segfault in ECC test

Hi, thanks for the great work.

After building successfully on OSX Catalina, I get a segfault in the ecc test:

benediamond@Benjamins-MBP emp-tool % ./bin/ecc   
zsh: segmentation fault  ./bin/ecc

after doing some digging, it looks like the bad line is the add_mod call:

emp-tool/test/ecc.cpp

Line 22 in 4274548

ic = ia.add_mod(ib, G.order);

the reason is that ctx is default-assigned to nullptr here:

emp-tool/emp-tool/utils/group_openssl.h

Lines 46 to 50 in 4274548

    
           inline BigInt BigInt::add_mod(const BigInt & b, const BigInt &m,  BN_CTX *ctx) { 
        
           	BigInt ret; 
        
           	BN_mod_add(ret.n, n, b.n, m.n, ctx); 
        
           	return ret; 
        
           }

it can be fixed by replacing line 22 with:

    ic = ia.add_mod(ib, G.order, G.bn_ctx);

let me know if you'd like me to raise a PR. thanks.

Thank you for pointing the bug. The code has been updated to address this. Also removed the default parameters to enforce a bn_ctx has to be provided.

	inline BigInt BigInt::add_mod(const BigInt & b, const BigInt &m, BN_CTX *ctx) {
	BigInt ret;
	BN_mod_add(ret.n, n, b.n, m.n, ctx);
	return ret;
	}