4 files changed, 731 insertions, 0 deletions
diff --git a/lib/rubygems/security/policies.rb b/lib/rubygems/security/policies.rb
new file mode 100644
index 0000000000..41f66043ad
--- /dev/null
+++ b/lib/rubygems/security/policies.rb
@@ -0,0 +1,114 @@
+# frozen_string_literal: true
+
+module Gem::Security
+  ##
+  # No security policy: all package signature checks are disabled.
+
+  NoSecurity = Policy.new(
+    "No Security",
+    verify_data: false,
+    verify_signer: false,
+    verify_chain: false,
+    verify_root: false,
+    only_trusted: false,
+    only_signed: false
+  )
+
+  ##
+  # AlmostNo security policy: only verify that the signing certificate is the
+  # one that actually signed the data.  Make no attempt to verify the signing
+  # certificate chain.
+  #
+  # This policy is basically useless. better than nothing, but can still be
+  # easily spoofed, and is not recommended.
+
+  AlmostNoSecurity = Policy.new(
+    "Almost No Security",
+    verify_data: true,
+    verify_signer: false,
+    verify_chain: false,
+    verify_root: false,
+    only_trusted: false,
+    only_signed: false
+  )
+
+  ##
+  # Low security policy: only verify that the signing certificate is actually
+  # the gem signer, and that the signing certificate is valid.
+  #
+  # This policy is better than nothing, but can still be easily spoofed, and
+  # is not recommended.
+
+  LowSecurity = Policy.new(
+    "Low Security",
+    verify_data: true,
+    verify_signer: true,
+    verify_chain: false,
+    verify_root: false,
+    only_trusted: false,
+    only_signed: false
+  )
+
+  ##
+  # Medium security policy: verify the signing certificate, verify the signing
+  # certificate chain all the way to the root certificate, and only trust root
+  # certificates that we have explicitly allowed trust for.
+  #
+  # This security policy is reasonable, but it allows unsigned packages, so a
+  # malicious person could simply delete the package signature and pass the
+  # gem off as unsigned.
+
+  MediumSecurity = Policy.new(
+    "Medium Security",
+    verify_data: true,
+    verify_signer: true,
+    verify_chain: true,
+    verify_root: true,
+    only_trusted: true,
+    only_signed: false
+  )
+
+  ##
+  # High security policy: only allow signed gems to be installed, verify the
+  # signing certificate, verify the signing certificate chain all the way to
+  # the root certificate, and only trust root certificates that we have
+  # explicitly allowed trust for.
+  #
+  # This security policy is significantly more difficult to bypass, and offers
+  # a reasonable guarantee that the contents of the gem have not been altered.
+
+  HighSecurity = Policy.new(
+    "High Security",
+    verify_data: true,
+    verify_signer: true,
+    verify_chain: true,
+    verify_root: true,
+    only_trusted: true,
+    only_signed: true
+  )
+
+  ##
+  # Policy used to verify a certificate and key when signing a gem
+
+  SigningPolicy = Policy.new(
+    "Signing Policy",
+    verify_data: false,
+    verify_signer: true,
+    verify_chain: true,
+    verify_root: true,
+    only_trusted: false,
+    only_signed: false
+  )
+
+  ##
+  # Hash of configured security policies
+
+  Policies = {
+    "NoSecurity" => NoSecurity,
+    "AlmostNoSecurity" => AlmostNoSecurity,
+    "LowSecurity" => LowSecurity,
+    "MediumSecurity" => MediumSecurity,
+    "HighSecurity" => HighSecurity,
+    # SigningPolicy is not intended for use by `gem -P` so do not list it
+  }.freeze
+end
diff --git a/lib/rubygems/security/policy.rb b/lib/rubygems/security/policy.rb
new file mode 100644
index 0000000000..128958ab80
--- /dev/null
+++ b/lib/rubygems/security/policy.rb
@@ -0,0 +1,288 @@
+# frozen_string_literal: true
+
+require_relative "../user_interaction"
+
+##
+# A Gem::Security::Policy object encapsulates the settings for verifying
+# signed gem files.  This is the base class.  You can either declare an
+# instance of this or use one of the preset security policies in
+# Gem::Security::Policies.
+
+class Gem::Security::Policy
+  include Gem::UserInteraction
+
+  attr_reader :name
+
+  attr_accessor :only_signed
+  attr_accessor :only_trusted
+  attr_accessor :verify_chain
+  attr_accessor :verify_data
+  attr_accessor :verify_root
+  attr_accessor :verify_signer
+
+  ##
+  # Create a new Gem::Security::Policy object with the given mode and
+  # options.
+
+  def initialize(name, policy = {}, opt = {})
+    @name = name
+
+    @opt = opt
+
+    # Default to security
+    @only_signed   = true
+    @only_trusted  = true
+    @verify_chain  = true
+    @verify_data   = true
+    @verify_root   = true
+    @verify_signer = true
+
+    policy.each_pair do |key, val|
+      case key
+      when :verify_data   then @verify_data   = val
+      when :verify_signer then @verify_signer = val
+      when :verify_chain  then @verify_chain  = val
+      when :verify_root   then @verify_root   = val
+      when :only_trusted  then @only_trusted  = val
+      when :only_signed   then @only_signed   = val
+      end
+    end
+  end
+
+  ##
+  # Verifies each certificate in +chain+ has signed the following certificate
+  # and is valid for the given +time+.
+
+  def check_chain(chain, time)
+    raise Gem::Security::Exception, "missing signing chain" unless chain
+    raise Gem::Security::Exception, "empty signing chain" if chain.empty?
+
+    begin
+      chain.each_cons 2 do |issuer, cert|
+        check_cert cert, issuer, time
+      end
+
+      true
+    rescue Gem::Security::Exception => e
+      raise Gem::Security::Exception, "invalid signing chain: #{e.message}"
+    end
+  end
+
+  ##
+  # Verifies that +data+ matches the +signature+ created by +public_key+ and
+  # the +digest+ algorithm.
+
+  def check_data(public_key, digest, signature, data)
+    raise Gem::Security::Exception, "invalid signature" unless
+      public_key.verify digest, signature, data.digest
+
+    true
+  end
+
+  ##
+  # Ensures that +signer+ is valid for +time+ and was signed by the +issuer+.
+  # If the +issuer+ is +nil+ no verification is performed.
+
+  def check_cert(signer, issuer, time)
+    raise Gem::Security::Exception, "missing signing certificate" unless
+      signer
+
+    message = "certificate #{signer.subject}"
+
+    if (not_before = signer.not_before) && not_before > time
+      raise Gem::Security::Exception,
+            "#{message} not valid before #{not_before}"
+    end
+
+    if (not_after = signer.not_after) && not_after < time
+      raise Gem::Security::Exception, "#{message} not valid after #{not_after}"
+    end
+
+    if issuer && !signer.verify(issuer.public_key)
+      raise Gem::Security::Exception,
+            "#{message} was not issued by #{issuer.subject}"
+    end
+
+    true
+  end
+
+  ##
+  # Ensures the public key of +key+ matches the public key in +signer+
+
+  def check_key(signer, key)
+    unless signer && key
+      return true unless @only_signed
+
+      raise Gem::Security::Exception, "missing key or signature"
+    end
+
+    raise Gem::Security::Exception,
+      "certificate #{signer.subject} does not match the signing key" unless
+        signer.check_private_key(key)
+
+    true
+  end
+
+  ##
+  # Ensures the root certificate in +chain+ is self-signed and valid for
+  # +time+.
+
+  def check_root(chain, time)
+    raise Gem::Security::Exception, "missing signing chain" unless chain
+
+    root = chain.first
+
+    raise Gem::Security::Exception, "missing root certificate" unless root
+
+    raise Gem::Security::Exception,
+          "root certificate #{root.subject} is not self-signed " \
+          "(issuer #{root.issuer})" if
+      root.issuer != root.subject
+
+    check_cert root, root, time
+  end
+
+  ##
+  # Ensures the root of +chain+ has a trusted certificate in Gem::Security.trust_dir and
+  # the digests of the two certificates match according to +digester+
+
+  def check_trust(chain, digester, trust_dir)
+    raise Gem::Security::Exception, "missing signing chain" unless chain
+
+    root = chain.first
+
+    raise Gem::Security::Exception, "missing root certificate" unless root
+
+    path = Gem::Security.trust_dir.cert_path root
+
+    unless File.exist? path
+      message = "root cert #{root.subject} is not trusted".dup
+
+      message << " (root of signing cert #{chain.last.subject})" if
+        chain.length > 1
+
+      raise Gem::Security::Exception, message
+    end
+
+    save_cert = OpenSSL::X509::Certificate.new File.read path
+    save_dgst = digester.digest save_cert.public_key.to_pem
+
+    pkey_str = root.public_key.to_pem
+    cert_dgst = digester.digest pkey_str
+
+    raise Gem::Security::Exception,
+          "trusted root certificate #{root.subject} checksum " \
+          "does not match signing root certificate checksum" unless
+      save_dgst == cert_dgst
+
+    true
+  end
+
+  ##
+  # Extracts the email or subject from +certificate+
+
+  def subject(certificate) # :nodoc:
+    certificate.extensions.each do |extension|
+      next unless extension.oid == "subjectAltName"
+
+      return extension.value
+    end
+
+    certificate.subject.to_s
+  end
+
+  def inspect # :nodoc:
+    format("[Policy: %s - data: %p signer: %p chain: %p root: %p " \
+     "signed-only: %p trusted-only: %p]", @name, @verify_chain, @verify_data, @verify_root, @verify_signer, @only_signed, @only_trusted)
+  end
+
+  ##
+  # For +full_name+, verifies the certificate +chain+ is valid, the +digests+
+  # match the signatures +signatures+ created by the signer depending on the
+  # +policy+ settings.
+  #
+  # If +key+ is given it is used to validate the signing certificate.
+
+  def verify(chain, key = nil, digests = {}, signatures = {}, full_name = "(unknown)")
+    if signatures.empty?
+      if @only_signed
+        raise Gem::Security::Exception,
+          "unsigned gems are not allowed by the #{name} policy"
+      elsif digests.empty?
+        # lack of signatures is irrelevant if there is nothing to check
+        # against
+      else
+        alert_warning "#{full_name} is not signed"
+        return
+      end
+    end
+
+    opt       = @opt
+    digester  = Gem::Security.create_digest
+    trust_dir = opt[:trust_dir]
+    time      = Time.now
+
+    _, signer_digests = digests.find do |_algorithm, file_digests|
+      file_digests.values.first.name == Gem::Security::DIGEST_NAME
+    end
+
+    if @verify_data
+      raise Gem::Security::Exception, "no digests provided (probable bug)" if
+        signer_digests.nil? || signer_digests.empty?
+    else
+      signer_digests = {}
+    end
+
+    signer = chain.last
+
+    check_key signer, key if key
+
+    check_cert signer, nil, time if @verify_signer
+
+    check_chain chain, time if @verify_chain
+
+    check_root chain, time if @verify_root
+
+    if @only_trusted
+      check_trust chain, digester, trust_dir
+    elsif signatures.empty? && digests.empty?
+      # trust is irrelevant if there's no signatures to verify
+    else
+      alert_warning "#{subject signer} is not trusted for #{full_name}"
+    end
+
+    signatures.each do |file, _|
+      digest = signer_digests[file]
+
+      raise Gem::Security::Exception, "missing digest for #{file}" unless
+        digest
+    end
+
+    signer_digests.each do |file, digest|
+      signature = signatures[file]
+
+      raise Gem::Security::Exception, "missing signature for #{file}" unless
+        signature
+
+      check_data signer.public_key, digester, signature, digest if @verify_data
+    end
+
+    true
+  end
+
+  ##
+  # Extracts the certificate chain from the +spec+ and calls #verify to ensure
+  # the signatures and certificate chain is valid according to the policy..
+
+  def verify_signatures(spec, digests, signatures)
+    chain = spec.cert_chain.map do |cert_pem|
+      OpenSSL::X509::Certificate.new cert_pem
+    end
+
+    verify chain, nil, digests, signatures, spec.full_name
+
+    true
+  end
+
+  alias_method :to_s, :name # :nodoc:
+end
diff --git a/lib/rubygems/security/signer.rb b/lib/rubygems/security/signer.rb
new file mode 100644
index 0000000000..eeeeb52906
--- /dev/null
+++ b/lib/rubygems/security/signer.rb
@@ -0,0 +1,212 @@
+# frozen_string_literal: true
+
+##
+# Basic OpenSSL-based package signing class.
+
+require_relative "../user_interaction"
+
+class Gem::Security::Signer
+  include Gem::UserInteraction
+
+  ##
+  # The chain of certificates for signing including the signing certificate
+
+  attr_accessor :cert_chain
+
+  ##
+  # The private key for the signing certificate
+
+  attr_accessor :key
+
+  ##
+  # The digest algorithm used to create the signature
+
+  attr_reader :digest_algorithm
+
+  ##
+  # The name of the digest algorithm, used to pull digests out of the hash by
+  # name.
+
+  attr_reader :digest_name # :nodoc:
+
+  ##
+  # Gem::Security::Signer options
+
+  attr_reader :options
+
+  DEFAULT_OPTIONS = {
+    expiration_length_days: 365,
+  }.freeze
+
+  ##
+  # Attempts to re-sign an expired cert with a given private key
+  def self.re_sign_cert(expired_cert, expired_cert_path, private_key)
+    return unless expired_cert.not_after < Time.now
+
+    expiry = expired_cert.not_after.strftime("%Y%m%d%H%M%S")
+    expired_cert_file = "#{File.basename(expired_cert_path)}.expired.#{expiry}"
+    new_expired_cert_path = File.join(Gem.user_home, ".gem", expired_cert_file)
+
+    Gem::Security.write(expired_cert, new_expired_cert_path)
+
+    re_signed_cert = Gem::Security.re_sign(
+      expired_cert,
+      private_key,
+      Gem::Security::ONE_DAY * Gem.configuration.cert_expiration_length_days
+    )
+
+    Gem::Security.write(re_signed_cert, expired_cert_path)
+
+    yield(expired_cert_path, new_expired_cert_path) if block_given?
+  end
+
+  ##
+  # Creates a new signer with an RSA +key+ or path to a key, and a certificate
+  # +chain+ containing X509 certificates, encoding certificates or paths to
+  # certificates.
+
+  def initialize(key, cert_chain, passphrase = nil, options = {})
+    @cert_chain = cert_chain
+    @key        = key
+    @passphrase = passphrase
+    @options = DEFAULT_OPTIONS.merge(options)
+
+    unless @key
+      default_key = File.join Gem.default_key_path
+      @key = default_key if File.exist? default_key
+    end
+
+    unless @cert_chain
+      default_cert = File.join Gem.default_cert_path
+      @cert_chain = [default_cert] if File.exist? default_cert
+    end
+
+    @digest_name      = Gem::Security::DIGEST_NAME
+    @digest_algorithm = Gem::Security.create_digest(@digest_name)
+
+    if @key && !@key.is_a?(OpenSSL::PKey::PKey)
+      @key = OpenSSL::PKey.read(File.read(@key), @passphrase)
+    end
+
+    if @cert_chain
+      @cert_chain = @cert_chain.compact.map do |cert|
+        next cert if OpenSSL::X509::Certificate === cert
+
+        cert = File.read cert if File.exist? cert
+
+        OpenSSL::X509::Certificate.new cert
+      end
+
+      load_cert_chain
+    end
+  end
+
+  ##
+  # Extracts the full name of +cert+.  If the certificate has a subjectAltName
+  # this value is preferred, otherwise the subject is used.
+
+  def extract_name(cert) # :nodoc:
+    subject_alt_name = cert.extensions.find {|e| e.oid == "subjectAltName" }
+
+    if subject_alt_name
+      /\Aemail:/ =~ subject_alt_name.value # rubocop:disable Performance/StartWith
+
+      $' || subject_alt_name.value
+    else
+      cert.subject
+    end
+  end
+
+  ##
+  # Loads any missing issuers in the cert chain from the trusted certificates.
+  #
+  # If the issuer does not exist it is ignored as it will be checked later.
+
+  def load_cert_chain # :nodoc:
+    return if @cert_chain.empty?
+
+    while @cert_chain.first.issuer.to_s != @cert_chain.first.subject.to_s do
+      issuer = Gem::Security.trust_dir.issuer_of @cert_chain.first
+
+      break unless issuer # cert chain is verified later
+
+      @cert_chain.unshift issuer
+    end
+  end
+
+  ##
+  # Sign data with given digest algorithm
+
+  def sign(data)
+    return unless @key
+
+    raise Gem::Security::Exception, "no certs provided" if @cert_chain.empty?
+
+    if @cert_chain.length == 1 && @cert_chain.last.not_after < Time.now
+      alert("Your certificate has expired, trying to re-sign it...")
+
+      re_sign_key(
+        expiration_length: (Gem::Security::ONE_DAY * options[:expiration_length_days])
+      )
+    end
+
+    full_name = extract_name @cert_chain.last
+
+    Gem::Security::SigningPolicy.verify @cert_chain, @key, {}, {}, full_name
+
+    @key.sign @digest_algorithm.new, data
+  end
+
+  ##
+  # Attempts to re-sign the private key if the signing certificate is expired.
+  #
+  # The key will be re-signed if:
+  # * The expired certificate is self-signed
+  # * The expired certificate is saved at ~/.gem/gem-public_cert.pem
+  #   and the private key is saved at ~/.gem/gem-private_key.pem
+  # * There is no file matching the expiry date at
+  #   ~/.gem/gem-public_cert.pem.expired.%Y%m%d%H%M%S
+  #
+  # If the signing certificate can be re-signed the expired certificate will
+  # be saved as ~/.gem/gem-public_cert.pem.expired.%Y%m%d%H%M%S where the
+  # expiry time (not after) is used for the timestamp.
+
+  def re_sign_key(expiration_length: Gem::Security::ONE_YEAR) # :nodoc:
+    old_cert = @cert_chain.last
+
+    disk_cert_path = File.join(Gem.default_cert_path)
+    disk_cert = begin
+                  File.read(disk_cert_path)
+                rescue StandardError
+                  nil
+                end
+
+    disk_key_path = File.join(Gem.default_key_path)
+    disk_key = begin
+                 OpenSSL::PKey.read(File.read(disk_key_path), @passphrase)
+               rescue StandardError
+                 nil
+               end
+
+    return unless disk_key
+
+    if disk_key.to_pem == @key.to_pem && disk_cert == old_cert.to_pem
+      expiry = old_cert.not_after.strftime("%Y%m%d%H%M%S")
+      old_cert_file = "gem-public_cert.pem.expired.#{expiry}"
+      old_cert_path = File.join(Gem.user_home, ".gem", old_cert_file)
+
+      unless File.exist?(old_cert_path)
+        Gem::Security.write(old_cert, old_cert_path)
+
+        cert = Gem::Security.re_sign(old_cert, @key, expiration_length)
+
+        Gem::Security.write(cert, disk_cert_path)
+
+        alert("Your cert: #{disk_cert_path} has been auto re-signed with the key: #{disk_key_path}")
+        alert("Your expired cert will be located at: #{old_cert_path}")
+
+        @cert_chain = [cert]
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/security/trust_dir.rb b/lib/rubygems/security/trust_dir.rb
new file mode 100644
index 0000000000..d23d161cfe
--- /dev/null
+++ b/lib/rubygems/security/trust_dir.rb
@@ -0,0 +1,117 @@
+# frozen_string_literal: true
+
+##
+# The TrustDir manages the trusted certificates for gem signature
+# verification.
+
+class Gem::Security::TrustDir
+  ##
+  # Default permissions for the trust directory and its contents
+
+  DEFAULT_PERMISSIONS = {
+    trust_dir: 0o700,
+    trusted_cert: 0o600,
+  }.freeze
+
+  ##
+  # The directory where trusted certificates will be stored.
+
+  attr_reader :dir
+
+  ##
+  # Creates a new TrustDir using +dir+ where the directory and file
+  # permissions will be checked according to +permissions+
+
+  def initialize(dir, permissions = DEFAULT_PERMISSIONS)
+    @dir = dir
+    @permissions = permissions
+
+    @digester = Gem::Security.create_digest
+  end
+
+  ##
+  # Returns the path to the trusted +certificate+
+
+  def cert_path(certificate)
+    name_path certificate.subject
+  end
+
+  ##
+  # Enumerates trusted certificates.
+
+  def each_certificate
+    return enum_for __method__ unless block_given?
+
+    glob = File.join @dir, "*.pem"
+
+    Dir[glob].each do |certificate_file|
+      certificate = load_certificate certificate_file
+
+      yield certificate, certificate_file
+    rescue OpenSSL::X509::CertificateError
+      next # HACK: warn
+    end
+  end
+
+  ##
+  # Returns the issuer certificate of the given +certificate+ if it exists in
+  # the trust directory.
+
+  def issuer_of(certificate)
+    path = name_path certificate.issuer
+
+    return unless File.exist? path
+
+    load_certificate path
+  end
+
+  ##
+  # Returns the path to the trusted certificate with the given ASN.1 +name+
+
+  def name_path(name)
+    digest = @digester.hexdigest name.to_s
+
+    File.join @dir, "cert-#{digest}.pem"
+  end
+
+  ##
+  # Loads the given +certificate_file+
+
+  def load_certificate(certificate_file)
+    pem = File.read certificate_file
+
+    OpenSSL::X509::Certificate.new pem
+  end
+
+  ##
+  # Add a certificate to trusted certificate list.
+
+  def trust_cert(certificate)
+    verify
+
+    destination = cert_path certificate
+
+    File.open destination, "wb", 0o600 do |io|
+      io.write certificate.to_pem
+      io.chmod(@permissions[:trusted_cert])
+    end
+  end
+
+  ##
+  # Make sure the trust directory exists.  If it does exist, make sure it's
+  # actually a directory.  If not, then create it with the appropriate
+  # permissions.
+
+  def verify
+    require "fileutils"
+    if File.exist? @dir
+      raise Gem::Security::Exception,
+        "trust directory #{@dir} is not a directory" unless
+          File.directory? @dir
+
+      FileUtils.chmod 0o700, @dir
+    else
+      FileUtils.mkdir_p @dir, mode: @permissions[:trust_dir]
+    end
+  end
+end