putty/cproxy.c

/*
 * Routines to do cryptographic interaction with proxies in PuTTY.
 * This is in a separate module from proxy.c, so that it can be
 * conveniently removed in PuTTYtel by replacing this module with
 * the stub version nocproxy.c.
 */

#include <assert.h>
#include <ctype.h>
#include <string.h>

#include "putty.h"
#include "ssh.h" /* For MD5 support */
#include "network.h"
#include "proxy.h"
#include "marshal.h"

static void hmacmd5_chap(const unsigned char *challenge, int challen,
                         const char *passwd, unsigned char *response)
{
    mac_simple(&ssh_hmac_md5, ptrlen_from_asciz(passwd),
               make_ptrlen(challenge, challen), response);
}

void proxy_socks5_offerencryptedauth(BinarySink *bs)
{
    put_byte(bs, 0x03);              /* CHAP */
}

int proxy_socks5_handlechap (ProxySocket *p)
{

    /* CHAP authentication reply format:
     *  version number (1 bytes) = 1
     *  number of commands (1 byte)
     *
     * For each command:
     *  command identifier (1 byte)
     *  data length (1 byte)
     */
    unsigned char data[260];
    unsigned char outbuf[20];

    while(p->chap_num_attributes == 0 ||
          p->chap_num_attributes_processed < p->chap_num_attributes) {
        if (p->chap_num_attributes == 0 ||
            p->chap_current_attribute == -1) {
            /* CHAP normally reads in two bytes, either at the
             * beginning or for each attribute/value pair.  But if
             * we're waiting for the value's data, we might not want
             * to read 2 bytes.
             */

            if (bufchain_size(&p->pending_input_data) < 2)
                return 1;              /* not got anything yet */

            /* get the response */
            bufchain_fetch(&p->pending_input_data, data, 2);
            bufchain_consume(&p->pending_input_data, 2);
        }

        if (p->chap_num_attributes == 0) {
            /* If there are no attributes, this is our first msg
             * with the server, where we negotiate version and
             * number of attributes
             */
            if (data[0] != 0x01) {
                plug_closing(p->plug, "Proxy error: SOCKS proxy wants"
                             " a different CHAP version",
                             PROXY_ERROR_GENERAL, 0);
                return 1;
            }
            if (data[1] == 0x00) {
                plug_closing(p->plug, "Proxy error: SOCKS proxy won't"
                             " negotiate CHAP with us",
                             PROXY_ERROR_GENERAL, 0);
                return 1;
            }
            p->chap_num_attributes = data[1];
        } else {
            if (p->chap_current_attribute == -1) {
                /* We have to read in each attribute/value pair -
                 * those we don't understand can be ignored, but
                 * there are a few we'll need to handle.
                 */
                p->chap_current_attribute = data[0];
                p->chap_current_datalen = data[1];
            }
            if (bufchain_size(&p->pending_input_data) <
                p->chap_current_datalen)
                return 1;              /* not got everything yet */

            /* get the response */
            bufchain_fetch(&p->pending_input_data, data,
                           p->chap_current_datalen);

            bufchain_consume(&p->pending_input_data,
                             p->chap_current_datalen);

            switch (p->chap_current_attribute) {
              case 0x00:
                /* Successful authentication */
                if (data[0] == 0x00)
                    p->state = 2;
                else {
                    plug_closing(p->plug, "Proxy error: SOCKS proxy"
                                 " refused CHAP authentication",
                                 PROXY_ERROR_GENERAL, 0);
                    return 1;
                }
              break;
              case 0x03:
                outbuf[0] = 0x01; /* Version */
                outbuf[1] = 0x01; /* One attribute */
                outbuf[2] = 0x04; /* Response */
                outbuf[3] = 0x10; /* Length */
                hmacmd5_chap(data, p->chap_current_datalen,
                             conf_get_str(p->conf, CONF_proxy_password),
                             &outbuf[4]);
                sk_write(p->sub_socket, outbuf, 20);
              break;
              case 0x11:
                /* Chose a protocol */
                if (data[0] != 0x85) {
                    plug_closing(p->plug, "Proxy error: Server chose "
                                 "CHAP of other than HMAC-MD5 but we "
                                 "didn't offer it!",
                                 PROXY_ERROR_GENERAL, 0);
                    return 1;
                }
              break;
            }
            p->chap_current_attribute = -1;
            p->chap_num_attributes_processed++;
        }
        if (p->state == 8 &&
            p->chap_num_attributes_processed >= p->chap_num_attributes) {
            p->chap_num_attributes = 0;
            p->chap_num_attributes_processed = 0;
            p->chap_current_datalen = 0;
        }
    }
    return 0;
}

int proxy_socks5_selectchap(ProxySocket *p)
{
    char *username = conf_get_str(p->conf, CONF_proxy_username);
    char *password = conf_get_str(p->conf, CONF_proxy_password);
    if (username[0] || password[0]) {
        char chapbuf[514];
        int ulen;
        chapbuf[0] = '\x01'; /* Version */
        chapbuf[1] = '\x02'; /* Number of attributes sent */
        chapbuf[2] = '\x11'; /* First attribute - algorithms list */
        chapbuf[3] = '\x01'; /* Only one CHAP algorithm */
        chapbuf[4] = '\x85'; /* ...and it's HMAC-MD5, the core one */
        chapbuf[5] = '\x02'; /* Second attribute - username */

        ulen = strlen(username);
        if (ulen > 255) ulen = 255;
        if (ulen < 1) ulen = 1;

        chapbuf[6] = ulen;
        memcpy(chapbuf+7, username, ulen);

        sk_write(p->sub_socket, chapbuf, ulen + 7);
        p->chap_num_attributes = 0;
        p->chap_num_attributes_processed = 0;
        p->chap_current_attribute = -1;
        p->chap_current_datalen = 0;

        p->state = 8;
    } else
        plug_closing(p->plug, "Proxy error: Server chose "
                     "CHAP authentication but we didn't offer it!",
                 PROXY_ERROR_GENERAL, 0);
    return 1;
}