ssue #19183: Implement PEP 456 'secure and interchangeable hash algorithm'.

Python now uses SipHash24 on all major platforms.

1 files changed, 430 insertions, 0 deletions

diff --git a/Python/pyhash.c b/Python/pyhash.c
new file mode 100644
index 0000000..158c631
--- /dev/null
+++ b/Python/pyhash.c
@@ -0,0 +1,430 @@
+/* Set of hash utility functions to help maintaining the invariant that
+    if a==b then hash(a)==hash(b)
+
+   All the utility functions (_Py_Hash*()) return "-1" to signify an error.
+*/
+#include "Python.h"
+
+#ifdef __APPLE__
+#  include <libkern/OSByteOrder.h>
+#elif defined(HAVE_LE64TOH) && defined(HAVE_ENDIAN_H)
+#  include <endian.h>
+#elif defined(HAVE_LE64TOH) && defined(HAVE_SYS_ENDIAN_H)
+#  include <sys/endian.h>
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+_Py_HashSecret_t _Py_HashSecret;
+
+#if Py_HASH_ALGORITHM == Py_HASH_EXTERNAL
+extern PyHash_FuncDef PyHash_Func;
+#else
+static PyHash_FuncDef PyHash_Func;
+#endif
+
+/* Count _Py_HashBytes() calls */
+#ifdef Py_HASH_STATS
+#define Py_HASH_STATS_MAX 32
+static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0};
+#endif
+
+/* For numeric types, the hash of a number x is based on the reduction
+   of x modulo the prime P = 2**_PyHASH_BITS - 1.  It's designed so that
+   hash(x) == hash(y) whenever x and y are numerically equal, even if
+   x and y have different types.
+
+   A quick summary of the hashing strategy:
+
+   (1) First define the 'reduction of x modulo P' for any rational
+   number x; this is a standard extension of the usual notion of
+   reduction modulo P for integers.  If x == p/q (written in lowest
+   terms), the reduction is interpreted as the reduction of p times
+   the inverse of the reduction of q, all modulo P; if q is exactly
+   divisible by P then define the reduction to be infinity.  So we've
+   got a well-defined map
+
+      reduce : { rational numbers } -> { 0, 1, 2, ..., P-1, infinity }.
+
+   (2) Now for a rational number x, define hash(x) by:
+
+      reduce(x)   if x >= 0
+      -reduce(-x) if x < 0
+
+   If the result of the reduction is infinity (this is impossible for
+   integers, floats and Decimals) then use the predefined hash value
+   _PyHASH_INF for x >= 0, or -_PyHASH_INF for x < 0, instead.
+   _PyHASH_INF, -_PyHASH_INF and _PyHASH_NAN are also used for the
+   hashes of float and Decimal infinities and nans.
+
+   A selling point for the above strategy is that it makes it possible
+   to compute hashes of decimal and binary floating-point numbers
+   efficiently, even if the exponent of the binary or decimal number
+   is large.  The key point is that
+
+      reduce(x * y) == reduce(x) * reduce(y) (modulo _PyHASH_MODULUS)
+
+   provided that {reduce(x), reduce(y)} != {0, infinity}.  The reduction of a
+   binary or decimal float is never infinity, since the denominator is a power
+   of 2 (for binary) or a divisor of a power of 10 (for decimal).  So we have,
+   for nonnegative x,
+
+      reduce(x * 2**e) == reduce(x) * reduce(2**e) % _PyHASH_MODULUS
+
+      reduce(x * 10**e) == reduce(x) * reduce(10**e) % _PyHASH_MODULUS
+
+   and reduce(10**e) can be computed efficiently by the usual modular
+   exponentiation algorithm.  For reduce(2**e) it's even better: since
+   P is of the form 2**n-1, reduce(2**e) is 2**(e mod n), and multiplication
+   by 2**(e mod n) modulo 2**n-1 just amounts to a rotation of bits.
+
+   */
+
+Py_hash_t
+_Py_HashDouble(double v)
+{
+    int e, sign;
+    double m;
+    Py_uhash_t x, y;
+
+    if (!Py_IS_FINITE(v)) {
+        if (Py_IS_INFINITY(v))
+            return v > 0 ? _PyHASH_INF : -_PyHASH_INF;
+        else
+            return _PyHASH_NAN;
+    }
+
+    m = frexp(v, &e);
+
+    sign = 1;
+    if (m < 0) {
+        sign = -1;
+        m = -m;
+    }
+
+    /* process 28 bits at a time;  this should work well both for binary
+       and hexadecimal floating point. */
+    x = 0;
+    while (m) {
+        x = ((x << 28) & _PyHASH_MODULUS) | x >> (_PyHASH_BITS - 28);
+        m *= 268435456.0;  /* 2**28 */
+        e -= 28;
+        y = (Py_uhash_t)m;  /* pull out integer part */
+        m -= y;
+        x += y;
+        if (x >= _PyHASH_MODULUS)
+            x -= _PyHASH_MODULUS;
+    }
+
+    /* adjust for the exponent;  first reduce it modulo _PyHASH_BITS */
+    e = e >= 0 ? e % _PyHASH_BITS : _PyHASH_BITS-1-((-1-e) % _PyHASH_BITS);
+    x = ((x << e) & _PyHASH_MODULUS) | x >> (_PyHASH_BITS - e);
+
+    x = x * sign;
+    if (x == (Py_uhash_t)-1)
+        x = (Py_uhash_t)-2;
+    return (Py_hash_t)x;
+}
+
+Py_hash_t
+_Py_HashPointer(void *p)
+{
+    Py_hash_t x;
+    size_t y = (size_t)p;
+    /* bottom 3 or 4 bits are likely to be 0; rotate y by 4 to avoid
+       excessive hash collisions for dicts and sets */
+    y = (y >> 4) | (y << (8 * SIZEOF_VOID_P - 4));
+    x = (Py_hash_t)y;
+    if (x == -1)
+        x = -2;
+    return x;
+}
+
+Py_hash_t
+_Py_HashBytes(const void *src, Py_ssize_t len)
+{
+    Py_hash_t x;
+    /*
+      We make the hash of the empty string be 0, rather than using
+      (prefix ^ suffix), since this slightly obfuscates the hash secret
+    */
+    if (len == 0) {
+        return 0;
+    }
+
+#ifdef Py_HASH_STATS
+    hashstats[(len <= Py_HASH_STATS_MAX) ? len : 0]++;
+#endif
+
+#if Py_HASH_CUTOFF > 0
+    if (len < Py_HASH_CUTOFF) {
+        /* Optimize hashing of very small strings with inline DJBX33A. */
+        Py_uhash_t hash;
+        const unsigned char *p = src;
+        hash = 5381; /* DJBX33A starts with 5381 */
+
+        switch(len) {
+            /* ((hash << 5) + hash) + *p == hash * 33 + *p */
+            case 7: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 6: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 5: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 4: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 3: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 2: hash = ((hash << 5) + hash) + *p++; /* fallthrough */
+            case 1: hash = ((hash << 5) + hash) + *p++; break;
+            default:
+                assert(0);
+        }
+        hash ^= len;
+        hash ^= (Py_uhash_t) _Py_HashSecret.djbx33a.suffix;
+        x = (Py_hash_t)hash;
+    }
+    else
+#endif /* Py_HASH_CUTOFF */
+        x = PyHash_Func.hash(src, len);
+
+    if (x == -1)
+        return -2;
+    return x;
+}
+
+void
+_PyHash_Fini(void)
+{
+#ifdef Py_HASH_STATS
+    int i;
+    Py_ssize_t total = 0;
+    char *fmt = "%2i %8" PY_FORMAT_SIZE_T "d %8" PY_FORMAT_SIZE_T "d\n";
+
+    fprintf(stderr, "len   calls    total\n");
+    for (i = 1; i <= Py_HASH_STATS_MAX; i++) {
+        total += hashstats[i];
+        fprintf(stderr, fmt, i, hashstats[i], total);
+    }
+    total += hashstats[0];
+    fprintf(stderr, ">  %8" PY_FORMAT_SIZE_T "d %8" PY_FORMAT_SIZE_T "d\n",
+            hashstats[0], total);
+#endif
+}
+
+PyHash_FuncDef *
+PyHash_GetFuncDef(void)
+{
+    return &PyHash_Func;
+}
+
+/* Optimized memcpy() for Windows */
+#ifdef _MSC_VER
+#  if SIZEOF_PY_UHASH_T == 4
+#    define PY_UHASH_CPY(dst, src) do {                                    \
+       dst[0] = src[0]; dst[1] = src[1]; dst[2] = src[2]; dst[3] = src[3]; \
+       } while(0)
+#  elif SIZEOF_PY_UHASH_T == 8
+#    define PY_UHASH_CPY(dst, src) do {                                    \
+       dst[0] = src[0]; dst[1] = src[1]; dst[2] = src[2]; dst[3] = src[3]; \
+       dst[4] = src[4]; dst[5] = src[5]; dst[6] = src[6]; dst[7] = src[7]; \
+       } while(0)
+#  else
+#    error SIZEOF_PY_UHASH_T must be 4 or 8
+#  endif /* SIZEOF_PY_UHASH_T */
+#else /* not Windows */
+#  define PY_UHASH_CPY(dst, src) memcpy(dst, src, SIZEOF_PY_UHASH_T)
+#endif /* _MSC_VER */
+
+
+#if Py_HASH_ALGORITHM == Py_HASH_FNV
+/* **************************************************************************
+ * Modified Fowler-Noll-Vo (FNV) hash function
+ */
+static Py_hash_t
+fnv(const void *src, Py_ssize_t len)
+{
+    const unsigned char *p = src;
+    Py_uhash_t x;
+    Py_ssize_t remainder, blocks;
+    union {
+        Py_uhash_t value;
+        unsigned char bytes[SIZEOF_PY_UHASH_T];
+    } block;
+
+#ifdef Py_DEBUG
+    assert(_Py_HashSecret_Initialized);
+#endif
+    remainder = len % SIZEOF_PY_UHASH_T;
+    if (remainder == 0) {
+        /* Process at least one block byte by byte to reduce hash collisions
+         * for strings with common prefixes. */
+        remainder = SIZEOF_PY_UHASH_T;
+    }
+    blocks = (len - remainder) / SIZEOF_PY_UHASH_T;
+
+    x = (Py_uhash_t) _Py_HashSecret.fnv.prefix;
+    x ^= (Py_uhash_t) *p << 7;
+    while (blocks--) {
+        PY_UHASH_CPY(block.bytes, p);
+        x = (_PyHASH_MULTIPLIER * x) ^ block.value;
+        p += SIZEOF_PY_UHASH_T;
+    }
+    /* add remainder */
+    for (; remainder > 0; remainder--)
+        x = (_PyHASH_MULTIPLIER * x) ^ (Py_uhash_t) *p++;
+    x ^= (Py_uhash_t) len;
+    x ^= (Py_uhash_t) _Py_HashSecret.fnv.suffix;
+    if (x == -1) {
+        x = -2;
+    }
+    return x;
+}
+
+static PyHash_FuncDef PyHash_Func = {fnv, "fnv", 8 * SIZEOF_PY_HASH_T,
+                                     16 * SIZEOF_PY_HASH_T};
+
+#endif /* Py_HASH_ALGORITHM == Py_HASH_FNV */
+
+
+#if Py_HASH_ALGORITHM == Py_HASH_SIPHASH24
+/* **************************************************************************
+ <MIT License>
+ Copyright (c) 2013  Marek Majkowski <marek@popcount.org>
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ THE SOFTWARE.
+ </MIT License>
+
+ Original location:
+    https://github.com/majek/csiphash/
+
+ Solution inspired by code from:
+    Samuel Neves (supercop/crypto_auth/siphash24/little)
+    djb (supercop/crypto_auth/siphash24/little2)
+    Jean-Philippe Aumasson (https://131002.net/siphash/siphash24.c)
+
+ Modified for Python by Christian Heimes:
+    - C89 / MSVC compatibility
+    - PY_UINT64_T, PY_UINT32_T and PY_UINT8_T
+    - _rotl64() on Windows
+    - letoh64() fallback
+*/
+
+typedef unsigned char PY_UINT8_T;
+
+/* byte swap little endian to host endian
+ * Endian conversion not only ensures that the hash function returns the same
+ * value on all platforms. It is also required to for a good dispersion of
+ * the hash values' least significant bits.
+ */
+#if PY_LITTLE_ENDIAN
+#  define _le64toh(x) ((PY_UINT64_T)(x))
+#elif defined(__APPLE__)
+#  define _le64toh(x) OSSwapLittleToHostInt64(x)
+#elif defined(HAVE_LETOH64)
+#  define _le64toh(x) le64toh(x)
+#else
+#  define _le64toh(x) (((PY_UINT64_T)(x) << 56) | \
+                      (((PY_UINT64_T)(x) << 40) & 0xff000000000000ULL) | \
+                      (((PY_UINT64_T)(x) << 24) & 0xff0000000000ULL) | \
+                      (((PY_UINT64_T)(x) << 8)  & 0xff00000000ULL) | \
+                      (((PY_UINT64_T)(x) >> 8)  & 0xff000000ULL) | \
+                      (((PY_UINT64_T)(x) >> 24) & 0xff0000ULL) | \
+                      (((PY_UINT64_T)(x) >> 40) & 0xff00ULL) | \
+                      ((PY_UINT64_T)(x)  >> 56))
+#endif
+
+
+#ifdef _MSC_VER
+#  define ROTATE(x, b)  _rotl64(x, b)
+#else
+#  define ROTATE(x, b) (PY_UINT64_T)( ((x) << (b)) | ( (x) >> (64 - (b))) )
+#endif
+
+#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 DOUBLE_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);
+
+
+static Py_hash_t
+siphash24(const void *src, Py_ssize_t src_sz) {
+    PY_UINT64_T k0 = _le64toh(_Py_HashSecret.siphash.k0);
+    PY_UINT64_T k1 = _le64toh(_Py_HashSecret.siphash.k1);
+    PY_UINT64_T b = (PY_UINT64_T)src_sz << 56;
+    const PY_UINT64_T *in = (PY_UINT64_T*)src;
+
+    PY_UINT64_T v0 = k0 ^ 0x736f6d6570736575ULL;
+    PY_UINT64_T v1 = k1 ^ 0x646f72616e646f6dULL;
+    PY_UINT64_T v2 = k0 ^ 0x6c7967656e657261ULL;
+    PY_UINT64_T v3 = k1 ^ 0x7465646279746573ULL;
+
+    PY_UINT64_T t;
+    PY_UINT8_T *pt;
+    PY_UINT8_T *m;
+
+    while (src_sz >= 8) {
+        PY_UINT64_T mi = _le64toh(*in);
+        in += 1;
+        src_sz -= 8;
+        v3 ^= mi;
+        DOUBLE_ROUND(v0,v1,v2,v3);
+        v0 ^= mi;
+    }
+
+    t = 0;
+    pt = (PY_UINT8_T *)&t;
+    m = (PY_UINT8_T *)in;
+    switch (src_sz) {
+        case 7: pt[6] = m[6];
+        case 6: pt[5] = m[5];
+        case 5: pt[4] = m[4];
+        case 4: *((PY_UINT32_T*)&pt[0]) = *((PY_UINT32_T*)&m[0]); break;
+        case 3: pt[2] = m[2];
+        case 2: pt[1] = m[1];
+        case 1: pt[0] = m[0];
+    }
+    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);
+#if SIZEOF_VOID_P == 4
+    t ^= (t >> 32);
+#endif
+    return (Py_hash_t)t;
+}
+
+static PyHash_FuncDef PyHash_Func = {siphash24, "siphash24", 64, 128};
+
+#endif /* Py_HASH_ALGORITHM == Py_HASH_SIPHASH24 */
+
+#ifdef __cplusplus
+}
+#endif