From de12cebee17ce9faee2ef09e8dc46cdd0b143589 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Wed, 6 Oct 2021 14:03:45 +0900
Subject: [PATCH 01/18] Use SipHash-1-3 instead of SipHash-2-4.

---
 Include/pyhash.h |  8 ++++----
 Python/pyhash.c  | 23 +++++++++++------------
 configure.ac     |  8 ++++----
 3 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/Include/pyhash.h b/Include/pyhash.h
index a314ea907b7fe2..d199241243b074 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -114,11 +114,11 @@ 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_SIPHASH13 and Py_HASH_FNV are hard-coded in the
  * configure script.
  *
  * - FNV is available on all platforms and architectures.
- * - SIPHASH24 only works on platforms that don't require aligned memory for integers.
+ * - SIPHASH 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 = {...};
@@ -126,12 +126,12 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
  * XXX: Figure out __declspec() for extern PyHash_FuncDef.
  */
 #define Py_HASH_EXTERNAL 0
-#define Py_HASH_SIPHASH24 1
+#define Py_HASH_SIPHASH 1
 #define Py_HASH_FNV 2
 
 #ifndef Py_HASH_ALGORITHM
 #  ifndef HAVE_ALIGNED_REQUIRED
-#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH24
+#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH
 #  else
 #    define Py_HASH_ALGORITHM Py_HASH_FNV
 #  endif /* uint64_t && uint32_t && aligned */
diff --git a/Python/pyhash.c b/Python/pyhash.c
index f0c82356f1e26c..60ed73b171052a 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -364,15 +364,13 @@ 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)       \
-    HALF_ROUND(v0,v1,v2,v3,13,16);      \
-    HALF_ROUND(v2,v1,v0,v3,17,21);      \
+#define SINGLE_ROUND(v0,v1,v2,v3)       \
     HALF_ROUND(v0,v1,v2,v3,13,16);      \
     HALF_ROUND(v2,v1,v0,v3,17,21);
 
 
 static uint64_t
-siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
+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;
 
@@ -391,7 +389,7 @@ siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
         in += sizeof(mi);
         src_sz -= sizeof(mi);
         v3 ^= mi;
-        DOUBLE_ROUND(v0,v1,v2,v3);
+        SINGLE_ROUND(v0,v1,v2,v3);
         v0 ^= mi;
     }
 
@@ -409,11 +407,12 @@ siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     b |= _le64toh(t);
 
     v3 ^= b;
-    DOUBLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
     v0 ^= b;
     v2 ^= 0xff;
-    DOUBLE_ROUND(v0,v1,v2,v3);
-    DOUBLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
+    SINGLE_ROUND(v0,v1,v2,v3);
 
     /* modified */
     t = (v0 ^ v1) ^ (v2 ^ v3);
@@ -423,19 +422,19 @@ siphash24(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
 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_SIPHASH24
+#if Py_HASH_ALGORITHM == Py_HASH_SIPHASH
 static Py_hash_t
 pysiphash(const void *src, Py_ssize_t src_sz) {
-    return (Py_hash_t)siphash24(
+    return (Py_hash_t)siphash13(
         _le64toh(_Py_HashSecret.siphash.k0), _le64toh(_Py_HashSecret.siphash.k1),
         src, src_sz);
 }
 
-static PyHash_FuncDef PyHash_Func = {pysiphash, "siphash24", 64, 128};
+static PyHash_FuncDef PyHash_Func = {pysiphash, "siphash13", 64, 128};
 #endif
 
 #ifdef __cplusplus
diff --git a/configure.ac b/configure.ac
index 48d86ef79199e1..8964f0dca7e014 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3036,17 +3036,17 @@ 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])
+   SipHash: 1, FNV: 2, 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@:>@],
-                           [select hash algorithm for use in Python/pyhash.c (default is SipHash24)]),
+            AS_HELP_STRING([--with-hash-algorithm=@<:@fnv|siphash@:>@],
+                           [select hash algorithm for use in Python/pyhash.c (default is SipHash)]),
 [
 AC_MSG_RESULT($withval)
 case "$withval" in
-    siphash24)
+    siphash)
         AC_DEFINE(Py_HASH_ALGORITHM, 1)
         ;;
     fnv)

From 196d5a640b635bfd663076f0179283e761e2b19c Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Wed, 6 Oct 2021 17:57:44 +0900
Subject: [PATCH 02/18] fix tests

---
 Lib/test/test_hash.py | 12 ++++++------
 Lib/test/test_imp.py  |  4 ++--
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index c68e0d8f815377..c5e75b848f5816 100644
--- a/Lib/test/test_hash.py
+++ b/Lib/test/test_hash.py
@@ -206,18 +206,18 @@ class StringlikeHashRandomizationTests(HashRandomizationTests):
             # seed 42, 'abc'
             [-678966196, 573763426263223372, -820489388, -4282905804826039665],
             ],
-        'siphash24': [
+        'siphash': [
             # NOTE: PyUCS2 layout depends on endianness
             # seed 0, 'abc'
-            [1198583518, 4596069200710135518, 1198583518, 4596069200710135518],
+            [1198583518, 4596069200710135518, 1198583518, -4594863902769663758],
             # seed 42, 'abc'
-            [273876886, -4501618152524544106, 273876886, -4501618152524544106],
+            [273876886, -4501618152524544106, 273876886, 3869580338025362921],
             # seed 42, 'abcdefghijk'
-            [-1745215313, 4436719588892876975, -1745215313, 4436719588892876975],
+            [-1745215313, 4436719588892876975, -1745215313, 7764564197781545852],
             # seed 0, 'äú∑ℇ'
-            [493570806, 5749986484189612790, -1006381564, -5915111450199468540],
+            [493570806, 5749986484189612790, -1006381564, -2810468059467891395],
             # seed 42, 'äú∑ℇ'
-            [-1677110816, -2947981342227738144, -1860207793, -4296699217652516017],
+            [-1677110816, -2947981342227738144, -1860207793, -2845126246016066802],
         ],
         'fnv': [
             # seed 0, 'abc'
diff --git a/Lib/test/test_imp.py b/Lib/test/test_imp.py
index 99312cc1625c42..1a21025fe6eaff 100644
--- a/Lib/test/test_imp.py
+++ b/Lib/test/test_imp.py
@@ -351,8 +351,8 @@ def test_issue_35321(self):
         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(43, b'hi'), b'\x85\x9765\xf8\x9a\x8b9')
+        self.assertEqual(_imp.source_hash(42, b'hi'), b'\xfb\xd9G\x05\xaf$\x9b~')
+        self.assertEqual(_imp.source_hash(43, b'hi'), b'\xd0/\x87C\xccC\xff\xe2')
 
     def test_pyc_invalidation_mode_from_cmdline(self):
         cases = [

From b121503b9dfb1f97182466f7d6f521e8f86cded3 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Thu, 7 Oct 2021 17:10:43 +0900
Subject: [PATCH 03/18] Update Lib/test/test_hash.py

Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@innova.no>
---
 Lib/test/test_hash.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index c5e75b848f5816..626086415482f1 100644
--- a/Lib/test/test_hash.py
+++ b/Lib/test/test_hash.py
@@ -206,7 +206,7 @@ class StringlikeHashRandomizationTests(HashRandomizationTests):
             # seed 42, 'abc'
             [-678966196, 573763426263223372, -820489388, -4282905804826039665],
             ],
-        'siphash': [
+        'siphash13': [
             # NOTE: PyUCS2 layout depends on endianness
             # seed 0, 'abc'
             [1198583518, 4596069200710135518, 1198583518, -4594863902769663758],

From 381253bf4b247386dcfcacb4cbefe157a5084a33 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Thu, 7 Oct 2021 19:04:23 +0900
Subject: [PATCH 04/18] Add Py_HASH_SIPHASH24 and
 --with-hash-algorithm=siphash24.

They is just alias for siphash13.
---
 Include/pyhash.h |  5 +++--
 Python/pyhash.c  |  2 +-
 configure        | 10 ++++++++--
 configure.ac     | 12 ++++++++----
 pyconfig.h.in    |  8 ++++----
 5 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/Include/pyhash.h b/Include/pyhash.h
index d199241243b074..dc3bf70a2527d9 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -126,12 +126,13 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
  * XXX: Figure out __declspec() for extern PyHash_FuncDef.
  */
 #define Py_HASH_EXTERNAL 0
-#define Py_HASH_SIPHASH 1
+#define Py_HASH_SIPHASH13 1
+#define Py_HASH_SIPHASH24 1  /* deprecated */
 #define Py_HASH_FNV 2
 
 #ifndef Py_HASH_ALGORITHM
 #  ifndef HAVE_ALIGNED_REQUIRED
-#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH
+#    define Py_HASH_ALGORITHM Py_HASH_SIPHASH13
 #  else
 #    define Py_HASH_ALGORITHM Py_HASH_FNV
 #  endif /* uint64_t && uint32_t && aligned */
diff --git a/Python/pyhash.c b/Python/pyhash.c
index 60ed73b171052a..7f4ebea1b44689 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -426,7 +426,7 @@ _Py_KeyedHash(uint64_t key, const void *src, Py_ssize_t src_sz)
 }
 
 
-#if Py_HASH_ALGORITHM == Py_HASH_SIPHASH
+#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(
diff --git a/configure b/configure
index 4acf91f22107f4..d46eee9e1b62d6 100755
--- a/configure
+++ b/configure
@@ -1556,9 +1556,9 @@ 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]
                           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
 
@@ -10420,7 +10420,13 @@ 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 1" >>confdefs.h
+
+        ;;
     siphash24)
+        { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --with-hash-algorithm=siphash24 is deprecated. Use siphash13" >&5
+$as_echo "$as_me: WARNING: --with-hash-algorithm=siphash24 is deprecated. Use siphash13" >&2;}
         $as_echo "#define Py_HASH_ALGORITHM 1" >>confdefs.h
 
         ;;
diff --git a/configure.ac b/configure.ac
index 8964f0dca7e014..3101176a23eeee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3036,17 +3036,21 @@ fi
 # str, bytes and memoryview hash algorithm
 AH_TEMPLATE(Py_HASH_ALGORITHM,
   [Define hash algorithm for str, bytes and memoryview.
-   SipHash: 1, FNV: 2, externally defined: 0])
+   SipHash13: 1, FNV: 2, 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|siphash@:>@],
-                           [select hash algorithm for use in Python/pyhash.c (default is SipHash)]),
+            AS_HELP_STRING([--with-hash-algorithm=@<:@fnv|siphash13@:>@],
+                           [select hash algorithm for use in Python/pyhash.c (default is SipHash13)]),
 [
 AC_MSG_RESULT($withval)
 case "$withval" in
-    siphash)
+    siphash13)
+        AC_DEFINE(Py_HASH_ALGORITHM, 1)
+        ;;
+    siphash24)
+        AC_MSG_WARN([--with-hash-algorithm=siphash24 is deprecated. Use siphash13])
         AC_DEFINE(Py_HASH_ALGORITHM, 1)
         ;;
     fnv)
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 23d7111b9f77e7..1c1f83ac34493b 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -136,15 +136,15 @@
 /* Define to 1 if you have the `clock' function. */
 #undef HAVE_CLOCK
 
-/* Define to 1 if you have the `clock_nanosleep' function. */
-#undef HAVE_CLOCK_NANOSLEEP
-
 /* Define to 1 if you have the `clock_getres' function. */
 #undef HAVE_CLOCK_GETRES
 
 /* Define to 1 if you have the `clock_gettime' function. */
 #undef HAVE_CLOCK_GETTIME
 
+/* Define to 1 if you have the `clock_nanosleep' function. */
+#undef HAVE_CLOCK_NANOSLEEP
+
 /* Define to 1 if you have the `clock_settime' function. */
 #undef HAVE_CLOCK_SETTIME
 
@@ -1435,7 +1435,7 @@
 /* Defined if Python is built as a shared library. */
 #undef Py_ENABLE_SHARED
 
-/* Define hash algorithm for str, bytes and memoryview. SipHash24: 1, FNV: 2,
+/* Define hash algorithm for str, bytes and memoryview. SipHash13: 1, FNV: 2,
    externally defined: 0 */
 #undef Py_HASH_ALGORITHM
 

From 996313514873ecb7a6e4432934d59c72d34d80d8 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Thu, 7 Oct 2021 19:09:23 +0900
Subject: [PATCH 05/18] Update doc, add NEWS and What's New entry.

---
 Doc/using/configure.rst                                   | 8 ++++++--
 Doc/whatsnew/3.11.rst                                     | 2 ++
 .../2021-10-07-19-09-12.bpo-29410.bg5SYp.rst              | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index a545d5a9372ac0..2b20410bd282d8 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -416,15 +416,19 @@ Libraries options
 Security Options
 ----------------
 
-.. cmdoption:: --with-hash-algorithm=[fnv|siphash24]
+.. cmdoption:: --with-hash-algorithm=[fnv|siphash13]
 
    Select hash algorithm for use in ``Python/pyhash.c``:
 
-   * ``siphash24`` (default).
+   * ``siphash13`` (default).
    * ``fnv``;
 
    .. versionadded:: 3.4
 
+   .. versionchanged:: 3.11
+      ``siphash24`` is replaced with ``siphash13``. ``siphash13`` is faster and
+      safe enough.
+
 .. cmdoption:: --with-builtin-hashlib-hashes=md5,sha1,sha256,sha512,sha3,blake2
 
    Built-in hash modules:
diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index d01d2e263199ad..4cb2c2ccf98ed3 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -175,6 +175,8 @@ Other CPython Implementation Changes
   support :class:`typing.SupportsComplex` and :class:`typing.SupportsBytes` protocols.
   (Contributed by Mark Dickinson and Dong-hee Na in :issue:`24234`.)
 
+* Hash algorithm for strings is changed from SipHash24 to SipHash13.
+  (Contributed by Inada Naoki in :issue:`29410`.)
 
 New Modules
 ===========
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst b/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst
new file mode 100644
index 00000000000000..13cf9ec8c52f7d
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst	
@@ -0,0 +1 @@
+Hash algorithm for strings is changed from SipHash24 to SipHash13.

From add336e5e4ad1a2bf6d8d41f56b9ec59847c0774 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:00:56 +0900
Subject: [PATCH 06/18] Apply suggestions from code review

Co-authored-by: Christian Heimes <christian@python.org>
---
 Include/pyhash.h | 4 ++--
 configure.ac     | 6 +++---
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Include/pyhash.h b/Include/pyhash.h
index dc3bf70a2527d9..3ca7b252e452f1 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -114,7 +114,7 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
 
 /* hash algorithm selection
  *
- * The values for Py_HASH_SIPHASH13 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.
@@ -126,9 +126,9 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
  * XXX: Figure out __declspec() for extern PyHash_FuncDef.
  */
 #define Py_HASH_EXTERNAL 0
-#define Py_HASH_SIPHASH13 1
 #define Py_HASH_SIPHASH24 1  /* deprecated */
 #define Py_HASH_FNV 2
+#define Py_HASH_SIPHASH13 3
 
 #ifndef Py_HASH_ALGORITHM
 #  ifndef HAVE_ALIGNED_REQUIRED
diff --git a/configure.ac b/configure.ac
index 3101176a23eeee..3474b38f7d86d5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3036,18 +3036,18 @@ fi
 # str, bytes and memoryview hash algorithm
 AH_TEMPLATE(Py_HASH_ALGORITHM,
   [Define hash algorithm for str, bytes and memoryview.
-   SipHash13: 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|siphash13@:>@],
+            AS_HELP_STRING([--with-hash-algorithm=@<:@fnv|siphash13|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, 1)
+        AC_DEFINE(Py_HASH_ALGORITHM, 3)
         ;;
     siphash24)
         AC_MSG_WARN([--with-hash-algorithm=siphash24 is deprecated. Use siphash13])

From b8c6f69f21b23965333ab6d4d17b0c9b85857611 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:02:28 +0900
Subject: [PATCH 07/18] Back siphash24

---
 Doc/using/configure.rst | 12 ++++++------
 Doc/whatsnew/3.11.rst   |  3 ++-
 configure.ac            |  1 -
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index 2b20410bd282d8..1d1f04fb89d76c 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -416,18 +416,18 @@ Libraries options
 Security Options
 ----------------
 
-.. cmdoption:: --with-hash-algorithm=[fnv|siphash13]
+.. cmdoption:: --with-hash-algorithm=[fnv|siphash13|siphash24]
 
    Select hash algorithm for use in ``Python/pyhash.c``:
 
-   * ``siphash13`` (default).
-   * ``fnv``;
+   * ``siphash13`` (default);
+   * ``siphash24``;
+   * ``fnv``.
 
    .. versionadded:: 3.4
 
-   .. versionchanged:: 3.11
-      ``siphash24`` is replaced with ``siphash13``. ``siphash13`` is faster and
-      safe enough.
+   .. versionadded:: 3.11
+      ``siphash13`` is added and it is the new default.
 
 .. cmdoption:: --with-builtin-hashlib-hashes=md5,sha1,sha256,sha512,sha3,blake2
 
diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 4cb2c2ccf98ed3..0600dfa3421cce 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -175,7 +175,8 @@ Other CPython Implementation Changes
   support :class:`typing.SupportsComplex` and :class:`typing.SupportsBytes` protocols.
   (Contributed by Mark Dickinson and Dong-hee Na in :issue:`24234`.)
 
-* Hash algorithm for strings is changed from SipHash24 to SipHash13.
+* ``siphash13`` is added as a new internal hash algorithm for strings, and the default
+  algorithm is changed from ``siphash24`` to ``siphash13``.
   (Contributed by Inada Naoki in :issue:`29410`.)
 
 New Modules
diff --git a/configure.ac b/configure.ac
index 3474b38f7d86d5..9c8ac8a2a8eebd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3050,7 +3050,6 @@ case "$withval" in
         AC_DEFINE(Py_HASH_ALGORITHM, 3)
         ;;
     siphash24)
-        AC_MSG_WARN([--with-hash-algorithm=siphash24 is deprecated. Use siphash13])
         AC_DEFINE(Py_HASH_ALGORITHM, 1)
         ;;
     fnv)

From b83e3f0aeb7395c36eb8b60f48dd3c6972ed4150 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:04:31 +0900
Subject: [PATCH 08/18] Add siphash24 again

---
 Lib/test/test_hash.py | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index 626086415482f1..baf7e745e457e8 100644
--- a/Lib/test/test_hash.py
+++ b/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"}
-    msg = "Requires SipHash24 or FNV"
+    ok = sys.hash_info.algorithm in {"fnv", "siphash13", "siphash24"}
+    msg = "Requires SipHash13, SipHash24 or FNV"
     return test if ok else unittest.skip(msg)(test)
 
 
@@ -219,6 +219,19 @@ class StringlikeHashRandomizationTests(HashRandomizationTests):
             # seed 42, 'äú∑ℇ'
             [-1677110816, -2947981342227738144, -1860207793, -2845126246016066802],
         ],
+        'siphash24': [
+            # NOTE: PyUCS2 layout depends on endianness
+            # seed 0, 'abc'
+            [1198583518, 4596069200710135518, 1198583518, 4596069200710135518],
+            # seed 42, 'abc'
+            [273876886, -4501618152524544106, 273876886, -4501618152524544106],
+            # seed 42, 'abcdefghijk'
+            [-1745215313, 4436719588892876975, -1745215313, 4436719588892876975],
+            # seed 0, 'äú∑ℇ'
+            [493570806, 5749986484189612790, -1006381564, -5915111450199468540],
+            # seed 42, 'äú∑ℇ'
+            [-1677110816, -2947981342227738144, -1860207793, -4296699217652516017],
+        ],
         'fnv': [
             # seed 0, 'abc'
             [-1600925533, 1453079729188098211, -1600925533,

From ac6e8ecb1237c26d4e0d8f9ed1b4e37432c77d30 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:06:00 +0900
Subject: [PATCH 09/18] autoreconf

---
 configure     | 6 ++----
 pyconfig.h.in | 4 ++--
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/configure b/configure
index d46eee9e1b62d6..c8c3d742b62acc 100755
--- a/configure
+++ b/configure
@@ -1556,7 +1556,7 @@ Optional Packages:
   --with-undefined-behavior-sanitizer
                           enable UndefinedBehaviorSanitizer undefined
                           behaviour detector, 'ubsan' (default is no)
-  --with-hash-algorithm=[fnv|siphash13]
+  --with-hash-algorithm=[fnv|siphash13|siphash24]
                           select hash algorithm for use in Python/pyhash.c
                           (default is SipHash13)
   --with-tzpath=<list of absolute paths separated by pathsep>
@@ -10421,12 +10421,10 @@ if test "${with_hash_algorithm+set}" = set; then :
 $as_echo "$withval" >&6; }
 case "$withval" in
     siphash13)
-        $as_echo "#define Py_HASH_ALGORITHM 1" >>confdefs.h
+        $as_echo "#define Py_HASH_ALGORITHM 3" >>confdefs.h
 
         ;;
     siphash24)
-        { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --with-hash-algorithm=siphash24 is deprecated. Use siphash13" >&5
-$as_echo "$as_me: WARNING: --with-hash-algorithm=siphash24 is deprecated. Use siphash13" >&2;}
         $as_echo "#define Py_HASH_ALGORITHM 1" >>confdefs.h
 
         ;;
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 1c1f83ac34493b..bd3083bb72ca3a 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -1435,8 +1435,8 @@
 /* Defined if Python is built as a shared library. */
 #undef Py_ENABLE_SHARED
 
-/* Define hash algorithm for str, bytes and memoryview. SipHash13: 1, FNV: 2,
-   externally defined: 0 */
+/* Define hash algorithm for str, bytes and memoryview. SipHash24: 1, FNV: 2,
+   SipHash13: 3, externally defined: 0 */
 #undef Py_HASH_ALGORITHM
 
 /* Define if you want to enable tracing references for debugging purpose */

From 5e7a4ad54261f65a35f6a888cef00967e72d2548 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:06:40 +0900
Subject: [PATCH 10/18] Undeprecate siphash24

---
 Include/pyhash.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Include/pyhash.h b/Include/pyhash.h
index 3ca7b252e452f1..0185ae947fb156 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -126,7 +126,7 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
  * XXX: Figure out __declspec() for extern PyHash_FuncDef.
  */
 #define Py_HASH_EXTERNAL 0
-#define Py_HASH_SIPHASH24 1  /* deprecated */
+#define Py_HASH_SIPHASH24 1
 #define Py_HASH_FNV 2
 #define Py_HASH_SIPHASH13 3
 

From 5d2e6f224800a7394a95da696f22ff7e3d7919fa Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 12:14:31 +0900
Subject: [PATCH 11/18] Add siphash24() again.

---
 Python/pyhash.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 68 insertions(+), 4 deletions(-)

diff --git a/Python/pyhash.c b/Python/pyhash.c
index 7f4ebea1b44689..b866cec3f87371 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -358,16 +358,20 @@ static PyHash_FuncDef PyHash_Func = {fnv, "fnv", 8 * SIZEOF_PY_HASH_T,
 #  define ROTATE(x, b) (uint64_t)( ((x) << (b)) | ( (x) >> (64 - (b))) )
 #endif
 
-#define HALF_ROUND(a,b,c,d,s,t)         \
-    a += b; c += d;             \
+#define HALF_ROUND(a,b,c,d,s,t)     \
+    a += b; c += d;                 \
     b = ROTATE(b, s) ^ a;           \
     d = ROTATE(d, t) ^ c;           \
     a = ROTATE(a, 32);
 
-#define SINGLE_ROUND(v0,v1,v2,v3)       \
-    HALF_ROUND(v0,v1,v2,v3,13,16);      \
+#define SINGLE_ROUND(v0,v1,v2,v3)   \
+    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) {
@@ -419,6 +423,55 @@ siphash13(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     return t;
 }
 
+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;
+    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;
+        DOUBLE_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;
+    DOUBLE_ROUND(v0,v1,v2,v3);
+    v0 ^= b;
+    v2 ^= 0xff;
+    DOUBLE_ROUND(v0,v1,v2,v3);
+    DOUBLE_ROUND(v0,v1,v2,v3);
+
+    /* modified */
+    t = (v0 ^ v1) ^ (v2 ^ v3);
+    return t;
+}
+
 uint64_t
 _Py_KeyedHash(uint64_t key, const void *src, Py_ssize_t src_sz)
 {
@@ -437,6 +490,17 @@ pysiphash(const void *src, Py_ssize_t 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) {
+    return (Py_hash_t)siphash24(
+        _le64toh(_Py_HashSecret.siphash.k0), _le64toh(_Py_HashSecret.siphash.k1),
+        src, src_sz);
+}
+
+static PyHash_FuncDef PyHash_Func = {pysiphash, "siphash24", 64, 128};
+#endif
+
 #ifdef __cplusplus
 }
 #endif

From 69c9d12c2b7e2aa4a622e1b83355ba7fc75e0bb1 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 13:38:09 +0900
Subject: [PATCH 12/18] test_hash: fix known hash

---
 Lib/test/test_hash.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index baf7e745e457e8..cf9db66a29ae11 100644
--- a/Lib/test/test_hash.py
+++ b/Lib/test/test_hash.py
@@ -209,15 +209,15 @@ class StringlikeHashRandomizationTests(HashRandomizationTests):
         'siphash13': [
             # NOTE: PyUCS2 layout depends on endianness
             # seed 0, 'abc'
-            [1198583518, 4596069200710135518, 1198583518, -4594863902769663758],
+            [69611762, -4594863902769663758, 69611762, -4594863902769663758],
             # seed 42, 'abc'
-            [273876886, -4501618152524544106, 273876886, 3869580338025362921],
+            [-975800855, 3869580338025362921, -975800855, 3869580338025362921],
             # seed 42, 'abcdefghijk'
-            [-1745215313, 4436719588892876975, -1745215313, 7764564197781545852],
+            [-595844228, 7764564197781545852, -595844228, 7764564197781545852],
             # seed 0, 'äú∑ℇ'
-            [493570806, 5749986484189612790, -1006381564, -2810468059467891395],
+            [-1093288643, -2810468059467891395, -1041341092, 4925090034378237276],
             # seed 42, 'äú∑ℇ'
-            [-1677110816, -2947981342227738144, -1860207793, -2845126246016066802],
+            [-585999602, -2845126246016066802, -817336969, -2219421378907968137],
         ],
         'siphash24': [
             # NOTE: PyUCS2 layout depends on endianness

From 0dce1e791925fec133267acf0a2a1d8ae4a5ef68 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 14:48:21 +0900
Subject: [PATCH 13/18] Suppress warning

---
 Python/pyhash.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Python/pyhash.c b/Python/pyhash.c
index b866cec3f87371..d5ac9f83be61cc 100644
--- a/Python/pyhash.c
+++ b/Python/pyhash.c
@@ -423,6 +423,7 @@ siphash13(uint64_t k0, uint64_t k1, const void *src, Py_ssize_t src_sz) {
     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;
@@ -471,6 +472,7 @@ 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)

From 23d06e16c2455e718b70ea27dbdd50c0460c9620 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 14:50:17 +0900
Subject: [PATCH 14/18] update NEWS entry

---
 .../Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst b/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst
index 13cf9ec8c52f7d..b08999e78d84ae 100644
--- a/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst	
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-10-07-19-09-12.bpo-29410.bg5SYp.rst	
@@ -1 +1 @@
-Hash algorithm for strings is changed from SipHash24 to SipHash13.
+Add SipHash13 for string hash algorithm and use it by default.

From 2de4af1dc16bded9bb9178277b2c7df5d417eda1 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 14:57:35 +0900
Subject: [PATCH 15/18] fix test_sys

---
 Lib/test/test_sys.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 3b80904b28d3e2..72a8176297f107 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -508,7 +508,7 @@ def test_attributes(self):
         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 @@ def test_attributes(self):
                 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)

From cfa006035db165d55b02c6ec7da3eb7b178c09c4 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Fri, 8 Oct 2021 17:53:58 +0900
Subject: [PATCH 16/18] Fix comment

---
 Include/pyhash.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Include/pyhash.h b/Include/pyhash.h
index 0185ae947fb156..182d223fab1cac 100644
--- a/Include/pyhash.h
+++ b/Include/pyhash.h
@@ -117,8 +117,7 @@ PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
  * The values for Py_HASH_* are hard-coded in the
  * configure script.
  *
- * - FNV is available on all platforms and architectures.
- * - SIPHASH only works on platforms that don't require aligned memory for integers.
+ * - FNV and SIPHASH* are available on all platforms and architectures.
  * - With EXTERNAL embedders can provide an alternative implementation with::
  *
  *     PyHash_FuncDef PyHash_Func = {...};

From a096bca02b7bb1ce2ba2096d6a66328c6be905d4 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Sat, 9 Oct 2021 11:48:11 +0900
Subject: [PATCH 17/18] Use suggested doc.

---
 Doc/whatsnew/3.11.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 0600dfa3421cce..97df1fe83747d9 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -175,8 +175,9 @@ 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 hash algorithm for strings, and the default
-  algorithm is changed from ``siphash24`` to ``siphash13``.
+* ``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()``.
   (Contributed by Inada Naoki in :issue:`29410`.)
 
 New Modules

From 86cf6c60e5b5a8696136f47512318951766d4080 Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Sun, 10 Oct 2021 11:30:12 +0900
Subject: [PATCH 18/18] Update Doc/whatsnew/3.11.rst

Co-authored-by: Christian Heimes <christian@python.org>
---
 Doc/whatsnew/3.11.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 97df1fe83747d9..8106d47022a5c5 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -177,7 +177,8 @@ Other CPython Implementation Changes
 
 * ``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()``.
+  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