c++ - Aggregate ‘BIGNUM foo’ has incomplete type and cannot be defined

Question

I tried to compile opendcp, but error occurred.

$ make

...

[ 10%] Building CXX object libasdcp/CMakeFiles/opendcp-asdcp.dir/KM_prng.cpp.o
/home/jwel/opendcp/libasdcp/KM_prng.cpp: In function ‘void Kumu::Gen_FIPS_186_Value(const byte_t*, ui32_t, byte_t*, ui32_t)’:
/home/jwel/opendcp/libasdcp/KM_prng.cpp:219:10: error: aggregate ‘BIGNUM c_2powb’ has incomplete type and cannot be defined
   BIGNUM c_2powb, c_2, c_b;
          ^~~~~~~
/home/jwel/opendcp/libasdcp/KM_prng.cpp:219:19: error: aggregate ‘BIGNUM c_2’ has incomplete type and cannot be defined
   BIGNUM c_2powb, c_2, c_b;
                   ^~~
/home/jwel/opendcp/libasdcp/KM_prng.cpp:219:24: error: aggregate ‘BIGNUM c_b’ has incomplete type and cannot be defined
   BIGNUM c_2powb, c_2, c_b;
                        ^~~
/home/jwel/opendcp/libasdcp/KM_prng.cpp:220:19: error: ‘BN_init’ was not declared in this scope
   BN_init(&c_2powb);  BN_init(&c_2);  BN_init(&c_b);
                   ^
/home/jwel/opendcp/libasdcp/KM_prng.cpp:248:14: error: aggregate ‘BIGNUM bn_tmp’ has incomplete type and cannot be defined
       BIGNUM bn_tmp, bn_xkey, bn_x_n;
              ^~~~~~
/home/jwel/opendcp/libasdcp/KM_prng.cpp:248:22: error: aggregate ‘BIGNUM bn_xkey’ has incomplete type and cannot be defined
       BIGNUM bn_tmp, bn_xkey, bn_x_n;
                      ^~~~~~~
/home/jwel/opendcp/libasdcp/KM_prng.cpp:248:31: error: aggregate ‘BIGNUM bn_x_n’ has incomplete type and cannot be defined
       BIGNUM bn_tmp, bn_xkey, bn_x_n;
                               ^~~~~~
libasdcp/CMakeFiles/opendcp-asdcp.dir/build.make:110: recipe for target 'libasdcp/CMakeFiles/opendcp-asdcp.dir/KM_prng.cpp.o' failed
make[2]: *** [libasdcp/CMakeFiles/opendcp-asdcp.dir/KM_prng.cpp.o] Error 1
make[1]: *** [libasdcp/CMakeFiles/opendcp-asdcp.dir/all] Error 2
make: *** [all] Error 2

It looks like openssl problem for me, so I tried to test this:

$ cat testBIGNUM.cpp
#include <openssl/bn.h>
int main(){
    BIGNUM bn;
}

$ g++ testBIGNUM.cpp
testBIGNUM.cpp: In function ‘int main()’:
testBIGNUM.cpp:4:9: error: aggregate ‘BIGNUM bn’ has incomplete type and cannot be defined
  BIGNUM bn;
         ^~

my openssl version is 1.1.0d-2 and I don't know how to fix it.

Answer 1

There were big changes between OpenSSL 1.0.2 and OpenSSL 1.1.0 and they are not fully source compatible. Specifically many data structures which were in the 1.0.2 header files are now opaque. Applications that use OpenSSL need to make some small changes to be compatible.

In the case of BIGNUM, you need to do it like this:

#include <openssl/bn.h>
int main() {
    BIGNUM *bn;

    bn = BN_new();

    ...
    BN_free(bn);

    return 0;
}

In the case of opendcp probably the answer is to just downgrade to OpenSSL 1.0.2 instead.