			|| sk->protect.s2k.mode == 3 ) {

g10/seckey-cert.c

@@ -90,31 +90,54 @@ do_check( PKT_secret_key *sk, const char *tryagain_text )
 	    cipher_decrypt( cipher_hd, data, p, ndata );
 	    mpi_free( sk->skey[i] ); sk->skey[i] = NULL ;
 	    p = data;
-	    if( ndata < 2 ) {
+            if (sk->protect.sha1chk) {
-		log_error("not enough bytes for checksum\n");
+                /* This is the new SHA1 checksum method to detect
-		sk->csum = 0;
+                   tampering with the key as used by the Klima/Rosa
-		csum = 1;
+                   attack */
-	    }
+                sk->csum = 0;
-	    else {
+                csum = 1;
-		csum = checksum( data, ndata-2);
+                if( ndata < 20 ) 
-		sk->csum = data[ndata-2] << 8 | data[ndata-1];
+                    log_error("not enough bytes for SHA-1 checksum\n");
-                if ( sk->csum != csum ) {
+                else {
-                    /* This is a PGP 7.0.0 workaround */
+                    MD_HANDLE h = md_open (DIGEST_ALGO_SHA1, 1);
-                    sk->csum = csumc; /* take the encrypted one */
+                    if (!h)
+                        BUG(); /* algo not available */
+                    md_write (h, data, ndata - 20);
+                    md_final (h);
+                    if (!memcmp (md_read (h, DIGEST_ALGO_SHA1),
+                                 data + ndata - 20, 20) )
+                        csum = 0; /* digest does match */
+                    md_close (h);
                 }
-	    }
+            }
+            else {
+                if( ndata < 2 ) {
+                    log_error("not enough bytes for checksum\n");
+                    sk->csum = 0;
+                    csum = 1;
+                }
+                else {
+                    csum = checksum( data, ndata-2);
+                    sk->csum = data[ndata-2] << 8 | data[ndata-1];
+                    if ( sk->csum != csum ) {
+                        /* This is a PGP 7.0.0 workaround */
+                        sk->csum = csumc; /* take the encrypted one */
+                    }
+                }
+            }
                 
-	    /* must check it here otherwise the mpi_read_xx would fail
+            /* must check it here otherwise the mpi_read_xx would fail
-	     * because the length may have an arbitrary value */
+               because the length may have an arbitrary value */
-	    if( sk->csum == csum ) {
+            if( sk->csum == csum ) {
-		for( ; i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {
+                for( ; i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {
-		    nbytes = ndata;
+                    nbytes = ndata;
-		    sk->skey[i] = mpi_read_from_buffer(p, &nbytes, 1 );
+                    sk->skey[i] = mpi_read_from_buffer(p, &nbytes, 1 );
-		    ndata -= nbytes;
+                    ndata -= nbytes;
-		    p += nbytes;
+                    p += nbytes;
-		}
+                }
-                /* at this point ndata should be equal to 2 (the checksum) */
+                /* Note: at this point ndata should be 2 for a simple
-	    }
+                   checksum or 20 for the sha1 digest */
+            }
 	    m_free(data);
 	}
 	else {
@@ -265,7 +288,7 @@ protect_secret_key( PKT_secret_key *sk, DEK *dek )
 		}
 		for( ; j < PUBKEY_MAX_NSKEY; j++ )
 		    bufarr[j] = NULL;
-		ndata += 2; /* for checksum */
+		ndata += opt.simple_sk_checksum? 2 : 20; /* for checksum */
 
 		data = m_alloc_secure( ndata );
 		p = data;
@@ -277,11 +300,30 @@ protect_secret_key( PKT_secret_key *sk, DEK *dek )
 		    p += narr[j];
 		    m_free(bufarr[j]);
 		}
-		csum = checksum( data, ndata-2);
+                
-		sk->csum = csum;
+                if (opt.simple_sk_checksum) {
-		*p++ =	csum >> 8;
+                    log_info (_("generating the deprecated 16-bit checksum"
-		*p++ =	csum;
+                              " for secret key protection\n")); 
-		assert( p == data+ndata );
+                    csum = checksum( data, ndata-2);
+                    sk->csum = csum;
+                    *p++ =	csum >> 8;
+                    *p++ =	csum;
+                    sk->protect.sha1chk = 0;
+                }
+                else {
+                    MD_HANDLE h = md_open (DIGEST_ALGO_SHA1, 1);
+                    if (!h)
+                        BUG(); /* algo not available */
+                    md_write (h, data, ndata - 20);
+                    md_final (h);
+                    memcpy (p, md_read (h, DIGEST_ALGO_SHA1), 20);
+                    p += 20;
+                    md_close (h);
+                    sk->csum = csum = 0;
+                    sk->protect.sha1chk = 1;
+                }
+                assert( p == data+ndata );
+
 		cipher_encrypt( cipher_hd, data, data, ndata );
 		for(i = pubkey_get_npkey(sk->pubkey_algo);
 			i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {