In file included from chainparams.h:9:0,
                 from protocol.h:13,
                 from addrman.h:9,
                 from addrman.cpp:5:
bignum.h:56:24: error: invalid use of incomplete type ‘BIGNUM {aka struct bignum_st}’
 class CBigNum : public BIGNUM
                        ^~~~~~
In file included from /usr/include/openssl/crypto.h:31:0,
                 from allocators.h:15,
                 from serialize.h:9,
                 from netbase.h:13,
                 from addrman.h:8,
                 from addrman.cpp:5:
/usr/include/openssl/ossl_typ.h:80:16: note: forward declaration of ‘BIGNUM {aka struct bignum_st}’
 typedef struct bignum_st BIGNUM;
                ^~~~~~~~~
In file included from chainparams.h:9:0,
                 from protocol.h:13,
                 from addrman.h:9,
                 from addrman.cpp:5:
bignum.h: In constructor ‘CBigNum::CBigNum()’:
bignum.h:61:21: error: ‘BN_init’ was not declared in this scope
         BN_init(this);