bpo-32433: Optimized HMAC digest (#5023)

The hmac module now has hmac.digest(), which provides an optimized HMAC
digest for short messages. hmac.digest() is up to three times faster
than hmac.HMAC().digest().

Signed-off-by: Christian Heimes <christian@python.org>

Modules/_hashopenssl.c

@@ -21,6 +21,7 @@
 
 /* EVP is the preferred interface to hashing in OpenSSL */
 #include <openssl/evp.h>
+#include <openssl/hmac.h>
 /* We use the object interface to discover what hashes OpenSSL supports. */
 #include <openssl/objects.h>
 #include "openssl/err.h"
@@ -528,8 +529,6 @@ EVP_new(PyObject *self, PyObject *args, PyObject *kwdict)
     return ret_obj;
 }
 
-
-
 #if (OPENSSL_VERSION_NUMBER >= 0x10000000 && !defined(OPENSSL_NO_HMAC) \
      && !defined(OPENSSL_NO_SHA))
 
@@ -849,6 +848,61 @@ _hashlib_scrypt_impl(PyObject *module, Py_buffer *password, Py_buffer *salt,
 }
 #endif
 
+/* Fast HMAC for hmac.digest()
+ */
+
+/*[clinic input]
+_hashlib.hmac_digest
+
+    key: Py_buffer
+    msg: Py_buffer
+    digest: str
+
+Single-shot HMAC
+[clinic start generated code]*/
+
+static PyObject *
+_hashlib_hmac_digest_impl(PyObject *module, Py_buffer *key, Py_buffer *msg,
+                          const char *digest)
+/*[clinic end generated code: output=75630e684cdd8762 input=10e964917921e2f2]*/
+{
+    unsigned char md[EVP_MAX_MD_SIZE] = {0};
+    unsigned int md_len = 0;
+    unsigned char *result;
+    const EVP_MD *evp;
+
+    evp = EVP_get_digestbyname(digest);
+    if (evp == NULL) {
+        PyErr_SetString(PyExc_ValueError, "unsupported hash type");
+        return NULL;
+    }
+    if (key->len > INT_MAX) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "key is too long.");
+        return NULL;
+    }
+    if (msg->len > INT_MAX) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "msg is too long.");
+        return NULL;
+    }
+
+    Py_BEGIN_ALLOW_THREADS
+    result = HMAC(
+        evp,
+        (const void*)key->buf, (int)key->len,
+        (const unsigned char*)msg->buf, (int)msg->len,
+        md, &md_len
+    );
+    Py_END_ALLOW_THREADS
+
+    if (result == NULL) {
+        _setException(PyExc_ValueError);
+        return NULL;
+    }
+    return PyBytes_FromStringAndSize((const char*)md, md_len);
+}
+
 /* State for our callback function so that it can accumulate a result. */
 typedef struct _internal_name_mapper_state {
     PyObject *set;
@@ -982,6 +1036,7 @@ static struct PyMethodDef EVP_functions[] = {
      pbkdf2_hmac__doc__},
 #endif
     _HASHLIB_SCRYPT_METHODDEF
+    _HASHLIB_HMAC_DIGEST_METHODDEF
     CONSTRUCTOR_METH_DEF(md5),
     CONSTRUCTOR_METH_DEF(sha1),
     CONSTRUCTOR_METH_DEF(sha224),

Modules/clinic/_hashopenssl.c.h

@@ -54,7 +54,49 @@ exit:
 
 #endif /* (OPENSSL_VERSION_NUMBER > 0x10100000L && !defined(OPENSSL_NO_SCRYPT) && !defined(LIBRESSL_VERSION_NUMBER)) */
 
+PyDoc_STRVAR(_hashlib_hmac_digest__doc__,
+"hmac_digest($module, /, key, msg, digest)\n"
+"--\n"
+"\n"
+"Single-shot HMAC");
+
+#define _HASHLIB_HMAC_DIGEST_METHODDEF    \
+    {"hmac_digest", (PyCFunction)_hashlib_hmac_digest, METH_FASTCALL|METH_KEYWORDS, _hashlib_hmac_digest__doc__},
+
+static PyObject *
+_hashlib_hmac_digest_impl(PyObject *module, Py_buffer *key, Py_buffer *msg,
+                          const char *digest);
+
+static PyObject *
+_hashlib_hmac_digest(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"key", "msg", "digest", NULL};
+    static _PyArg_Parser _parser = {"y*y*s:hmac_digest", _keywords, 0};
+    Py_buffer key = {NULL, NULL};
+    Py_buffer msg = {NULL, NULL};
+    const char *digest;
+
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &key, &msg, &digest)) {
+        goto exit;
+    }
+    return_value = _hashlib_hmac_digest_impl(module, &key, &msg, digest);
+
+exit:
+    /* Cleanup for key */
+    if (key.obj) {
+       PyBuffer_Release(&key);
+    }
+    /* Cleanup for msg */
+    if (msg.obj) {
+       PyBuffer_Release(&msg);
+    }
+
+    return return_value;
+}
+
 #ifndef _HASHLIB_SCRYPT_METHODDEF
     #define _HASHLIB_SCRYPT_METHODDEF
 #endif /* !defined(_HASHLIB_SCRYPT_METHODDEF) */
-/*[clinic end generated code: output=1ea7d0397f38e2c2 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=b5b90821caf05391 input=a9049054013a1b77]*/