Adding upstream version 3.7.9.upstream/3.7.9upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 852 insertions, 0 deletions

diff --git a/lib/srp.c b/lib/srp.c
new file mode 100644
index 0000000..78bcbfd
--- /dev/null
+++ b/lib/srp.c
@@ -0,0 +1,852 @@
+/*
+ * Copyright (C) 2001-2016 Free Software Foundation, Inc.
+ * Copyright (C) 2015-2016 Red Hat, Inc.
+ *
+ * Author: Nikos Mavrogiannopoulos
+ *
+ * This file is part of GnuTLS.
+ *
+ * The GnuTLS is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>
+ *
+ */
+
+#include "gnutls_int.h"
+#include "errors.h"
+#include <auth/srp_kx.h>
+#include <state.h>
+
+#ifdef ENABLE_SRP
+
+#include "srp.h"
+#include <auth/srp_passwd.h>
+#include <mpi.h>
+#include <num.h>
+#include <file.h>
+#include <algorithms.h>
+#include <random.h>
+
+#include "debug.h"
+
+
+/* Here functions for SRP (like g^x mod n) are defined 
+ */
+
+static int
+_gnutls_srp_gx(uint8_t * text, size_t textsize, uint8_t ** result,
+	       bigint_t g, bigint_t prime)
+{
+	bigint_t x, e = NULL;
+	size_t result_size;
+	int ret;
+
+	if (_gnutls_mpi_init_scan_nz(&x, text, textsize)) {
+		gnutls_assert();
+		return GNUTLS_E_MPI_SCAN_FAILED;
+	}
+
+	ret = _gnutls_mpi_init(&e);
+	if (ret < 0)
+		goto cleanup;
+
+	/* e = g^x mod prime (n) */
+	ret = _gnutls_mpi_powm(e, g, x, prime);
+	if (ret < 0)
+		goto cleanup;
+
+	ret = _gnutls_mpi_print(e, NULL, &result_size);
+	if (ret == GNUTLS_E_SHORT_MEMORY_BUFFER) {
+		*result = gnutls_malloc(result_size);
+		if ((*result) == NULL) {
+			ret = GNUTLS_E_MEMORY_ERROR;
+			goto cleanup;
+		}
+
+		ret = _gnutls_mpi_print(e, *result, &result_size);
+		if (ret < 0)
+			goto cleanup;
+
+		ret = result_size;
+	} else {
+		gnutls_assert();
+		ret = GNUTLS_E_MPI_PRINT_FAILED;
+	}
+
+cleanup:
+	_gnutls_mpi_release(&e);
+	_gnutls_mpi_release(&x);
+
+	return ret;
+
+}
+
+
+/****************
+ * Choose a random value b and calculate B = (k* v + g^b) % N.
+ * where k == SHA1(N|g)
+ * Return: B and if ret_b is not NULL b.
+ */
+bigint_t
+_gnutls_calc_srp_B(bigint_t * ret_b, bigint_t g, bigint_t n, bigint_t v)
+{
+	bigint_t tmpB = NULL, tmpV = NULL;
+	bigint_t b = NULL, B = NULL, k = NULL;
+	int ret;
+
+	/* calculate:  B = (k*v + g^b) % N 
+	 */
+	ret = _gnutls_mpi_init_multi(&tmpV, &tmpB, &B, &b, NULL);
+	if (ret < 0)
+		return NULL;
+
+	_gnutls_mpi_random_modp(b, n, GNUTLS_RND_RANDOM);
+
+	k = _gnutls_calc_srp_u(n, g, n);
+	if (k == NULL) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = _gnutls_mpi_mulm(tmpV, k, v, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = _gnutls_mpi_powm(tmpB, g, b, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = _gnutls_mpi_addm(B, tmpV, tmpB, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	_gnutls_mpi_release(&k);
+	_gnutls_mpi_release(&tmpB);
+	_gnutls_mpi_release(&tmpV);
+
+	if (ret_b)
+		*ret_b = b;
+	else
+		_gnutls_mpi_release(&b);
+
+	return B;
+
+      error:
+	_gnutls_mpi_release(&b);
+	_gnutls_mpi_release(&B);
+	_gnutls_mpi_release(&k);
+	_gnutls_mpi_release(&tmpB);
+	_gnutls_mpi_release(&tmpV);
+	return NULL;
+
+}
+
+/* This calculates the SHA1(A | B)
+ * A and B will be left-padded with zeros to fill n_size.
+ */
+bigint_t _gnutls_calc_srp_u(bigint_t A, bigint_t B, bigint_t n)
+{
+	size_t b_size, a_size;
+	uint8_t *holder, hd[MAX_HASH_SIZE];
+	size_t holder_size, hash_size, n_size;
+	int ret;
+	bigint_t res;
+
+	/* get the size of n in bytes */
+	_gnutls_mpi_print(n, NULL, &n_size);
+
+	_gnutls_mpi_print(A, NULL, &a_size);
+	_gnutls_mpi_print(B, NULL, &b_size);
+
+	if (a_size > n_size || b_size > n_size) {
+		gnutls_assert();
+		return NULL;	/* internal error */
+	}
+
+	holder_size = n_size + n_size;
+
+	holder = gnutls_calloc(1, holder_size);
+	if (holder == NULL)
+		return NULL;
+
+	_gnutls_mpi_print(A, &holder[n_size - a_size], &a_size);
+	_gnutls_mpi_print(B, &holder[n_size + n_size - b_size], &b_size);
+
+	ret = _gnutls_hash_fast(GNUTLS_DIG_SHA1, holder, holder_size, hd);
+	if (ret < 0) {
+		gnutls_free(holder);
+		gnutls_assert();
+		return NULL;
+	}
+
+	/* convert the bytes of hd to integer
+	 */
+	hash_size = 20;		/* SHA */
+	ret = _gnutls_mpi_init_scan_nz(&res, hd, hash_size);
+	gnutls_free(holder);
+
+	if (ret < 0) {
+		gnutls_assert();
+		return NULL;
+	}
+
+	return res;
+}
+
+/* S = (A * v^u) ^ b % N 
+ * this is our shared key (server premaster secret)
+ */
+bigint_t
+_gnutls_calc_srp_S1(bigint_t A, bigint_t b, bigint_t u, bigint_t v,
+		    bigint_t n)
+{
+	bigint_t tmp1 = NULL, tmp2 = NULL;
+	bigint_t S = NULL;
+	int ret;
+
+	ret = _gnutls_mpi_init_multi(&S, &tmp1, &tmp2, NULL);
+	if (ret < 0)
+		return NULL;
+
+	ret = _gnutls_mpi_powm(tmp1, v, u, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = _gnutls_mpi_mulm(tmp2, A, tmp1, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	_gnutls_mpi_powm(S, tmp2, b, n);
+
+	_gnutls_mpi_release(&tmp1);
+	_gnutls_mpi_release(&tmp2);
+
+	return S;
+
+error:
+	_gnutls_mpi_release(&S);
+	_gnutls_mpi_release(&tmp1);
+	_gnutls_mpi_release(&tmp2);
+	return NULL;
+}
+
+/* A = g^a % N 
+ * returns A and a (which is random)
+ */
+bigint_t _gnutls_calc_srp_A(bigint_t * a, bigint_t g, bigint_t n)
+{
+	bigint_t tmpa;
+	bigint_t A;
+	int ret;
+
+	ret = _gnutls_mpi_init_multi(&A, &tmpa, NULL);
+	if (ret < 0) {
+		gnutls_assert();
+		return NULL;
+	}
+
+	_gnutls_mpi_random_modp(tmpa, n, GNUTLS_RND_RANDOM);
+
+	ret = _gnutls_mpi_powm(A, g, tmpa, n);
+	if (ret < 0)
+		goto error;
+
+	if (a != NULL)
+		*a = tmpa;
+	else
+		_gnutls_mpi_release(&tmpa);
+
+	return A;
+error:
+	_gnutls_mpi_release(&tmpa);
+	_gnutls_mpi_release(&A);
+	return NULL;
+}
+
+/* generate x = SHA(s | SHA(U | ":" | p))
+ * The output is exactly 20 bytes
+ */
+static int
+_gnutls_calc_srp_sha(const char *username, const char *_password,
+		     uint8_t * salt, int salt_size, size_t * size,
+		     void *digest, unsigned allow_invalid_pass)
+{
+	digest_hd_st td;
+	uint8_t res[MAX_HASH_SIZE];
+	int ret;
+	const mac_entry_st *me = mac_to_entry(GNUTLS_MAC_SHA1);
+	char *password;
+	gnutls_datum_t pout;
+
+	*size = 20;
+
+	ret = _gnutls_utf8_password_normalize(_password, strlen(_password), &pout, allow_invalid_pass);
+	if (ret < 0)
+		return gnutls_assert_val(ret);
+	password = (char*)pout.data;
+
+	ret = _gnutls_hash_init(&td, me);
+	if (ret < 0) {
+		ret = GNUTLS_E_MEMORY_ERROR;
+		goto cleanup;
+	}
+	_gnutls_hash(&td, username, strlen(username));
+	_gnutls_hash(&td, ":", 1);
+	_gnutls_hash(&td, password, strlen(password));
+
+	_gnutls_hash_deinit(&td, res);
+
+	ret = _gnutls_hash_init(&td, me);
+	if (ret < 0) {
+		ret = GNUTLS_E_MEMORY_ERROR;
+		goto cleanup;
+	}
+
+	_gnutls_hash(&td, salt, salt_size);
+	_gnutls_hash(&td, res, 20);	/* 20 bytes is the output of sha1 */
+
+	_gnutls_hash_deinit(&td, digest);
+	ret = 0;
+
+ cleanup:
+	gnutls_free(password);
+	return ret;
+}
+
+int
+_gnutls_calc_srp_x(char *username, char *password, uint8_t * salt,
+		   size_t salt_size, size_t * size, void *digest)
+{
+
+	return _gnutls_calc_srp_sha(username, password, salt,
+				    salt_size, size, digest, 1);
+}
+
+
+/* S = (B - k*g^x) ^ (a + u * x) % N
+ * this is our shared key (client premaster secret)
+ */
+bigint_t
+_gnutls_calc_srp_S2(bigint_t B, bigint_t g, bigint_t x, bigint_t a,
+		    bigint_t u, bigint_t n)
+{
+	bigint_t S = NULL, tmp1 = NULL, tmp2 = NULL;
+	bigint_t tmp4 = NULL, tmp3 = NULL, k = NULL;
+	int ret;
+
+	ret = _gnutls_mpi_init_multi(&S, &tmp1, &tmp2, &tmp3, &tmp4, NULL);
+	if (ret < 0)
+		return NULL;
+
+	k = _gnutls_calc_srp_u(n, g, n);
+	if (k == NULL) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_powm(tmp1, g, x, n);	/* g^x */
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_mulm(tmp3, tmp1, k, n);	/* k*g^x mod n */
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_subm(tmp2, B, tmp3, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_mul(tmp1, u, x);
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_add(tmp4, a, tmp1);
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	ret = _gnutls_mpi_powm(S, tmp2, tmp4, n);
+	if (ret < 0) {
+		gnutls_assert();
+		goto freeall;
+	}
+
+	_gnutls_mpi_release(&tmp1);
+	_gnutls_mpi_release(&tmp2);
+	_gnutls_mpi_release(&tmp3);
+	_gnutls_mpi_release(&tmp4);
+	_gnutls_mpi_release(&k);
+
+	return S;
+
+      freeall:
+	_gnutls_mpi_release(&k);
+	_gnutls_mpi_release(&tmp1);
+	_gnutls_mpi_release(&tmp2);
+	_gnutls_mpi_release(&tmp3);
+	_gnutls_mpi_release(&tmp4);
+	_gnutls_mpi_release(&S);
+	return NULL;
+}
+
+/**
+ * gnutls_srp_free_client_credentials:
+ * @sc: is a #gnutls_srp_client_credentials_t type.
+ *
+ * Free a gnutls_srp_client_credentials_t structure.
+ **/
+void gnutls_srp_free_client_credentials(gnutls_srp_client_credentials_t sc)
+{
+	gnutls_free(sc->username);
+	gnutls_free(sc->password);
+	gnutls_free(sc);
+}
+
+/**
+ * gnutls_srp_allocate_client_credentials:
+ * @sc: is a pointer to a #gnutls_srp_server_credentials_t type.
+ *
+ * Allocate a gnutls_srp_client_credentials_t structure.
+ *
+ * Returns: On success, %GNUTLS_E_SUCCESS (0) is returned, or an
+ *   error code.
+ **/
+int
+gnutls_srp_allocate_client_credentials(gnutls_srp_client_credentials_t *
+				       sc)
+{
+	*sc = gnutls_calloc(1, sizeof(srp_client_credentials_st));
+
+	if (*sc == NULL)
+		return GNUTLS_E_MEMORY_ERROR;
+
+	return 0;
+}
+
+/**
+ * gnutls_srp_set_client_credentials:
+ * @res: is a #gnutls_srp_client_credentials_t type.
+ * @username: is the user's userid
+ * @password: is the user's password
+ *
+ * This function sets the username and password, in a
+ * #gnutls_srp_client_credentials_t type.  Those will be used in
+ * SRP authentication.  @username should be an ASCII string or UTF-8
+ * string. In case of a UTF-8 string it is recommended to be following
+ * the PRECIS framework for usernames (rfc8265). The password can
+ * be in ASCII format, or normalized using gnutls_utf8_password_normalize().
+
+ * Returns: On success, %GNUTLS_E_SUCCESS (0) is returned, or an
+ *   error code.
+ **/
+int
+gnutls_srp_set_client_credentials(gnutls_srp_client_credentials_t res,
+				  const char *username,
+				  const char *password)
+{
+
+	if (username == NULL || password == NULL) {
+		gnutls_assert();
+		return GNUTLS_E_INVALID_REQUEST;
+	}
+
+	res->username = gnutls_strdup(username);
+	if (res->username == NULL)
+		return GNUTLS_E_MEMORY_ERROR;
+
+	res->password = gnutls_strdup(password);
+	if (res->password == NULL) {
+		gnutls_free(res->username);
+		return GNUTLS_E_MEMORY_ERROR;
+	}
+
+	return 0;
+}
+
+/**
+ * gnutls_srp_free_server_credentials:
+ * @sc: is a #gnutls_srp_server_credentials_t type.
+ *
+ * Free a gnutls_srp_server_credentials_t structure.
+ **/
+void gnutls_srp_free_server_credentials(gnutls_srp_server_credentials_t sc)
+{
+	gnutls_free(sc->password_file);
+	gnutls_free(sc->password_conf_file);
+
+	gnutls_free(sc);
+}
+
+/* Size of the default (random) seed if
+ * gnutls_srp_set_server_fake_salt_seed() is not called to set
+ * a seed.
+ */
+#define DEFAULT_FAKE_SALT_SEED_SIZE 20
+
+/* Size of the fake salts generated if
+ * gnutls_srp_set_server_fake_salt_seed() is not called to set
+ * another size.
+ */
+#define DEFAULT_FAKE_SALT_SIZE 16
+
+/**
+ * gnutls_srp_allocate_server_credentials:
+ * @sc: is a pointer to a #gnutls_srp_server_credentials_t type.
+ *
+ * Allocate a gnutls_srp_server_credentials_t structure.
+ *
+ * Returns: On success, %GNUTLS_E_SUCCESS (0) is returned, or an
+ *   error code.
+ **/
+int
+gnutls_srp_allocate_server_credentials(gnutls_srp_server_credentials_t *
+				       sc)
+{
+	int ret;
+	*sc = gnutls_calloc(1, sizeof(srp_server_cred_st));
+
+	if (*sc == NULL)
+		return GNUTLS_E_MEMORY_ERROR;
+
+	(*sc)->fake_salt_seed_size = DEFAULT_FAKE_SALT_SEED_SIZE;
+	ret = gnutls_rnd(GNUTLS_RND_RANDOM, (*sc)->fake_salt_seed,
+			 DEFAULT_FAKE_SALT_SEED_SIZE);
+
+	if (ret < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+
+	(*sc)->fake_salt_length = DEFAULT_FAKE_SALT_SIZE;
+	return 0;
+
+cleanup:
+	gnutls_free(*sc);
+	return ret;
+}
+
+/**
+ * gnutls_srp_set_server_credentials_file:
+ * @res: is a #gnutls_srp_server_credentials_t type.
+ * @password_file: is the SRP password file (tpasswd)
+ * @password_conf_file: is the SRP password conf file (tpasswd.conf)
+ *
+ * This function sets the password files, in a
+ * #gnutls_srp_server_credentials_t type.  Those password files
+ * hold usernames and verifiers and will be used for SRP
+ * authentication.
+ *
+ * Returns: On success, %GNUTLS_E_SUCCESS (0) is returned, or an
+ *   error code.
+ **/
+int
+gnutls_srp_set_server_credentials_file(gnutls_srp_server_credentials_t res,
+				       const char *password_file,
+				       const char *password_conf_file)
+{
+
+	if (password_file == NULL || password_conf_file == NULL) {
+		gnutls_assert();
+		return GNUTLS_E_INVALID_REQUEST;
+	}
+
+	/* Check if the files can be opened */
+	if (_gnutls_file_exists(password_file) != 0) {
+		gnutls_assert();
+		return GNUTLS_E_FILE_ERROR;
+	}
+
+	if (_gnutls_file_exists(password_conf_file) != 0) {
+		gnutls_assert();
+		return GNUTLS_E_FILE_ERROR;
+	}
+
+	res->password_file = gnutls_strdup(password_file);
+	if (res->password_file == NULL) {
+		gnutls_assert();
+		return GNUTLS_E_MEMORY_ERROR;
+	}
+
+	res->password_conf_file = gnutls_strdup(password_conf_file);
+	if (res->password_conf_file == NULL) {
+		gnutls_assert();
+		gnutls_free(res->password_file);
+		return GNUTLS_E_MEMORY_ERROR;
+	}
+
+	return 0;
+}
+
+
+/**
+ * gnutls_srp_set_server_credentials_function:
+ * @cred: is a #gnutls_srp_server_credentials_t type.
+ * @func: is the callback function
+ *
+ * This function can be used to set a callback to retrieve the user's
+ * SRP credentials.  The callback's function form is:
+ *
+ * int (*callback)(gnutls_session_t, const char* username,
+ *  gnutls_datum_t *salt, gnutls_datum_t *verifier, gnutls_datum_t *generator,
+ *  gnutls_datum_t *prime);
+ *
+ * @username contains the actual username.
+ * The @salt, @verifier, @generator and @prime must be filled
+ * in using the gnutls_malloc(). For convenience @prime and @generator
+ * may also be one of the static parameters defined in gnutls.h.
+ *
+ * Initially, the data field is NULL in every #gnutls_datum_t
+ * structure that the callback has to fill in. When the
+ * callback is done GnuTLS deallocates all of those buffers
+ * which are non-NULL, regardless of the return value.
+ *
+ * In order to prevent attackers from guessing valid usernames,
+ * if a user does not exist, g and n values should be filled in
+ * using a random user's parameters. In that case the callback must
+ * return the special value (1).
+ * See #gnutls_srp_set_server_fake_salt_seed too.
+ * If this is not required for your application, return a negative
+ * number from the callback to abort the handshake.
+ *
+ * The callback function will only be called once per handshake.
+ * The callback function should return 0 on success, while
+ * -1 indicates an error.
+ **/
+void
+gnutls_srp_set_server_credentials_function(gnutls_srp_server_credentials_t
+					   cred,
+					   gnutls_srp_server_credentials_function
+					   *func)
+{
+	cred->pwd_callback = func;
+}
+
+/**
+ * gnutls_srp_set_client_credentials_function:
+ * @cred: is a #gnutls_srp_server_credentials_t type.
+ * @func: is the callback function
+ *
+ * This function can be used to set a callback to retrieve the
+ * username and password for client SRP authentication.  The
+ * callback's function form is:
+ *
+ * int (*callback)(gnutls_session_t, char** username, char**password);
+ *
+ * The @username and @password must be allocated using
+ * gnutls_malloc().
+ *
+ * The @username should be an ASCII string or UTF-8
+ * string. In case of a UTF-8 string it is recommended to be following
+ * the PRECIS framework for usernames (rfc8265). The password can
+ * be in ASCII format, or normalized using gnutls_utf8_password_normalize().
+ *
+ * The callback function will be called once per handshake before the
+ * initial hello message is sent.
+ *
+ * The callback should not return a negative error code the second
+ * time called, since the handshake procedure will be aborted.
+ *
+ * The callback function should return 0 on success.
+ * -1 indicates an error.
+ **/
+void
+gnutls_srp_set_client_credentials_function(gnutls_srp_client_credentials_t
+					   cred,
+					   gnutls_srp_client_credentials_function
+					   * func)
+{
+	cred->get_function = func;
+}
+
+
+/**
+ * gnutls_srp_server_get_username:
+ * @session: is a gnutls session
+ *
+ * This function will return the username of the peer.  This should
+ * only be called in case of SRP authentication and in case of a
+ * server.  Returns NULL in case of an error.
+ *
+ * Returns: SRP username of the peer, or NULL in case of error.
+ **/
+const char *gnutls_srp_server_get_username(gnutls_session_t session)
+{
+	srp_server_auth_info_t info;
+
+	CHECK_AUTH_TYPE(GNUTLS_CRD_SRP, NULL);
+
+	info = _gnutls_get_auth_info(session, GNUTLS_CRD_SRP);
+	if (info == NULL)
+		return NULL;
+	return info->username;
+}
+
+/**
+ * gnutls_srp_verifier:
+ * @username: is the user's name
+ * @password: is the user's password
+ * @salt: should be some randomly generated bytes
+ * @generator: is the generator of the group
+ * @prime: is the group's prime
+ * @res: where the verifier will be stored.
+ *
+ * This function will create an SRP verifier, as specified in
+ * RFC2945.  The @prime and @generator should be one of the static
+ * parameters defined in gnutls/gnutls.h or may be generated.
+ *
+ * The verifier will be allocated with @gnutls_malloc() and will be stored in
+ * @res using binary format.
+ *
+ * Returns: On success, %GNUTLS_E_SUCCESS (0) is returned, or an
+ *   error code.
+ **/
+int
+gnutls_srp_verifier(const char *username, const char *password,
+		    const gnutls_datum_t * salt,
+		    const gnutls_datum_t * generator,
+		    const gnutls_datum_t * prime, gnutls_datum_t * res)
+{
+	bigint_t _n, _g;
+	int ret;
+	size_t digest_size = 20, size;
+	uint8_t digest[20];
+
+	ret = _gnutls_calc_srp_sha(username, password, salt->data,
+				   salt->size, &digest_size, digest, 0);
+	if (ret < 0) {
+		gnutls_assert();
+		return ret;
+	}
+
+	size = prime->size;
+	if (_gnutls_mpi_init_scan_nz(&_n, prime->data, size)) {
+		gnutls_assert();
+		return GNUTLS_E_MPI_SCAN_FAILED;
+	}
+
+	size = generator->size;
+	if (_gnutls_mpi_init_scan_nz(&_g, generator->data, size)) {
+		gnutls_assert();
+		_gnutls_mpi_release(&_n);
+		return GNUTLS_E_MPI_SCAN_FAILED;
+	}
+
+	ret = _gnutls_srp_gx(digest, 20, &res->data, _g, _n);
+	if (ret < 0) {
+		gnutls_assert();
+		_gnutls_mpi_release(&_n);
+		_gnutls_mpi_release(&_g);
+		return ret;
+	}
+	res->size = ret;
+
+	_gnutls_mpi_release(&_n);
+	_gnutls_mpi_release(&_g);
+
+	return 0;
+}
+
+/**
+ * gnutls_srp_set_prime_bits:
+ * @session: is a #gnutls_session_t type.
+ * @bits: is the number of bits
+ *
+ * This function sets the minimum accepted number of bits, for use in
+ * an SRP key exchange.  If zero, the default 2048 bits will be used.
+ *
+ * In the client side it sets the minimum accepted number of bits.  If
+ * a server sends a prime with less bits than that
+ * %GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER will be returned by the
+ * handshake.
+ *
+ * This function has no effect in server side.
+ *
+ * Since: 2.6.0
+ **/
+void gnutls_srp_set_prime_bits(gnutls_session_t session, unsigned int bits)
+{
+	session->internals.dh_prime_bits = bits;
+}
+
+/**
+ * gnutls_srp_set_server_fake_salt_seed:
+ * @cred: is a #gnutls_srp_server_credentials_t type
+ * @seed: is the seed data, only needs to be valid until the function
+ * returns; size of the seed must be greater than zero
+ * @salt_length: is the length of the generated fake salts
+ *
+ * This function sets the seed that is used to generate salts for
+ * invalid (non-existent) usernames.
+ *
+ * In order to prevent attackers from guessing valid usernames,
+ * when a user does not exist gnutls generates a salt and a verifier
+ * and proceeds with the protocol as usual.
+ * The authentication will ultimately fail, but the client cannot tell
+ * whether the username is valid (exists) or invalid.
+ *
+ * If an attacker learns the seed, given a salt (which is part of the
+ * handshake) which was generated when the seed was in use, it can tell
+ * whether or not the authentication failed because of an unknown username.
+ * This seed cannot be used to reveal application data or passwords.
+ *
+ * @salt_length should represent the salt length your application uses.
+ * Generating fake salts longer than 20 bytes is not supported.
+ *
+ * By default the seed is a random value, different each time a
+ * #gnutls_srp_server_credentials_t is allocated and fake salts are
+ * 16 bytes long.
+ *
+ * Since: 3.3.0
+ **/
+void
+gnutls_srp_set_server_fake_salt_seed(gnutls_srp_server_credentials_t cred,
+				     const gnutls_datum_t * seed,
+				     unsigned int salt_length)
+{
+	unsigned seed_size = seed->size;
+	const unsigned char *seed_data = seed->data;
+
+	if (seed_size > sizeof(cred->fake_salt_seed))
+		seed_size = sizeof(cred->fake_salt_seed);
+
+	memcpy(cred->fake_salt_seed, seed_data, seed_size);
+	cred->fake_salt_seed_size = seed_size;
+
+	/* Cap the salt length at the output size of the MAC algorithm
+	 * we are using to generate the fake salts.
+	 */
+	const mac_entry_st * me = mac_to_entry(SRP_FAKE_SALT_MAC);
+	const size_t mac_len = me->output_size;
+
+	cred->fake_salt_length = (salt_length < mac_len ? salt_length : mac_len);
+}
+
+#endif				/* ENABLE_SRP */