Openssl In C

The following page is a combination of the INSTALL file provided with the OpenSSL library and notes from the field. If you have questions about what you are doing or seeing, then you should consult INSTALL since it contains the commands and specifies the behavior by the development team.

1. Using Openssl In C++
2. Openssl Commands
3. Openssl In Centos
4. C++ Openssl Tutorial
5. Openssl Examples
6. Install Openssl In Centos 7

OpenSSL uses a custom build system to configure the library. Configuration will allow the library to set up the recursive makefiles from makefile.org. Once configured, you use make to build the library. You should avoid custom build systems because they often miss details, like each architecture and platform has a unique opensslconf.h and bn.h generated by Configure.

Jul 08, 2020 openssl/crypto/sha/sha256.c. Levitte Add and use internal header that implements endianness check. Latest commit e23d850 on Jul 8, 2020 History. OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. It is also a general-purpose cryptography library. For more information about the team and community around the project, or to start making your own contributions, start with the community page.

You must use a C compiler to build the OpenSSL library. You cannot use a C++ compiler. Later, once the library is built, it is OK to create user programs with a C++ compiler. But the library proper must be built with a C compiler.

There are two generations of build system. First is the build system used in OpenSSL 1.0.2 and below. The instructions below apply to it. Second is the build system for OpenSSL 1.1.0 and above. The instructions are similar, but not the same. For example, the second generation abandons the monolithic Configure and places individual configurations in the Configurations directory. Also, the second generation is more platform agnostic and uses templates to produce a final, top level build file (Makefile, descrip.mms, what have you).

After you configure and build the library, you should always perform a make test to ensure the library performs as expected under its self tests. If you are building OpenSSL 1.1.0 and above, then you will also need PERL 5.10 or higher (see README.PERL for details).

OpenSSL's build system does not rely upon autotools or libtool. Also see Why aren't tools like 'autoconf' and 'libtool' used? in the OpenSSL FAQ.

• 2Configuration
• 3Configure Options
• 4Compilation
• 5Platfom specific
  • 5.1Linux
  • 5.2Windows
  • 5.3OpenSSL 1.1.0
  • 5.4OpenSSL 1.0.2
  • 5.6iOS
  • 5.8More

Retrieve source code[edit]

The OpenSSL source code can be downloaded from OpenSSL Source Tarballs or any suitable ftp mirror. There are various versions including stable as well as unstable versions.

The source code is managed via Git. It's referred to as Master. The repository is

git://git.openssl.org/openssl.git

The source is also available via a GitHub mirror. This repository is updated every 15 minutes.

Configuration[edit]

OpenSSL is configured for a particular platform with protocol and behavior options using Configure and config.

You should avoid custom build systems because they often miss details, like each architecture and platform has a unique opensslconf.h and bn.h generated by Configure.

Supported Platforms[edit]

You can run Configure LIST to see a list of available platforms.

If your platform is not listed, then use a similar platform and tune the $cflags and $ldflags by making a copy of the configure line and giving it its own name. $cflags and $ldflags correspond to fields 2 and 6 in a configure line. An example of using a similar configure line is presented in Using RPATHs.

Configure & Config[edit]

You use Configure and config to tune the compile and installation process through options and switches. The difference between is Configure properly handles the host-arch-compiler triplet, and config does not. config attempts to guess the triplet, so it's a lot like autotool's config.guess.

You can usually use config and it will do the right thing (from Ubuntu 13.04, x64):

Mac OS X can have issues (it's often a neglected platform), and you will have to use Configure:

You can also configure on Darwin by exporting KERNEL_BITS:

If you provide a option not known to configure or ask for help, then you get a brief help message:

And if you supply an unknown triplet:

Dependencies[edit]

If you are prompted to run make depend, then you must do so. For OpenSSL 1.0.2 and below, it's required to update the standard distribution once configuration options change.

OpenSSL 1.1.0 and above performs the dependency step for you, so you should not see the message. However, you should perform a make clean to ensure the list of objects files is accurate after a reconfiguration.

Configure Options[edit]

OpenSSL has been around a long time, and it carries around a lot of cruft. For example, from above, SSLv2 is enabled by default. SSLv2 is completely broken, and you should disable it during configuration. You can disable protocols and provide other options through Configure and config, and the following lists some of them.

Note: if you specify a non-existent option, then the configure scripts will proceed without warning. For example, if you inadvertently specify no-sslv2 rather than no-ssl2 no-ssl3, the script will configure with SSLv2 and without warning for the unknown no-sslv2.

Note: when building a shared object, both the static archive and shared objects are built. You do not need to do anything special to build both when shared is specified.

Note: on older OSes, like CentOS 5, BSD 5, and Windows XP or Vista, you will need to configure with no-async when building OpenSSL 1.1.0 and above. The configuration system does not detect lack of the Posix feature on the platforms.

Note: you can verify compiler support for __uint128_t with the following:

PREFIX and OPENSSLDIR[edit]

--prefix and --openssldir control the configuration of installed components. The behavior and interactions of --prefix and --openssldir are slightly different between OpenSSL 1.0.2 and below, and OpenSSL 1.1.0 and above.

The rule of thumb to use when you want something that 'just works' for all recent versions of OpenSSL, including OpenSSL 1.0.2 and 1.1.0, is:

• specify both--prefix and --openssldir
• set --prefix and --openssldir to the same location

One word of caution is avoid--prefix=/usr when OpenSSL versions are notbinary compatible. You will replace the distro's version of OpenSSL with your version of OpenSSL. It will most likely break everything, including the package management system.

OpenSSL 1.0.2 and below

It is usually not necessary to specify --prefix. If --prefix is not specified, then --openssldir is used. However, specifying only--prefix may result in broken builds because the 1.0.2 build system attempts to build in a FIPS configuration.

You can omit If --prefix and use --openssldir. In this case, the paths for --openssldir will be used during configuration. If --openssldir is not specified, the the default /usr/local/ssl is used.

The takeaway is /usr/local/ssl is used by default, and it can be overridden with --openssldir. The rule of thumb applies for path overrides: specify both--prefix and --openssldir.

OpenSSL 1.1.0 and above

OpenSSL 1.1.0 changed the behavior of install rules. You should specify both --prefix and --openssldir to ensure make install works as expected.

The takeaway is /usr/local/ssl is used by default, and it can be overridden with both--prefix and --openssldir. The rule of thumb applies for path overrides: specify both--prefix and --openssldir.

Debug Configuration[edit]

From the list above, it's possible to quickly configure a 'debug' build with ./config -d. However, you can often get into a more amicable state without the Electric Fence dependency by issuing:

Don't be alarmed about both -O3 and -O0. The last setting 'sticks', and that's the -O0.

If you are working in Visual Studio and you can't step into library calls, then see Step into not working, but can force stepping after some asm steps on Stack Overflow.

Modifying Build Settings[edit]

Sometimes you need to work around OpenSSL's selections for building the library. For example, you might want to use -Os for a mobile device (rather than -O3), or you might want to use the clang compiler (rather than gcc).

In case like these, its' often easier to modify Configure and Makefile.org rather than trying to add targets to the configure scripts. Below is a patch that modifies Configure and Makefile.org for use under the iOS 7.0 SDK (which lacks gcc in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/):

• Modifies Configure to use clang
• Modifies Makefile.org to use clang
• Modifies CFLAG to use -Os
• Modifies MAKEDEPPROG to use $(CC) -M

Setting and resetting of LANG is required on Mac OSX to work around a sed bug or limitation.

After modification, be sure to dclean and configure again so the new settings are picked up:

Using RPATHs[edit]

RPATH's are supported by default on the BSD platforms, but not others. If you are working on Linux and compatibles, then you have to manually add an RPATH. One of the easiest ways to add a RPATH is to configure with it as shown below.

For modern Linux you should also use -Wl,--enable-new-dtags. The linker option sets a RUNPATH as opposed to a RPATH. A RUNPATH allows library path overrides at runtime, while a RPATH does not.

Note well: you should use a RPATH or RUNPATH when building both OpenSSL and your program. If you don't add a RPATH or RUNPATH to both, then your program could runtime-link to the wrong version of OpenSSL. Linking against random versions of a security library is not a good idea.

You can also add an RPATH or RUNPATH by hard coding the RPATH into a configure line. For example, on Debian x86_64 open the file Configure in an editor, copy linux-x86_64, name it linux-x86_64-rpath, and make the following change to add the -rpath option. Notice the addition of -Wl,-rpath=.. in two places.

Above, fields 2 and 6 were changed. They correspond to $cflag and $ldflag in OpenSSL's builds system.

Then, Configure with the new configuration:

Finally, after make, verify the settings stuck:

Once you perform make install, then ldd will produce expected results:

FIPS Capable Library[edit]

If you want to use FIPS validated cryptography, you download, build and install the FIPS Object Module (openssl-fips-2.0.5.tar.gz) according to the FIPS User Guide 2.0 and FIPS 140-2 Security Policy. You then download, build and install the FIPS Capable Library (openssl-1.0.1e.tar.gz).

When configuring the FIPS Capable Library, you must use fips as an option:

If you are configuring the FIPS Capable Library with only prime curves (openssl-fips-ecp-2.0.5.tar.gz), then you must configure with no-ec2m:

Compile Time Checking[edit]

If you disable an option during configure, you can check if it's available through OPENSSL_NO_* defines. OpenSSL writes the configure options to . For example, if you want to know if SSLv3 is available, then you would perform the following in your code:

Compilation[edit]

After configuring the library, you should run make. If prompted, there's usually no need to make depend since you are building from a clean download.

Quick[edit]

Various options can be found examining the Configure file (there is a well commented block at its top). OpenSSL ships with SSLv2, SSLv3 and Compression enabled by default (see my $disabled), so you might want to use no-ssl2 no-ssl3, no-ssl3, and no-comp.

Platfom specific[edit]

Linux[edit]

Intel[edit]

ARM[edit]

X32 (ILP32)[edit]

X32 uses the 32-bit data model (ILP32) on x86_64/amd64. To properly configure for X32 under current OpenSSL distributions, you must use Configure and use the x32 triplet:

Then:

If using an amd64-compatible processor and GCC with that supports __uint128_t, then you usually add enable-ec_nistp_64_gcc_128 in addition to your other flags.

Windows[edit]

3noch wrote a VERY good guide in 2012 here (PLEASE NOTE: the guide was written in 2012 and is no longer available at the original location; the link now points to an archived version at the Internet Archive Wayback Machine).

Like he said in his article, make absolutely sure to create separate directories for 32 and 64 bit versions.

W32 / Windows NT - Windows 9x[edit]

type INSTALL.W32

• you need Perl for Win32. Unless you will build on Cygwin, you will need ActiveState Perl, available from http://www.activestate.com/ActivePerl.
• one of the following C compilers:
  • Visual C++
  • Borland C
  • GNU C (Cygwin or MinGW)
• Netwide Assembler, a.k.a. NASM, available from http://nasm.sourceforge.net/ is required if you intend to utilize assembler modules. Note that NASM is now the only supported assembler.

W64[edit]

Read first the INSTALL.W64 documentation note containing some specific 64bits information.See also INSTALL.W32 that still provides additonnal build information common to both the 64 and 32 bit versions.

You may be surprised: the 64bit artefacts are indeed output in the out32* sub-directories and bear names ending *32.dll. Fact is the 64 bit compile target is so far an incremental change over the legacy 32bit windows target. Numerous compile flags are still labelled '32' although those do apply to both 32 and 64bit targets.

The important pre-requisites are to have PERL available (for essential file processing so as to prepare sources and scripts for the target OS) and of course a C compiler like Microsoft Visual Studio for C/C++. Also note the procedure changed at OpenSSL 1.1.0 and is more streamlined. Also see Why there is no msdo_ms.bat after perl Configure VC-WIN64A on Stack Overflow.

OpenSSL 1.1.0[edit]

For OpenSSL 1.1.0 and above perform these steps:

1. Ensure you have perl installed on your machine (e.g. ActiveState or Strawberry), and available on your %PATH%
2. Ensure you have NASM installed on your machine, and available on your %PATH%
3. Extract the source files to your folder, here cd c:myPathopenssl
4. Launch Visual Studio tool x64 Cross Tools Command prompt
5. Goto your defined folder cd c:myPathopenssl
6. Configure for the target OS with perl Configure VC-WIN64A or other configurations to be found in the INSTALL file (e.g. UNIX targets).
   1. For instance: perl Configure VC-WIN64A.
7. (Optional) In case you compiled before on 32 or 64-bits, make sure you run nmake clean to prevent trouble across 32 and 64-bits which share output folder.
8. Now build with: nmake
9. Output can be found in the root of your folder as libcrypto-1_1x64.dll and libssl-1_1-x64.dll (with all the build additionals such as .pdb .lik or static .lib). You may check this is true 64bit code using the Visual Studio tool 'dumpbin'. For instance dumpbin /headers libcrypto-1_1x64.dll | more, and look at the FILE HEADER section.
10. Test the code using the 'test' make target, by running nmake test.
11. Reminder, clean your code to prevent issues the next time you compile for a different target. See step 7.

Windows CE[edit]

Not specified

OpenSSL 1.0.2[edit]

For OpenSSL 1.0.2 and earlier the procedure is as follows.

1. Ensure you have perl installed on your machine (e.g. ActiveState or Strawberry), and available on your %PATH%
2. Ensure you have NASM installed on your machine, and available on your %PATH%
3. launch a Visual Studio tool x64 Cross Tools Command prompt
4. change to the directory where you have copied openssl sources cd c:myPathopenssl
5. configure for the target OS with the command perl Configure VC-WIN64A. You may also be interested to set more configuration options as documented in the general INSTALL note (for UNIX targets). For instance: perl Configure VC-WIN64A.
6. prepare the target environment with the command: msdo_win64a
7. ensure you start afresh and notably without linkable products from a previous 32bit compile (as 32 and 64 bits compiling still share common directories) with the command: nmake -f msntdll.mak clean for the DLL target and nmake -f msnt.mak clean for static libraries.
8. build the code with: nmake -f msntdll.mak (respectively nmake -f msnt.mak )
9. the artefacts will be found in sub directories out32dll and out32dll.dbg (respectively out32 and out32.dbg for static libraries). The libcrypto and ssl libraries are still named libeay32.lib and ssleay32.lib, and associated includes in inc32 ! You may check this is true 64bit code using the Visual Studio tool 'dumpbin'. For instance dumpbin /headers out32dll/libeay32.lib | more, and look at the FILE HEADER section.
10. test the code using the various *test.exe programs in out32dll. Use the 'test' make target to run all tests as in nmake -f msntdll.mak test
11. we recommend that you move/copy needed includes and libraries from the '32' directories under a new explicit directory tree for 64bit applications from where you will import and link your target applications, similar to that explained in INSTALL.W32.

Windows CE[edit]

OS X[edit]

The earlier discussion presented a lot of information (and some of it had OS X information). Here are the TLDR versions to configure, build and install the library.

If configuring for 64-bit OS X, then use a command similar to:

If configuring for 32-bit OS X, then use a command similar to:

If you want to build a multiarch OpenSSL library, then see this answer on Stack Overflow: Build Multiarch OpenSSL on OS X.

iOS[edit]

The following builds OpenSSL for iOS using the iPhoneOS SDK. The configuration avoids the dynamic library the DSO interface and engines.

If you run make install, then the headers will be installed in /usr/local/openssl-ios/include and libraries will be installed in /usr/local/openssl-ios/lib.

32-bit[edit]

For OpenSSL 1.1.0 and above, a 32-bit iOS cross-compiles uses the ios-cross target, and options similar to --prefix=/usr/local/openssl-ios.

If you are working with OpenSSL 1.0.2 or below, then use the iphoneos-cross target.

64-bit[edit]

For OpenSSL 1.1.0 , a 64-bit iOS cross-compiles uses the ios64-cross target, and --prefix=/usr/local/openssl-ios64. ios64-cross. There is no built-in 64-bit iOS support for OpenSSL 1.0.2 or below.

Android[edit]

Visit Android and FIPS Library and Android.

More[edit]

VAX/VMS[edit]

I you wonder what are files ending with .com like test/testca.com those are VAX/VMX scripts.This code is still maintained.

OS/2[edit]

NetWare[edit]

5.x 6.x

HP-UX[edit]

Autoconf[edit]

Using Openssl In C++

OpenSSL uses its own configuration system, and does not use Autoconf. However, a number of popular projects use both OpenSSL and Autoconf, and it would be useful to detect either OPENSSL_init_ssl or SSL_library_init from libssl. To craft a feature test for OpenSSL that recognizes both OPENSSL_init_ssl and SSL_library_init, you can use the following.

Many thanks to the Postgres folks for donating part of their configure.in. Also see How to tell Autoconf 'require symbol A or B' from LIB? on Stack Overflow.

Disclaimer: I am NOT a crypto expert. Don't take the information here as 100% correct; you should verify it yourself. You are dangerously bad at crypto.

This post details the EVP functions for RSA. If you're looking for a pure RSA implementation or want something in C rather than C++, see my other post on this.

In my seemingly endless side project to implement RSA and AES encryption to my Alsa Server project, I wrote a while ago about doing simple RSA encryption with OpenSSL. Now, I'm here to say that I was doing it all wrong. In my first post about RSA encryption and OpenSSL my code was using the low level RSA functions when I should have been using the high level EVP (envelope) functions, which are much nicer to work with once you get the hang of them.

Being that this code is eventually going to be merged in my Alsa server project, I went ahead and also implemented AES encryption/decryption and put everything in an easy to use C++ class.

I assume that readers are familiar with encryption and OpenSSL terminology (things like IV, key lengths, public vs private keys, etc.). If not, look it up since there are much better explanations out there than I could write.

Why use the EVP (envelope) functions for RSA encryption rather than the actual RSA functions? Becasue the EVP functions don't actually encrypt your data with RSA. Rather, they encrypted a symmetric key with RSA and then encrypt your data with the symmetric key. There's a few reasons for this. The main one being that RSA has a max length limit to how much data can be encrypted at once. Symmetric ciphers do not have this limit. If you want pure RSA, see my post about that, otherwise, you probably want to be using the EVP functions.

Moving on. First up, since all the code presented is in various functions from a class (full listing is at the end), let's look at the class members, and constructors first to understand where some of these variables are coming from. Below are all the class members. I know, not exactly intuitive, but bear with me.

• The EVP_PKEY variables store the public and private keys for the server, or just the public key for the client.
• The EVP_CIPHER_CTX variables keep track of the RSA and AES encryption/decryption processes and do all the hard, behind the scenes work.
• aesKey and aesIV are the symmetric key and IV used for the AES functions.

So now we need to initialize all these guys. In the class there are two constructors, each with different arguments so let's look at the default constructor for simplicity's sake.

The RSA keys are just set to NULL because their values will be initialized later when the RSA/AES functions are called. The #ifdef line certainly peaks some interest. Since this class is eventually going to be dropped in a server, it will be using the client's public key to encrypt data, but we don't have a client yet, so we define a fake client and generate another RSA key pair to simulate a client. The process of generating this key pair is identical to how we're about to generate the key pair for the server so let's look at this. This is all contained in the init() function.

Openssl Commands

There's a lot of strange function calls in here. Most of this function deals with the OpenSSL API and how to generate keys and initialize EVP contexts. I'll give a high level overview here, but the best way to understand this process is to read up on documentation. The first thing we do is allocate the proper amount of memory for the EVP contexts and then called the EVP_CIPHER_CTX_init() function which does some magic to initialize them. Then we use a few RSA functions to generate the RSA keys for the server. Again, the documentation for these functions will help you understand better than my explanation can, but you'll see a pattern emerge, initialize the context, pass it along with some options and an output argument to a function and you'll get what you want. It's the same way for RSA. We initialize the key context with EVP_PKEY_CTX_new_id() and EVP_PKEY_keygen_init(), set the key length to use with EVP_PKEY_CTX_set_rsa_keygen_bits() (see the full listing for the actual length if you really need to–2056 bits is sufficient for most cases; use 4096 if you're paranoid) and then actually generate the keys with EVP_PKEY_keygen().

The AES key is much simpler; it's just random data so we call RAND_bytes() to get the number of random bytes needed for the AES encrypted key and IV. There is also the option to use the EVP_BytesToKey() function which is a PBKDF. This function, as I called it, will generate a 256 bit key in CBC mode, with a salt and passphrase that are random data (the password being random data is just for demonstration purposes). The number of rounds (or count as the documentation calls it) is the strength of randomness to use. Higher numbers are better, but slower.

If you are prompted to run make depend, then you must do so. For OpenSSL 1.0.2 and below, it's required to update the standard distribution once configuration options change.

OpenSSL 1.1.0 and above performs the dependency step for you, so you should not see the message. However, you should perform a make clean to ensure the list of objects files is accurate after a reconfiguration.

Configure Options[edit]

OpenSSL has been around a long time, and it carries around a lot of cruft. For example, from above, SSLv2 is enabled by default. SSLv2 is completely broken, and you should disable it during configuration. You can disable protocols and provide other options through Configure and config, and the following lists some of them.

Note: if you specify a non-existent option, then the configure scripts will proceed without warning. For example, if you inadvertently specify no-sslv2 rather than no-ssl2 no-ssl3, the script will configure with SSLv2 and without warning for the unknown no-sslv2.

Note: when building a shared object, both the static archive and shared objects are built. You do not need to do anything special to build both when shared is specified.

Note: on older OSes, like CentOS 5, BSD 5, and Windows XP or Vista, you will need to configure with no-async when building OpenSSL 1.1.0 and above. The configuration system does not detect lack of the Posix feature on the platforms.

Note: you can verify compiler support for __uint128_t with the following:

PREFIX and OPENSSLDIR[edit]

--prefix and --openssldir control the configuration of installed components. The behavior and interactions of --prefix and --openssldir are slightly different between OpenSSL 1.0.2 and below, and OpenSSL 1.1.0 and above.

The rule of thumb to use when you want something that 'just works' for all recent versions of OpenSSL, including OpenSSL 1.0.2 and 1.1.0, is:

• specify both--prefix and --openssldir
• set --prefix and --openssldir to the same location

One word of caution is avoid--prefix=/usr when OpenSSL versions are notbinary compatible. You will replace the distro's version of OpenSSL with your version of OpenSSL. It will most likely break everything, including the package management system.

OpenSSL 1.0.2 and below

It is usually not necessary to specify --prefix. If --prefix is not specified, then --openssldir is used. However, specifying only--prefix may result in broken builds because the 1.0.2 build system attempts to build in a FIPS configuration.

You can omit If --prefix and use --openssldir. In this case, the paths for --openssldir will be used during configuration. If --openssldir is not specified, the the default /usr/local/ssl is used.

The takeaway is /usr/local/ssl is used by default, and it can be overridden with --openssldir. The rule of thumb applies for path overrides: specify both--prefix and --openssldir.

OpenSSL 1.1.0 and above

OpenSSL 1.1.0 changed the behavior of install rules. You should specify both --prefix and --openssldir to ensure make install works as expected.

The takeaway is /usr/local/ssl is used by default, and it can be overridden with both--prefix and --openssldir. The rule of thumb applies for path overrides: specify both--prefix and --openssldir.

Debug Configuration[edit]

From the list above, it's possible to quickly configure a 'debug' build with ./config -d. However, you can often get into a more amicable state without the Electric Fence dependency by issuing:

Don't be alarmed about both -O3 and -O0. The last setting 'sticks', and that's the -O0.

If you are working in Visual Studio and you can't step into library calls, then see Step into not working, but can force stepping after some asm steps on Stack Overflow.

Modifying Build Settings[edit]

Sometimes you need to work around OpenSSL's selections for building the library. For example, you might want to use -Os for a mobile device (rather than -O3), or you might want to use the clang compiler (rather than gcc).

In case like these, its' often easier to modify Configure and Makefile.org rather than trying to add targets to the configure scripts. Below is a patch that modifies Configure and Makefile.org for use under the iOS 7.0 SDK (which lacks gcc in /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/):

• Modifies Configure to use clang
• Modifies Makefile.org to use clang
• Modifies CFLAG to use -Os
• Modifies MAKEDEPPROG to use $(CC) -M

Setting and resetting of LANG is required on Mac OSX to work around a sed bug or limitation.

After modification, be sure to dclean and configure again so the new settings are picked up:

Using RPATHs[edit]

RPATH's are supported by default on the BSD platforms, but not others. If you are working on Linux and compatibles, then you have to manually add an RPATH. One of the easiest ways to add a RPATH is to configure with it as shown below.

For modern Linux you should also use -Wl,--enable-new-dtags. The linker option sets a RUNPATH as opposed to a RPATH. A RUNPATH allows library path overrides at runtime, while a RPATH does not.

Note well: you should use a RPATH or RUNPATH when building both OpenSSL and your program. If you don't add a RPATH or RUNPATH to both, then your program could runtime-link to the wrong version of OpenSSL. Linking against random versions of a security library is not a good idea.

You can also add an RPATH or RUNPATH by hard coding the RPATH into a configure line. For example, on Debian x86_64 open the file Configure in an editor, copy linux-x86_64, name it linux-x86_64-rpath, and make the following change to add the -rpath option. Notice the addition of -Wl,-rpath=.. in two places.

Above, fields 2 and 6 were changed. They correspond to $cflag and $ldflag in OpenSSL's builds system.

Then, Configure with the new configuration:

Finally, after make, verify the settings stuck:

Once you perform make install, then ldd will produce expected results:

FIPS Capable Library[edit]

If you want to use FIPS validated cryptography, you download, build and install the FIPS Object Module (openssl-fips-2.0.5.tar.gz) according to the FIPS User Guide 2.0 and FIPS 140-2 Security Policy. You then download, build and install the FIPS Capable Library (openssl-1.0.1e.tar.gz).

When configuring the FIPS Capable Library, you must use fips as an option:

If you are configuring the FIPS Capable Library with only prime curves (openssl-fips-ecp-2.0.5.tar.gz), then you must configure with no-ec2m:

Compile Time Checking[edit]

If you disable an option during configure, you can check if it's available through OPENSSL_NO_* defines. OpenSSL writes the configure options to . For example, if you want to know if SSLv3 is available, then you would perform the following in your code:

Compilation[edit]

After configuring the library, you should run make. If prompted, there's usually no need to make depend since you are building from a clean download.

Quick[edit]

Various options can be found examining the Configure file (there is a well commented block at its top). OpenSSL ships with SSLv2, SSLv3 and Compression enabled by default (see my $disabled), so you might want to use no-ssl2 no-ssl3, no-ssl3, and no-comp.

Platfom specific[edit]

Linux[edit]

Intel[edit]

ARM[edit]

X32 (ILP32)[edit]

X32 uses the 32-bit data model (ILP32) on x86_64/amd64. To properly configure for X32 under current OpenSSL distributions, you must use Configure and use the x32 triplet:

Then:

If using an amd64-compatible processor and GCC with that supports __uint128_t, then you usually add enable-ec_nistp_64_gcc_128 in addition to your other flags.

Windows[edit]

3noch wrote a VERY good guide in 2012 here (PLEASE NOTE: the guide was written in 2012 and is no longer available at the original location; the link now points to an archived version at the Internet Archive Wayback Machine).

Like he said in his article, make absolutely sure to create separate directories for 32 and 64 bit versions.

W32 / Windows NT - Windows 9x[edit]

type INSTALL.W32

• you need Perl for Win32. Unless you will build on Cygwin, you will need ActiveState Perl, available from http://www.activestate.com/ActivePerl.
• one of the following C compilers:
  • Visual C++
  • Borland C
  • GNU C (Cygwin or MinGW)
• Netwide Assembler, a.k.a. NASM, available from http://nasm.sourceforge.net/ is required if you intend to utilize assembler modules. Note that NASM is now the only supported assembler.

W64[edit]

Read first the INSTALL.W64 documentation note containing some specific 64bits information.See also INSTALL.W32 that still provides additonnal build information common to both the 64 and 32 bit versions.

You may be surprised: the 64bit artefacts are indeed output in the out32* sub-directories and bear names ending *32.dll. Fact is the 64 bit compile target is so far an incremental change over the legacy 32bit windows target. Numerous compile flags are still labelled '32' although those do apply to both 32 and 64bit targets.

The important pre-requisites are to have PERL available (for essential file processing so as to prepare sources and scripts for the target OS) and of course a C compiler like Microsoft Visual Studio for C/C++. Also note the procedure changed at OpenSSL 1.1.0 and is more streamlined. Also see Why there is no msdo_ms.bat after perl Configure VC-WIN64A on Stack Overflow.

OpenSSL 1.1.0[edit]

For OpenSSL 1.1.0 and above perform these steps:

1. Ensure you have perl installed on your machine (e.g. ActiveState or Strawberry), and available on your %PATH%
2. Ensure you have NASM installed on your machine, and available on your %PATH%
3. Extract the source files to your folder, here cd c:myPathopenssl
4. Launch Visual Studio tool x64 Cross Tools Command prompt
5. Goto your defined folder cd c:myPathopenssl
6. Configure for the target OS with perl Configure VC-WIN64A or other configurations to be found in the INSTALL file (e.g. UNIX targets).
   1. For instance: perl Configure VC-WIN64A.
7. (Optional) In case you compiled before on 32 or 64-bits, make sure you run nmake clean to prevent trouble across 32 and 64-bits which share output folder.
8. Now build with: nmake
9. Output can be found in the root of your folder as libcrypto-1_1x64.dll and libssl-1_1-x64.dll (with all the build additionals such as .pdb .lik or static .lib). You may check this is true 64bit code using the Visual Studio tool 'dumpbin'. For instance dumpbin /headers libcrypto-1_1x64.dll | more, and look at the FILE HEADER section.
10. Test the code using the 'test' make target, by running nmake test.
11. Reminder, clean your code to prevent issues the next time you compile for a different target. See step 7.

Windows CE[edit]

Not specified

OpenSSL 1.0.2[edit]

For OpenSSL 1.0.2 and earlier the procedure is as follows.

1. Ensure you have perl installed on your machine (e.g. ActiveState or Strawberry), and available on your %PATH%
2. Ensure you have NASM installed on your machine, and available on your %PATH%
3. launch a Visual Studio tool x64 Cross Tools Command prompt
4. change to the directory where you have copied openssl sources cd c:myPathopenssl
5. configure for the target OS with the command perl Configure VC-WIN64A. You may also be interested to set more configuration options as documented in the general INSTALL note (for UNIX targets). For instance: perl Configure VC-WIN64A.
6. prepare the target environment with the command: msdo_win64a
7. ensure you start afresh and notably without linkable products from a previous 32bit compile (as 32 and 64 bits compiling still share common directories) with the command: nmake -f msntdll.mak clean for the DLL target and nmake -f msnt.mak clean for static libraries.
8. build the code with: nmake -f msntdll.mak (respectively nmake -f msnt.mak )
9. the artefacts will be found in sub directories out32dll and out32dll.dbg (respectively out32 and out32.dbg for static libraries). The libcrypto and ssl libraries are still named libeay32.lib and ssleay32.lib, and associated includes in inc32 ! You may check this is true 64bit code using the Visual Studio tool 'dumpbin'. For instance dumpbin /headers out32dll/libeay32.lib | more, and look at the FILE HEADER section.
10. test the code using the various *test.exe programs in out32dll. Use the 'test' make target to run all tests as in nmake -f msntdll.mak test
11. we recommend that you move/copy needed includes and libraries from the '32' directories under a new explicit directory tree for 64bit applications from where you will import and link your target applications, similar to that explained in INSTALL.W32.

Windows CE[edit]

OS X[edit]

The earlier discussion presented a lot of information (and some of it had OS X information). Here are the TLDR versions to configure, build and install the library.

If configuring for 64-bit OS X, then use a command similar to:

If configuring for 32-bit OS X, then use a command similar to:

If you want to build a multiarch OpenSSL library, then see this answer on Stack Overflow: Build Multiarch OpenSSL on OS X.

iOS[edit]

The following builds OpenSSL for iOS using the iPhoneOS SDK. The configuration avoids the dynamic library the DSO interface and engines.

If you run make install, then the headers will be installed in /usr/local/openssl-ios/include and libraries will be installed in /usr/local/openssl-ios/lib.

32-bit[edit]

For OpenSSL 1.1.0 and above, a 32-bit iOS cross-compiles uses the ios-cross target, and options similar to --prefix=/usr/local/openssl-ios.

If you are working with OpenSSL 1.0.2 or below, then use the iphoneos-cross target.

64-bit[edit]

For OpenSSL 1.1.0 , a 64-bit iOS cross-compiles uses the ios64-cross target, and --prefix=/usr/local/openssl-ios64. ios64-cross. There is no built-in 64-bit iOS support for OpenSSL 1.0.2 or below.

Android[edit]

Visit Android and FIPS Library and Android.

More[edit]

VAX/VMS[edit]

I you wonder what are files ending with .com like test/testca.com those are VAX/VMX scripts.This code is still maintained.

OS/2[edit]

NetWare[edit]

5.x 6.x

HP-UX[edit]

Autoconf[edit]

Using Openssl In C++

OpenSSL uses its own configuration system, and does not use Autoconf. However, a number of popular projects use both OpenSSL and Autoconf, and it would be useful to detect either OPENSSL_init_ssl or SSL_library_init from libssl. To craft a feature test for OpenSSL that recognizes both OPENSSL_init_ssl and SSL_library_init, you can use the following.

Many thanks to the Postgres folks for donating part of their configure.in. Also see How to tell Autoconf 'require symbol A or B' from LIB? on Stack Overflow.

Disclaimer: I am NOT a crypto expert. Don't take the information here as 100% correct; you should verify it yourself. You are dangerously bad at crypto.

This post details the EVP functions for RSA. If you're looking for a pure RSA implementation or want something in C rather than C++, see my other post on this.

In my seemingly endless side project to implement RSA and AES encryption to my Alsa Server project, I wrote a while ago about doing simple RSA encryption with OpenSSL. Now, I'm here to say that I was doing it all wrong. In my first post about RSA encryption and OpenSSL my code was using the low level RSA functions when I should have been using the high level EVP (envelope) functions, which are much nicer to work with once you get the hang of them.

Being that this code is eventually going to be merged in my Alsa server project, I went ahead and also implemented AES encryption/decryption and put everything in an easy to use C++ class.

I assume that readers are familiar with encryption and OpenSSL terminology (things like IV, key lengths, public vs private keys, etc.). If not, look it up since there are much better explanations out there than I could write.

Why use the EVP (envelope) functions for RSA encryption rather than the actual RSA functions? Becasue the EVP functions don't actually encrypt your data with RSA. Rather, they encrypted a symmetric key with RSA and then encrypt your data with the symmetric key. There's a few reasons for this. The main one being that RSA has a max length limit to how much data can be encrypted at once. Symmetric ciphers do not have this limit. If you want pure RSA, see my post about that, otherwise, you probably want to be using the EVP functions.

Moving on. First up, since all the code presented is in various functions from a class (full listing is at the end), let's look at the class members, and constructors first to understand where some of these variables are coming from. Below are all the class members. I know, not exactly intuitive, but bear with me.

• The EVP_PKEY variables store the public and private keys for the server, or just the public key for the client.
• The EVP_CIPHER_CTX variables keep track of the RSA and AES encryption/decryption processes and do all the hard, behind the scenes work.
• aesKey and aesIV are the symmetric key and IV used for the AES functions.

So now we need to initialize all these guys. In the class there are two constructors, each with different arguments so let's look at the default constructor for simplicity's sake.

The RSA keys are just set to NULL because their values will be initialized later when the RSA/AES functions are called. The #ifdef line certainly peaks some interest. Since this class is eventually going to be dropped in a server, it will be using the client's public key to encrypt data, but we don't have a client yet, so we define a fake client and generate another RSA key pair to simulate a client. The process of generating this key pair is identical to how we're about to generate the key pair for the server so let's look at this. This is all contained in the init() function.

Openssl Commands

There's a lot of strange function calls in here. Most of this function deals with the OpenSSL API and how to generate keys and initialize EVP contexts. I'll give a high level overview here, but the best way to understand this process is to read up on documentation. The first thing we do is allocate the proper amount of memory for the EVP contexts and then called the EVP_CIPHER_CTX_init() function which does some magic to initialize them. Then we use a few RSA functions to generate the RSA keys for the server. Again, the documentation for these functions will help you understand better than my explanation can, but you'll see a pattern emerge, initialize the context, pass it along with some options and an output argument to a function and you'll get what you want. It's the same way for RSA. We initialize the key context with EVP_PKEY_CTX_new_id() and EVP_PKEY_keygen_init(), set the key length to use with EVP_PKEY_CTX_set_rsa_keygen_bits() (see the full listing for the actual length if you really need to–2056 bits is sufficient for most cases; use 4096 if you're paranoid) and then actually generate the keys with EVP_PKEY_keygen().

The AES key is much simpler; it's just random data so we call RAND_bytes() to get the number of random bytes needed for the AES encrypted key and IV. There is also the option to use the EVP_BytesToKey() function which is a PBKDF. This function, as I called it, will generate a 256 bit key in CBC mode, with a salt and passphrase that are random data (the password being random data is just for demonstration purposes). The number of rounds (or count as the documentation calls it) is the strength of randomness to use. Higher numbers are better, but slower.

I mentioned above that we generate a separate client key pair for testing. I won't do a write-up on it since it's the same process as generating the server key pair, only we store the keys in their own variables of course, but you can see the genTestClientKey() function in the full code listing below for how this is done.

On to the fun part, the actual encryption. Let's start with AES since it's a little easier to understand. The AES encryption function:

The arguments are probably as you would expect, the message to be encrypted, the length of that message, and an output string for the encrypted message (which should just be a NULL pointer unless you like memory leaks).

The first step is allocate memory for the encrypted message. Because the message will be padded for extra space left over in the last block, we need to allocate the length of the unencrypted message plus the max size of an AES block to make sure there's enough room in the buffer.

A pattern quickly emerges when doing encryption/decryption with both AES and RSA. First there's a call to an init function, EVP_EncryptInit_ex() in this case, then a call to an update function, EVP_EncryptUpdate() here and finally a call to a finalize function, or EVP_EncryptFinal_ex(). Each of these functions has two versions, a 'regular' one and one suffixed with _ex. The _ex versions just provide a few extra parameters. See the documentation for the exact differences; I only used the _ex functions where necessary.

So, a little more info on the encryption process. First, we call the init function to initialize the context for encryption. Then the update function actually starts encrypting the message. This may involve multiple calls to the update function so if you were say, encrypting an entire file, you could read the file line by line, calling the update function as you read each line to encrypt it in a loop. In this case, we're only encrypting a single message so we only need to call it once. The update function will return the number of bytes that were encrypted. It is our responsibility to keep track of the total number of bytes encrypted and to advance the encrypted message pointer for each subsequent call to the update and finalize function, otherwise you will be overwriting previously encrypted data. I bold this because the documentation does not make reference to this and was the source of much confusion when I was originally writing these functions. Thankfully, one of the smart people over at Stack Overflow helped me out. Now, the last step is to finalize the encryption. This is will pad extra space in the buffer to fill up the last block and then that completes the encryption! In my function I update the number of bytes encrypted and return that to the caller. It is important to return the number of bytes encrypted so the caller can keep track of the encrypted message length because it is now a binary string and calling strlen() on it won't give the correct length. Though it's possible to convert it to base64.

Lastly, clean up the context to avoid memory leaks.

On to decryption!

The AES decryption function looks very similar to the encryption function. The arguments are the encrypted message, its length, and a double pointer to an output buffer for the decrypted string (should be NULL as well else memory leaks). The decryption process is very similar to encryption so I won't go into as much detail as I did with encryption here. First we allocate memory for the decrypted string, init our decryption context, call the update function on the encrypted message (note we have to keep track of the number of decrypted bytes here too), and then finalize the decryption. That's all there is to it.

Next up, RSA.

Again, RSA is very similar to AES. The major difference being that we're now using the 'Seal' functions. The OpenSSL API differentiates between Seal & Open for encrypting with public keys and decrypting with private keys and Sign & Verify for encrypting with private keys and decrypting with public keys. Since I will eventually be dropping this in a server, I want to be encrypting with public keys so I'm using the Seal functions here.

As before, we first allocate memory for the encrypted message. A limitation of RSA is that the max length of the encrypted message is roughly equal to the length of the key it's being encrypted with. However, a key point of the EVP functions is that they don't acutally encrypt your data with RSA, but rather encrypt a symmetric key with RSA and then use the symmetric key to encrypt your data since there is no max length on symmetric key encryption. This is also what the ek argument is. It will returned the encrypted symmetric key that the data is actually encrypted with. To decrypt it, we'll need the symmetric key and the IV. This is a lot of data to keep track of, but that's part of the challenge of using encryption.

From here we init the context again, call the update function (only once since we only have one message) and then finalize it all while keeping track of the number of bytes that were encrypted.

Openssl In Centos

Decryption time.

Once again, the decryption is similar to AES decryption so I won't go into much detail. One interesting note, however, is the #ifdef. This is where the client key pair I made in the init function way above comes into place. Because this is all just a test of the crypto functions, I don't have a client to give me a public key from yet. So we generated an extra key pair at the beginning to simulate the client's keypair key with. In the future, decryption will be done with the server's private key and we will, of course, not have access to the client's private key so that's where the #ifdef comes from. Chegg discord.

Other than that, the typical init, update, finalize process is in effect again. After decryption we have a regular char string again so don't forget about the null terminator.

Okay, so we have all these functions now. How about seeing them in action? First, let's look at how to compile this guy.

C++ Openssl Tutorial

So here we have debugging and warnings turned on. class_test.cpp is my main file and Crypto.cpp is my class with all the encryption/decryption functions in it. The key part is linking with the OpenSSL library, called the crypto library at the end of the command. Note that like all libraries with g++, it must be after the source files. Also, make sure you have a recent version of OpenSSL. I wrote this with version 1.0.1. YMMV with other versions.

Openssl Examples

Finally, let's run this guy with a test program (available on GitHub at the link below):

Install Openssl In Centos 7

Arrested Development references aside, you can see that it, at the very least, does encrypt and decrypt our messages. You'll notice that the output has been converted to base64 so it can be printed out as a regular ASCII string.

Full code listing (and more!) is available on GitHub.