#       OpenPGP installation directory was successfully detected and added
  #       to the PATH -OR- detecting and adding it was not necessary because
  #       it already appeared to be available for use.
  #
  # <internal>
  proc probeForOpenPgpInstallation {} {
    global env
    variable openPgpFileNamesOnly
    variable openPgpInstalledDirectories

    if {[catch {openPgpMustBeInstalled}] == 0} then {
      return true
    }

    if {![info exists openPgpFileNamesOnly]} then {
      return false
    }

    if {![info exists openPgpInstalledDirectories]} then {
      return false
    }

    if {[isWindows]} then {
      if {[info exists env(ProgramFiles(x86))]} then {
        set programFiles $env(ProgramFiles\(x86\))
      } elseif {[info exists env(ProgramFiles)]} then {
        set programFiles $env(ProgramFiles)
      } else {
        return false
      }
    }

    foreach directory $openPgpInstalledDirectories {
      if {[isWindows]} then {
        set subDirectory [file join $programFiles $directory]
      } else {
        set subDirectory $directory
      }

      if {[file isdirectory $subDirectory]} then {


        foreach fileNameOnly $openPgpFileNamesOnly {
          set fileName [file join $subDirectory $fileNameOnly]

          if {[file exists $fileName] && [file isfile $fileName]} then {
            return [addToPath $subDirectory]
          }
        }
      }
    }

    return false
  }

  #
  # NOTE: This procedure attempts to verify that a configured implementation

  #
  proc setupRepositoryOpenPgpVars { force } {
    #
    # NOTE: This is the name of the sub-directory containing the OpenPGP
    #       implementation.  It is platform-specific.  On Windows, this
    #       sub-directory is relative to the "Program Files" directory.
    #
    variable openPgpInstalledDirectories; # DEFAULT: [list ...]

    if {$force || ![info exists openPgpInstalledDirectories]} then {
      if {[isWindows]} then {
        set openPgpInstalledDirectories [list \
            [file join gnupg] [file join GNU GnuPG]]
      } else {
        set openPgpInstalledDirectories [list \
            [file join / usr bin]]
      }
    }

    #
    # NOTE: These are the candidate names of the executable file used to
    #       invoke the OpenPGP implementation, possibly without a file
    #       extension.
    #
    variable openPgpFileNamesOnly; # DEFAULT: [list gpg2 gpg]

    if {$force || ![info exists openPgpFileNamesOnly]} then {
      if {[isWindows]} then {
        set openPgpFileNamesOnly [list gpg2.exe gpg.exe]
      } else {
        set openPgpFileNamesOnly [list gpg2 gpg]
      }
    }

    #
    # NOTE: This is the name of the executable file used to invoke the
    #       OpenPGP implementation, possibly without a file extension.
    #
    variable openPgpFileNameOnly; # DEFAULT: <unset>

    #
    # NOTE: The command to use when attempting to import an OpenPGP key
    #       file.  This must be configured according to the implementation
    #       of OpenPGP in use.
    #
    variable openPgpImportCommand; # DEFAULT: gpg2 --import

    if {$force || ![info exists openPgpImportCommand]} then {
      set openPgpImportCommand \
          {{${openPgpFileNameOnly}} --import {${fileName}}}
    }

    #
    # NOTE: The regular expression pattern used when attempting to verify
    #       that OpenPGP successfully imported one or more keys.  This must
    #       be configured according to the implementation of OpenPGP in use.
    #
    variable openPgpImportPattern; # DEFAULT: ^gpg: Total number processed...

    if {$force || ![info exists openPgpImportPattern]} then {
      set openPgpImportPattern {^gpg: Total number processed: [1-9]\d*$}
    }

    #
    # NOTE: The command to use when attempting to verify that OpenPGP is
    #       installed locally.  This must be configured according to the
    #       implementation of OpenPGP in use.
    #
    variable openPgpInstalledCommand; # DEFAULT: gpg2 --version --homedir {}

    if {$force || ![info exists openPgpInstalledCommand]} then {
      set openPgpInstalledCommand {{${fileName}} --version --homedir {}}
    }

    #
    # NOTE: The regular expression pattern used when attempting to verify
    #       that OpenPGP is installed locally.  This must be configured
    #       according to the implementation of OpenPGP in use.
    #
    variable openPgpInstalledPattern; # DEFAULT: ^gpg \(GnuPG\) 2\.[0123]\.

    if {$force || ![info exists openPgpInstalledPattern]} then {
      set openPgpInstalledPattern {^gpg \(GnuPG\) 2\.[0123]\.}
    }

    #
    # NOTE: The command to use when verifying OpenPGP signatures for the
    #       downloaded package scripts.  This must be configured according
    #       to the implementation of OpenPGP in use.
    #
    variable openPgpVerifyCommand; # DEFAULT: gpg2 --verify {${fileName}}

    if {$force || ![info exists openPgpVerifyCommand]} then {
      set openPgpVerifyCommand \
          {{${openPgpFileNameOnly}} --verify {${fileName}}}
    }

    #
    # NOTE: The command to use when creating OpenPGP signatures for the
    #       downloaded package scripts.  This must be configured according
    #       to the implementation of OpenPGP in use.
    #
    variable openPgpSignCommand; # DEFAULT: gpg2 --detach-sign ...

    if {$force || ![info exists openPgpSignCommand]} then {
      set openPgpSignCommand ""

      append openPgpSignCommand \
          {{${openPgpFileNameOnly}} --detach-sign --armor}

      append openPgpSignCommand \
          { --passphrase-file [formatExecArgument [getOpenPgpPassphraseFile]]}