https://github.com/k--kato/osxcsharp/blob/master/README.md
を参考にしました。

$ brew install openssl
Error: Your Xcode (7.3) is outdated.
Please update to Xcode 8.0 (or delete it).
Xcode can be updated from the App Store.

と怒られるので、
App Store で、
Xcode インストール。

$ brew install openssl
Error: You have not agreed to the Xcode license. Please resolve this by running:
  sudo xcodebuild -license

インストールしただけではダメ。
Xcode 起動、ライセンス認証しますが、
iTunes の停止が必要です。

$ brew install openssl
==> Downloading https://homebrew.bintray.com/bottles/openssl-1.0.2j.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring openssl-1.0.2j.sierra.bottle.tar.gz
==> Using the sandbox
==> Caveats
A CA file has been bootstrapped using certificates from the SystemRoots
keychain. To add additional certificates (e.g. the certificates added in
the System keychain), place .pem files in
  /usr/local/etc/openssl/certs

and run
  /usr/local/opt/openssl/bin/c_rehash

This formula is keg-only, which means it was not symlinked into /usr/local.

Apple has deprecated use of OpenSSL in favor of its own TLS and crypto libraries

Generally there are no consequences of this for you. If you build your
own software and it requires this formula, you'll need to add to your
build variables:

    LDFLAGS:  -L/usr/local/opt/openssl/lib
    CPPFLAGS: -I/usr/local/opt/openssl/include
    PKG_CONFIG_PATH: /usr/local/opt/openssl/lib/pkgconfig

==> Summary
🍻/usr/local/Cellar/openssl/1.0.2j: 1,695 files, 12M

$ brew link --force openssl
Warning: Refusing to link: openssl
Linking keg-only openssl means you may end up linking against the insecure,
deprecated system OpenSSL while using the headers from Homebrew's openssl.
Instead, pass the full include/library paths to your compiler e.g.:
  -I/usr/local/opt/openssl/include -L/usr/local/opt/openssl/lib
  
  
  https://www.microsoft.com/net/core#macos
  を参考にして、.NET Core SDK　インストール。
  
  
  $ dotnet new

Unhandled Exception: System.TypeInitializationException: The type initializer for 'Crypto' threw an exception. ---> System.TypeInitializationException: The type initializer for 'CryptoInitializer' threw an exception. ---> System.DllNotFoundException: Unable to load DLL 'System.Security.Cryptography.Native': The specified module could not be found.
 (Exception from HRESULT: 0x8007007E)
   at Interop.CryptoInitializer.EnsureOpenSslInitialized()
   at Interop.CryptoInitializer..cctor()
   --- End of inner exception stack trace ---
   at Interop.Crypto..cctor()
   --- End of inner exception stack trace ---
   at Interop.Crypto.GetRandomBytes(Byte* buf, Int32 num)
   at System.IO.Path.GetCryptoRandomBytes(Byte* bytes, Int32 byteCount)
   at System.IO.Path.GetRandomFileName()
   at Microsoft.DotNet.InternalAbstractions.TemporaryDirectory..ctor()
   at Microsoft.Extensions.EnvironmentAbstractions.DirectoryWrapper.CreateTemporaryDirectory()
   at Microsoft.DotNet.Configurer.NuGetPackagesArchiver..ctor()
   at Microsoft.DotNet.Cli.Program.ConfigureDotNetForFirstTimeUse(INuGetCacheSentinel nugetCacheSentinel)
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, ITelemetry telemetryClient)
   at Microsoft.DotNet.Cli.Program.Main(String[] args)
Abort trap: 6

$ ln -s /usr/local/opt/openssl/lib/libcrypto.1.0.0.dylib /usr/local/lib/
$ ln -s /usr/local/opt/openssl/lib/libssl.1.0.0.dylib /usr/local/lib/

$ dotnet new

Welcome to .NET Core!
---------------------
Learn more about .NET Core @ https://aka.ms/dotnet-docs. Use dotnet --help to see available commands or go to https://aka.ms/dotnet-cli-docs.
Telemetry
--------------
The .NET Core tools collect usage data in order to improve your experience. The data is anonymous and does not include commandline arguments. The data is collected by Microsoft and shared with the community.
You can opt out of telemetry by setting a DOTNET_CLI_TELEMETRY_OPTOUT environment variable to 1 using your favorite shell.
You can read more about .NET Core tools telemetry @ https://aka.ms/dotnet-cli-telemetry.
Configuring...
-------------------
A command is running to initially populate your local package cache, to improve restore speed and enable offline access. This command will take up to a minute to complete and will only happen once.
Decompressing 100% 2768 ms
Expanding 100% 10406 ms
Created new C# project in /pathToMyProject.

$ dotnet restore
log  : Restoring packages for /pathToMyProject/project.json...
log  : Writing lock file to disk. Path: /pathToMyProject/project.lock.json
log  : /pathToMyProject/project.json
log  : Restore completed in 1198ms.

$ dotnet run
Project Csharp (.NETCoreApp,Version=v1.0) will be compiled because expected outputs are missing
Compiling MyProject for .NETCoreApp,Version=v1.0

Compilation succeeded.
    0 Warning(s)
    0 Error(s)

Time elapsed 00:00:02.0358667
 

Hello World!

準備完了。