Sha512 hash in QT via OpenSSL - c++

Question

I'm trying to use the Sha512 function in openSSL but can't seem to get it to work as I get compiler errors just starting into the code. I include #include <openssl/sha.h> at the top of the .cpp file, then in the action of a button event I put just the following code below.
SHA512_CTX ctx;
SHA512_Init(&ctx);
//Will uncomment below in later if I get SHA512_Init to work
//SHA512_Update(&ctx, string, strlen(string));
//SHA512_Final(digest, &ctx);
I get a linker error telling my undefined symbols for architecture x86_64, implying the function does not exist?
I'm aware QT 5 has a hash function, but I'm limited to QT 4.8 so I can not use the cryptographic sha512 hash function available in the QT 5+ framework.
Any help is appreciated!
Used macports to install openssl
I'm using Mac OS 10.9.2
MAKE FILE
#-------------------------------------------------
#
# Project created by QtCreator 2014-06-11T20:27:49
#
#-------------------------------------------------
QT += core gui network
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = ExchangeTab
TEMPLATE = app
LIBS += -L/usr/include/openssl -openssl
INCLUDEPATH += /usr/include/openssl
SOURCES += main.cpp\
mainwindow.cpp \
httpsocket.cpp \
cloaksend.cpp \
exchange.cpp
HEADERS += mainwindow.h \
httpsocket.h \
cloaksend.h \
exchange.h
FORMS += mainwindow.ui
RESOURCES += \
AppResources.qrc
Looking for cross platform solution please.

Answer 1

You need to link to the right library (openSSL)
Have a look here: How to Include OpenSSL in a Qt project
Specifically, add this to your .pro file.:
LIBS += -L/opt/local/lib/ -lcrypto
For including .h files add this line to your .pro file :
INCLUDEPATH += /opt/local/include
[1] says that the default include path will be /opt/local/include/.

Answer 2

LIBS += -L/usr/include/openssl -openssl
INCLUDEPATH += /usr/include/openssl
This looks incorrect. The OpenSSL libraries are libcrypto (-lcrypto) and libssl (-lssl). There is nolibopenssl(-lopenssl). Try:
LIBS += -L/usr/lib -lcrypto
INCLUDEPATH += /usr/include/openssl
But the libraries are version 0.9.8. You might consider upgrading to 1.0.1h.
$ ls /usr/lib | grep crypto
libcrypto.0.9.7.dylib
libcrypto.0.9.8.dylib
libcrypto.dylib
libk5crypto.dylib
And
$ /usr/bin/openssl version
OpenSSL 0.9.8y 5 Feb 2013
If you choose to upgrade, OpenSSL will install into /usr/local/ssl. Avoid mixing/matching version of OpenSSL with the following.
INCLUDEPATH += /usr/local/ssl/include/openssl
LIBS += /usr/local/ssl/lib/libcrypto.a
Its OK to specify objects and archives in LIBS. See How to add object files to a project in Qt.

Answer 3

Okay so I may have answered my own question but I will need some help understanding why it worked.
My make file was indeed the problem. I added the following 3 lines.
INCLUDEPATH += $$OPENSSL_INCLUDE_PATH
LIBS += $$join(OPENSSL_LIB_PATH,,-L,)
LIBS += -lcrypto
Then it magically compiled just fine. I found these in another project made with QT that compiled for OpenSSL.
Interestingly enough. I removed the top two lines so only the following remained. Then ran the clean on my project to be sure the code was being recompiled.
LIBS += -lcrypto
This also just 'worked' without linker errors. It looks like that is the only command I need. Question is... will that be cross platform friendly if I take this code and compile on linux or windows? That I am not sure, but this worked.