c++ - Add OpenSSL support for Linux Qt Application

Question

Good day.

I am creating an application that requires the use of OpenSSL.

Problem:

The problem is having read the documentation several times over, I still do not quite understand how I can add SSL support.

There are numerous threads for adding SSL to windows applications, but extremely few for Linux, which does not provide alot of details.

I reviewed the provided project file, but no ssl linking is done here.

What I tried:

In my application, I run the following code:

if (!QSslSocket::supportsSsl()) {
    QMessageBox::critical(0, "Application Notice", "We care about your security. 
Please install OpenSSL.");
    return -1;
}

Which displays the message when the check is done.

To added SSL support, I reviewed the QT provided example securesocketclient of implementing SSL

• Environment Variable

Adding OPENSSL_LIBS environment variable

Reviewing the documentation, it mentions adding an environment variable which allows qmake to find the location of the openssl lib file.

I have a standard openssl installation with headers

Binary location

$ which openssl
/usr/bin/openssl

Headers location

$ locate openssl/aes.h
/opt/Qt5.9.1/5.9.1/Src/qtwebengine/src/3rdparty/chromium/third_party/boringssl/src/include/openssl/aes.h
/usr/include/openssl/aes.h
/usr/include/openssl-1.0/openssl/aes.h

Libs location

/usr/lib/libssl.so
/usr/lib/libssl.so.1.0.0
/usr/lib/libssl.so.1.1
/usr/lib/libssl3.so
/usr/lib/openssl-1.0/libssl.so
/usr/lib/openssl-1.0/pkgconfig/libssl.pc

/usr/lib32/libssl.so
/usr/lib32/libssl.so.1.0.0
/usr/lib32/libssl.so.1.1
/usr/lib32/libssl3.so
/usr/lib32/openssl-1.0/libssl.so
/usr/lib32/openssl-1.0/pkgconfig/libssl.pc

I figure that the provided env variable points to the incorrect location:

OPENSSL_LIBS='-L/opt/ssl/lib -lssl -lcrypto'

I modified it according to my system (I do not think this is correct though):

OPENSSL_LIBS='-L/usr/lib -lssl -lcrypto'

• Configuration Flag

Also noted in the documentation, a configuration flag -openssl-linked is required.

Having searched for a way to add this flag to a configuration file (as there is none present in my project directory)

According to this, I added the flag to my project file:

QMAKE_CXXFLAGS += -openssl-linked

BUT, still no SSL support.

Question:

Given my .pro file below, how can I add OpenSSL support to my Qt application given a standard install of OpenSSL?

---

Application Output

Debugging starts
qt.network.ssl: QSslSocket: cannot resolve CRYPTO_num_locks
qt.network.ssl: QSslSocket: cannot resolve CRYPTO_set_id_callback
qt.network.ssl: QSslSocket: cannot resolve CRYPTO_set_locking_callback
qt.network.ssl: QSslSocket: cannot resolve ERR_free_strings
qt.network.ssl: QSslSocket: cannot resolve EVP_CIPHER_CTX_cleanup
qt.network.ssl: QSslSocket: cannot resolve EVP_CIPHER_CTX_init
qt.network.ssl: QSslSocket: cannot resolve sk_new_null
qt.network.ssl: QSslSocket: cannot resolve sk_push
qt.network.ssl: QSslSocket: cannot resolve sk_free
qt.network.ssl: QSslSocket: cannot resolve sk_num
qt.network.ssl: QSslSocket: cannot resolve sk_pop_free
qt.network.ssl: QSslSocket: cannot resolve sk_value
qt.network.ssl: QSslSocket: cannot resolve SSL_library_init
qt.network.ssl: QSslSocket: cannot resolve SSL_load_error_strings
qt.network.ssl: QSslSocket: cannot resolve SSL_get_ex_new_index
qt.network.ssl: QSslSocket: cannot resolve SSLv2_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv3_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv23_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv2_server_method
qt.network.ssl: QSslSocket: cannot resolve SSLv3_server_method
qt.network.ssl: QSslSocket: cannot resolve SSLv23_server_method
qt.network.ssl: QSslSocket: cannot resolve X509_STORE_CTX_get_chain
qt.network.ssl: QSslSocket: cannot resolve OPENSSL_add_all_algorithms_noconf
qt.network.ssl: QSslSocket: cannot resolve OPENSSL_add_all_algorithms_conf
qt.network.ssl: QSslSocket: cannot resolve SSLeay
qt.network.ssl: QSslSocket: cannot resolve SSLeay_version
qt.network.ssl: Incompatible version of OpenSSL
Debugging has finished

pro file

#-------------------------------------------------
#
# Project created by QtCreator 2017-12-02T18:53:15
#
#-------------------------------------------------

QT       += core gui network

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = MySSLApp
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0


SOURCES += 
    main.cpp 
    mainwindow.cpp 
    loginform.cpp 
    networkthread.cpp 
    sslclient.cpp

HEADERS += 
    mainwindow.h 
    loginform.h 
    networkthread.h 
    sslclient.h

FORMS += 
    mainwindow.ui 
    loginform.ui

RESOURCES += 
    resources.qrc

OPENSSL_LIBS='-L/usr/lib -lssl -lcrypto'

QMAKE_CXXFLAGS += -openssl-linked

Answer 1

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