bpo-29410: Change the default hash algorithm to SipHash13. (GH-28752)

Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@innova.no>
Co-authored-by: Christian Heimes <christian@python.org>

Doc/using/configure.rst

@@ -416,15 +416,19 @@ Libraries options
 Security Options
 ----------------
 
-.. cmdoption:: --with-hash-algorithm=[fnv|siphash24]
+.. cmdoption:: --with-hash-algorithm=[fnv|siphash13|siphash24]
 
    Select hash algorithm for use in ``Python/pyhash.c``:
 
-   * ``siphash24`` (default).
+   * ``siphash13`` (default);
-   * ``fnv``;
+   * ``siphash24``;
+   * ``fnv``.
 
    .. versionadded:: 3.4
 
+   .. versionadded:: 3.11
+      ``siphash13`` is added and it is the new default.
+
 .. cmdoption:: --with-builtin-hashlib-hashes=md5,sha1,sha256,sha512,sha3,blake2
 
    Built-in hash modules:

Doc/whatsnew/3.11.rst

@@ -175,6 +175,11 @@ Other CPython Implementation Changes
   support :class:`typing.SupportsComplex` and :class:`typing.SupportsBytes` protocols.
   (Contributed by Mark Dickinson and Dong-hee Na in :issue:`24234`.)
 
+* ``siphash13`` is added as a new internal hashing algorithms. It's has similar security
+  properties as ``siphash24`` but it is slightly faster for long inputs. ``str``, ``bytes``,
+  and some other types now use it as default algorithm for ``hash()``. :pep:`552`
+  hash-based pyc files now use ``siphash13``, too.
+  (Contributed by Inada Naoki in :issue:`29410`.)
 
 New Modules
 ===========

Include/pyhash.h

@@ -114,11 +114,10 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
 
 /* hash algorithm selection
  *
- * The values for Py_HASH_SIPHASH24 and Py_HASH_FNV are hard-coded in the
+ * The values for Py_HASH_* are hard-coded in the
  * configure script.
  *
- * - FNV is available on all platforms and architectures.
+ * - FNV and SIPHASH* are available on all platforms and architectures.
- * - SIPHASH24 only works on platforms that don't require aligned memory for integers.
  * - With EXTERNAL embedders can provide an alternative implementation with::
  *
  *     PyHash_FuncDef PyHash_Func = {...};
@@ -128,10 +127,11 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
 #define Py_HASH_EXTERNAL 0
 #define Py_HASH_SIPHASH24 1
 #define Py_HASH_FNV 2
+#define Py_HASH_SIPHASH13 3
 
 #ifndef Py_HASH_ALGORITHM
 #  ifndef HAVE_ALIGNED_REQUIRED
-#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH24
+#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH13
 #  else
 #    define Py_HASH_ALGORITHM Py_HASH_FNV
 #  endif /* uint64_t && uint32_t && aligned */

Lib/test/test_hash.py

@@ -42,8 +42,8 @@ def pysiphash(uint64):
 
 def skip_unless_internalhash(test):
     """Skip decorator for tests that depend on SipHash24 or FNV"""
-    ok = sys.hash_info.algorithm in {"fnv", "siphash24"}
+    ok = sys.hash_info.algorithm in {"fnv", "siphash13", "siphash24"}
-    msg = "Requires SipHash24 or FNV"
+    msg = "Requires SipHash13, SipHash24 or FNV"
     return test if ok else unittest.skip(msg)(test)
 
 
@@ -206,6 +206,19 @@ class StringlikeHashRandomizationTests(HashRandomizationTests):
             # seed 42, 'abc'
             [-678966196, 573763426263223372, -820489388, -4282905804826039665],
             ],
+        'siphash13': [
+            # NOTE: PyUCS2 layout depends on endianness
+            # seed 0, 'abc'
+            [69611762, -4594863902769663758, 69611762, -4594863902769663758],
+            # seed 42, 'abc'
+            [-975800855, 3869580338025362921, -975800855, 3869580338025362921],
+            # seed 42, 'abcdefghijk'
+            [-595844228, 7764564197781545852, -595844228, 7764564197781545852],
+            # seed 0, 'äú∑ℇ'
+            [-1093288643, -2810468059467891395, -1041341092, 4925090034378237276],
+            # seed 42, 'äú∑ℇ'
+            [-585999602, -2845126246016066802, -817336969, -2219421378907968137],
+        ],
         'siphash24': [
             # NOTE: PyUCS2 layout depends on endianness
             # seed 0, 'abc'

Lib/test/test_imp.py

@@ -351,8 +351,8 @@ class ImportTests(unittest.TestCase):
         self.assertEqual(_frozen_importlib.__spec__.origin, "frozen")
 
     def test_source_hash(self):
-        self.assertEqual(_imp.source_hash(42, b'hi'), b'\xc6\xe7Z\r\x03:}\xab')
+        self.assertEqual(_imp.source_hash(42, b'hi'), b'\xfb\xd9G\x05\xaf$\x9b~')
-        self.assertEqual(_imp.source_hash(43, b'hi'), b'\x85\x9765\xf8\x9a\x8b9')
+        self.assertEqual(_imp.source_hash(43, b'hi'), b'\xd0/\x87C\xccC\xff\xe2')
 
     def test_pyc_invalidation_mode_from_cmdline(self):
         cases = [

Lib/test/test_sys.py

@@ -508,7 +508,7 @@ class SysModuleTest(unittest.TestCase):
         self.assertIsInstance(sys.hash_info.nan, int)
         self.assertIsInstance(sys.hash_info.imag, int)
         algo = sysconfig.get_config_var("Py_HASH_ALGORITHM")
-        if sys.hash_info.algorithm in {"fnv", "siphash24"}:
+        if sys.hash_info.algorithm in {"fnv", "siphash13", "siphash24"}:
             self.assertIn(sys.hash_info.hash_bits, {32, 64})
             self.assertIn(sys.hash_info.seed_bits, {32, 64, 128})
 
@@ -516,8 +516,10 @@ class SysModuleTest(unittest.TestCase):
                 self.assertEqual(sys.hash_info.algorithm, "siphash24")
             elif algo == 2:
                 self.assertEqual(sys.hash_info.algorithm, "fnv")
+            elif algo == 3:
+                self.assertEqual(sys.hash_info.algorithm, "siphash13")
             else:
-                self.assertIn(sys.hash_info.algorithm, {"fnv", "siphash24"})
+                self.assertIn(sys.hash_info.algorithm, {"fnv", "siphash13", "siphash24"})
         else:
             # PY_HASH_EXTERNAL
             self.assertEqual(algo, 0)

Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst

@@ -0,0 +1 @@
+Add SipHash13 for string hash algorithm and use it by default.

Python/pyhash.c

@@ -364,13 +364,66 @@ static PyHash_FuncDef PyHash_Func = {fnv, "fnv", 8 * SIZEOF_PY_HASH_T,
     d = ROTATE(d, t) ^ c;           \
     a = ROTATE(a, 32);
 
-#define DOUBLE_ROUND(v0,v1,v2,v3)       \
+#define SINGLE_ROUND(v0,v1,v2,v3)   \
-    HALF_ROUND(v0,v1,v2,v3,13,16);      \
-    HALF_ROUND(v2,v1,v0,v3,17,21);      \
     HALF_ROUND(v0,v1,v2,v3,13,16);  \
     HALF_ROUND(v2,v1,v0,v3,17,21);
 
+#define DOUBLE_ROUND(v0,v1,v2,v3)   \
+    SINGLE_ROUND(v0,v1,v2,v3);      \
+    SINGLE_ROUND(v0,v1,v2,v3);
 
+
+static uint64_t
+siphash13(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
+    uint64_t b = (uint64_t)src_sz << 56;
+    const uint8_t *in = (const uint8_t*)src;
+
+    uint64_t v0 = k0 ^ 0x736f6d6570736575ULL;
+    uint64_t v1 = k1 ^ 0x646f72616e646f6dULL;
+    uint64_t v2 = k0 ^ 0x6c7967656e657261ULL;
+    uint64_t v3 = k1 ^ 0x7465646279746573ULL;
+
+    uint64_t t;
+    uint8_t *pt;
+
+    while (src_sz >= 8) {
+        uint64_t mi;
+        memcpy(&mi, in, sizeof(mi));
+        mi = _le64toh(mi);
+        in += sizeof(mi);
+        src_sz -= sizeof(mi);
+        v3 ^= mi;
+        SINGLE_ROUND(v0,v1,v2,v3);
+        v0 ^= mi;
+    }
+
+    t = 0;
+    pt = (uint8_t *)&t;
+    switch (src_sz) {
+        case 7: pt[6] = in[6]; /* fall through */
+        case 6: pt[5] = in[5]; /* fall through */
+        case 5: pt[4] = in[4]; /* fall through */
+        case 4: memcpy(pt, in, sizeof(uint32_t)); break;
+        case 3: pt[2] = in[2]; /* fall through */
+        case 2: pt[1] = in[1]; /* fall through */
+        case 1: pt[0] = in[0]; /* fall through */
+    }
+    b |= _le64toh(t);
+
+    v3 ^= b;
+    SINGLE_ROUND(v0,v1,v2,v3);
+    v0 ^= b;
+    v2 ^= 0xff;
+    SINGLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
+
+    /* modified */
+    t = (v0 ^ v1) ^ (v2 ^ v3);
+    return t;
+}
+
+#if Py_HASH_ALGORITHM == Py_HASH_SIPHASH24
 static uint64_t
 siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     uint64_t b = (uint64_t)src_sz << 56;
@@ -419,14 +472,26 @@ siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     t = (v0 ^ v1) ^ (v2 ^ v3);
     return t;
 }
+#endif
 
 uint64_t
 _Py_KeyedHash(uint64_t key, const void *src, Py_ssize_t src_sz)
 {
-    return siphash24(key, 0, src, src_sz);
+    return siphash13(key, 0, src, src_sz);
 }
 
 
+#if Py_HASH_ALGORITHM == Py_HASH_SIPHASH13
+static Py_hash_t
+pysiphash(const void *src, Py_ssize_t src_sz) {
+    return (Py_hash_t)siphash13(
+        _le64toh(_Py_HashSecret.siphash.k0), _le64toh(_Py_HashSecret.siphash.k1),
+        src, src_sz);
+}
+
+static PyHash_FuncDef PyHash_Func = {pysiphash, "siphash13", 64, 128};
+#endif
+
 #if Py_HASH_ALGORITHM == Py_HASH_SIPHASH24
 static Py_hash_t
 pysiphash(const void *src, Py_ssize_t src_sz) {

configure

@@ -1561,9 +1561,9 @@ Optional Packages:
   --with-undefined-behavior-sanitizer
                           enable UndefinedBehaviorSanitizer undefined
                           behaviour detector, 'ubsan' (default is no)
-  --with-hash-algorithm=[fnv|siphash24]
+  --with-hash-algorithm=[fnv|siphash13|siphash24]
                           select hash algorithm for use in Python/pyhash.c
-                          (default is SipHash24)
+                          (default is SipHash13)
   --with-tzpath=<list of absolute paths separated by pathsep>
                            Select the default time zone search path for zoneinfo.TZPATH
 
@@ -10431,6 +10431,10 @@ if test "${with_hash_algorithm+set}" = set; then :
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $withval" >&5
 $as_echo "$withval" >&6; }
 case "$withval" in
+    siphash13)
+        $as_echo "#define Py_HASH_ALGORITHM 3" >>confdefs.h
+
+        ;;
     siphash24)
         $as_echo "#define Py_HASH_ALGORITHM 1" >>confdefs.h
 

configure.ac

@@ -3036,16 +3036,19 @@ fi
 # str, bytes and memoryview hash algorithm
 AH_TEMPLATE(Py_HASH_ALGORITHM,
   [Define hash algorithm for str, bytes and memoryview.
-   SipHash24: 1, FNV: 2, externally defined: 0])
+   SipHash24: 1, FNV: 2, SipHash13: 3, externally defined: 0])
 
 AC_MSG_CHECKING(for --with-hash-algorithm)
 dnl quadrigraphs "@<:@" and "@:>@" produce "[" and "]" in the output
 AC_ARG_WITH(hash_algorithm,
-            AS_HELP_STRING([--with-hash-algorithm=@<:@fnv|siphash24@:>@],
+            AS_HELP_STRING([--with-hash-algorithm=@<:@fnv|siphash13|siphash24@:>@],
-                           [select hash algorithm for use in Python/pyhash.c (default is SipHash24)]),
+                           [select hash algorithm for use in Python/pyhash.c (default is SipHash13)]),
 [
 AC_MSG_RESULT($withval)
 case "$withval" in
+    siphash13)
+        AC_DEFINE(Py_HASH_ALGORITHM, 3)
+        ;;
     siphash24)
         AC_DEFINE(Py_HASH_ALGORITHM, 1)
         ;;

pyconfig.h.in

@@ -1439,7 +1439,7 @@
 #undef Py_ENABLE_SHARED
 
 /* Define hash algorithm for str, bytes and memoryview. SipHash24: 1, FNV: 2,
-   externally defined: 0 */
+   SipHash13: 3, externally defined: 0 */
 #undef Py_HASH_ALGORITHM
 
 /* Define if you want to enable tracing references for debugging purpose */