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venv/Lib/site-packages/django/utils/crypto.py

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+"""
+Django's standard crypto functions and utilities.
+"""
+import hashlib
+import hmac
+import secrets
+
+from django.conf import settings
+from django.utils.encoding import force_bytes
+
+
+class InvalidAlgorithm(ValueError):
+    """Algorithm is not supported by hashlib."""
+    pass
+
+
+def salted_hmac(key_salt, value, secret=None, *, algorithm='sha1'):
+    """
+    Return the HMAC of 'value', using a key generated from key_salt and a
+    secret (which defaults to settings.SECRET_KEY). Default algorithm is SHA1,
+    but any algorithm name supported by hashlib can be passed.
+
+    A different key_salt should be passed in for every application of HMAC.
+    """
+    if secret is None:
+        secret = settings.SECRET_KEY
+
+    key_salt = force_bytes(key_salt)
+    secret = force_bytes(secret)
+    try:
+        hasher = getattr(hashlib, algorithm)
+    except AttributeError as e:
+        raise InvalidAlgorithm(
+            '%r is not an algorithm accepted by the hashlib module.'
+            % algorithm
+        ) from e
+    # We need to generate a derived key from our base key.  We can do this by
+    # passing the key_salt and our base key through a pseudo-random function.
+    key = hasher(key_salt + secret).digest()
+    # If len(key_salt + secret) > block size of the hash algorithm, the above
+    # line is redundant and could be replaced by key = key_salt + secret, since
+    # the hmac module does the same thing for keys longer than the block size.
+    # However, we need to ensure that we *always* do this.
+    return hmac.new(key, msg=force_bytes(value), digestmod=hasher)
+
+
+RANDOM_STRING_CHARS = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
+
+
+def get_random_string(length, allowed_chars=RANDOM_STRING_CHARS):
+    """
+    Return a securely generated random string.
+
+    The bit length of the returned value can be calculated with the formula:
+        log_2(len(allowed_chars)^length)
+
+    For example, with default `allowed_chars` (26+26+10), this gives:
+      * length: 12, bit length =~ 71 bits
+      * length: 22, bit length =~ 131 bits
+    """
+    return ''.join(secrets.choice(allowed_chars) for i in range(length))
+
+
+def constant_time_compare(val1, val2):
+    """Return True if the two strings are equal, False otherwise."""
+    return secrets.compare_digest(force_bytes(val1), force_bytes(val2))
+
+
+def pbkdf2(password, salt, iterations, dklen=0, digest=None):
+    """Return the hash of password using pbkdf2."""
+    if digest is None:
+        digest = hashlib.sha256
+    dklen = dklen or None
+    password = force_bytes(password)
+    salt = force_bytes(salt)
+    return hashlib.pbkdf2_hmac(digest().name, password, salt, iterations, dklen)