Disallow X509 certificate serial numbers bigger than 159 bits (#3064) (#3067)

3 files changed, 89 insertions, 13 deletions

diff --git a/src/cryptography/x509/base.py b/src/cryptography/x509/base.py
index ab70fe75..5c4e3aad 100644
--- a/src/cryptography/x509/base.py
+++ b/src/cryptography/x509/base.py
@@ -425,10 +425,13 @@ class CertificateBuilder(object):
             raise TypeError('Serial number must be of integral type.')
         if self._serial_number is not None:
             raise ValueError('The serial number may only be set once.')
-        if number < 0:
-            raise ValueError('The serial number should be non-negative.')
-        if utils.bit_length(number) > 160:  # As defined in RFC 5280
-            raise ValueError('The serial number should not be more than 160 '
+        if number <= 0:
+            raise ValueError('The serial number should be positive.')
+
+        # ASN.1 integers are always signed, so most significant bit must be
+        # zero.
+        if utils.bit_length(number) >= 160:  # As defined in RFC 5280
+            raise ValueError('The serial number should not be more than 159 '
                              'bits.')
         return CertificateBuilder(
             self._issuer_name, self._subject_name,
@@ -635,10 +638,13 @@ class RevokedCertificateBuilder(object):
             raise TypeError('Serial number must be of integral type.')
         if self._serial_number is not None:
             raise ValueError('The serial number may only be set once.')
-        if number < 0:
-            raise ValueError('The serial number should be non-negative.')
-        if utils.bit_length(number) > 160:  # As defined in RFC 5280
-            raise ValueError('The serial number should not be more than 160 '
+        if number <= 0:
+            raise ValueError('The serial number should be positive')
+
+        # ASN.1 integers are always signed, so most significant bit must be
+        # zero.
+        if utils.bit_length(number) >= 160:  # As defined in RFC 5280
+            raise ValueError('The serial number should not be more than 159 '
                              'bits.')
         return RevokedCertificateBuilder(
             number, self._revocation_date, self._extensions
diff --git a/tests/test_x509.py b/tests/test_x509.py
index 40efb6da..1ce8c611 100644
--- a/tests/test_x509.py
+++ b/tests/test_x509.py
@@ -1689,12 +1689,55 @@ class TestCertificateBuilder(object):
 
     def test_serial_number_must_be_non_negative(self):
         with pytest.raises(ValueError):
-            x509.CertificateBuilder().serial_number(-10)
+            x509.CertificateBuilder().serial_number(-1)
+
+    def test_serial_number_must_be_positive(self):
+        with pytest.raises(ValueError):
+            x509.CertificateBuilder().serial_number(0)
+
+    @pytest.mark.requires_backend_interface(interface=RSABackend)
+    @pytest.mark.requires_backend_interface(interface=X509Backend)
+    def test_minimal_serial_number(self, backend):
+        subject_private_key = RSA_KEY_2048.private_key(backend)
+        builder = x509.CertificateBuilder().serial_number(
+            1
+        ).subject_name(x509.Name([
+            x509.NameAttribute(NameOID.COUNTRY_NAME, u'RU'),
+        ])).issuer_name(x509.Name([
+            x509.NameAttribute(NameOID.COUNTRY_NAME, u'RU'),
+        ])).public_key(
+            subject_private_key.public_key()
+        ).not_valid_before(
+            datetime.datetime(2002, 1, 1, 12, 1)
+        ).not_valid_after(
+            datetime.datetime(2030, 12, 31, 8, 30)
+        )
+        cert = builder.sign(subject_private_key, hashes.SHA256(), backend)
+        assert cert.serial_number == 1
+
+    @pytest.mark.requires_backend_interface(interface=RSABackend)
+    @pytest.mark.requires_backend_interface(interface=X509Backend)
+    def test_biggest_serial_number(self, backend):
+        subject_private_key = RSA_KEY_2048.private_key(backend)
+        builder = x509.CertificateBuilder().serial_number(
+            (1 << 159) - 1
+        ).subject_name(x509.Name([
+            x509.NameAttribute(NameOID.COUNTRY_NAME, u'RU'),
+        ])).issuer_name(x509.Name([
+            x509.NameAttribute(NameOID.COUNTRY_NAME, u'RU'),
+        ])).public_key(
+            subject_private_key.public_key()
+        ).not_valid_before(
+            datetime.datetime(2002, 1, 1, 12, 1)
+        ).not_valid_after(
+            datetime.datetime(2030, 12, 31, 8, 30)
+        )
+        cert = builder.sign(subject_private_key, hashes.SHA256(), backend)
+        assert cert.serial_number == (1 << 159) - 1
 
     def test_serial_number_must_be_less_than_160_bits_long(self):
         with pytest.raises(ValueError):
-            # 2 raised to the 160th power is actually 161 bits
-            x509.CertificateBuilder().serial_number(2 ** 160)
+            x509.CertificateBuilder().serial_number(1 << 159)
 
     def test_serial_number_may_only_be_set_once(self):
         builder = x509.CertificateBuilder().serial_number(10)
diff --git a/tests/test_x509_revokedcertbuilder.py b/tests/test_x509_revokedcertbuilder.py
index 5aa90630..bd64b600 100644
--- a/tests/test_x509_revokedcertbuilder.py
+++ b/tests/test_x509_revokedcertbuilder.py
@@ -21,10 +21,37 @@ class TestRevokedCertificateBuilder(object):
         with pytest.raises(ValueError):
             x509.RevokedCertificateBuilder().serial_number(-1)
 
+    def test_serial_number_must_be_positive(self):
+        with pytest.raises(ValueError):
+            x509.RevokedCertificateBuilder().serial_number(0)
+
+    @pytest.mark.requires_backend_interface(interface=X509Backend)
+    def test_minimal_serial_number(self, backend):
+        revocation_date = datetime.datetime(2002, 1, 1, 12, 1)
+        builder = x509.RevokedCertificateBuilder().serial_number(
+            1
+        ).revocation_date(
+            revocation_date
+        )
+
+        revoked_certificate = builder.build(backend)
+        assert revoked_certificate.serial_number == 1
+
+    @pytest.mark.requires_backend_interface(interface=X509Backend)
+    def test_biggest_serial_number(self, backend):
+        revocation_date = datetime.datetime(2002, 1, 1, 12, 1)
+        builder = x509.RevokedCertificateBuilder().serial_number(
+            (1 << 159) - 1
+        ).revocation_date(
+            revocation_date
+        )
+
+        revoked_certificate = builder.build(backend)
+        assert revoked_certificate.serial_number == (1 << 159) - 1
+
     def test_serial_number_must_be_less_than_160_bits_long(self):
         with pytest.raises(ValueError):
-            # 2 raised to the 160th power is actually 161 bits
-            x509.RevokedCertificateBuilder().serial_number(2 ** 160)
+            x509.RevokedCertificateBuilder().serial_number(1 << 159)
 
     def test_set_serial_number_twice(self):
         builder = x509.RevokedCertificateBuilder().serial_number(3)