diff --git a/.github/workflows/ci-home.yml b/.github/workflows/ci-home.yml
index fdc5ba3c..ecb5a070 100644
--- a/.github/workflows/ci-home.yml
+++ b/.github/workflows/ci-home.yml
@@ -45,13 +45,14 @@ jobs:
       - run: nix-shell '<home-manager>' -A install
       - uses: actions/checkout@v3
       - run: home-manager switch -b backup -f ./home-manager/user-github-actions.nix
-      - name: Print paths
+      - name: Print some paths and versions
         run: |
           which fish
           which zsh
           which bash
           which ruby
           which irb
+          which ssh
       # Do not use interactive mode here.
       # Solutions as https://github.com/actions/runner/issues/241#issuecomment-924327172 will not fit with several problems
       - name: Run customized dependencies
@@ -60,5 +61,6 @@ jobs:
           zsh -c 'which dprint'
           zsh -c 'ruby --version'
           zsh -c 'irb --version'
+          zsh -c 'ssh -V'
       - name: Run homemade commands
         run: zsh -c 'la'
diff --git a/home-manager/home.nix b/home-manager/home.nix
index 1825f82f..170e6fe7 100644
--- a/home-manager/home.nix
+++ b/home-manager/home.nix
@@ -6,6 +6,7 @@
     ./bash.nix
     ./zsh.nix
     ./fish.nix
+    ./ssh.nix
     ./git.nix
     ./darwin.nix # Omit needless parts for Linux in the file
     ./homemade.nix
diff --git a/home-manager/packages.nix b/home-manager/packages.nix
index abfb223e..35793063 100644
--- a/home-manager/packages.nix
+++ b/home-manager/packages.nix
@@ -33,6 +33,10 @@
     # Required in many asdf plugins
     unzip
 
+    # In macOS, starting ssh-agent is still /usr/bin/ssh-agent even added the nixpkgs
+    # So avoiding to add it for now
+    # openssh
+
     git
     tig
     lazygit
diff --git a/home-manager/ssh.nix b/home-manager/ssh.nix
new file mode 100644
index 00000000..e542c742
--- /dev/null
+++ b/home-manager/ssh.nix
@@ -0,0 +1,87 @@
+{ config, pkgs, ... }:
+
+let
+  # SSH files cannot use XDG Base Directory.
+  # I don't have permission to read https://bugzilla.mindrot.org/show_bug.cgi?id=2050, but several sources tells us, it is the answer
+  #   - https://wiki.archlinux.jp/index.php/XDG_Base_Directory
+  #   - https://superuser.com/a/1606519/120469
+  sshDir = "${config.home.homeDirectory}/.ssh";
+
+  # - id_*: Do NOT share in different machines, do NOT tell to anyone. They are secrets.
+  # - id_*.pub: I CAN register them for different services.
+in
+{
+  # These hosts are taken from the public resources of each provider.
+  #   - https://docs.github.com/ja/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints
+  #   - https://docs.gitlab.com/ee/user/gitlab_com/#ssh-known_hosts-entries
+  #   - https://bitbucket.org/site/ssh
+  home.file.".ssh/known_hosts".text = ''
+    github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl
+    github.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBEmKSENjQEezOmxkZMy7opKgwFB9nkt5YRrYMjNuG5N87uRgg6CLrbo5wAdT/y6v0mKV0U2w0WZ2YB/++Tpockg=
+    github.com ssh-rsa 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
+    gitlab.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAfuCHKVTjquxvt6CM6tdG4SLp1Btn/nOeHHE5UOzRdf
+    gitlab.com ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCsj2bNKTBSpIYDEGk9KxsGh3mySTRgMtXL583qmBpzeQ+jqCMRgBqB98u3z++J1sKlXHWfM9dyhSevkMwSbhoR8XIq/U0tCNyokEi/ueaBMCvbcTHhO7FcwzY92WK4Yt0aGROY5qX2UKSeOvuP4D6TPqKF1onrSzH9bx9XUf2lEdWT/ia1NEKjunUqu1xOB/StKDHMoX4/OKyIzuS0q/T1zOATthvasJFoPrAjkohTyaDUz2LN5JoH839hViyEG82yB+MjcFV5MU3N1l1QL3cVUCh93xSaua1N85qivl+siMkPGbO5xR/En4iEY6K2XPASUEMaieWVNTRCtJ4S8H+9
+    gitlab.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFSMqzJeV9rUzU4kWitGjeR4PWSa29SPqJ1fVkhtj3Hw9xjLVXVYrU9QlYWrOLXBpQ6KWjbjTDTdDkoohFzgbEY=
+    bitbucket.org ssh-rsa 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
+    bitbucket.org ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBPIQmuzMBuKdWeF4+a2sjSSpBK0iqitSQ+5BM9KhpexuGt20JpTVM7u5BDZngncgrqDMbWdxMWWOGtZ9UgbqgZE=
+    bitbucket.org ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIIazEu89wgQZ4bqs3d63QSMzYVa0MuJ2e2gKTKqu+UUO
+  '';
+
+  # https://github.com/nix-community/home-manager/blob/master/modules/programs/ssh.nix
+  programs.ssh = {
+    enable = true;
+
+    # https://groups.google.com/g/opensshunixdev/c/e5-kTKpxcaI/m/bdVNyL4BBAAJ
+    hashKnownHosts = false;
+    userKnownHostsFile = "${sshDir}/known_hosts";
+
+    # unit: seconds
+    serverAliveInterval = 60;
+
+    forwardAgent = true;
+
+    controlMaster = "auto";
+    controlPersist = "10m";
+
+    # Enable custom or temporary config without `home-manager switch`
+    includes = [
+      "${sshDir}/config.local"
+    ];
+
+    # https://www.clear-code.com/blog/2023/4/3/recommended-ssh-config.html
+    # https://gitlab.com/clear-code/ssh.d/-/blob/main/global.conf?ref_type=heads
+    extraConfig = ''
+      AddKeysToAgent yes
+
+      PasswordAuthentication no
+
+      # default: "ask" - I'm disabling it for now
+      StrictHostKeyChecking yes
+
+      # https://serverfault.com/a/1109184/112217
+      CheckHostIP no
+
+      # `UseKeychain` only provided by darwin ssh agent, in Linux and pkgs.openssh, it isn't
+      IgnoreUnknown UseKeychain
+      UseKeychain yes
+    '';
+
+    # No problem to register the same *.pub in different services
+    matchBlocks = {
+      "github.com" = {
+        identityFile = "${sshDir}/id_ed25519";
+        user = "git";
+      };
+
+      "gitlab.com" = {
+        identityFile = "${sshDir}/id_ed25519";
+        user = "git";
+      };
+
+      "bitbucket.org" = {
+        identityFile = "${sshDir}/id_ed25519";
+        user = "git";
+      };
+    };
+  };
+}