Implicit declaration of function 'BN_init' error

Question

I was checking out how to generate public keys from a private bitcoin address.
I found the following page:
How do I obtain the public key from an ECDSA private key in OpenSSL?

But when I try to compile with gcc -Wall -Werror -O3 -o public_key public_key.c -lcrypto, I get the following errors:

public_key.c: In function 'generate_pubic_key':
public_key.c:26:13: error: storage size of 'start' isn't known
      BIGNUM start;
             ^~~~~
public_key.c:32:6: error: implicit declaration of function 'BN_init' [-Werror=implicit-function-declaration]
      BN_init(&start);
      ^~~~~~~
public_key.c:26:13: error: unused variable 'start' [-Werror=unused-variable]
      BIGNUM start;
             ^~~~~
cc1: all warnings being treated as errors

I have OpenSSL installed and haven't had any programing errors related to it, until now. Can someone point out what it is that I'm doing wrong?

Chances are that you have openssl 1.1.0 or later, and that you are using previously deprecated and now fully removed functionality. See answer below — Ahmed Masud, Dec 31 '17 at 22:31

score 4 · Accepted Answer · answered Dec 31 '17 at 22:30

You are using ~~deprecated~~ removed API.

As per BN_new(3) man page:

REMOVED FUNCTIONALITY void BN_init(BIGNUM *);

BN_init() is no longer available as of OpenSSL 1.1.0. It was used to initialize an existing uninitialized BIGNUM. Typically this would be done as follows:
 BIGNUM a;
 BN_init(&a);
Applications should replace use of BN_init with BN_new instead:
 BIGNUM *a;
 a = BN_new();
 if(!a) /* Handle error */
 ...
 BN_free(a);

Implicit declaration of function 'BN_init' error

1 Answers1