/*

 * cram.c -- CRAM-MD5 authentication (see RFC 2195)

 *

 * For license terms, see the file COPYING in this directory.

 */

#include  "config.h"

#include  <stdio.h>

#include  <string.h>

#include  <ctype.h>

#if defined(STDC_HEADERS)

#include  <stdlib.h>

#endif

#include  "fetchmail.h"

#include  "socket.h"

#include  "i18n.h"

#include "fm_md5.h"

void hmac_md5 (const unsigned char *password,  size_t pass_len,

               const unsigned char *challenge, size_t chal_len,

               unsigned char *response,  size_t resp_len)

{

    int i;

    unsigned char ipad[64];

    unsigned char opad[64];

    unsigned char hash_passwd[16];

    MD5_CTX ctx;

    if (resp_len != 16)

        return;

    if (pass_len > sizeof (ipad))

    {

        MD5Init (&ctx);

        MD5Update (&ctx, password, pass_len);

        MD5Final (hash_passwd, &ctx);

        password = hash_passwd; pass_len = sizeof (hash_passwd);

    }

    memset (ipad, 0, sizeof (ipad));

    memset (opad, 0, sizeof (opad));

    memcpy (ipad, password, pass_len);

    memcpy (opad, password, pass_len);

    for (i=0; i<64; i++) {

        ipad[i] ^= 0x36;

        opad[i] ^= 0x5c;

    }

    MD5Init (&ctx);

    MD5Update (&ctx, ipad, sizeof (ipad));

    MD5Update (&ctx, challenge, chal_len);

    MD5Final (response, &ctx);

    MD5Init (&ctx);

    MD5Update (&ctx, opad, sizeof (opad));

    MD5Update (&ctx, response, resp_len);

    MD5Final (response, &ctx);

}

int do_cram_md5 (int sock, const char *command, struct query *ctl, const char *strip)

/* authenticate as per RFC2195 */

{

    int result;

    int len;

    char buf1[1024];

    char msg_id[768];

    unsigned char response[16];

    char reply[1024];

    char *respdata;

    gen_send (sock, "%s CRAM-MD5", command);

    /* From RFC2195:

     * The data encoded in the first ready response contains an

     * presumptively arbitrary string of random digits, a timestamp, and the

     * fully-qualified primary host name of the server.  The syntax of the

     * unencoded form must correspond to that of an RFC 822 'msg-id'

     * [RFC822] as described in [POP3].

     */

    if ((result = gen_recv (sock, buf1, sizeof (buf1)))) {

	return result;

    }

    /* caller may specify a response prefix we should strip if present */

    respdata = buf1;

    if (strip && strncmp(buf1, strip, strlen(strip)) == 0)

	respdata += strlen(strip);

    len = from64tobits (msg_id, respdata, sizeof(msg_id));

    if (len < 0) {

	report (stderr, GT_("could not decode BASE64 challenge\n"));

	return PS_AUTHFAIL;

    } else if ((size_t)len < sizeof (msg_id)) {

        msg_id[len] = 0;

    } else {

        msg_id[sizeof (msg_id)-1] = 0;

    }

    if (outlevel >= O_DEBUG) {

        report (stdout, GT_("decoded as %s\n"), msg_id);

    }

    /* The client makes note of the data and then responds with a string

     * consisting of the user name, a space, and a 'digest'.  The latter is

     * computed by applying the keyed MD5 algorithm from [KEYED-MD5] where

     * the key is a shared secret and the digested text is the timestamp

     * (including angle-brackets).

     */

    hmac_md5((unsigned char *)ctl->password, strlen(ctl->password),

              (unsigned char *)msg_id, strlen (msg_id),

              response, sizeof (response));

    snprintf (reply, sizeof(reply),

              "%s %02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x", 

              ctl->remotename,

              response[0], response[1], response[2], response[3],

              response[4], response[5], response[6], response[7],

              response[8], response[9], response[10], response[11],

              response[12], response[13], response[14], response[15]);

    to64frombits (buf1, reply, strlen(reply));

    /* ship the authentication back, accept the server's responses */

    /* PMDF5.2 IMAP has a bug that requires this to be a single write */

    suppress_tags = TRUE;

    result = gen_transact(sock, "%s", buf1);

    suppress_tags = FALSE;

    if (result)

	return(result);

    else

	return(PS_SUCCESS);

}

/* cram.c ends here */