Add GCD testing infrastructure.

This commit adds testing and Known Answer Tests (KATs) to OpenSSL for
the `BN_gcd` function.

(cherry picked from commit b75d6310857bc44ef2851bde68a1979c18bb4807)
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NNicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10122)

test/bntest.c

@@ -1634,6 +1634,30 @@ static int file_modsqrt(STANZA *s)
     return st;
 }
 
+static int file_gcd(STANZA *s)
+{
+    BIGNUM *a = NULL, *b = NULL, *gcd = NULL, *ret = NULL;
+    int st = 0;
+
+    if (!TEST_ptr(a = getBN(s, "A"))
+            || !TEST_ptr(b = getBN(s, "B"))
+            || !TEST_ptr(gcd = getBN(s, "GCD"))
+            || !TEST_ptr(ret = BN_new()))
+        goto err;
+
+    if (!TEST_true(BN_gcd(ret, a, b, ctx))
+            || !equalBN("gcd(A,B)", gcd, ret))
+        goto err;
+
+    st = 1;
+ err:
+    BN_free(a);
+    BN_free(b);
+    BN_free(gcd);
+    BN_free(ret);
+    return st;
+}
+
 static int test_bn2padded(void)
 {
 #if HAVE_BN_PADDED
@@ -2352,6 +2376,34 @@ static int test_ctx_consttime_flag(void)
     return st;
 }
 
+static int test_gcd_prime(void)
+{
+    BIGNUM *a = NULL, *b = NULL, *gcd = NULL;
+    int i, st = 0;
+
+    if (!TEST_ptr(a = BN_new())
+            || !TEST_ptr(b = BN_new())
+            || !TEST_ptr(gcd = BN_new()))
+        goto err;
+
+    if (!TEST_true(BN_generate_prime_ex(a, 1024, 0, NULL, NULL, NULL)))
+            goto err;
+    for (i = 0; i < NUM0; i++) {
+        if (!TEST_true(BN_generate_prime_ex(b, 1024, 0,
+                                            NULL, NULL, NULL))
+                || !TEST_true(BN_gcd(gcd, a, b, ctx))
+                || !TEST_true(BN_is_one(gcd)))
+            goto err;
+    }
+
+    st = 1;
+ err:
+    BN_free(a);
+    BN_free(b);
+    BN_free(gcd);
+    return st;
+}
+
 static int file_test_run(STANZA *s)
 {
     static const FILETEST filetests[] = {
@@ -2366,6 +2418,7 @@ static int file_test_run(STANZA *s)
         {"ModExp", file_modexp},
         {"Exp", file_exp},
         {"ModSqrt", file_modsqrt},
+        {"GCD", file_gcd},
     };
     int numtests = OSSL_NELEM(filetests);
     const FILETEST *tp = filetests;
@@ -2454,6 +2507,7 @@ int setup_tests(void)
 #endif
         ADD_ALL_TESTS(test_is_prime, (int)OSSL_NELEM(primes));
         ADD_ALL_TESTS(test_not_prime, (int)OSSL_NELEM(not_primes));
+        ADD_TEST(test_gcd_prime);
     } else {
         ADD_ALL_TESTS(run_file_tests, n);
     }

test/recipes/10-test_bn.t

@@ -16,9 +16,8 @@ use OpenSSL::Test qw/:DEFAULT data_file/;
 
 setup("test_bn");
 
-my @files = (
-    "bnexp.txt", "bnmod.txt", "bnmul.txt", "bnshift.txt", "bnsum.txt"
-    );
+my @files = qw( bnexp.txt bnmod.txt bnmul.txt bnshift.txt bnsum.txt bngcd.txt );
+
 plan tests => 1 + scalar(@files);
 
 foreach my $f ( @files ) {