/* tls.c - STARTTLS helper functions for imapd
 * Tim Martin
 * 9/21/99
 *
 * Based upon Lutz Jaenicke's TLS patches for postfix
 *
 * Copyright (c) 1994-2008 Carnegie Mellon University.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Carnegie Mellon University
 *      Center for Technology Transfer and Enterprise Creation
 *      4615 Forbes Avenue
 *      Suite 302
 *      Pittsburgh, PA  15213
 *      (412) 268-7393, fax: (412) 268-7395
 *      innovation@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
* NAME
*       tls
* SUMMARY
*       interface to openssl routines
* SYNOPSIS
*       #include <tls.h>
*
* DESCRIPTION
*       This module is the interface between Cyrus Imapd and the OpenSSL library.
*       As of now only one filedescriptor can be handled, so only one
*       TLS channel can be open at a time.
*
*       tls_init_serverengine() is called once when the server is started
*       in order to initialize as much of the TLS stuff as possible.
*       The certificate handling is also decided during the setup phase,
*       so that a peer specific handling is not possible.
*
*       tls_start_servertls() activates the TLS feature for the
*       filedescriptor selected with tls_setfd() before. We expect
*       that all buffers are flushed and the TLS handshake can begin
*       immediately.
*
*       tls_stop_servertls() sends the "close notify" alert via
*       SSL_shutdown() to the peer and resets all connection specific
*       TLS data. As RFC2487 does not specify a separate shutdown, it
*       is supposed that the underlying TCP connection is shut down
*       immediately afterwards, so we don't care about additional data
*       coming through the channel.
*
*       Once the TLS connection is initiated, information about the TLS
*       state is available:
*       tls_protocol holds the protocol name (SSLv2, SSLv3, TLSv1),
*       tls_cipher_name the cipher name (e.g. RC4/MD5),
*       tls_cipher_usebits the number of bits actually used (e.g. 40),
*       tls_cipher_algbits the number of bits the algorithm is based on
*       (e.g. 128).
*       The last two values may be different when talking to a crippled
*       - ahem - export controled peer (e.g. 40/128).
*
* xxx we need to offer a callback to do peer issuer certification.
*     data that should be available for inspection:
*       If the peer offered a certifcate _and_ the certificate could be
*       verified successfully, part of the certificate data are available as:
*       tls_peer_subject X509v3-oneline with the DN of the peer
*       pfixlts_peer_CN extracted CommonName of the peer
*       tls_peer_issuer  X509v3-oneline with the DN of the issuer
*       pfixlts_peer_CN extracted CommonName of the issuer
*       tls_peer_fingerprint fingerprint of the certificate
*
*/

#include <config.h>

#ifdef HAVE_SSL

/* System library. */

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>

/* OpenSSL library. */

#include <openssl/lhash.h>
#include <openssl/bn.h>
#include <openssl/err.h>
#include <openssl/pem.h>
#include <openssl/x509.h>
#include <openssl/ssl.h>

/* Application-specific. */
#include "assert.h"
#include "nonblock.h"
#include "util.h"
#include "xmalloc.h"
#include "tls.h"
#include "tls_th-lock.h"

/* Session caching/reuse stuff */
#include "global.h"
#include "cyrusdb.h"

#define DB (config_tls_sessions_db) /* sessions are binary -> MUST use DB3 */

static struct db *sessdb = NULL;
static int sess_dbopen = 0;

enum {
    var_imapd_tls_loglevel = 0,
    var_proxy_tls_loglevel = 0,
    CCERT_BUFSIZ = 256
};

static int verify_depth = 5;
static int verify_error = X509_V_OK;

static SSL_CTX *s_ctx = NULL, *c_ctx = NULL;

static int tls_serverengine = 0; /* server engine initialized? */
static int tls_clientengine = 0; /* client engine initialized? */
static int do_dump = 0;         /* actively dumping protocol? */

#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
static DH *dh_params = NULL;
#endif


EXPORTED int tls_enabled(void)
{
    const char *val;

    val = config_getstring(IMAPOPT_TLS_SERVER_CERT);
    if (!val || !strcasecmp(val, "disabled")) return 0;

    val = config_getstring(IMAPOPT_TLS_SERVER_KEY);
    if (!val || !strcasecmp(val, "disabled")) return 0;

    if (config_getswitch(IMAPOPT_CHATTY))
            syslog(LOG_INFO, "TLS is available.");

    return 1;
}

/* taken from OpenSSL apps/s_cb.c
 * tim - this seems to just be giving logging messages
 */

static void apps_ssl_info_callback(const SSL * s, int where, int ret)
{
    char   *str;
    int     w;

    if (var_imapd_tls_loglevel==0) return;

    w = where & ~SSL_ST_MASK;

    if (w & SSL_ST_CONNECT)
        str = "SSL_connect";
    else if (w & SSL_ST_ACCEPT)
        str = "SSL_accept";
    else
        str = "undefined";

    if (where & SSL_CB_LOOP) {
        if (tls_serverengine && (var_imapd_tls_loglevel >= 2))
            syslog(LOG_DEBUG, "%s:%s", str, SSL_state_string_long(s));
    } else if (where & SSL_CB_ALERT) {
        str = (where & SSL_CB_READ) ? "read" : "write";
        if ((tls_serverengine && (var_imapd_tls_loglevel >= 2)) ||
            ((ret & 0xff) != SSL3_AD_CLOSE_NOTIFY))
            syslog(LOG_DEBUG, "SSL3 alert %s:%s:%s", str,
                   SSL_alert_type_string_long(ret),
                   SSL_alert_desc_string_long(ret));
    } else if (where & SSL_CB_EXIT) {
        if (ret == 0)
            syslog(LOG_DEBUG, "%s:failed in %s",
                   str, SSL_state_string_long(s));
        else if (ret < 0) {
            syslog(LOG_DEBUG, "%s:error in %s",
                   str, SSL_state_string_long(s));
        }
    }
}

#if OPENSSL_VERSION_NUMBER < 0x10100000L
/* taken from OpenSSL apps/s_cb.c
   not thread safe! */
static RSA *tmp_rsa_cb(SSL * s __attribute__((unused)),
                       int export __attribute__((unused)),
                       int keylength)
{
    static RSA *rsa_tmp = NULL;

    if (rsa_tmp == NULL) {
        rsa_tmp = RSA_generate_key(keylength, RSA_F4, NULL, NULL);
    }
    return (rsa_tmp);
}
#endif

#if OPENSSL_VERSION_NUMBER < 0x10100000L || (defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER < 0x20700000L)
/* replacements for new 1.1 API accessors */
/* XXX probably put these somewhere central */
static int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g)
{
    if (p == NULL || g == NULL) return 0;
    dh->p = p;
    dh->q = q; /* optional */
    dh->g = g;
    return 1;
}
#endif

#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
/* Logic copied from OpenSSL apps/s_server.c: give the TLS context
 * DH params to work with DHE-* cipher suites. Hardcoded fallback
 * in case no DH params in server_key or server_cert.
 * Modified quite a bit for openssl 1.1.0 compatibility.
 * XXX we might be able to just replace this with DH_get_1024_160?
 * XXX the apps/s_server.c example doesn't use this anymore at all.
 */
static DH *get_dh1024(void)
{
    /* Second Oakley group 1024-bits MODP group from RFC2409 */
    DH *dh;
    BIGNUM *p = NULL, *g = NULL;

    dh = DH_new();
    if (!dh) return NULL;

    p = get_rfc2409_prime_1024(NULL);
    BN_dec2bn(&g, "2");

    if (DH_set0_pqg(dh, p, NULL, g))
        return dh;

    if (g) BN_free(g);
    if (p) BN_free(p);
    DH_free(dh);

    return NULL;
}

static DH *load_dh_param(const char *keyfile, const char *certfile)
{
    DH *ret=NULL;
    BIO *bio = NULL;

    if (keyfile) bio = BIO_new_file(keyfile, "r");

    if ((bio == NULL) && certfile) bio = BIO_new_file(certfile,"r");

    if (bio) ret=PEM_read_bio_DHparams(bio,NULL,NULL,NULL);

    if (ret == NULL) {
        ret = get_dh1024();
        syslog(LOG_NOTICE, "inittls: Loading hard-coded DH parameters");
    } else {
        syslog(LOG_NOTICE, "inittls: Loading DH parameters from file");
    }

    if (bio != NULL) BIO_free(bio);

    return(ret);
}
#endif /* OPENSSL_VERSION_NUMBER >= 0x009080fL */

/* taken from OpenSSL apps/s_cb.c */

static int verify_callback(int ok, X509_STORE_CTX * ctx)
{
    char    buf[256];
    X509   *err_cert;
    int     err;
    int     depth;

    syslog(LOG_DEBUG, "Doing a peer verify");

    err_cert = X509_STORE_CTX_get_current_cert(ctx);
    err = X509_STORE_CTX_get_error(ctx);
    depth = X509_STORE_CTX_get_error_depth(ctx);

    X509_NAME_oneline(X509_get_subject_name(err_cert), buf, sizeof(buf));
    if (ok==0)
    {
      syslog(LOG_ERR, "verify error:num=%d:%s", err,
             X509_verify_cert_error_string(err));

        if (verify_depth >= depth) {
            ok = 0;
            verify_error = X509_V_OK;
        } else {
            ok = 0;
            verify_error = X509_V_ERR_CERT_CHAIN_TOO_LONG;
        }
    }
    switch (err) {
    case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
        X509_NAME_oneline(X509_get_issuer_name(err_cert), buf, sizeof(buf));
        syslog(LOG_NOTICE, "issuer= %s", buf);
        break;
    case X509_V_ERR_CERT_NOT_YET_VALID:
    case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
        syslog(LOG_NOTICE, "cert not yet valid");
        break;
    case X509_V_ERR_CERT_HAS_EXPIRED:
    case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
        syslog(LOG_NOTICE, "cert has expired");
        break;
    }

    return (ok);
}


#if (OPENSSL_VERSION_NUMBER >= 0x0090806fL)
static int servername_callback(SSL *ssl, int *ad __attribute__((unused)),
                               void *arg __attribute__((unused)))
{
    const char *servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);

    if (servername) {
        syslog(LOG_DEBUG, "TLS Server Name Indication (SNI) Extension: \"%s\"",
               servername);
    }

    return SSL_TLSEXT_ERR_OK;
}
#endif


/*
 * taken from OpenSSL crypto/bio/b_dump.c, modified to save a lot of strcpy
 * and strcat by Matti Aarnio.
 */

#define TRUNCATE
#define DUMP_WIDTH      16

static int tls_dump(const char *s, int len)
{
    int     ret = 0;
    char    buf[160 + 1];
    char    *ss;
    int     i;
    int     j;
    int     rows;
    int     trunc;
    unsigned char ch;

    trunc = 0;

#ifdef TRUNCATE
    for (; (len > 0) && ((s[len - 1] == ' ') || (s[len - 1] == '\0')); len--)
        trunc++;
#endif

    rows = (len / DUMP_WIDTH);
    if ((rows * DUMP_WIDTH) < len)
        rows++;

    for (i = 0; i < rows; i++) {
        unsigned int val;
        buf[0] = '\0';                          /* start with empty string */
        ss = buf;

        val = i * DUMP_WIDTH;
        assert(val <= 0xFFFF);
        sprintf(ss, "%04x ", i * DUMP_WIDTH);
        ss += strlen(ss);

        for (j = 0; j < DUMP_WIDTH; j++) {
            if (((i * DUMP_WIDTH) + j) >= len) {
                strcpy(ss, "   ");
            } else {
                ch = ((unsigned char) *((char *) (s) + i * DUMP_WIDTH + j))
                    & 0xFF;

                sprintf(ss, "%02x%c", ch, j == 7 ? '|' : ' ');
                ss += 3;
            }
        }
        ss += strlen(ss);
        *ss+= ' ';
        for (j = 0; j < DUMP_WIDTH; j++) {
            if (((i * DUMP_WIDTH) + j) >= len)
                break;
            ch = ((unsigned char) *((char *) (s) + i * DUMP_WIDTH + j)) & 0xff;
            *ss+= (((ch >= ' ') && (ch <= '~')) ? ch : '.');
            if (j == 7) *ss+= ' ';
        }
        *ss = 0;
        /*
         * if this is the last call then update the ddt_dump thing so that
         * we will move the selection point in the debug window
         */
        if (var_imapd_tls_loglevel>0)
          syslog(LOG_DEBUG, "%s", buf);
        ret += strlen(buf);
    }
#ifdef TRUNCATE
    if (trunc > 0) {
        snprintf(buf, sizeof(buf), "%04x - <SPACES/NULS>\n", len+ trunc);
        if (var_imapd_tls_loglevel>0)
          syslog(LOG_DEBUG, "%s", buf);
        ret += strlen(buf);
    }
#endif
    return (ret);
}

 /*
  * Set up the cert things on the server side. We do need both the
  * private key (in key_file) and the cert (in cert_file).
  * Both files may be identical.
  *
  * This function is taken from OpenSSL apps/s_cb.c
  */

static int set_cert_stuff(SSL_CTX * ctx,
                          const char *cert_file, const char *key_file)
{
    if (cert_file != NULL) {
        /* SSL_CTX_use_certificate_chain_file() requires an empty error stack.
         * To make sure there is no error from previous op, we clear it here...
         */
        ERR_clear_error();
        if (SSL_CTX_use_certificate_chain_file(ctx, cert_file) <= 0) {
            syslog(LOG_ERR, "unable to get certificate from '%s'", cert_file);
            return (0);
        }
        if (key_file == NULL)
            key_file = cert_file;
        if (SSL_CTX_use_PrivateKey_file(ctx, key_file,
                                        SSL_FILETYPE_PEM) <= 0) {
            syslog(LOG_ERR, "unable to get private key from '%s'", key_file);
            return (0);
        }
        /* Now we know that a key and cert have been set against
         * the SSL context */
        if (!SSL_CTX_check_private_key(ctx)) {
            syslog(
                    LOG_ERR,
                    "Private key '%s' does not match public key '%s'",
                    cert_file,
                    key_file
                );

            return (0);
        }
    }
    return (1);
}

/*
 * The new_session_cb() is called, whenever a new session has been
 * negotiated and session caching is enabled.  We save the session in
 * a database so that we can share sessions between processes.
 */
static int new_session_cb(SSL *ssl __attribute__((unused)),
                          SSL_SESSION *sess)
{
    int len;
    unsigned char *data = NULL;
    time_t expire;
    int ret = -1;
    unsigned char *asn;
    const unsigned char *session_id = NULL;
    unsigned int session_id_length = 0;

    assert(sess);

    if (!sess_dbopen) return 0;

    /* find the size of the ASN1 representation of the session */
    len = i2d_SSL_SESSION(sess, NULL);

    /*
     * create the data buffer.  the data is stored as:
     * <expire time><ASN1 data>
     */
    data = (unsigned char *) xmalloc(sizeof(time_t)+len*sizeof(unsigned char));

    /* transform the session into its ASN1 representation */
    asn = data + sizeof(time_t);
    len = i2d_SSL_SESSION(sess, &asn);
    if (!len) syslog(LOG_ERR, "i2d_SSL_SESSION failed");

    /* set the expire time for the external cache, and prepend it to data */
    expire = SSL_SESSION_get_time(sess) + SSL_SESSION_get_timeout(sess);
    memcpy(data, &expire, sizeof(time_t));

    if (len) {
        /* store the session in our database */

        session_id = SSL_SESSION_get_id(sess, &session_id_length);
        if (session_id_length) {
            do {
                ret = cyrusdb_store(sessdb, (const char *) session_id,
                                session_id_length,
                                (const char *) data, len + sizeof(time_t), NULL);
            } while (ret == CYRUSDB_AGAIN);
        }
    }

    free(data);

    /* log this transaction */
    if (var_imapd_tls_loglevel > 0) {
        unsigned int i;
        char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];
        for (i = 0; i < session_id_length; i++) {
            sprintf(idstr+i*2, "%02X", session_id[i]);
        }
        syslog(LOG_DEBUG, "new TLS session: id=%s, expire=%s, status=%s",
               idstr, ctime(&expire), ret ? "failed" : "ok");
    }

    return (ret == 0);
}

/*
 * Function for removing a session from our database.
 */
static void remove_session(const unsigned char *id, int idlen)
{
    int ret;

    assert(id);
    assert(idlen <= SSL_MAX_SSL_SESSION_ID_LENGTH);

    if (!idlen) return;
    if (!sess_dbopen) return;

    do {
        ret = cyrusdb_delete(sessdb, (const char *) id, idlen, NULL, 1);
    } while (ret == CYRUSDB_AGAIN);

    /* log this transaction */
    if (var_imapd_tls_loglevel > 0) {
        char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];

        bin_to_hex(id, idlen, idstr, BH_UPPER);
        syslog(LOG_DEBUG, "remove TLS session: id=%s", idstr);
    }
}

/*
 * The remove_session_cb() is called, whenever the SSL engine removes
 * a session from the internal cache. This happens if the session is
 * removed because it is expired or when a connection was not shutdown
 * cleanly.
 */
static void remove_session_cb(SSL_CTX *ctx __attribute__((unused)),
                              SSL_SESSION *sess)
{
    const unsigned char *session_id = NULL;
    unsigned int session_id_length = 0;

    assert(sess);

    session_id = SSL_SESSION_get_id(sess, &session_id_length);

    remove_session(session_id, session_id_length);
}

/*
 * The get_session_cb() is only called on SSL/TLS servers with the
 * session id proposed by the client. The get_session_cb() is always
 * called, also when session caching was disabled.  We lookup the
 * session in our database in case it was stored by another process.
 */
#if OPENSSL_VERSION_NUMBER >= 0x10100000L
static SSL_SESSION *get_session_cb(SSL *ssl __attribute__((unused)),
                                   const unsigned char *id, int idlen, int *copy)
#else
static SSL_SESSION *get_session_cb(SSL *ssl __attribute__((unused)),
                                   unsigned char *id, int idlen, int *copy)
#endif
{
    int ret;
    const char *data = NULL;
    size_t len = 0;
    time_t expire = 0, now = time(0);
    SSL_SESSION *sess = NULL;

    assert(id);
    assert(idlen <= SSL_MAX_SSL_SESSION_ID_LENGTH);

    if (!sess_dbopen) return NULL;

    do {
        ret = cyrusdb_fetch(sessdb, (const char *) id, idlen, &data, &len, NULL);
    } while (ret == CYRUSDB_AGAIN);

    if (!ret && data) {
        assert(len >= (int) sizeof(time_t));

        /* grab the expire time */
        memcpy(&expire, data, sizeof(time_t));

        /* check if the session has expired */
        if (expire < now) {
            remove_session(id, idlen);
        }
        else {
            /* transform the ASN1 representation of the session
               into an SSL_SESSION object */
            const unsigned char *asn = (unsigned char *) data + sizeof(time_t);
            sess = d2i_SSL_SESSION(NULL, &asn, len - sizeof(time_t));
            if (!sess) syslog(LOG_ERR, "d2i_SSL_SESSION failed: %m");
        }
    }

    /* log this transaction */
    if (var_imapd_tls_loglevel > 0) {
        int i;
        char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];
        for (i = 0; i < idlen; i++)
            sprintf(idstr+i*2, "%02X", id[i]);

        syslog(LOG_DEBUG, "get TLS session: id=%s, expire=%s, status=%s",
               idstr, ctime(&expire),
               !data ? "not found" : expire < now ? "expired" : "ok");
    }

    *copy = 0;
    return sess;
}

/*
 * Seed the random number generator.
 */
static int tls_rand_init(void)
{
#ifdef EGD_SOCKET
    return (RAND_egd(EGD_SOCKET));
#else
    /* otherwise let OpenSSL do it internally */
    return 0;
#endif
}

 /*
  * This is the setup routine for the SSL server. As smtpd might be called
  * more than once, we only want to do the initialization one time.
  *
  * The skeleton of this function is taken from OpenSSL apps/s_server.c.

  * returns -1 on error
  */

/* must be called after cyrus_init */
// I am the server
EXPORTED int     tls_init_serverengine(const char *ident,
                              int verifydepth,
                              int askcert,
                              SSL_CTX **ret)
{
    int     off = 0;
    int     verify_flags = SSL_VERIFY_NONE;
    const char   *cipher_list;
    const char   *client_ca_dir;
    const char   *client_ca_file;
    const char   *server_ca_file;
    const char   *server_cert_file;
    const char   *server_key_file;
    enum enum_value tls_client_certs;
    int server_cipher_order;
    int timeout;

    if (ret) *ret = s_ctx;

    /* Whether or not to use any client certificate CA context to
     * verify client SSL certificates with.
     *
     * This is initially switched off by a value of "off" for the
     * tls_client_certs setting, or should no client_ca_dir nor
     * client_ca_file be specified. */
    int use_client_certs = 1;

    if (tls_serverengine)
        return (0);                             /* already running */

    if (var_imapd_tls_loglevel >= 2)
        syslog(LOG_DEBUG, "starting TLS server engine");

    SSL_library_init();
    SSL_load_error_strings();
    if (tls_rand_init() == -1) {
        syslog(LOG_ERR,"TLS server engine: cannot seed PRNG");
        return -1;
    }

#if (OPENSSL_VERSION_NUMBER >= 0x10100000L)
    s_ctx = SSL_CTX_new(TLS_server_method());
#else
    s_ctx = SSL_CTX_new(SSLv23_server_method());
#endif

    if (s_ctx == NULL) {
        return (-1);
    };

    off |= SSL_OP_ALL;            /* Work around all known bugs */
    off |= SSL_OP_NO_SSLv2;       /* Disable insecure SSLv2 */
    off |= SSL_OP_NO_SSLv3;       /* Disable insecure SSLv3 */
    off |= SSL_OP_NO_COMPRESSION; /* Disable TLS compression */

    const char *tls_versions = config_getstring(IMAPOPT_TLS_VERSIONS);

    if (strstr(tls_versions, "tls1_2") == NULL) {
#if (OPENSSL_VERSION_NUMBER >= 0x1000105fL)
        //syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.2");
        off |= SSL_OP_NO_TLSv1_2;
#else
        syslog(LOG_ERR, "ERROR: TLSv1.2 configured, OpenSSL < 1.0.1e insufficient");
#endif // (OPENSSL_VERSION_NUMBER >= 0x1000105fL)
    }

    if (strstr(tls_versions, "tls1_1") == NULL) {
#if (OPENSSL_VERSION_NUMBER >= 0x1000000fL)
        //syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.1");
        off |= SSL_OP_NO_TLSv1_1;
#else
        syslog(LOG_ERR, "ERROR: TLSv1.1 configured, OpenSSL < 1.0.0 insufficient");
#endif // (OPENSSL_VERSION_NUMBER >= 0x1000000fL)
    }

    if (strstr(tls_versions, "tls1_0") == NULL) {
        //syslog(LOG_DEBUG, "TLS server engine: Disabled TLSv1.0");
        off |= SSL_OP_NO_TLSv1;
    }

    server_cipher_order = config_getswitch(IMAPOPT_TLS_PREFER_SERVER_CIPHERS);
    if (server_cipher_order)
        off |= SSL_OP_CIPHER_SERVER_PREFERENCE;

    SSL_CTX_set_options(s_ctx, off);
    SSL_CTX_set_info_callback(s_ctx, apps_ssl_info_callback);

    cipher_list = config_getstring(IMAPOPT_TLS_CIPHERS);
    if (!SSL_CTX_set_cipher_list(s_ctx, cipher_list)) {
        syslog(
                LOG_ERR,
                "TLS server engine: cannot load cipher list '%s'",
                cipher_list
            );

        return (-1);
    }

    tls_client_certs = config_getenum(IMAPOPT_TLS_CLIENT_CERTS);

    if (tls_client_certs != IMAP_ENUM_TLS_CLIENT_CERTS_OFF) {
        // The use of client certificates for authentication is
        // optional or required.
        client_ca_dir  = config_getstring(IMAPOPT_TLS_CLIENT_CA_DIR);
        client_ca_file = config_getstring(IMAPOPT_TLS_CLIENT_CA_FILE);

            if (config_debug) {
                    syslog(
                        LOG_DEBUG, "tls_client_ca_dir=%s tls_client_ca_file=%s",
                        IS_NULL(client_ca_dir), IS_NULL(client_ca_file)
                    );
            }

        if (client_ca_dir || client_ca_file) {
            // Attempt to load client_ca_dir and/or client_ca_file
            if ((!SSL_CTX_load_verify_locations(s_ctx, client_ca_file, client_ca_dir)) ||
                (!SSL_CTX_set_default_verify_paths(s_ctx))) {

                // Just a warning since this is only necessary for client auth.
                syslog(
                        LOG_WARNING,
                        "TLS server engine: Failed loading client CA data, cert auth disabled."
                    );

                use_client_certs = 0;
            }
        } else { // (client_ca_dir || client_ca_file)
            // We have no CA to verify client certificates against.
            syslog(LOG_DEBUG, "TLS server engine: No client CA data configured.");

            // This is fatal should client certificates be required.
            if (tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE) {
                return (-1);
            }

            use_client_certs = 0;
        }

    } else { // (tls_client_certs != IMAP_ENUM_TLS_CLIENT_CERTS_OFF)
        // The use of client certificates is turned off.
        use_client_certs = 0;
    }

    server_ca_file = config_getstring(IMAPOPT_TLS_SERVER_CA_FILE);
    server_cert_file = config_getstring(IMAPOPT_TLS_SERVER_CERT);
    server_key_file = config_getstring(IMAPOPT_TLS_SERVER_KEY);

    if (config_debug) {
            syslog(
                LOG_DEBUG, "tls_server_cert=%s tls_server_key=%s",
                IS_NULL(server_cert_file), IS_NULL(server_key_file)
            );
    }

    /* Only consider adding additional CA certificates -used to verify certificates
     * issued to clients, which may have been issued by an intermediate CA and
     * not the CA that issued our server certificate- when indeed we are using
     * SSL/TLS on this server.
     */
    if (server_ca_file && !strcasecmp(server_cert_file, "disabled")) {
        SSL_CTX_set_mode(s_ctx,SSL_CTX_get_mode(s_ctx) | SSL_MODE_NO_AUTO_CHAIN);
        BIO *filebio = BIO_new_file(server_ca_file, "r");

        if (filebio) {
            X509 *cacert;

            syslog(
                    LOG_DEBUG,
                    "TLS server engine: loading additional client CA information from file %s",
                    server_ca_file
                );

            while ((cacert = PEM_read_bio_X509(filebio,NULL,NULL,NULL)) != NULL) {
                char buf[256];
                X509_NAME_oneline(X509_get_subject_name(cacert), buf, sizeof(buf));

                if (!SSL_CTX_add_extra_chain_cert(s_ctx, cacert)) {
                    syslog(
                            LOG_ERR,
                            "TLS server engine: failed to add client_ca_cert to chain: %s",
                            buf
                        );

                    X509_free(cacert);
                } else {
                    syslog(LOG_DEBUG, "TLS server engine: added CA cert to chain: %s", buf);
                }
            }

            BIO_free(filebio);
        } else {
            syslog(
                    LOG_ERR,
                    "TLS server engine: Cannot load additional client CA information from file %s",
                    server_ca_file
                );

            return (-1);
        }
    }

    if (!set_cert_stuff(s_ctx, server_cert_file, server_key_file)) {
        syslog(LOG_ERR, "TLS server engine: cannot load cert/key data, may be a cert/key mismatch?");
        return (-1);
    }

#if OPENSSL_VERSION_NUMBER < 0x10100000L
    SSL_CTX_set_tmp_rsa_callback(s_ctx, tmp_rsa_cb);
#endif

#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
    /* Load DH params for DHE-* key exchanges */
    dh_params = load_dh_param(server_key_file, server_cert_file);
    SSL_CTX_set_tmp_dh(s_ctx, dh_params);
#endif

#if (OPENSSL_VERSION_NUMBER >= 0x1000103fL)
    const char *ec = config_getstring(IMAPOPT_TLS_ECCURVE);
    int openssl_nid = OBJ_sn2nid(ec);
    if (openssl_nid != 0) {
        EC_KEY *ecdh;
        ecdh = EC_KEY_new_by_curve_name(openssl_nid);
        if (ecdh != NULL) {
            SSL_CTX_set_tmp_ecdh(s_ctx, ecdh);
            EC_KEY_free(ecdh);
        }
    }
#endif

    verify_depth = verifydepth;

    if (!use_client_certs) {
        if ((tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE) && askcert)
            syslog(LOG_ERR, "TLS server engine: No client cert CA specified.");

    } else {
        STACK_OF(X509_NAME) *CAnames = SSL_load_client_CA_file(client_ca_file);

        if (!CAnames || sk_X509_NAME_num(CAnames) < 1) {
            syslog(
                    LOG_ERR,
                    "TLS server engine: No client CA certs specified. Client side certs may not work"
                );

        } else {
            if (askcert || tls_client_certs)
                verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE;

            if (tls_client_certs == IMAP_ENUM_TLS_CLIENT_CERTS_REQUIRE)
                verify_flags |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;

            SSL_CTX_set_client_CA_list(s_ctx, CAnames);

            syslog(
                    LOG_DEBUG,
                    "Set client CA list: Client cert %srequested, %srequired",
                    verify_flags & SSL_VERIFY_PEER ? "" : "not ",
                    verify_flags & SSL_VERIFY_FAIL_IF_NO_PEER_CERT ? "":"not "
                );
        }
    }

    SSL_CTX_set_verify(s_ctx, verify_flags, verify_callback);

#if (OPENSSL_VERSION_NUMBER >= 0x0090806fL)
    SSL_CTX_set_tlsext_servername_callback(s_ctx, servername_callback);
#endif

    /* Don't use an internal session cache */
    SSL_CTX_sess_set_cache_size(s_ctx, 1);  /* 0 is unlimited, so use 1 */
    SSL_CTX_set_session_cache_mode(s_ctx, SSL_SESS_CACHE_SERVER |
                                   SSL_SESS_CACHE_NO_AUTO_CLEAR |
                                   SSL_SESS_CACHE_NO_INTERNAL_LOOKUP);

    /* Get the session timeout from the config file (in minutes) */
    timeout = config_getint(IMAPOPT_TLS_SESSION_TIMEOUT);
    if (timeout < 0) timeout = 0;
    if (timeout > 1440) timeout = 1440; /* 24 hours max */

    /* A timeout of zero disables session caching */
    if (timeout) {
        const char *fname = NULL;
        char *tofree = NULL;
        int r;

        /* Set the context for session reuse -- use the service ident */
        SSL_CTX_set_session_id_context(s_ctx, (void*) ident, strlen(ident));

        /* Set the timeout for the internal/external cache (in seconds) */
        SSL_CTX_set_timeout(s_ctx, timeout*60);

        /* Set the callback functions for the external session cache */
        SSL_CTX_sess_set_new_cb(s_ctx, new_session_cb);
        SSL_CTX_sess_set_remove_cb(s_ctx, remove_session_cb);
        SSL_CTX_sess_set_get_cb(s_ctx, get_session_cb);

        fname = config_getstring(IMAPOPT_TLS_SESSIONS_DB_PATH);

        /* create the name of the db file */
        if (!fname) {
            tofree = strconcat(config_dir, FNAME_TLSSESSIONS, (char *)NULL);
            fname = tofree;
        }

        r = cyrusdb_open(DB, fname, CYRUSDB_CREATE, &sessdb);
        if (r != 0) {
            syslog(LOG_ERR, "DBERROR: opening %s: %s",
                   fname, cyrusdb_strerror(ret));
        }
        else
            sess_dbopen = 1;

        free(tofree);
    }

    tls_serverengine = 1;
    if (ret) *ret = s_ctx;

    return (0);
}


/* taken from OpenSSL apps/s_cb.c */

static long bio_dump_cb(BIO * bio, int cmd, const char *argp, int argi,
                        long argl __attribute__((unused)), long ret)
{
    if (!do_dump)
        return (ret);

    if (cmd == (BIO_CB_READ | BIO_CB_RETURN)) {
        printf("read from %08lX [%08lX] (%d bytes => %ld (0x%lX))",
               (unsigned long)bio, (unsigned long)argp,
               argi, ret, ret);
        tls_dump(argp, (int) ret);
        return (ret);
    } else if (cmd == (BIO_CB_WRITE | BIO_CB_RETURN)) {
        printf("write to %08lX [%08lX] (%d bytes => %ld (0x%lX))",
               (unsigned long) bio, (unsigned long)argp,
               argi, ret, ret);
        tls_dump(argp, (int) ret);
    }
    return (ret);
}




 /*
  * This is the actual startup routine for the connection. We expect
  * that the buffers are flushed and the "Ready to start TLS" was
  * send to the client, so that we can immediately can start the TLS
  * handshake process.
  *
  * 'layerbits' and 'authid' are filled in on success. authid is only
  * filled in if the client authenticated. 'ret' is the SSL connection
  * on success.
  */
EXPORTED int tls_start_servertls(int readfd, int writefd, int timeout,
                        int *layerbits, char **authid, SSL **ret)
{
    int     sts;
    unsigned int n;
    const SSL_CIPHER *cipher;
    X509   *peer;
    const char *tls_protocol = NULL;
    const char *tls_cipher_name = NULL;
    const unsigned char *alpn = NULL;
    unsigned int alpn_len = 0;
    struct buf log = BUF_INITIALIZER;
    int tls_cipher_usebits = 0;
    int tls_cipher_algbits = 0;
    SSL *tls_conn;
    int r = 0;

    assert(tls_serverengine);
    assert(ret);
    if (var_imapd_tls_loglevel >= 1)
        syslog(LOG_DEBUG, "setting up TLS connection");

    if (authid) *authid = NULL;

    tls_conn = (SSL *) SSL_new(s_ctx);
    if (tls_conn == NULL) {
        *ret = NULL;
        r = -1;
        goto done;
    }
    SSL_clear(tls_conn);

    /* set the file descriptors for SSL to use */
    if ((SSL_set_rfd(tls_conn, readfd) == 0) ||
        (SSL_set_wfd(tls_conn, writefd) == 0)) {
        r = -1;
        goto done;
    }

    /*
     * This is the actual handshake routine. It will do all the negotiations
     * and will check the client cert etc.
     */
    SSL_set_accept_state(tls_conn);

    /*
     * We do have an SSL_set_fd() and now suddenly a BIO_ routine is called?
     * Well there is a BIO below the SSL routines that is automatically
     * created for us, so we can use it for debugging purposes.
     */
    if (var_imapd_tls_loglevel >= 3)
        BIO_set_callback(SSL_get_rbio(tls_conn), bio_dump_cb);

    /* Dump the negotiation for loglevels 3 and 4*/
    if (var_imapd_tls_loglevel >= 3)
        do_dump = 1;

    nonblock(readfd, 1);
    while (1) {
        fd_set rfds;
        struct timeval tv;
        int err;

        FD_ZERO(&rfds);
        FD_SET(readfd, &rfds);
        tv.tv_sec = timeout;
        tv.tv_usec = 0;

        sts = select(readfd+1, &rfds, NULL, NULL, &tv);
        if (sts <= 0) {
            if (sts == 0) {
                syslog(LOG_DEBUG, "SSL_accept() timed out -> fail");
            } else {
                syslog(LOG_DEBUG,
                       "tls_start_servertls() failed in select() -> fail: %m");
            }
            r = -1;
            goto done;
        }

        sts = SSL_accept(tls_conn);
        if (sts > 0) {
            syslog(LOG_DEBUG, "SSL_accept() succeeded -> done");
            break;
        }

        /* Check the error code */
        err = SSL_get_error(tls_conn, sts);
        switch (err) {
        case SSL_ERROR_WANT_READ:
        case SSL_ERROR_WANT_WRITE:
            syslog(LOG_DEBUG, "SSL_accept() incomplete -> wait");
            continue;
        case SSL_ERROR_SYSCALL:
            if (sts == 0) {
                syslog(LOG_DEBUG, "EOF in SSL_accept() -> fail");
            } else if (errno == EINTR || errno == EAGAIN) {
                syslog(LOG_DEBUG,
                       "SSL_accept() interrupted by signal %m -> retry");
                continue;
            } else {
                syslog(LOG_DEBUG,
                       "SSL_accept() interrupted by signal %m -> fail");
            }
            break;
        case SSL_ERROR_SSL:
            err = ERR_get_error();
            if (err == 0) {
                syslog(LOG_DEBUG, "protocol error in SSL_accept() -> fail");
            } else {
                syslog(LOG_DEBUG, "%s in SSL_accept() -> fail",
                       ERR_reason_error_string(err));
            }
            break;
        case SSL_ERROR_ZERO_RETURN:
            syslog(LOG_DEBUG,
                   "TLS/SSL connection closed in SSL_accept() -> fail");
            break;
        default:
            syslog(LOG_DEBUG,
                   "SSL_accept() failed with unknown error %d -> fail",
                   err);
            break;
        }
        r = -1;
        goto done;

        /* Should never get here */
    }

    /* Only loglevel==4 dumps everything */
    if (var_imapd_tls_loglevel < 4)
        do_dump = 0;

    /*
     * Lets see, whether a peer certificate is available and what is
     * the actual information. We want to save it for later use.
     */
    peer = SSL_get_peer_certificate(tls_conn);
    if (peer != NULL) {
        char fingerprint[EVP_MAX_MD_SIZE * 3];
        char issuer_CN[CCERT_BUFSIZ];
        char peer_issuer[CCERT_BUFSIZ];
        char peer_CN[CCERT_BUFSIZ];
        char peer_subject[CCERT_BUFSIZ];
        unsigned char md[EVP_MAX_MD_SIZE];

        syslog(LOG_DEBUG, "received client certificate");

        X509_NAME_oneline(X509_get_subject_name(peer),
                          peer_subject, CCERT_BUFSIZ);
        syslog(LOG_DEBUG, "subject=%s", peer_subject);
        X509_NAME_oneline(X509_get_issuer_name(peer),
                          peer_issuer, CCERT_BUFSIZ);
        if (var_imapd_tls_loglevel >= 2)
            syslog(LOG_DEBUG, "issuer=%s", peer_issuer);

        if (X509_digest(peer, EVP_md5(), md, &n)) {
            bin_to_hex(md, n, fingerprint, BH_UPPER|BH_SEPARATOR('_'));
            if (var_imapd_tls_loglevel >= 2)
                syslog(LOG_DEBUG, "fingerprint=%s", fingerprint);
        }
        X509_NAME_get_text_by_NID(X509_get_subject_name(peer),
                          NID_commonName, peer_CN, CCERT_BUFSIZ);
        X509_NAME_get_text_by_NID(X509_get_issuer_name(peer),
                          NID_commonName, issuer_CN, CCERT_BUFSIZ);
        if (var_imapd_tls_loglevel >= 3)
            syslog(LOG_DEBUG, "subject_CN=%s, issuer_CN=%s",
                   peer_CN, issuer_CN);

        /* xxx verify that we like the peer_issuer/issuer_CN */

        if (authid != NULL) {
            /* save the peer id for our caller */
            *authid = peer_CN[0] ? xstrdup(peer_CN) : NULL;
        }
        X509_free(peer);
    }
    tls_protocol = SSL_get_version(tls_conn);
    cipher = SSL_get_current_cipher(tls_conn);
    tls_cipher_name = SSL_CIPHER_get_name(cipher);
    tls_cipher_usebits = SSL_CIPHER_get_bits(cipher, &tls_cipher_algbits);

    if (layerbits != NULL) {
        *layerbits = tls_cipher_usebits;
    }

#if OPENSSL_VERSION_NUMBER >= 0x10002000L
    SSL_get0_alpn_selected(tls_conn, &alpn, &alpn_len);
#endif

    buf_printf(&log, "starttls: %s with cipher %s (%d/%d bits %s) ",
               tls_protocol, tls_cipher_name,
               tls_cipher_usebits, tls_cipher_algbits,
               SSL_session_reused(tls_conn) ? "reused" : "new");

    if (authid && *authid) {
        buf_printf(&log, "authenticated as %s", *authid);
    }
    else {
        buf_appendcstr(&log, "no authentication");
    }

    if (alpn) {
        buf_printf(&log, "; application protocol = %.*s",
                   alpn_len, (const char *) alpn);
    }

    syslog(LOG_NOTICE, "%s", buf_cstring(&log));
    buf_free(&log);

 done:
    nonblock(readfd, 0);
    if (r && tls_conn) {
        /* error; clean up */
        SSL_SESSION *session = SSL_get_session(tls_conn);
        if (session) {
            SSL_CTX_remove_session(s_ctx, session);
        }
        SSL_free(tls_conn);
        tls_conn = NULL;
    }
    *ret = tls_conn;
    return r;
}

EXPORTED int tls_reset_servertls(SSL **conn)
{
    int r = 0;

    if (*conn) {
        if (TLS_FAST_SHUTDOWN) {
            /*
             * Don't bother spending time closing the TLS session,
             * but make sure its available for reuse.
             */
            SSL_set_shutdown(*conn,SSL_SENT_SHUTDOWN|SSL_RECEIVED_SHUTDOWN);
        }
        else {
            /* Follow the TLS protocol and do a shutdown handshake */
            r = SSL_shutdown(*conn);
            if (r == 0) {
                /* Just sent, now wait for peer to ack */
                r = SSL_shutdown(*conn);
            }
            if (r == 0) r = -1;
        }
        SSL_free(*conn);
    }

    return r;
}

EXPORTED int tls_shutdown_serverengine(void)
{
    int r;

    if (tls_serverengine) {
        if (sess_dbopen) {
            r = cyrusdb_close(sessdb);
            if (r) {
                syslog(LOG_ERR, "DBERROR: error closing tlsdb: %s",
                       cyrusdb_strerror(r));
            }
            sessdb = NULL;
            sess_dbopen = 0;
        }

#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL)
        if (dh_params) DH_free(dh_params);
#endif
    }

    return 0;

}

/*
 * Delete expired sessions.
 */
struct prunerock {
    int count;
    int deletions;
};

static int prune_p(void *rock, const char *id, size_t idlen,
                   const char *data, size_t datalen)
{
    struct prunerock *prock = (struct prunerock *) rock;
    time_t expire;

    prock->count++;

    assert(datalen >= (int) sizeof(time_t));

    /* grab the expire time */
    memcpy(&expire, data, sizeof(time_t));

    /* log this transaction */
    if (var_imapd_tls_loglevel > 0) {
        size_t i;
        char idstr[SSL_MAX_SSL_SESSION_ID_LENGTH*2 + 1];

        assert(idlen <= SSL_MAX_SSL_SESSION_ID_LENGTH);

        for (i = 0; i < idlen; i++) {
            sprintf(idstr+i*2, "%02X", (unsigned char) id[i]);
        }

        syslog(LOG_DEBUG, "found TLS session: id=%s, expire=%s",
               idstr, ctime(&expire));
    }

    /* check if the session has expired */
    return (expire < time(0));
}

static int prune_cb(void *rock, const char *id, size_t idlen,
                    const char *data __attribute__((unused)),
                    size_t datalen __attribute__((unused)))
{
    struct prunerock *prock = (struct prunerock *) rock;

    prock->deletions++;

    remove_session((unsigned char*) id, idlen);

    return 0;
}

/* must be called after cyrus_init */
EXPORTED int tls_prune_sessions(void)
{
    const char *fname = NULL;
    char *tofree = NULL;
    int ret;
    struct prunerock prock;

    fname = config_getstring(IMAPOPT_TLS_SESSIONS_DB_PATH);

   /* create the name of the db file */
    if (!fname) {
        tofree = strconcat(config_dir, FNAME_TLSSESSIONS, (char *)NULL);
        fname = tofree;
    }

    ret = cyrusdb_open(DB, fname, 0, &sessdb);
    if (ret == CYRUSDB_OK) {
        /* check each session in our database */
        sess_dbopen = 1;
        prock.count = prock.deletions = 0;
        cyrusdb_foreach(sessdb, "", 0, &prune_p, &prune_cb, &prock, NULL);
        cyrusdb_close(sessdb);
        sessdb = NULL;
        sess_dbopen = 0;

        syslog(LOG_NOTICE, "tls_prune: purged %d out of %d entries",
               prock.deletions, prock.count);
    }
    else if (ret == CYRUSDB_NOTFOUND) {
        syslog(LOG_NOTICE, "tls_prune: %s not found, nothing to do", fname);
        ret = 0;
    }
    else {
        syslog(LOG_ERR, "DBERROR: opening %s: %s",
               fname, cyrusdb_strerror(ret));
    }

    if (tofree)
	free(tofree);

    return ret;
}

/* fill string buffer with info about tls connection */
EXPORTED int tls_get_info(SSL *conn, char *buf, size_t len)
{
    int usebits = 0;
    int algbits = 0;

    usebits = SSL_get_cipher_bits(conn, &algbits);
    snprintf(buf, len, "version=%s cipher=%s bits=%d/%d verify=%s",
             SSL_get_cipher_version(conn), SSL_get_cipher_name(conn),
             usebits, algbits,
             SSL_get_verify_result(conn) == X509_V_OK ? "YES" : "NO");

    return (strlen(buf));
}

// I am the client
HIDDEN int tls_init_clientengine(int verifydepth,
                          const char *var_server_cert,
                          const char *var_server_key)
{
    int     off = 0;
    int     verify_flags = SSL_VERIFY_NONE;
    const char   *server_ca_dir;
    const char   *server_ca_file;
    char   *client_cert;
    char   *client_key;

    if (tls_clientengine)
        return (0);                             /* already running */

    if (var_proxy_tls_loglevel >= 2)
        syslog(LOG_DEBUG, "starting TLS client engine");

    SSL_library_init();
    SSL_load_error_strings();
    if (tls_rand_init() == -1) {
        printf("TLS client engine: cannot seed PRNG\n");
        return -1;
    }

#if (OPENSSL_VERSION_NUMBER >= 0x10100000L)
    c_ctx = SSL_CTX_new(TLS_client_method());
#else
    c_ctx = SSL_CTX_new(SSLv23_client_method());
#endif
    if (c_ctx == NULL) {
        return (-1);
    };

    off |= SSL_OP_ALL;            /* Work around all known bugs */
    off |= SSL_OP_NO_SSLv2;       /* Disable insecure SSLv2 */
    off |= SSL_OP_NO_SSLv3;       /* Disable insecure SSLv3 */
    off |= SSL_OP_NO_COMPRESSION; /* Disable TLS compression */

    SSL_CTX_set_options(c_ctx, off);
    SSL_CTX_set_info_callback(c_ctx, apps_ssl_info_callback);

    server_ca_dir = config_getstring(IMAPOPT_TLS_SERVER_CA_DIR);
    server_ca_file = config_getstring(IMAPOPT_TLS_SERVER_CA_FILE);

    if (config_debug) {
            syslog(
                LOG_DEBUG, "tls_server_ca_dir=%s tls_server_ca_file=%s",
                IS_NULL(server_ca_dir), IS_NULL(server_ca_file)
            );
    }

    if (server_ca_dir || server_ca_file) {
        if ((!SSL_CTX_load_verify_locations(c_ctx, server_ca_file, server_ca_dir)) ||
            (!SSL_CTX_set_default_verify_paths(c_ctx))) {
            /* just a warning since this is only necessary for client auth */
            syslog(LOG_NOTICE,"TLS client engine: cannot load CA data");
        }
    }

    if (!var_server_cert || strlen(var_server_cert) == 0)
        client_cert = NULL;
    else
        client_cert = xstrdup(var_server_cert);

    if (!var_server_key || strlen(var_server_key) == 0)
        client_key = NULL;
    else
        client_key = xstrdup(var_server_key);

    if (client_cert || client_key) {
        if (!set_cert_stuff(c_ctx, client_cert, client_key)) {
            syslog(LOG_ERR,"TLS client engine: cannot load cert/key data, may be a cert/key mismatch?");
            return (-1);
        }
    }

#if OPENSSL_VERSION_NUMBER < 0x10100000L
    SSL_CTX_set_tmp_rsa_callback(c_ctx, tmp_rsa_cb);
#endif

    verify_depth = verifydepth;
    SSL_CTX_set_verify(c_ctx, verify_flags, verify_callback);

    tls_clientengine = 1;
    return (0);
}

HIDDEN int tls_start_clienttls(int readfd, int writefd,
                        int *layerbits, char **authid, SSL **ret,
                        SSL_SESSION **sess)
{
    int     sts;
    const SSL_CIPHER *cipher;
    X509   *peer;
    const char *tls_protocol = NULL;
    const char *tls_cipher_name = NULL;
    int tls_cipher_usebits = 0;
    int tls_cipher_algbits = 0;
    SSL *tls_conn;
    int r = 0;

    assert(tls_clientengine);
    assert(ret);
    if (var_proxy_tls_loglevel >= 1)
        syslog(LOG_DEBUG, "setting up TLS connection");

    if (authid) *authid = NULL;

    tls_conn = (SSL *) SSL_new(c_ctx);
    if (tls_conn == NULL) {
        *ret = NULL;
        r = -1;
        goto done;
    }
    SSL_clear(tls_conn);

    /* set the file descriptors for SSL to use */
    if ((SSL_set_rfd(tls_conn, readfd) == 0) ||
        (SSL_set_wfd(tls_conn, writefd) == 0)) {
        r = -1;
        goto done;
    }

    /*
     * This is the actual handshake routine. It will do all the negotiations
     * and will check the client cert etc.
     */
    SSL_set_connect_state(tls_conn);

    /*
     * We do have an SSL_set_fd() and now suddenly a BIO_ routine is called?
     * Well there is a BIO below the SSL routines that is automatically
     * created for us, so we can use it for debugging purposes.
     */
    if (var_proxy_tls_loglevel >= 3)
        BIO_set_callback(SSL_get_rbio(tls_conn), bio_dump_cb);

    /* Dump the negotiation for loglevels 3 and 4*/
    if (var_proxy_tls_loglevel >= 3)
        do_dump = 1;

    if (sess && *sess)  /* Reuse a session if we have one */
        SSL_set_session(tls_conn, *sess);

    if ((sts = SSL_connect(tls_conn)) <= 0) {
        SSL_SESSION *session = SSL_get_session(tls_conn);
        if (session) {
            SSL_CTX_remove_session(c_ctx, session);
        }
        if (sess) *sess = NULL;
        r = -1;
        goto done;
    }
    if (sess) *sess = SSL_get_session(tls_conn);

    /* Only loglevel==4 dumps everything */
    if (var_proxy_tls_loglevel < 4)
        do_dump = 0;

    /*
     * Lets see, whether a peer certificate is available and what is
     * the actual information. We want to save it for later use.
     */
    peer = SSL_get_peer_certificate(tls_conn);
    if (peer != NULL) {
        char issuer_CN[CCERT_BUFSIZ];
        char peer_CN[CCERT_BUFSIZ];

        syslog(LOG_DEBUG, "received server certificate");

        X509_NAME_get_text_by_NID(X509_get_subject_name(peer),
                                  NID_commonName, peer_CN, CCERT_BUFSIZ);
        X509_NAME_get_text_by_NID(X509_get_issuer_name(peer),
                                  NID_commonName, issuer_CN, CCERT_BUFSIZ);
        if (var_proxy_tls_loglevel >= 3)
            syslog(LOG_DEBUG, "subject_CN=%s, issuer_CN=%s",
                   peer_CN, issuer_CN);

        /* xxx verify that we like the peer_issuer/issuer_CN */

        if (authid != NULL) {
            /* save the peer id for our caller */
            *authid = peer_CN[0] ? xstrdup(peer_CN) : NULL;
        }
        X509_free(peer);
    }
    tls_protocol = SSL_get_version(tls_conn);
    cipher = SSL_get_current_cipher(tls_conn);
    tls_cipher_name = SSL_CIPHER_get_name(cipher);
    tls_cipher_usebits = SSL_CIPHER_get_bits(cipher, &tls_cipher_algbits);

    if (layerbits != NULL)
        *layerbits = tls_cipher_usebits;

    syslog(LOG_DEBUG, "starttls: %s with cipher %s (%d/%d bits %s client)"
           " no authentication",
           tls_protocol, tls_cipher_name,
           tls_cipher_usebits, tls_cipher_algbits,
           SSL_session_reused(tls_conn) ? "reused" : "new");

  done:
    if (r && tls_conn) {
        /* error; clean up */
        SSL_free(tls_conn);
        tls_conn = NULL;
    }
    *ret = tls_conn;

    return r;
}

#else

EXPORTED int tls_enabled(void)
{
    return 0;
}

#endif /* HAVE_SSL */
