What version of bitcoin-core are you using?

GitHub latest master. (3192e52)

Describe the issue

"compressed" argument of ec_privkey_export_der() seems to be bool-typed.

ec_privkey_export_der function has a "compressed" argument and it accepts bool-typed value (0 or not 0) as far as I see the implementation of the function.

https://github.com/bitcoin/bitcoin/blob/master/src/key.cpp#L70
https://github.com/bitcoin/bitcoin/blob/master/src/secp256k1/contrib/lax_der_privatekey_parsing.c#L56

if (compressed) {
    ....
} else {
    ....
}

Passed values for the "compressed" are NOT ZERO ALWAYS.

Actually, however, the passed values for the argument "compressed" are SECP256K1_EC_COMPRESSED or SECP256K1_EC_UNCOMPRESSED only, and Both of them are NOT ZERO.

• SECP256K1_EC_COMPRESSED equals 0x102. (NOT ZERO)
• SECP256K1_EC_UNCOMPRESSED equals 0x2. (NOT ZERO)

https://github.com/bitcoin/bitcoin/blob/master/src/key.cpp#L149

ret = ec_privkey_export_der(secp256k1_context_sign,
  (unsigned char*)&privkey[0], &privkeylen, begin(),
  fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);

https://github.com/bitcoin/bitcoin/blob/master/src/secp256k1/include/secp256k1.h#L147

#define SECP256K1_FLAGS_TYPE_COMPRESSION (1 << 1)
#define SECP256K1_FLAGS_BIT_COMPRESSION (1 << 8)
#define SECP256K1_EC_COMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION | SECP256K1_FLAGS_BIT_COMPRESSION)
#define SECP256K1_EC_UNCOMPRESSED (SECP256K1_FLAGS_TYPE_COMPRESSION)

My idea: Ignoring fCompressed variable.

I think fCompressed makes no sense when calling ec_privkey_export_der(). Though, to keep compatibility, ec_privkey_export_der() should be called as compressed mode only as in the past, I think.

I also think the fCompressed variable on ec_privkey_export_der() calling is now only noise and should be removed. I'd suggest my idea that calling ec_privkey_export_der() without considering fCompressed, as follows.

// idea1
ret = ec_privkey_export_der(secp256k1_context_sign,
  (unsigned char*)&privkey[0], &privkeylen, begin(), SECP256K1_EC_COMPRESSED);

// idea2
ret = ec_privkey_export_der(secp256k1_context_sign,
  (unsigned char*)&privkey[0], &privkeylen, begin(), 1);

What do you think of that?

BTW: The implementation of ec_privkey_export_der() seems to be the copy of the library code, so I thought it's not good to change it. Actually is that right?