Support OpenSSL versions >= 1.1 for ENABLE_OPENSSL_TESTS

The only reason OpenSSL 1.1 was not supported was the removal of direct
access to r and s in ECDSA_SIG. This commit adds a simplified version of
ECDSA_SIG_get0 for < 1.1 that can be used like ECDSA_SIG_get0 in >= 1.1

build-aux/m4/bitcoin_secp.m4

@@ -48,7 +48,6 @@ if test x"$has_libcrypto" = x"yes" && test x"$has_openssl_ec" = x; then
     EC_KEY_free(eckey);
     ECDSA_SIG *sig_openssl;
     sig_openssl = ECDSA_SIG_new();
-    (void)sig_openssl->r;
     ECDSA_SIG_free(sig_openssl);
   ]])],[has_openssl_ec=yes],[has_openssl_ec=no])
   AC_MSG_RESULT([$has_openssl_ec])

src/tests.c

@@ -23,6 +23,9 @@
 #include "openssl/ec.h"
 #include "openssl/ecdsa.h"
 #include "openssl/obj_mac.h"
+# if OPENSSL_VERSION_NUMBER < 0x10100000L
+void ECDSA_SIG_get0(const ECDSA_SIG *sig, const BIGNUM **pr, const BIGNUM **ps) {*pr = sig->r; *ps = sig->s;}
+# endif
 #endif
 
 #include "contrib/lax_der_parsing.c"
@@ -4150,6 +4153,7 @@ int test_ecdsa_der_parse(const unsigned char *sig, size_t siglen, int certainly_
 
 #ifdef ENABLE_OPENSSL_TESTS
     ECDSA_SIG *sig_openssl;
+    const BIGNUM *r = NULL, *s = NULL;
     const unsigned char *sigptr;
     unsigned char roundtrip_openssl[2048];
     int len_openssl = 2048;
@@ -4201,15 +4205,16 @@ int test_ecdsa_der_parse(const unsigned char *sig, size_t siglen, int certainly_
     sigptr = sig;
     parsed_openssl = (d2i_ECDSA_SIG(&sig_openssl, &sigptr, siglen) != NULL);
     if (parsed_openssl) {
-        valid_openssl = !BN_is_negative(sig_openssl->r) && !BN_is_negative(sig_openssl->s) && BN_num_bits(sig_openssl->r) > 0 && BN_num_bits(sig_openssl->r) <= 256 && BN_num_bits(sig_openssl->s) > 0 && BN_num_bits(sig_openssl->s) <= 256;
+        ECDSA_SIG_get0(sig_openssl, &r, &s);
+        valid_openssl = !BN_is_negative(r) && !BN_is_negative(s) && BN_num_bits(r) > 0 && BN_num_bits(r) <= 256 && BN_num_bits(s) > 0 && BN_num_bits(s) <= 256;
         if (valid_openssl) {
             unsigned char tmp[32] = {0};
-            BN_bn2bin(sig_openssl->r, tmp + 32 - BN_num_bytes(sig_openssl->r));
+            BN_bn2bin(r, tmp + 32 - BN_num_bytes(r));
             valid_openssl = memcmp(tmp, max_scalar, 32) < 0;
         }
         if (valid_openssl) {
             unsigned char tmp[32] = {0};
-            BN_bn2bin(sig_openssl->s, tmp + 32 - BN_num_bytes(sig_openssl->s));
+            BN_bn2bin(s, tmp + 32 - BN_num_bytes(s));
             valid_openssl = memcmp(tmp, max_scalar, 32) < 0;
         }
     }