From eeb21772effdd385e44eed547d717f171487987e Mon Sep 17 00:00:00 2001
From: Matt Caswell <matt@openssl.org>
Date: Fri, 27 May 2016 13:26:03 +0100
Subject: [PATCH] Add dhparam sanity check and update DH_check documentation

The -check argument to dhparam should never identify any problems if we
have just generated the parameters. Add a sanity check for this and print
an error and fail if necessary.

Also updates the documentation for the -check argument, and the DH_check()
function.

RT#4244

Reviewed-by: Richard Levitte <levitte@openssl.org>
---
 apps/dhparam.c                        | 25 ++++++++++++---
 doc/apps/dhparam.pod                  |  3 +-
 doc/crypto/DH_generate_parameters.pod | 46 ++++++++++++++++++++-------
 3 files changed, 57 insertions(+), 17 deletions(-)

diff --git a/apps/dhparam.c b/apps/dhparam.c
index 350dd28196..f86e315599 100644
--- a/apps/dhparam.c
+++ b/apps/dhparam.c
@@ -270,15 +270,30 @@ int dhparam_main(int argc, char **argv)
             goto end;
         }
         if (i & DH_CHECK_P_NOT_PRIME)
-            printf("p value is not prime\n");
+            BIO_printf(bio_err, "WARNING: p value is not prime\n");
         if (i & DH_CHECK_P_NOT_SAFE_PRIME)
-            printf("p value is not a safe prime\n");
+            BIO_printf(bio_err, "WARNING: p value is not a safe prime\n");
+        if (i & DH_CHECK_Q_NOT_PRIME)
+            BIO_printf(bio_err, "WARNING: q value is not a prime\n");
+        if (i & DH_CHECK_INVALID_Q_VALUE)
+            BIO_printf(bio_err, "WARNING: q value is invalid\n");
+        if (i & DH_CHECK_INVALID_J_VALUE)
+            BIO_printf(bio_err, "WARNING: j value is invalid\n");
         if (i & DH_UNABLE_TO_CHECK_GENERATOR)
-            printf("unable to check the generator value\n");
+            BIO_printf(bio_err,
+                       "WARNING: unable to check the generator value\n");
         if (i & DH_NOT_SUITABLE_GENERATOR)
-            printf("the g value is not a generator\n");
+            BIO_printf(bio_err, "WARNING: the g value is not a generator\n");
         if (i == 0)
-            printf("DH parameters appear to be ok.\n");
+            BIO_printf(bio_err, "DH parameters appear to be ok.\n");
+        if (num != 0 && i != 0) {
+            /*
+             * We have generated parameters but DH_check() indicates they are
+             * invalid! This should never happen!
+             */
+            BIO_printf(bio_err, "ERROR: Invalid parameters generated\n");
+            goto end;
+        }
     }
     if (C) {
         unsigned char *data;
diff --git a/doc/apps/dhparam.pod b/doc/apps/dhparam.pod
index 63cc0d372b..addd88a540 100644
--- a/doc/apps/dhparam.pod
+++ b/doc/apps/dhparam.pod
@@ -72,7 +72,8 @@ avoid small-subgroup attacks that may be possible otherwise.
 
 =item B<-check>
 
-check if the parameters are valid primes and generator.
+Performs numerous checks to see if the supplied parameters are valid and
+displays a warning if not.
 
 =item B<-2>, B<-5>
 
diff --git a/doc/crypto/DH_generate_parameters.pod b/doc/crypto/DH_generate_parameters.pod
index 71fa4363d4..8970aae444 100644
--- a/doc/crypto/DH_generate_parameters.pod
+++ b/doc/crypto/DH_generate_parameters.pod
@@ -37,12 +37,41 @@ number is generated, and when a prime has been found, B<BN_GENCB_call(cb, 3, 0)>
 is called. See L<BN_generate_prime(3)> for information on
 the BN_GENCB_call() function.
 
-DH_check() validates Diffie-Hellman parameters. It checks that B<p> is
-a safe prime, and that B<g> is a suitable generator. In the case of an
-error, the bit flags DH_CHECK_P_NOT_SAFE_PRIME or
-DH_NOT_SUITABLE_GENERATOR are set in B<*codes>.
-DH_UNABLE_TO_CHECK_GENERATOR is set if the generator cannot be
-checked, i.e. it does not equal 2 or 5.
+DH_check() confirms that the Diffie-Hellman parameters B<dh> are valid. The
+value of B<*codes> is updated with any problems found. If B<*codes> is zero then
+no problems were found, otherwise the following bits may be set:
+
+=over 4
+
+=item DH_CHECK_P_NOT_PRIME
+
+The parameter B<p> is not prime.
+
+=item DH_CHECK_P_NOT_SAFE_PRIME
+
+The parameter B<p> is not a safe prime and no B<q> value is present.
+
+=item DH_UNABLE_TO_CHECK_GENERATOR
+
+The generator B<g> cannot be checked for suitability.
+
+=item DH_NOT_SUITABLE_GENERATOR
+
+The generator B<g> is not suitable.
+
+=item DH_CHECK_Q_NOT_PRIME
+
+The parameter B<q> is not prime.
+
+=item DH_CHECK_INVALID_Q_VALUE
+
+The parameter B<q> is invalid.
+
+=item DH_CHECK_INVALID_J_VALUE
+
+The parameter B<j> is invalid.
+
+=back
 
 =head1 RETURN VALUES
 
@@ -62,11 +91,6 @@ hours before finding a suitable prime.
 The parameters generated by DH_generate_parameters_ex() and DH_generate_parameters()
 are not to be used in signature schemes.
 
-=head1 BUGS
-
-If B<generator> is not 2 or 5, B<dh-E<gt>g>=B<generator> is not
-a usable generator.
-
 =head1 SEE ALSO
 
 L<dh(3)>, L<ERR_get_error(3)>, L<rand(3)>,
-- 
2.25.1