Copy secrets module from CPython 3.8

Lib/secrets.py

@@ -0,0 +1,73 @@
+"""Generate cryptographically strong pseudo-random numbers suitable for
+managing secrets such as account authentication, tokens, and similar.
+
+See PEP 506 for more information.
+https://www.python.org/dev/peps/pep-0506/
+
+"""
+
+__all__ = ['choice', 'randbelow', 'randbits', 'SystemRandom',
+           'token_bytes', 'token_hex', 'token_urlsafe',
+           'compare_digest',
+           ]
+
+
+import base64
+import binascii
+import os
+
+from hmac import compare_digest
+from random import SystemRandom
+
+_sysrand = SystemRandom()
+
+randbits = _sysrand.getrandbits
+choice = _sysrand.choice
+
+def randbelow(exclusive_upper_bound):
+    """Return a random int in the range [0, n)."""
+    if exclusive_upper_bound <= 0:
+        raise ValueError("Upper bound must be positive.")
+    return _sysrand._randbelow(exclusive_upper_bound)
+
+DEFAULT_ENTROPY = 32  # number of bytes to return by default
+
+def token_bytes(nbytes=None):
+    """Return a random byte string containing *nbytes* bytes.
+
+    If *nbytes* is ``None`` or not supplied, a reasonable
+    default is used.
+
+    >>> token_bytes(16)  #doctest:+SKIP
+    b'\\xebr\\x17D*t\\xae\\xd4\\xe3S\\xb6\\xe2\\xebP1\\x8b'
+
+    """
+    if nbytes is None:
+        nbytes = DEFAULT_ENTROPY
+    return os.urandom(nbytes)
+
+def token_hex(nbytes=None):
+    """Return a random text string, in hexadecimal.
+
+    The string has *nbytes* random bytes, each byte converted to two
+    hex digits.  If *nbytes* is ``None`` or not supplied, a reasonable
+    default is used.
+
+    >>> token_hex(16)  #doctest:+SKIP
+    'f9bf78b9a18ce6d46a0cd2b0b86df9da'
+
+    """
+    return binascii.hexlify(token_bytes(nbytes)).decode('ascii')
+
+def token_urlsafe(nbytes=None):
+    """Return a random URL-safe text string, in Base64 encoding.
+
+    The string has *nbytes* random bytes.  If *nbytes* is ``None``
+    or not supplied, a reasonable default is used.
+
+    >>> token_urlsafe(16)  #doctest:+SKIP
+    'Drmhze6EPcv0fN_81Bj-nA'
+
+    """
+    tok = token_bytes(nbytes)
+    return base64.urlsafe_b64encode(tok).rstrip(b'=').decode('ascii')

Lib/test/test_secrets.py

@@ -0,0 +1,124 @@
+"""Test the secrets module.
+
+As most of the functions in secrets are thin wrappers around functions
+defined elsewhere, we don't need to test them exhaustively.
+"""
+
+
+import secrets
+import unittest
+import string
+
+
+# === Unit tests ===
+
+class Compare_Digest_Tests(unittest.TestCase):
+    """Test secrets.compare_digest function."""
+
+    def test_equal(self):
+        # Test compare_digest functionality with equal (byte/text) strings.
+        for s in ("a", "bcd", "xyz123"):
+            a = s*100
+            b = s*100
+            self.assertTrue(secrets.compare_digest(a, b))
+            self.assertTrue(secrets.compare_digest(a.encode('utf-8'), b.encode('utf-8')))
+
+    def test_unequal(self):
+        # Test compare_digest functionality with unequal (byte/text) strings.
+        self.assertFalse(secrets.compare_digest("abc", "abcd"))
+        self.assertFalse(secrets.compare_digest(b"abc", b"abcd"))
+        for s in ("x", "mn", "a1b2c3"):
+            a = s*100 + "q"
+            b = s*100 + "k"
+            self.assertFalse(secrets.compare_digest(a, b))
+            self.assertFalse(secrets.compare_digest(a.encode('utf-8'), b.encode('utf-8')))
+
+    def test_bad_types(self):
+        # Test that compare_digest raises with mixed types.
+        a = 'abcde'
+        b = a.encode('utf-8')
+        assert isinstance(a, str)
+        assert isinstance(b, bytes)
+        self.assertRaises(TypeError, secrets.compare_digest, a, b)
+        self.assertRaises(TypeError, secrets.compare_digest, b, a)
+
+    def test_bool(self):
+        # Test that compare_digest returns a bool.
+        self.assertIsInstance(secrets.compare_digest("abc", "abc"), bool)
+        self.assertIsInstance(secrets.compare_digest("abc", "xyz"), bool)
+
+
+class Random_Tests(unittest.TestCase):
+    """Test wrappers around SystemRandom methods."""
+
+    def test_randbits(self):
+        # Test randbits.
+        errmsg = "randbits(%d) returned %d"
+        for numbits in (3, 12, 30):
+            for i in range(6):
+                n = secrets.randbits(numbits)
+                self.assertTrue(0 <= n < 2**numbits, errmsg % (numbits, n))
+
+    def test_choice(self):
+        # Test choice.
+        items = [1, 2, 4, 8, 16, 32, 64]
+        for i in range(10):
+            self.assertTrue(secrets.choice(items) in items)
+
+    def test_randbelow(self):
+        # Test randbelow.
+        for i in range(2, 10):
+            self.assertIn(secrets.randbelow(i), range(i))
+        self.assertRaises(ValueError, secrets.randbelow, 0)
+        self.assertRaises(ValueError, secrets.randbelow, -1)
+
+
+class Token_Tests(unittest.TestCase):
+    """Test token functions."""
+
+    def test_token_defaults(self):
+        # Test that token_* functions handle default size correctly.
+        for func in (secrets.token_bytes, secrets.token_hex,
+                     secrets.token_urlsafe):
+            with self.subTest(func=func):
+                name = func.__name__
+                try:
+                    func()
+                except TypeError:
+                    self.fail("%s cannot be called with no argument" % name)
+                try:
+                    func(None)
+                except TypeError:
+                    self.fail("%s cannot be called with None" % name)
+        size = secrets.DEFAULT_ENTROPY
+        self.assertEqual(len(secrets.token_bytes(None)), size)
+        self.assertEqual(len(secrets.token_hex(None)), 2*size)
+
+    def test_token_bytes(self):
+        # Test token_bytes.
+        for n in (1, 8, 17, 100):
+            with self.subTest(n=n):
+                self.assertIsInstance(secrets.token_bytes(n), bytes)
+                self.assertEqual(len(secrets.token_bytes(n)), n)
+
+    def test_token_hex(self):
+        # Test token_hex.
+        for n in (1, 12, 25, 90):
+            with self.subTest(n=n):
+                s = secrets.token_hex(n)
+                self.assertIsInstance(s, str)
+                self.assertEqual(len(s), 2*n)
+                self.assertTrue(all(c in string.hexdigits for c in s))
+
+    def test_token_urlsafe(self):
+        # Test token_urlsafe.
+        legal = string.ascii_letters + string.digits + '-_'
+        for n in (1, 11, 28, 76):
+            with self.subTest(n=n):
+                s = secrets.token_urlsafe(n)
+                self.assertIsInstance(s, str)
+                self.assertTrue(all(c in legal for c in s))
+
+
+if __name__ == '__main__':
+    unittest.main()