OpenSSL changed "BN_zero" causing error

[bbosch-d]

Hi, when I try to install bplib on Ubuntu 22.04, I get this error:

      bplib/src/bp_fp2.c: In function ‘FP2_zero’:
      bplib/src/bp_fp2.c:111:9: error: invalid use of void expression
        111 |     if (!BN_zero(a->f[0]) || !BN_zero(a->f[1]))
            |         ^
      bplib/src/bp_fp2.c:111:30: error: invalid use of void expression
        111 |     if (!BN_zero(a->f[0]) || !BN_zero(a->f[1]))
            |                              ^
      error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
      [end of output]

I searched for this problem online and it seems that OpenSSL changed the behavior of BN_zero which no longer returns a success integer. They essentially changed BN_zero to do what BN_zero_ex used to do.

For an ultra quick fix I changed the following and it seems to work:

index 6d7d1c7..062dd32 100644
--- a/bplib/src/bp_fp2.c
+++ b/bplib/src/bp_fp2.c
@@ -108,8 +108,9 @@ void FP2_clear_free(FP2 *a)
 
 int FP2_zero(FP2 *a)
 {
-    if (!BN_zero(a->f[0]) || !BN_zero(a->f[1]))
-        return 0;
+    BN_zero(a->f[0]);
+    BN_zero(a->f[1]);
+
     return 1;
 }