/* Module that wraps all OpenSSL hash algorithms */

/*
 * Copyright (C) 2005-2010   Gregory P. Smith (greg@krypto.org)
 * Licensed to PSF under a Contributor Agreement.
 *
 * Derived from a skeleton of shamodule.c containing work performed by:
 *
 * Andrew Kuchling (amk@amk.ca)
 * Greg Stein (gstein@lyra.org)
 *
 */

#define PY_SSIZE_T_CLEAN

#include "Python.h"
#include "structmember.h"
#include "hashlib.h"
#include "pystrhex.h"


/* 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"

#if (OPENSSL_VERSION_NUMBER < 0x10100000L) || defined(LIBRESSL_VERSION_NUMBER)
/* OpenSSL < 1.1.0 */
#define EVP_MD_CTX_new EVP_MD_CTX_create
#define EVP_MD_CTX_free EVP_MD_CTX_destroy
#endif

#define MUNCH_SIZE INT_MAX

typedef struct {
    PyObject_HEAD
    EVP_MD_CTX          *ctx;   /* OpenSSL message digest context */
    PyThread_type_lock   lock;  /* OpenSSL context lock */
} EVPobject;


static PyTypeObject EVPtype;

#include "clinic/_hashopenssl.c.h"
/*[clinic input]
module _hashlib
class _hashlib.HASH "EVPobject *" "&EVPtype"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=a881a5092eecad28]*/


/* LCOV_EXCL_START */
static PyObject *
_setException(PyObject *exc)
{
    unsigned long errcode;
    const char *lib, *func, *reason;

    errcode = ERR_peek_last_error();
    if (!errcode) {
        PyErr_SetString(exc, "unknown reasons");
        return NULL;
    }
    ERR_clear_error();

    lib = ERR_lib_error_string(errcode);
    func = ERR_func_error_string(errcode);
    reason = ERR_reason_error_string(errcode);

    if (lib && func) {
        PyErr_Format(exc, "[%s: %s] %s", lib, func, reason);
    }
    else if (lib) {
        PyErr_Format(exc, "[%s] %s", lib, reason);
    }
    else {
        PyErr_SetString(exc, reason);
    }
    return NULL;
}
/* LCOV_EXCL_STOP */

static EVPobject *
newEVPobject(void)
{
    EVPobject *retval = (EVPobject *)PyObject_New(EVPobject, &EVPtype);
    if (retval == NULL) {
        return NULL;
    }

    retval->lock = NULL;

    retval->ctx = EVP_MD_CTX_new();
    if (retval->ctx == NULL) {
        Py_DECREF(retval);
        PyErr_NoMemory();
        return NULL;
    }

    return retval;
}

static int
EVP_hash(EVPobject *self, const void *vp, Py_ssize_t len)
{
    unsigned int process;
    const unsigned char *cp = (const unsigned char *)vp;
    while (0 < len) {
        if (len > (Py_ssize_t)MUNCH_SIZE)
            process = MUNCH_SIZE;
        else
            process = Py_SAFE_DOWNCAST(len, Py_ssize_t, unsigned int);
        if (!EVP_DigestUpdate(self->ctx, (const void*)cp, process)) {
            _setException(PyExc_ValueError);
            return -1;
        }
        len -= process;
        cp += process;
    }
    return 0;
}

/* Internal methods for a hash object */

static void
EVP_dealloc(EVPobject *self)
{
    if (self->lock != NULL)
        PyThread_free_lock(self->lock);
    EVP_MD_CTX_free(self->ctx);
    PyObject_Del(self);
}

static int
locked_EVP_MD_CTX_copy(EVP_MD_CTX *new_ctx_p, EVPobject *self)
{
    int result;
    ENTER_HASHLIB(self);
    result = EVP_MD_CTX_copy(new_ctx_p, self->ctx);
    LEAVE_HASHLIB(self);
    return result;
}

/* External methods for a hash object */

/*[clinic input]
_hashlib.HASH.copy as EVP_copy

Return a copy of the hash object.
[clinic start generated code]*/

static PyObject *
EVP_copy_impl(EVPobject *self)
/*[clinic end generated code: output=b370c21cdb8ca0b4 input=31455b6a3e638069]*/
{
    EVPobject *newobj;

    if ( (newobj = newEVPobject())==NULL)
        return NULL;

    if (!locked_EVP_MD_CTX_copy(newobj->ctx, self)) {
        Py_DECREF(newobj);
        return _setException(PyExc_ValueError);
    }
    return (PyObject *)newobj;
}

/*[clinic input]
_hashlib.HASH.digest as EVP_digest

Return the digest value as a bytes object.
[clinic start generated code]*/

static PyObject *
EVP_digest_impl(EVPobject *self)
/*[clinic end generated code: output=0f6a3a0da46dc12d input=03561809a419bf00]*/
{
    unsigned char digest[EVP_MAX_MD_SIZE];
    EVP_MD_CTX *temp_ctx;
    PyObject *retval;
    unsigned int digest_size;

    temp_ctx = EVP_MD_CTX_new();
    if (temp_ctx == NULL) {
        PyErr_NoMemory();
        return NULL;
    }

    if (!locked_EVP_MD_CTX_copy(temp_ctx, self)) {
        return _setException(PyExc_ValueError);
    }
    digest_size = EVP_MD_CTX_size(temp_ctx);
    if (!EVP_DigestFinal(temp_ctx, digest, NULL)) {
        _setException(PyExc_ValueError);
        return NULL;
    }

    retval = PyBytes_FromStringAndSize((const char *)digest, digest_size);
    EVP_MD_CTX_free(temp_ctx);
    return retval;
}

/*[clinic input]
_hashlib.HASH.hexdigest as EVP_hexdigest

Return the digest value as a string of hexadecimal digits.
[clinic start generated code]*/

static PyObject *
EVP_hexdigest_impl(EVPobject *self)
/*[clinic end generated code: output=18e6decbaf197296 input=aff9cf0e4c741a9a]*/
{
    unsigned char digest[EVP_MAX_MD_SIZE];
    EVP_MD_CTX *temp_ctx;
    unsigned int digest_size;

    temp_ctx = EVP_MD_CTX_new();
    if (temp_ctx == NULL) {
        PyErr_NoMemory();
        return NULL;
    }

    /* Get the raw (binary) digest value */
    if (!locked_EVP_MD_CTX_copy(temp_ctx, self)) {
        return _setException(PyExc_ValueError);
    }
    digest_size = EVP_MD_CTX_size(temp_ctx);
    if (!EVP_DigestFinal(temp_ctx, digest, NULL)) {
        _setException(PyExc_ValueError);
        return NULL;
    }

    EVP_MD_CTX_free(temp_ctx);

    return _Py_strhex((const char *)digest, (Py_ssize_t)digest_size);
}

/*[clinic input]
_hashlib.HASH.update as EVP_update

    obj: object
    /

Update this hash object's state with the provided string.
[clinic start generated code]*/

static PyObject *
EVP_update(EVPobject *self, PyObject *obj)
/*[clinic end generated code: output=ec1d55ed2432e966 input=9b30ec848f015501]*/
{
    int result;
    Py_buffer view;

    GET_BUFFER_VIEW_OR_ERROUT(obj, &view);

    if (self->lock == NULL && view.len >= HASHLIB_GIL_MINSIZE) {
        self->lock = PyThread_allocate_lock();
        /* fail? lock = NULL and we fail over to non-threaded code. */
    }

    if (self->lock != NULL) {
        Py_BEGIN_ALLOW_THREADS
        PyThread_acquire_lock(self->lock, 1);
        result = EVP_hash(self, view.buf, view.len);
        PyThread_release_lock(self->lock);
        Py_END_ALLOW_THREADS
    } else {
        result = EVP_hash(self, view.buf, view.len);
    }

    PyBuffer_Release(&view);

    if (result == -1)
        return NULL;
    Py_RETURN_NONE;
}

static PyMethodDef EVP_methods[] = {
    EVP_UPDATE_METHODDEF
    EVP_DIGEST_METHODDEF
    EVP_HEXDIGEST_METHODDEF
    EVP_COPY_METHODDEF
    {NULL, NULL}  /* sentinel */
};

static PyObject *
EVP_get_block_size(EVPobject *self, void *closure)
{
    long block_size;
    block_size = EVP_MD_CTX_block_size(self->ctx);
    return PyLong_FromLong(block_size);
}

static PyObject *
EVP_get_digest_size(EVPobject *self, void *closure)
{
    long size;
    size = EVP_MD_CTX_size(self->ctx);
    return PyLong_FromLong(size);
}

static PyObject *
EVP_get_name(EVPobject *self, void *closure)
{
    const char *name = EVP_MD_name(EVP_MD_CTX_md(self->ctx));
    PyObject *name_obj, *name_lower;

    name_obj = PyUnicode_FromString(name);
    if (!name_obj) {
        return NULL;
    }
    name_lower = PyObject_CallMethod(name_obj, "lower", NULL);
    Py_DECREF(name_obj);
    return name_lower;
}

static PyGetSetDef EVP_getseters[] = {
    {"digest_size",
     (getter)EVP_get_digest_size, NULL,
     NULL,
     NULL},
    {"block_size",
     (getter)EVP_get_block_size, NULL,
     NULL,
     NULL},
    {"name",
     (getter)EVP_get_name, NULL,
     NULL,
     PyDoc_STR("algorithm name.")},
    {NULL}  /* Sentinel */
};


static PyObject *
EVP_repr(EVPobject *self)
{
    PyObject *name_obj, *repr;
    name_obj = EVP_get_name(self, NULL);
    if (!name_obj) {
        return NULL;
    }
    repr = PyUnicode_FromFormat("<%U HASH object @ %p>", name_obj, self);
    Py_DECREF(name_obj);
    return repr;
}

PyDoc_STRVAR(hashtype_doc,
"HASH(name, string=b\'\')\n"
"--\n"
"\n"
"A hash is an object used to calculate a checksum of a string of information.\n"
"\n"
"Methods:\n"
"\n"
"update() -- updates the current digest with an additional string\n"
"digest() -- return the current digest value\n"
"hexdigest() -- return the current digest as a string of hexadecimal digits\n"
"copy() -- return a copy of the current hash object\n"
"\n"
"Attributes:\n"
"\n"
"name -- the hash algorithm being used by this object\n"
"digest_size -- number of bytes in this hashes output");

static PyTypeObject EVPtype = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "_hashlib.HASH",    /*tp_name*/
    sizeof(EVPobject),  /*tp_basicsize*/
    0,                  /*tp_itemsize*/
    /* methods */
    (destructor)EVP_dealloc, /*tp_dealloc*/
    0,                  /*tp_vectorcall_offset*/
    0,                  /*tp_getattr*/
    0,                  /*tp_setattr*/
    0,                  /*tp_as_async*/
    (reprfunc)EVP_repr, /*tp_repr*/
    0,                  /*tp_as_number*/
    0,                  /*tp_as_sequence*/
    0,                  /*tp_as_mapping*/
    0,                  /*tp_hash*/
    0,                  /*tp_call*/
    0,                  /*tp_str*/
    0,                  /*tp_getattro*/
    0,                  /*tp_setattro*/
    0,                  /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
    hashtype_doc,       /*tp_doc*/
    0,                  /*tp_traverse*/
    0,                  /*tp_clear*/
    0,                  /*tp_richcompare*/
    0,                  /*tp_weaklistoffset*/
    0,                  /*tp_iter*/
    0,                  /*tp_iternext*/
    EVP_methods,        /* tp_methods */
    NULL,        /* tp_members */
    EVP_getseters,      /* tp_getset */
    0,                  /* tp_base */
    0,                  /* tp_dict */
    0,                  /* tp_descr_get */
    0,                  /* tp_descr_set */
    0,                  /* tp_dictoffset */
};

static PyObject *
EVPnew(const EVP_MD *digest,
       const unsigned char *cp, Py_ssize_t len)
{
    int result = 0;
    EVPobject *self;

    if (!digest) {
        PyErr_SetString(PyExc_ValueError, "unsupported hash type");
        return NULL;
    }

    if ((self = newEVPobject()) == NULL)
        return NULL;

    if (!EVP_DigestInit(self->ctx, digest)) {
        _setException(PyExc_ValueError);
        Py_DECREF(self);
        return NULL;
    }

    if (cp && len) {
        if (len >= HASHLIB_GIL_MINSIZE) {
            Py_BEGIN_ALLOW_THREADS
            result = EVP_hash(self, cp, len);
            Py_END_ALLOW_THREADS
        } else {
            result = EVP_hash(self, cp, len);
        }
        if (result == -1) {
            Py_DECREF(self);
            return NULL;
        }
    }

    return (PyObject *)self;
}


/* The module-level function: new() */

/*[clinic input]
_hashlib.new as EVP_new

    name as name_obj: object
    string as data_obj: object(py_default="b''") = NULL

Return a new hash object using the named algorithm.

An optional string argument may be provided and will be
automatically hashed.

The MD5 and SHA1 algorithms are always supported.
[clinic start generated code]*/

static PyObject *
EVP_new_impl(PyObject *module, PyObject *name_obj, PyObject *data_obj)
/*[clinic end generated code: output=9e7cf664e04b0226 input=1c46e40e0fec91f3]*/
{
    Py_buffer view = { 0 };
    PyObject *ret_obj;
    char *name;
    const EVP_MD *digest;

    if (!PyArg_Parse(name_obj, "s", &name)) {
        PyErr_SetString(PyExc_TypeError, "name must be a string");
        return NULL;
    }

    if (data_obj)
        GET_BUFFER_VIEW_OR_ERROUT(data_obj, &view);

    digest = EVP_get_digestbyname(name);

    ret_obj = EVPnew(digest, (unsigned char*)view.buf, view.len);

    if (data_obj)
        PyBuffer_Release(&view);
    return ret_obj;
}

static PyObject*
EVP_fast_new(PyObject *module, PyObject *data_obj, const EVP_MD *digest)
{
    Py_buffer view = { 0 };
    PyObject *ret_obj;

    if (data_obj)
        GET_BUFFER_VIEW_OR_ERROUT(data_obj, &view);

    ret_obj = EVPnew(digest, (unsigned char*)view.buf, view.len);

    if (data_obj)
        PyBuffer_Release(&view);

    return ret_obj;
}

/*[clinic input]
_hashlib.openssl_md5

    string as data_obj: object(py_default="b''") = NULL

Returns a md5 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_md5_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=6caae75b73e22c3f input=52010d3869e1b1a7]*/
{
    return EVP_fast_new(module, data_obj, EVP_md5());
}


/*[clinic input]
_hashlib.openssl_sha1

    string as data_obj: object(py_default="b''") = NULL

Returns a sha1 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_sha1_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=07606d8f75153e61 input=16807d30e4aa8ae9]*/
{
    return EVP_fast_new(module, data_obj, EVP_sha1());
}


/*[clinic input]
_hashlib.openssl_sha224

    string as data_obj: object(py_default="b''") = NULL

Returns a sha224 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_sha224_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=55e848761bcef0c9 input=5dbc2f1d84eb459b]*/
{
    return EVP_fast_new(module, data_obj, EVP_sha224());
}


/*[clinic input]
_hashlib.openssl_sha256

    string as data_obj: object(py_default="b''") = NULL

Returns a sha256 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_sha256_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=05851d7cce34ac65 input=a68a5d21cda5a80f]*/
{
    return EVP_fast_new(module, data_obj, EVP_sha256());
}


/*[clinic input]
_hashlib.openssl_sha384

    string as data_obj: object(py_default="b''") = NULL

Returns a sha384 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_sha384_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=5101a4704a932c2f input=6bdfa006622b64ea]*/
{
    return EVP_fast_new(module, data_obj, EVP_sha384());
}


/*[clinic input]
_hashlib.openssl_sha512

    string as data_obj: object(py_default="b''") = NULL

Returns a sha512 hash object; optionally initialized with a string

[clinic start generated code]*/

static PyObject *
_hashlib_openssl_sha512_impl(PyObject *module, PyObject *data_obj)
/*[clinic end generated code: output=20c8e63ee560a5cb input=ece50182ad4b76a6]*/
{
    return EVP_fast_new(module, data_obj, EVP_sha512());
}


/*[clinic input]
_hashlib.pbkdf2_hmac as pbkdf2_hmac

    hash_name: str
    password: Py_buffer
    salt: Py_buffer
    iterations: long
    dklen as dklen_obj: object = None

Password based key derivation function 2 (PKCS #5 v2.0) with HMAC as pseudorandom function.
[clinic start generated code]*/

static PyObject *
pbkdf2_hmac_impl(PyObject *module, const char *hash_name,
                 Py_buffer *password, Py_buffer *salt, long iterations,
                 PyObject *dklen_obj)
/*[clinic end generated code: output=144b76005416599b input=ed3ab0d2d28b5d5c]*/
{
    PyObject *key_obj = NULL;
    char *key;
    long dklen;
    int retval;
    const EVP_MD *digest;

    digest = EVP_get_digestbyname(hash_name);
    if (digest == NULL) {
        PyErr_SetString(PyExc_ValueError, "unsupported hash type");
        goto end;
    }

    if (password->len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "password is too long.");
        goto end;
    }

    if (salt->len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "salt is too long.");
        goto end;
    }

    if (iterations < 1) {
        PyErr_SetString(PyExc_ValueError,
                        "iteration value must be greater than 0.");
        goto end;
    }
    if (iterations > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "iteration value is too great.");
        goto end;
    }

    if (dklen_obj == Py_None) {
        dklen = EVP_MD_size(digest);
    } else {
        dklen = PyLong_AsLong(dklen_obj);
        if ((dklen == -1) && PyErr_Occurred()) {
            goto end;
        }
    }
    if (dklen < 1) {
        PyErr_SetString(PyExc_ValueError,
                        "key length must be greater than 0.");
        goto end;
    }
    if (dklen > INT_MAX) {
        /* INT_MAX is always smaller than dkLen max (2^32 - 1) * hLen */
        PyErr_SetString(PyExc_OverflowError,
                        "key length is too great.");
        goto end;
    }

    key_obj = PyBytes_FromStringAndSize(NULL, dklen);
    if (key_obj == NULL) {
        goto end;
    }
    key = PyBytes_AS_STRING(key_obj);

    Py_BEGIN_ALLOW_THREADS
    retval = PKCS5_PBKDF2_HMAC((char*)password->buf, (int)password->len,
                               (unsigned char *)salt->buf, (int)salt->len,
                               iterations, digest, dklen,
                               (unsigned char *)key);
    Py_END_ALLOW_THREADS

    if (!retval) {
        Py_CLEAR(key_obj);
        _setException(PyExc_ValueError);
        goto end;
    }

  end:
    return key_obj;
}

#if OPENSSL_VERSION_NUMBER > 0x10100000L && !defined(OPENSSL_NO_SCRYPT) && !defined(LIBRESSL_VERSION_NUMBER)
#define PY_SCRYPT 1

/* XXX: Parameters salt, n, r and p should be required keyword-only parameters.
   They are optional in the Argument Clinic declaration only due to a
   limitation of PyArg_ParseTupleAndKeywords. */

/*[clinic input]
_hashlib.scrypt

    password: Py_buffer
    *
    salt: Py_buffer = None
    n as n_obj: object(subclass_of='&PyLong_Type') = None
    r as r_obj: object(subclass_of='&PyLong_Type') = None
    p as p_obj: object(subclass_of='&PyLong_Type') = None
    maxmem: long = 0
    dklen: long = 64


scrypt password-based key derivation function.
[clinic start generated code]*/

static PyObject *
_hashlib_scrypt_impl(PyObject *module, Py_buffer *password, Py_buffer *salt,
                     PyObject *n_obj, PyObject *r_obj, PyObject *p_obj,
                     long maxmem, long dklen)
/*[clinic end generated code: output=14849e2aa2b7b46c input=48a7d63bf3f75c42]*/
{
    PyObject *key_obj = NULL;
    char *key;
    int retval;
    unsigned long n, r, p;

    if (password->len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "password is too long.");
        return NULL;
    }

    if (salt->buf == NULL) {
        PyErr_SetString(PyExc_TypeError,
                        "salt is required");
        return NULL;
    }
    if (salt->len > INT_MAX) {
        PyErr_SetString(PyExc_OverflowError,
                        "salt is too long.");
        return NULL;
    }

    n = PyLong_AsUnsignedLong(n_obj);
    if (n == (unsigned long) -1 && PyErr_Occurred()) {
        PyErr_SetString(PyExc_TypeError,
                        "n is required and must be an unsigned int");
        return NULL;
    }
    if (n < 2 || n & (n - 1)) {
        PyErr_SetString(PyExc_ValueError,
                        "n must be a power of 2.");
        return NULL;
    }

    r = PyLong_AsUnsignedLong(r_obj);
    if (r == (unsigned long) -1 && PyErr_Occurred()) {
        PyErr_SetString(PyExc_TypeError,
                         "r is required and must be an unsigned int");
        return NULL;
    }

    p = PyLong_AsUnsignedLong(p_obj);
    if (p == (unsigned long) -1 && PyErr_Occurred()) {
        PyErr_SetString(PyExc_TypeError,
                         "p is required and must be an unsigned int");
        return NULL;
    }

    if (maxmem < 0 || maxmem > INT_MAX) {
        /* OpenSSL 1.1.0 restricts maxmem to 32 MiB. It may change in the
           future. The maxmem constant is private to OpenSSL. */
        PyErr_Format(PyExc_ValueError,
                     "maxmem must be positive and smaller than %d",
                      INT_MAX);
        return NULL;
    }

    if (dklen < 1 || dklen > INT_MAX) {
        PyErr_Format(PyExc_ValueError,
                    "dklen must be greater than 0 and smaller than %d",
                    INT_MAX);
        return NULL;
    }

    /* let OpenSSL validate the rest */
    retval = EVP_PBE_scrypt(NULL, 0, NULL, 0, n, r, p, maxmem, NULL, 0);
    if (!retval) {
        /* sorry, can't do much better */
        PyErr_SetString(PyExc_ValueError,
                        "Invalid parameter combination for n, r, p, maxmem.");
        return NULL;
   }

    key_obj = PyBytes_FromStringAndSize(NULL, dklen);
    if (key_obj == NULL) {
        return NULL;
    }
    key = PyBytes_AS_STRING(key_obj);

    Py_BEGIN_ALLOW_THREADS
    retval = EVP_PBE_scrypt(
        (const char*)password->buf, (size_t)password->len,
        (const unsigned char *)salt->buf, (size_t)salt->len,
        n, r, p, maxmem,
        (unsigned char *)key, (size_t)dklen
    );
    Py_END_ALLOW_THREADS

    if (!retval) {
        Py_CLEAR(key_obj);
        _setException(PyExc_ValueError);
        return NULL;
    }
    return key_obj;
}
#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=562d2f4249511bd3]*/
{
    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;
    int error;
} _InternalNameMapperState;


/* A callback function to pass to OpenSSL's OBJ_NAME_do_all(...) */
static void
_openssl_hash_name_mapper(const OBJ_NAME *openssl_obj_name, void *arg)
{
    _InternalNameMapperState *state = (_InternalNameMapperState *)arg;
    PyObject *py_name;

    assert(state != NULL);
    if (openssl_obj_name == NULL)
        return;
    /* Ignore aliased names, they pollute the list and OpenSSL appears to
     * have its own definition of alias as the resulting list still
     * contains duplicate and alternate names for several algorithms.     */
    if (openssl_obj_name->alias)
        return;

    py_name = PyUnicode_FromString(openssl_obj_name->name);
    if (py_name == NULL) {
        state->error = 1;
    } else {
        if (PySet_Add(state->set, py_name) != 0) {
            state->error = 1;
        }
        Py_DECREF(py_name);
    }
}


/* Ask OpenSSL for a list of supported ciphers, filling in a Python set. */
static PyObject*
generate_hash_name_list(void)
{
    _InternalNameMapperState state;
    state.set = PyFrozenSet_New(NULL);
    if (state.set == NULL)
        return NULL;
    state.error = 0;

    OBJ_NAME_do_all(OBJ_NAME_TYPE_MD_METH, &_openssl_hash_name_mapper, &state);

    if (state.error) {
        Py_DECREF(state.set);
        return NULL;
    }
    return state.set;
}

/* List of functions exported by this module */

static struct PyMethodDef EVP_functions[] = {
    EVP_NEW_METHODDEF
    PBKDF2_HMAC_METHODDEF
    _HASHLIB_SCRYPT_METHODDEF
    _HASHLIB_HMAC_DIGEST_METHODDEF
    _HASHLIB_OPENSSL_MD5_METHODDEF
    _HASHLIB_OPENSSL_SHA1_METHODDEF
    _HASHLIB_OPENSSL_SHA224_METHODDEF
    _HASHLIB_OPENSSL_SHA256_METHODDEF
    _HASHLIB_OPENSSL_SHA384_METHODDEF
    _HASHLIB_OPENSSL_SHA512_METHODDEF
    {NULL,      NULL}            /* Sentinel */
};


/* Initialize this module. */


static struct PyModuleDef _hashlibmodule = {
    PyModuleDef_HEAD_INIT,
    "_hashlib",
    NULL,
    -1,
    EVP_functions,
    NULL,
    NULL,
    NULL,
    NULL
};

PyMODINIT_FUNC
PyInit__hashlib(void)
{
    PyObject *m, *openssl_md_meth_names;

#ifndef OPENSSL_VERSION_1_1
    /* Load all digest algorithms and initialize cpuid */
    OPENSSL_add_all_algorithms_noconf();
    ERR_load_crypto_strings();
#endif

    /* TODO build EVP_functions openssl_* entries dynamically based
     * on what hashes are supported rather than listing many
     * but having some be unsupported.  Only init appropriate
     * constants. */

    Py_TYPE(&EVPtype) = &PyType_Type;
    if (PyType_Ready(&EVPtype) < 0)
        return NULL;

    m = PyModule_Create(&_hashlibmodule);
    if (m == NULL)
        return NULL;

    openssl_md_meth_names = generate_hash_name_list();
    if (openssl_md_meth_names == NULL) {
        Py_DECREF(m);
        return NULL;
    }
    if (PyModule_AddObject(m, "openssl_md_meth_names", openssl_md_meth_names)) {
        Py_DECREF(m);
        return NULL;
    }

    Py_INCREF((PyObject *)&EVPtype);
    PyModule_AddObject(m, "HASH", (PyObject *)&EVPtype);

    return m;
}