SRP ciphersuites were moved to the gnutls (lgpl) library.

1 files changed, 782 insertions, 0 deletions

diff --git a/lib/auth_srp.c b/lib/auth_srp.c
new file mode 100644
index 0000000000..671ec20fa0
--- /dev/null
+++ b/lib/auth_srp.c
@@ -0,0 +1,782 @@
+/*
+ * Copyright (C) 2001,2002,2003 Nikos Mavroyanopoulos
+ * Copyright (C) 2004 Free Software Foundation
+ *
+ * This file is part of GNUTLS.
+ *
+ *  The GNUTLS library 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 library; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ */
+
+#include <gnutls_int.h>
+
+#ifdef ENABLE_SRP
+
+#include "gnutls_errors.h"
+#include "auth_srp_passwd.h"
+#include "gnutls_auth.h"
+#include "gnutls_auth_int.h"
+#include "gnutls_srp.h"
+#include "debug.h"
+#include "gnutls_num.h"
+#include "auth_srp.h"
+#include <gnutls_str.h>
+#include <gnutls_datum.h>
+#include <gnutls_alert.h>
+
+int _gnutls_gen_srp_server_kx(gnutls_session_t, opaque **);
+int _gnutls_gen_srp_client_kx(gnutls_session_t, opaque **);
+
+int _gnutls_proc_srp_server_kx(gnutls_session_t, opaque *, size_t);
+int _gnutls_proc_srp_client_kx(gnutls_session_t, opaque *, size_t);
+
+const mod_auth_st srp_auth_struct = {
+    "SRP",
+    NULL,
+    NULL,
+    _gnutls_gen_srp_server_kx,
+    _gnutls_gen_srp_client_kx,
+    NULL,
+    NULL,
+
+    NULL,
+    NULL,			/* certificate */
+    _gnutls_proc_srp_server_kx,
+    _gnutls_proc_srp_client_kx,
+    NULL,
+    NULL
+};
+
+
+#define _b session->key->b
+#define B session->key->B
+#define _a session->key->a
+#define A session->key->A
+#define N session->key->client_p
+#define G session->key->client_g
+#define V session->key->x
+#define S session->key->KEY
+
+/* Checks if b%n==0 which is a fatal srp error.
+ * Returns a proper error code in that case, and 0 when
+ * all are ok.
+ */
+inline static int check_b_mod_n(mpi_t b, mpi_t n)
+{
+    int ret;
+    mpi_t r = _gnutls_mpi_alloc_like(b);
+
+    if (r == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_mpi_mod(r, b, n);
+    ret = _gnutls_mpi_cmp_ui(r, 0);
+
+    _gnutls_mpi_release(&r);
+
+    if (ret == 0) {
+	gnutls_assert();
+	return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+    }
+
+    return 0;
+}
+
+/* Checks if a%n==0,+1,-1%n which is a fatal srp error.
+ * Returns a proper error code in that case, and 0 when
+ * all are ok.
+ */
+inline static int check_a_mod_n(mpi_t a, mpi_t n)
+{
+    int ret;
+    mpi_t r = _gnutls_mpi_alloc_like(a);
+
+    if (r == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_mpi_mod(r, a, n);
+    ret = _gnutls_mpi_cmp_ui(r, 0);
+
+    _gnutls_mpi_release(&r);
+
+    if (ret == 0) {
+	gnutls_assert();
+	return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+    }
+
+    return 0;
+}
+
+
+/* Send the first key exchange message ( g, n, s) and append the verifier algorithm number 
+ * Data is allocated by the caller, and should have data_size size.
+ */
+int _gnutls_gen_srp_server_kx(gnutls_session_t session, opaque ** data)
+{
+    int ret;
+    uint8 *data_n, *data_s;
+    uint8 *data_g;
+    char *username;
+    SRP_PWD_ENTRY *pwd_entry;
+    srp_server_auth_info_t info;
+    ssize_t data_size;
+    size_t n_b, tmp_size;
+    char buf[64];
+    uint8 *data_b;
+
+    if ((ret =
+	 _gnutls_auth_info_set(session, GNUTLS_CRD_SRP,
+			       sizeof(srp_server_auth_info_st), 1)) < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+    info = _gnutls_get_auth_info(session);
+    username = info->username;
+
+    _gnutls_str_cpy(username, MAX_SRP_USERNAME,
+		    session->security_parameters.extensions.srp_username);
+
+    ret = _gnutls_srp_pwd_read_entry(session, username, &pwd_entry);
+
+    if (ret < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+    /* copy from pwd_entry to local variables (actually in session) */
+    if (_gnutls_mpi_scan(&G, pwd_entry->g.data, &pwd_entry->g.size) < 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    tmp_size = pwd_entry->n.size;
+    if (_gnutls_mpi_scan(&N, pwd_entry->n.data, &tmp_size) < 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    tmp_size = pwd_entry->v.size;
+    if (_gnutls_mpi_scan(&V, pwd_entry->v.data, &tmp_size) < 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    /* Calculate:  B = (k*v + g^b) % N 
+     */
+    B = _gnutls_calc_srp_B(&_b, G, N, V);
+    if (B == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    if (_gnutls_mpi_print(NULL, &n_b, B) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_PRINT_FAILED;
+    }
+
+
+    /* Allocate size to hold the N, g, s, B 
+     */
+
+    data_size = (pwd_entry->n.size + 2 + pwd_entry->g.size + 2 +
+		 pwd_entry->salt.size + 1) + (n_b + 2);
+
+    (*data) = gnutls_malloc(data_size);
+    if ((*data) == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    /* copy N (mod n) 
+     */
+    data_n = *data;
+    _gnutls_write_datum16(data_n, pwd_entry->n);
+
+
+    /* copy G (generator) to data 
+     */
+    data_g = &data_n[2 + pwd_entry->n.size];
+    _gnutls_write_datum16(data_g, pwd_entry->g);
+
+
+    /* copy the salt 
+     */
+    data_s = &data_g[2 + pwd_entry->g.size];
+    _gnutls_write_datum8(data_s, pwd_entry->salt);
+
+
+    /* Copy the B value
+     */
+
+    data_b = &data_s[1 + pwd_entry->salt.size];
+    if (_gnutls_mpi_print(&data_b[2], &n_b, B) != 0)
+	return GNUTLS_E_MPI_PRINT_FAILED;
+    _gnutls_write_uint16(n_b, data_b);
+
+    _gnutls_hard_log("INT: SRP B[%d]: %s\n", n_b,
+		     _gnutls_bin2hex(&data_b[2], n_b, buf, sizeof(buf)));
+
+    _gnutls_srp_entry_free(pwd_entry);
+
+    return data_size;
+}
+
+/* return A = g^a % N */
+int _gnutls_gen_srp_client_kx(gnutls_session_t session, opaque ** data)
+{
+    size_t n_a;
+    int ret;
+    uint8 *data_a;
+    char *username, *password;
+    size_t n_size = 0;
+    char buf[64];
+    const gnutls_srp_client_credentials_t cred =
+	_gnutls_get_cred(session->key, GNUTLS_CRD_SRP, NULL);
+
+    if (cred == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
+    }
+
+    if (session->internals.srp_username == NULL) {
+	username = cred->username;
+	password = cred->password;
+    } else {
+	username = session->internals.srp_username;
+	password = session->internals.srp_password;
+    }
+
+    if (username == NULL || password == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
+    }
+
+    /* calc A = g^a % N 
+     */
+    if (G == NULL || N == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
+    }
+
+    /* get the size of n in bytes */
+    _gnutls_mpi_print( NULL, &n_size, N);
+    
+    A = _gnutls_calc_srp_A(&_a, G, N);
+    if (A == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    /* Rest of SRP calculations 
+     */
+
+    /* calculate u */
+    session->key->u = _gnutls_calc_srp_u(A, B, n_size);
+    if (session->key->u == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_dump_mpi("SRP U: ", session->key->u);
+
+    /* S = (B - g^x) ^ (a + u * x) % N */
+    S = _gnutls_calc_srp_S2(B, G, session->key->x, _a, session->key->u, N);
+    if (S == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_dump_mpi("SRP B: ", B);
+
+    _gnutls_mpi_release(&_b);
+    _gnutls_mpi_release(&V);
+    _gnutls_mpi_release(&session->key->u);
+    _gnutls_mpi_release(&B);
+
+    ret = _gnutls_generate_session_key(session->key);
+    _gnutls_mpi_release(&S);
+
+    if (ret < 0)
+	return ret;
+
+    if (_gnutls_mpi_print(NULL, &n_a, A) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_PRINT_FAILED;
+    }
+
+    (*data) = gnutls_malloc(n_a + 2);
+    if ((*data) == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    /* copy A */
+    data_a = (*data);
+    if (_gnutls_mpi_print(&data_a[2], &n_a, A) != 0) {
+	gnutls_free(*data);
+	return GNUTLS_E_MPI_PRINT_FAILED;
+    }
+    _gnutls_hard_log("INT: SRP A[%d]: %s\n", n_a,
+		     _gnutls_bin2hex(&data_a[2], n_a, buf, sizeof(buf)));
+
+    _gnutls_mpi_release(&A);
+
+    _gnutls_write_uint16(n_a, data_a);
+
+    return n_a + 2;
+}
+
+
+/* just read A and put it to session */
+int _gnutls_proc_srp_client_kx(gnutls_session_t session, opaque * data,
+			       size_t _data_size)
+{
+    size_t _n_A;
+    ssize_t data_size = _data_size;
+    int ret;
+    size_t n_size = 0;
+
+    DECR_LEN(data_size, 2);
+    _n_A = _gnutls_read_uint16(&data[0]);
+
+    DECR_LEN(data_size, _n_A);
+    if (_gnutls_mpi_scan(&A, &data[2], &_n_A) || A == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    _gnutls_dump_mpi("SRP A: ", A);
+    _gnutls_dump_mpi("SRP B: ", B);
+
+    /* Checks if A % n == 0.
+     */
+    if ((ret = check_a_mod_n(A, N)) < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+    /* Start the SRP calculations.
+     * - Calculate u 
+     */
+    /* get the size of n in bytes */
+    _gnutls_mpi_print( NULL, &n_size, N);
+
+    session->key->u = _gnutls_calc_srp_u(A, B, n_size);
+    if (session->key->u == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_dump_mpi("SRP U: ", session->key->u);
+
+    /* S = (A * v^u) ^ b % N 
+     */
+    S = _gnutls_calc_srp_S1(A, _b, session->key->u, V, N);
+    if (S == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    _gnutls_dump_mpi("SRP S: ", S);
+
+    _gnutls_mpi_release(&A);
+    _gnutls_mpi_release(&_b);
+    _gnutls_mpi_release(&V);
+    _gnutls_mpi_release(&session->key->u);
+    _gnutls_mpi_release(&B);
+
+    ret = _gnutls_generate_session_key(session->key);
+    _gnutls_mpi_release(&S);
+
+    if (ret < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+    return 0;
+}
+
+
+
+/* Static parameters according to draft-ietf-tls-srp-07
+ * Note that if more parameters are added check_g_n()
+ * and _gnutls_srp_entry_free() should be changed.
+ */
+static const unsigned char srp_params_1024[] = {
+    0xEE, 0xAF, 0x0A, 0xB9, 0xAD, 0xB3, 0x8D, 0xD6,
+    0x9C, 0x33, 0xF8, 0x0A, 0xFA, 0x8F, 0xC5, 0xE8,
+    0x60, 0x72, 0x61, 0x87, 0x75, 0xFF, 0x3C, 0x0B,
+    0x9E, 0xA2, 0x31, 0x4C, 0x9C, 0x25, 0x65, 0x76,
+    0xD6, 0x74, 0xDF, 0x74, 0x96, 0xEA, 0x81, 0xD3,
+    0x38, 0x3B, 0x48, 0x13, 0xD6, 0x92, 0xC6, 0xE0,
+    0xE0, 0xD5, 0xD8, 0xE2, 0x50, 0xB9, 0x8B, 0xE4,
+    0x8E, 0x49, 0x5C, 0x1D, 0x60, 0x89, 0xDA, 0xD1,
+    0x5D, 0xC7, 0xD7, 0xB4, 0x61, 0x54, 0xD6, 0xB6,
+    0xCE, 0x8E, 0xF4, 0xAD, 0x69, 0xB1, 0x5D, 0x49,
+    0x82, 0x55, 0x9B, 0x29, 0x7B, 0xCF, 0x18, 0x85,
+    0xC5, 0x29, 0xF5, 0x66, 0x66, 0x0E, 0x57, 0xEC,
+    0x68, 0xED, 0xBC, 0x3C, 0x05, 0x72, 0x6C, 0xC0,
+    0x2F, 0xD4, 0xCB, 0xF4, 0x97, 0x6E, 0xAA, 0x9A,
+    0xFD, 0x51, 0x38, 0xFE, 0x83, 0x76, 0x43, 0x5B,
+    0x9F, 0xC6, 0x1D, 0x2F, 0xC0, 0xEB, 0x06, 0xE3
+};
+
+static const unsigned char srp_generator = 0x02;
+
+const gnutls_datum_t gnutls_srp_1024_group_prime = {
+    (void *) srp_params_1024, sizeof(srp_params_1024)
+};
+const gnutls_datum_t gnutls_srp_1024_group_generator = {
+    (void *) &srp_generator, sizeof(srp_generator)
+};
+
+static const unsigned char srp_params_1536[] = {
+    0x9D, 0xEF, 0x3C, 0xAF, 0xB9, 0x39, 0x27, 0x7A, 0xB1,
+    0xF1, 0x2A, 0x86, 0x17, 0xA4, 0x7B, 0xBB, 0xDB, 0xA5,
+    0x1D, 0xF4, 0x99, 0xAC, 0x4C, 0x80, 0xBE, 0xEE, 0xA9,
+    0x61, 0x4B, 0x19, 0xCC, 0x4D, 0x5F, 0x4F, 0x5F, 0x55,
+    0x6E, 0x27, 0xCB, 0xDE, 0x51, 0xC6, 0xA9, 0x4B, 0xE4,
+    0x60, 0x7A, 0x29, 0x15, 0x58, 0x90, 0x3B, 0xA0, 0xD0,
+    0xF8, 0x43, 0x80, 0xB6, 0x55, 0xBB, 0x9A, 0x22, 0xE8,
+    0xDC, 0xDF, 0x02, 0x8A, 0x7C, 0xEC, 0x67, 0xF0, 0xD0,
+    0x81, 0x34, 0xB1, 0xC8, 0xB9, 0x79, 0x89, 0x14, 0x9B,
+    0x60, 0x9E, 0x0B, 0xE3, 0xBA, 0xB6, 0x3D, 0x47, 0x54,
+    0x83, 0x81, 0xDB, 0xC5, 0xB1, 0xFC, 0x76, 0x4E, 0x3F,
+    0x4B, 0x53, 0xDD, 0x9D, 0xA1, 0x15, 0x8B, 0xFD, 0x3E,
+    0x2B, 0x9C, 0x8C, 0xF5, 0x6E, 0xDF, 0x01, 0x95, 0x39,
+    0x34, 0x96, 0x27, 0xDB, 0x2F, 0xD5, 0x3D, 0x24, 0xB7,
+    0xC4, 0x86, 0x65, 0x77, 0x2E, 0x43, 0x7D, 0x6C, 0x7F,
+    0x8C, 0xE4, 0x42, 0x73, 0x4A, 0xF7, 0xCC, 0xB7, 0xAE,
+    0x83, 0x7C, 0x26, 0x4A, 0xE3, 0xA9, 0xBE, 0xB8, 0x7F,
+    0x8A, 0x2F, 0xE9, 0xB8, 0xB5, 0x29, 0x2E, 0x5A, 0x02,
+    0x1F, 0xFF, 0x5E, 0x91, 0x47, 0x9E, 0x8C, 0xE7, 0xA2,
+    0x8C, 0x24, 0x42, 0xC6, 0xF3, 0x15, 0x18, 0x0F, 0x93,
+    0x49, 0x9A, 0x23, 0x4D, 0xCF, 0x76, 0xE3, 0xFE, 0xD1,
+    0x35, 0xF9, 0xBB
+};
+
+const gnutls_datum_t gnutls_srp_1536_group_prime = {
+    (void *) srp_params_1536, sizeof(srp_params_1536)
+};
+const gnutls_datum_t gnutls_srp_1536_group_generator = {
+    (void *) &srp_generator, sizeof(srp_generator)
+};
+
+static const unsigned char srp_params_2048[] = {
+    0xAC, 0x6B, 0xDB, 0x41, 0x32, 0x4A, 0x9A, 0x9B, 0xF1,
+    0x66, 0xDE, 0x5E, 0x13, 0x89, 0x58, 0x2F, 0xAF, 0x72,
+    0xB6, 0x65, 0x19, 0x87, 0xEE, 0x07, 0xFC, 0x31, 0x92,
+    0x94, 0x3D, 0xB5, 0x60, 0x50, 0xA3, 0x73, 0x29, 0xCB,
+    0xB4, 0xA0, 0x99, 0xED, 0x81, 0x93, 0xE0, 0x75, 0x77,
+    0x67, 0xA1, 0x3D, 0xD5, 0x23, 0x12, 0xAB, 0x4B, 0x03,
+    0x31, 0x0D, 0xCD, 0x7F, 0x48, 0xA9, 0xDA, 0x04, 0xFD,
+    0x50, 0xE8, 0x08, 0x39, 0x69, 0xED, 0xB7, 0x67, 0xB0,
+    0xCF, 0x60, 0x95, 0x17, 0x9A, 0x16, 0x3A, 0xB3, 0x66,
+    0x1A, 0x05, 0xFB, 0xD5, 0xFA, 0xAA, 0xE8, 0x29, 0x18,
+    0xA9, 0x96, 0x2F, 0x0B, 0x93, 0xB8, 0x55, 0xF9, 0x79,
+    0x93, 0xEC, 0x97, 0x5E, 0xEA, 0xA8, 0x0D, 0x74, 0x0A,
+    0xDB, 0xF4, 0xFF, 0x74, 0x73, 0x59, 0xD0, 0x41, 0xD5,
+    0xC3, 0x3E, 0xA7, 0x1D, 0x28, 0x1E, 0x44, 0x6B, 0x14,
+    0x77, 0x3B, 0xCA, 0x97, 0xB4, 0x3A, 0x23, 0xFB, 0x80,
+    0x16, 0x76, 0xBD, 0x20, 0x7A, 0x43, 0x6C, 0x64, 0x81,
+    0xF1, 0xD2, 0xB9, 0x07, 0x87, 0x17, 0x46, 0x1A, 0x5B,
+    0x9D, 0x32, 0xE6, 0x88, 0xF8, 0x77, 0x48, 0x54, 0x45,
+    0x23, 0xB5, 0x24, 0xB0, 0xD5, 0x7D, 0x5E, 0xA7, 0x7A,
+    0x27, 0x75, 0xD2, 0xEC, 0xFA, 0x03, 0x2C, 0xFB, 0xDB,
+    0xF5, 0x2F, 0xB3, 0x78, 0x61, 0x60, 0x27, 0x90, 0x04,
+    0xE5, 0x7A, 0xE6, 0xAF, 0x87, 0x4E, 0x73, 0x03, 0xCE,
+    0x53, 0x29, 0x9C, 0xCC, 0x04, 0x1C, 0x7B, 0xC3, 0x08,
+    0xD8, 0x2A, 0x56, 0x98, 0xF3, 0xA8, 0xD0, 0xC3, 0x82,
+    0x71, 0xAE, 0x35, 0xF8, 0xE9, 0xDB, 0xFB, 0xB6, 0x94,
+    0xB5, 0xC8, 0x03, 0xD8, 0x9F, 0x7A, 0xE4, 0x35, 0xDE,
+    0x23, 0x6D, 0x52, 0x5F, 0x54, 0x75, 0x9B, 0x65, 0xE3,
+    0x72, 0xFC, 0xD6, 0x8E, 0xF2, 0x0F, 0xA7, 0x11, 0x1F,
+    0x9E, 0x4A, 0xFF, 0x73
+};
+
+const gnutls_datum_t gnutls_srp_2048_group_prime = {
+    (void *) srp_params_2048, sizeof(srp_params_2048)
+};
+const gnutls_datum_t gnutls_srp_2048_group_generator = {
+    (void *) &srp_generator, sizeof(srp_generator)
+};
+
+
+/* Check if G and N are parameters from the SRP draft.
+ */
+static int check_g_n(const opaque * g, size_t n_g,
+		     const opaque * n, size_t n_n)
+{
+
+    if (n_g != 1 || g[0] != srp_generator)
+	return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+
+    if (n_n == sizeof(srp_params_1024) &&
+	memcmp(srp_params_1024, n, n_n) == 0) {
+	return 0;
+    }
+
+    if (n_n == sizeof(srp_params_1536) &&
+	memcmp(srp_params_1536, n, n_n) == 0) {
+	return 0;
+    }
+
+    if (n_n == sizeof(srp_params_2048) &&
+	memcmp(srp_params_2048, n, n_n) == 0) {
+	return 0;
+    }
+
+    return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+}
+
+/* Check if N is a prime and G a generator of the
+ * group.
+ */
+static int group_check_g_n(mpi_t g, mpi_t n)
+{
+    mpi_t q = NULL, two = NULL, w = NULL;
+    int ret;
+
+    /* N must be of the form N=2q+1
+     * where q is also a prime.
+     */
+    if (_gnutls_prime_check(n, 0) != 0) {
+	_gnutls_dump_mpi("no prime N: ", n);
+	gnutls_assert();
+	return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+    }
+
+    two = _gnutls_mpi_new(4);
+    if (two == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_MEMORY_ERROR;
+    }
+
+    q = _gnutls_mpi_alloc_like(n);
+    if (q == NULL) {
+	gnutls_assert();
+	ret = GNUTLS_E_MEMORY_ERROR;
+	goto error;
+    }
+
+    /* q = n-1 
+     */
+    _gnutls_mpi_sub_ui(q, n, 1);
+
+    /* q = q/2, remember that q is divisible by 2 (prime - 1)
+     */
+    _gnutls_mpi_set_ui(two, 2);
+    _gnutls_mpi_div(q, NULL, q, two, 0);
+
+    if (_gnutls_prime_check(q, 0) != 0) {
+	/* N was not on the form N=2q+1, where q = prime
+	 */
+	_gnutls_dump_mpi("no prime Q: ", q);
+	gnutls_assert();
+	return GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+    }
+
+    /* We also check whether g is a generator,
+     */
+
+    /* check if g < q < N
+     */
+    if (_gnutls_mpi_cmp(g, q) >= 0) {
+	gnutls_assert();
+	ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+	goto error;
+    }
+
+    w = _gnutls_mpi_alloc_like(q);
+    if (w == NULL) {
+	gnutls_assert();
+	ret = GNUTLS_E_MEMORY_ERROR;
+	goto error;
+    }
+
+    /* check if g^q mod N == N-1
+     * w = g^q mod N
+     */
+    _gnutls_mpi_powm(w, g, q, n);
+
+    /* w++
+     */
+    _gnutls_mpi_add_ui(w, w, 1);
+
+    if (_gnutls_mpi_cmp(w, n) != 0) {
+	gnutls_assert();
+	ret = GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER;
+	goto error;
+    }
+
+    ret = 0;
+
+  error:
+    _gnutls_mpi_release(&q);
+    _gnutls_mpi_release(&two);
+    _gnutls_mpi_release(&w);
+
+    return ret;
+
+}
+
+/* receive the key exchange message ( n, g, s, B) 
+ */
+int _gnutls_proc_srp_server_kx(gnutls_session_t session, opaque * data,
+			       size_t _data_size)
+{
+    uint8 n_s;
+    uint16 n_g, n_n, n_b;
+    size_t _n_s, _n_g, _n_n, _n_b;
+    const uint8 *data_n;
+    const uint8 *data_g;
+    const uint8 *data_s;
+    const uint8 *data_b;
+    int i, ret;
+    opaque hd[SRP_MAX_HASH_SIZE];
+    char *username, *password;
+    ssize_t data_size = _data_size;
+
+    const gnutls_srp_client_credentials_t cred =
+	_gnutls_get_cred(session->key, GNUTLS_CRD_SRP, NULL);
+
+    if (cred == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
+    }
+
+    if (session->internals.srp_username == NULL) {
+	username = cred->username;
+	password = cred->password;
+    } else {
+	username = session->internals.srp_username;
+	password = session->internals.srp_password;
+    }
+
+    if (username == NULL || password == NULL) {
+	gnutls_assert();
+	return GNUTLS_E_INSUFFICIENT_CREDENTIALS;
+    }
+
+    i = 0;
+
+    /* Read N 
+     */
+    DECR_LEN(data_size, 2);
+    n_n = _gnutls_read_uint16(&data[i]);
+    i += 2;
+
+    DECR_LEN(data_size, n_n);
+    data_n = &data[i];
+    i += n_n;
+
+    /* Read G 
+     */
+    DECR_LEN(data_size, 2);
+    n_g = _gnutls_read_uint16(&data[i]);
+    i += 2;
+
+    DECR_LEN(data_size, n_g);
+    data_g = &data[i];
+    i += n_g;
+
+    /* Read salt 
+     */
+    DECR_LEN(data_size, 1);
+    n_s = data[i];
+    i += 1;
+
+    DECR_LEN(data_size, n_s);
+    data_s = &data[i];
+    i += n_s;
+
+    /* Read B 
+     */
+    DECR_LEN(data_size, 2);
+    n_b = _gnutls_read_uint16(&data[i]);
+    i += 2;
+
+    DECR_LEN(data_size, n_b);
+    data_b = &data[i];
+    i += n_b;
+
+    _n_s = n_s;
+    _n_g = n_g;
+    _n_n = n_n;
+    _n_b = n_b;
+
+    if (_gnutls_mpi_scan(&N, data_n, &_n_n) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    if (_gnutls_mpi_scan(&G, data_g, &_n_g) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+    if (_gnutls_mpi_scan(&B, data_b, &_n_b) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+
+    /* Check if the g and n are from the SRP
+     * draft. Otherwise check if N is a prime and G
+     * a generator.
+     */
+    if ((ret = check_g_n(data_g, _n_g, data_n, _n_n)) < 0) {
+	_gnutls_x509_log("Checking the SRP group parameters.\n");
+	if ((ret = group_check_g_n(G, N)) < 0) {
+	    gnutls_assert();
+	    return ret;
+	}
+    }
+
+    /* Checks if b % n == 0
+     */
+    if ((ret = check_b_mod_n(B, N)) < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+
+    /* generate x = SHA(s | SHA(U | ":" | p))
+     * (or the equivalent using bcrypt)
+     */
+    if ((ret =
+	 _gnutls_calc_srp_x(username, password, (opaque *) data_s, n_s,
+			    &_n_g, hd)) < 0) {
+	gnutls_assert();
+	return ret;
+    }
+
+    if (_gnutls_mpi_scan(&session->key->x, hd, &_n_g) != 0) {
+	gnutls_assert();
+	return GNUTLS_E_MPI_SCAN_FAILED;
+    }
+
+
+    return i;			/* return the processed data
+				 * needed in auth_srp_rsa.
+				 */
+}
+
+#endif				/* ENABLE_SRP */