verify_digest(){	# $0 method file string
  case "$1" in
  *)
    DIGEST=`echo "$1" | tr a-z A-Z`
    [ "$DIGEST($2)= $3" = "`openssl $1 $2`" ]
    ;;
  esac
}
verify_signature(){	# $0 url|id sig
  case "$1" in
  0x*)
    gpg --recv-keys "$1" && gpg --verify "$2"
    ;;
  *)
    curl "$1" | gpg --import && gpg --verify "$2"
    ;;
  esac
}
error_out(){	# $0 message ...
  echo "$@" 1>&2
  exit 1
}

wget -N ftp://ftp.gnupg.org/gcrypt/gnupg/gnupg-1.4.7.tar.bz2
wget -N ftp://ftp.gnupg.org/gcrypt/gnupg/gnupg-1.4.7.tar.bz2.sig
verify_digest sha1 gnupg-1.4.7.tar.bz2 "22149105845c79068771837c8deb7d5ba0854927" || error_out "$0: stopped at line $LINENO"

tar xvjf gnupg-1.4.7.tar.bz2