Add checkpw (#76)

4 files changed, 83 insertions, 5 deletions

diff --git a/README.rst b/README.rst
index 62f189f..0883286 100644
--- a/README.rst
+++ b/README.rst
@@ -37,6 +37,10 @@ For Fedora and RHEL-derivatives, the following command will ensure that the requ
 Changelog
 =========
 
+3.1.0
+-----
+* Added support for ``checkpw`` as another method of verifying a password.
+
 3.0.0
 -----
 * Switched the C backend to code obtained from the OpenBSD project rather than
@@ -51,8 +55,8 @@ Changelog
 Usage
 -----
 
-Hashing
-~~~~~~~
+Password Hashing
+~~~~~~~~~~~~~~~~
 
 Hashing and then later checking that a password matches the previous hashed
 password is very simple:
@@ -63,9 +67,9 @@ password is very simple:
     >>> password = b"super secret password"
     >>> # Hash a password for the first time, with a randomly-generated salt
     >>> hashed = bcrypt.hashpw(password, bcrypt.gensalt())
-    >>> # Check that a unhashed password matches one that has previously been
-    >>> #   hashed
-    >>> if bcrypt.hashpw(password, hashed) == hashed:
+    >>> # Check that an unhashed password matches one that has previously been
+    >>> # hashed
+    >>> if bcrypt.checkpw(password, hashed):
     ...     print("It Matches!")
     ... else:
     ...     print("It Does not Match :(")
diff --git a/src/bcrypt/__init__.py b/src/bcrypt/__init__.py
index ad44e93..c2be96d 100644
--- a/src/bcrypt/__init__.py
+++ b/src/bcrypt/__init__.py
@@ -78,6 +78,24 @@ def hashpw(password, salt):
     return _bcrypt.ffi.string(hashed)
 
 
+def checkpw(password, hashed_password):
+    if (isinstance(password, six.text_type) or
+            isinstance(hashed_password, six.text_type)):
+        raise TypeError("Unicode-objects must be encoded before checking")
+
+    if b"\x00" in password or b"\x00" in hashed_password:
+        raise ValueError(
+            "password and hashed_password may not contain NUL bytes"
+        )
+
+    # If the user supplies a $2y$ prefix we normalize to $2b$
+    hashed_password = _normalize_prefix(hashed_password)
+
+    ret = hashpw(password, hashed_password)
+
+    return _bcrypt.lib.timingsafe_bcmp(ret, hashed_password, len(ret)) == 0
+
+
 def kdf(password, salt, desired_key_bytes, rounds):
     if isinstance(password, six.text_type) or isinstance(salt, six.text_type):
         raise TypeError("Unicode-objects must be encoded before hashing")
diff --git a/src/build_bcrypt.py b/src/build_bcrypt.py
index e7aca4c..3eec35c 100644
--- a/src/build_bcrypt.py
+++ b/src/build_bcrypt.py
@@ -25,6 +25,7 @@ int bcrypt_hashpass(const char *, const char *, char *, size_t);
 int encode_base64(char *, const uint8_t *, size_t);
 int bcrypt_pbkdf(const char *, size_t, const uint8_t *, size_t,
                  uint8_t *, size_t, unsigned int);
+int timingsafe_bcmp(const void *, const void *, size_t);
 """)
 
 ffi.set_source(
diff --git a/tests/test_bcrypt.py b/tests/test_bcrypt.py
index b506a7a..ea5cee3 100644
--- a/tests/test_bcrypt.py
+++ b/tests/test_bcrypt.py
@@ -217,6 +217,11 @@ def test_hashpw_new(password, salt, hashed):
 
 
 @pytest.mark.parametrize(("password", "salt", "hashed"), _test_vectors)
+def test_checkpw(password, salt, hashed):
+    assert bcrypt.checkpw(password, hashed) is True
+
+
+@pytest.mark.parametrize(("password", "salt", "hashed"), _test_vectors)
 def test_hashpw_existing(password, salt, hashed):
     assert bcrypt.hashpw(password, hashed) == hashed
 
@@ -226,11 +231,47 @@ def test_hashpw_2y_prefix(password, hashed, expected):
     assert bcrypt.hashpw(password, hashed) == expected
 
 
+@pytest.mark.parametrize(("password", "hashed", "expected"), _2y_test_vectors)
+def test_checkpw_2y_prefix(password, hashed, expected):
+    assert bcrypt.checkpw(password, hashed) is True
+
+
 def test_hashpw_invalid():
     with pytest.raises(ValueError):
         bcrypt.hashpw(b"password", b"$2z$04$cVWp4XaNU8a4v1uMRum2SO")
 
 
+def test_checkpw_wrong_password():
+    assert bcrypt.checkpw(
+        b"badpass",
+        b"$2b$04$2Siw3Nv3Q/gTOIPetAyPr.GNj3aO0lb1E5E9UumYGKjP9BYqlNWJe"
+    ) is False
+
+
+def test_checkpw_bad_salt():
+    with pytest.raises(ValueError):
+        bcrypt.checkpw(
+            b"badpass",
+            b"$2b$04$?Siw3Nv3Q/gTOIPetAyPr.GNj3aO0lb1E5E9UumYGKjP9BYqlNWJe"
+        )
+
+
+def test_checkpw_str_password():
+    with pytest.raises(TypeError):
+        bcrypt.checkpw(
+            six.text_type("password"),
+            b"$2b$04$cVWp4XaNU8a4v1uMRum2SO",
+        )
+
+
+def test_checkpw_str_salt():
+    with pytest.raises(TypeError):
+        bcrypt.checkpw(
+            b"password",
+            six.text_type("$2b$04$cVWp4XaNU8a4v1uMRum2SO"),
+        )
+
+
 def test_hashpw_str_password():
     with pytest.raises(TypeError):
         bcrypt.hashpw(
@@ -247,6 +288,20 @@ def test_hashpw_str_salt():
         )
 
 
+def test_checkpw_nul_byte():
+    with pytest.raises(ValueError):
+        bcrypt.checkpw(
+            b"abc\0def",
+            b"$2b$04$2Siw3Nv3Q/gTOIPetAyPr.GNj3aO0lb1E5E9UumYGKjP9BYqlNWJe"
+        )
+
+    with pytest.raises(ValueError):
+        bcrypt.checkpw(
+            b"abcdef",
+            b"$2b$04$2S\0w3Nv3Q/gTOIPetAyPr.GNj3aO0lb1E5E9UumYGKjP9BYqlNWJe"
+        )
+
+
 def test_hashpw_nul_byte():
     salt = bcrypt.gensalt(4)
     with pytest.raises(ValueError):