/********************************************************************* * * File : $Source: /cvsroot/ijbswa/current/ssl.c,v $ * * Purpose : File with TLS/SSL extension. Contains methods for * creating, using and closing TLS/SSL connections. * * Copyright : Written by and Copyright (c) 2017 Vaclav Svec. FIT CVUT. * Copyright (C) 2018-2020 by Fabian Keil * * This program is free software; you can redistribute it * and/or modify it under the terms of the GNU General * Public License as published by the Free Software * Foundation; either version 2 of the License, or (at * your option) any later version. * * This program 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 General Public * License for more details. * * The GNU General Public License should be included with * this file. If not, you can view it at * http://www.gnu.org/copyleft/gpl.html * or write to the Free Software Foundation, Inc., 59 * Temple Place - Suite 330, Boston, MA 02111-1307, USA. * *********************************************************************/ #include #include #if !defined(MBEDTLS_CONFIG_FILE) # include "mbedtls/config.h" #else # include MBEDTLS_CONFIG_FILE #endif #include "mbedtls/md5.h" #include "mbedtls/pem.h" #include "mbedtls/base64.h" #include "mbedtls/error.h" #include "config.h" #include "project.h" #include "miscutil.h" #include "errlog.h" #include "jcc.h" #include "ssl.h" /* * Macros for searching begin and end of certificates. * Necessary to convert structure mbedtls_x509_crt to crt file. */ #define PEM_BEGIN_CRT "-----BEGIN CERTIFICATE-----\n" #define PEM_END_CRT "-----END CERTIFICATE-----\n" /* * Macros for ssl.c */ #define ERROR_BUF_SIZE 1024 /* Size of buffer for error messages */ #define CERTIFICATE_BUF_SIZE 16384 /* Size of buffer to save certificate. Value 4096 is mbedtls library buffer size for certificate in DER form */ #define PRIVATE_KEY_BUF_SIZE 16000 /* Size of buffer to save private key. Value 16000 is taken from mbed TLS library examples. */ #define RSA_KEY_PUBLIC_EXPONENT 65537 /* Public exponent for RSA private key generating */ #define RSA_KEYSIZE 2048 /* Size of generated RSA keys */ #define GENERATED_CERT_VALID_FROM "20100101000000" /* Date and time, which will be set in generated certificates as parameter valid from */ #define GENERATED_CERT_VALID_TO "20401231235959" /* Date and time, which will be set in generated certificates as parameter valid to */ #define CERT_SIGNATURE_ALGORITHM MBEDTLS_MD_SHA256 /* The MD algorithm to use for the signature */ #define CERT_SERIAL_NUM_LENGTH 4 /* Bytes of hash to be used for creating serial number of certificate. Min=2 and max=16 */ #define INVALID_CERT_INFO_BUF_SIZE 2048 /* Size of buffer for message with information about reason of certificate invalidity. Data after the end of buffer will not be saved */ #define CERT_PARAM_COMMON_NAME "CN=" #define CERT_PARAM_ORGANIZATION ",O=" #define CERT_PARAM_ORG_UNIT ",OU=" #define CERT_PARAM_COUNTRY ",C=CZ" #define KEY_FILE_TYPE ".pem" #define CERT_FILE_TYPE ".crt" #define CERT_SUBJECT_PASSWORD "" #define CERT_INFO_PREFIX "" /* * Properties of cert for generating */ typedef struct { char *issuer_crt; /* filename of the issuer certificate */ char *subject_key; /* filename of the subject key file */ char *issuer_key; /* filename of the issuer key file */ const char *subject_pwd; /* password for the subject key file */ const char *issuer_pwd; /* password for the issuer key file */ char *output_file; /* where to store the constructed key file */ const char *subject_name; /* subject name for certificate */ char issuer_name[ISSUER_NAME_BUF_SIZE]; /* issuer name for certificate */ const char *not_before; /* validity period not before */ const char *not_after; /* validity period not after */ const char *serial; /* serial number string */ int is_ca; /* is a CA certificate */ int max_pathlen; /* maximum CA path length */ } cert_options; /* * Properties of key for generating */ typedef struct { mbedtls_pk_type_t type; /* type of key to generate */ int rsa_keysize; /* length of key in bits */ char *key_file_path; /* filename of the key file */ } key_options; static int generate_webpage_certificate(struct client_state *csp); static char *make_certs_path(const char *conf_dir, const char *file_name, const char *suffix); static int file_exists(const char *path); static int host_to_hash(struct client_state *csp); static int ssl_verify_callback(void *data, mbedtls_x509_crt *crt, int depth, uint32_t *flags); static void free_certificate_chain(struct client_state *csp); static unsigned int get_certificate_mutex_id(struct client_state *csp); static unsigned long get_certificate_serial(struct client_state *csp); static void free_client_ssl_structures(struct client_state *csp); static void free_server_ssl_structures(struct client_state *csp); static int seed_rng(struct client_state *csp); /********************************************************************* * * Function : client_use_ssl * * Description : Tests if client in current client state structure * should use SSL connection or standard connection. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : If client should use TLS/SSL connection, 1 is returned. * Otherwise 0 is returned. * *********************************************************************/ extern int client_use_ssl(const struct client_state *csp) { return csp->http->client_ssl; } /********************************************************************* * * Function : server_use_ssl * * Description : Tests if server in current client state structure * should use SSL connection or standard connection. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : If server should use TLS/SSL connection, 1 is returned. * Otherwise 0 is returned. * *********************************************************************/ extern int server_use_ssl(const struct client_state *csp) { return csp->http->server_ssl; } /********************************************************************* * * Function : is_ssl_pending * * Description : Tests if there are some waiting data on ssl connection * * Parameters : * 1 : ssl = SSL context to test * * Returns : 0 => No data are pending * >0 => Pending data length * *********************************************************************/ extern size_t is_ssl_pending(mbedtls_ssl_context *ssl) { if (ssl == NULL) { return 0; } return mbedtls_ssl_get_bytes_avail(ssl); } /********************************************************************* * * Function : ssl_send_data * * Description : Sends the content of buf (for n bytes) to given SSL * connection context. * * Parameters : * 1 : ssl = SSL context to send data to * 2 : buf = Pointer to data to be sent * 3 : len = Length of data to be sent to the SSL context * * Returns : Length of sent data or negative value on error. * *********************************************************************/ extern int ssl_send_data(mbedtls_ssl_context *ssl, const unsigned char *buf, size_t len) { int ret = 0; size_t max_fragment_size = 0; /* Maximal length of data in one SSL fragment*/ int send_len = 0; /* length of one data part to send */ int pos = 0; /* Position of unsent part in buffer */ if (len == 0) { return 0; } /* Getting maximal length of data sent in one fragment */ max_fragment_size = mbedtls_ssl_get_max_frag_len(ssl); /* * Whole buffer must be sent in many fragments, because each fragment * has its maximal length. */ while (pos < len) { /* Compute length of data, that can be send in next fragment */ if ((pos + (int)max_fragment_size) > len) { send_len = (int)len - pos; } else { send_len = (int)max_fragment_size; } log_error(LOG_LEVEL_WRITING, "TLS: %N", send_len, buf+pos); /* * Sending one part of the buffer */ while ((ret = mbedtls_ssl_write(ssl, (const unsigned char *)(buf + pos), (size_t)send_len)) < 0) { if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) { char err_buf[ERROR_BUF_SIZE]; mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Sending data over TLS/SSL failed: %s", err_buf); return -1; } } /* Adding count of sent bytes to position in buffer */ pos = pos + send_len; } return (int)len; } /********************************************************************* * * Function : ssl_recv_data * * Description : Receives data from given SSL context and puts * it into buffer. * * Parameters : * 1 : ssl = SSL context to receive data from * 2 : buf = Pointer to buffer where data will be written * 3 : max_length = Maximum number of bytes to read * * Returns : Number of bytes read, 0 for EOF, or -1 * on error. * *********************************************************************/ extern int ssl_recv_data(mbedtls_ssl_context *ssl, unsigned char *buf, size_t max_length) { int ret = 0; memset(buf, 0, max_length); /* * Receiving data from SSL context into buffer */ do { ret = mbedtls_ssl_read(ssl, buf, max_length); } while (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE); if (ret < 0) { char err_buf[ERROR_BUF_SIZE]; if (ret == MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY) { log_error(LOG_LEVEL_CONNECT, "The peer notified us that the connection is going to be closed"); return 0; } mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Receiving data over TLS/SSL failed: %s", err_buf); return -1; } log_error(LOG_LEVEL_RECEIVED, "TLS: %N", ret, buf); return ret; } /********************************************************************* * * Function : ssl_flush_socket * * Description : Send any pending "buffered" content with given * SSL connection. Alternative to function flush_socket. * * Parameters : * 1 : ssl = SSL context to send buffer to * 2 : iob = The I/O buffer to flush, usually csp->iob. * * Returns : On success, the number of bytes send are returned (zero * indicates nothing was sent). On error, -1 is returned. * *********************************************************************/ extern long ssl_flush_socket(mbedtls_ssl_context *ssl, struct iob *iob) { /* Computing length of buffer part to send */ long len = iob->eod - iob->cur; if (len <= 0) { return(0); } /* Sending data to given SSl context */ if (ssl_send_data(ssl, (const unsigned char *)iob->cur, (size_t)len) < 0) { return -1; } iob->eod = iob->cur = iob->buf; return(len); } /********************************************************************* * * Function : ssl_debug_callback * * Description : Debug callback function for mbedtls library. * Prints info into log file. * * Parameters : * 1 : ctx = File to save log in * 2 : level = Debug level * 3 : file = File calling debug message * 4 : line = Line calling debug message * 5 : str = Debug message * * Returns : N/A * *********************************************************************/ static void ssl_debug_callback(void *ctx, int level, const char *file, int line, const char *str) { /* ((void)level); fprintf((FILE *)ctx, "%s:%04d: %s", file, line, str); fflush((FILE *)ctx); log_error(LOG_LEVEL_INFO, "SSL debug message: %s:%04d: %s", file, line, str); */ } /********************************************************************* * * Function : create_client_ssl_connection * * Description : Creates TLS/SSL secured connection with client * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : 0 on success, negative value if connection wasn't created * successfully. * *********************************************************************/ extern int create_client_ssl_connection(struct client_state *csp) { /* Paths to certificates file and key file */ char *key_file = NULL; char *ca_file = NULL; char *cert_file = NULL; int ret = 0; char err_buf[ERROR_BUF_SIZE]; /* * Initializing mbedtls structures for TLS/SSL connection */ mbedtls_net_init(&(csp->mbedtls_client_attr.socket_fd)); mbedtls_ssl_init(&(csp->mbedtls_client_attr.ssl)); mbedtls_ssl_config_init(&(csp->mbedtls_client_attr.conf)); mbedtls_x509_crt_init(&(csp->mbedtls_client_attr.server_cert)); mbedtls_pk_init(&(csp->mbedtls_client_attr.prim_key)); #if defined(MBEDTLS_SSL_CACHE_C) mbedtls_ssl_cache_init(&(csp->mbedtls_client_attr.cache)); #endif /* * Preparing hash of host for creating certificates */ ret = host_to_hash(csp); if (ret != 0) { log_error(LOG_LEVEL_ERROR, "Generating hash of host failed: %d", ret); ret = -1; goto exit; } /* * Preparing paths to certificates files and key file */ ca_file = csp->config->ca_cert_file; cert_file = make_certs_path(csp->config->certificate_directory, (const char *)csp->http->hash_of_host_hex, CERT_FILE_TYPE); key_file = make_certs_path(csp->config->certificate_directory, (const char *)csp->http->hash_of_host_hex, KEY_FILE_TYPE); if (cert_file == NULL || key_file == NULL) { ret = -1; goto exit; } /* * Generating certificate for requested host. Mutex to prevent * certificate and key inconsistence must be locked. */ unsigned int cert_mutex_id = get_certificate_mutex_id(csp); privoxy_mutex_lock(&(certificates_mutexes[cert_mutex_id])); ret = generate_webpage_certificate(csp); if (ret < 0) { log_error(LOG_LEVEL_ERROR, "Generate_webpage_certificate failed: %d", ret); privoxy_mutex_unlock(&(certificates_mutexes[cert_mutex_id])); ret = -1; goto exit; } privoxy_mutex_unlock(&(certificates_mutexes[cert_mutex_id])); /* * Seed the RNG */ ret = seed_rng(csp); if (ret != 0) { ret = -1; goto exit; } /* * Loading CA file, webpage certificate and key files */ ret = mbedtls_x509_crt_parse_file(&(csp->mbedtls_client_attr.server_cert), cert_file); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Loading webpage certificate %s failed: %s", cert_file, err_buf); ret = -1; goto exit; } ret = mbedtls_x509_crt_parse_file(&(csp->mbedtls_client_attr.server_cert), ca_file); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Loading CA certificate %s failed: %s", ca_file, err_buf); ret = -1; goto exit; } ret = mbedtls_pk_parse_keyfile(&(csp->mbedtls_client_attr.prim_key), key_file, NULL); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Loading and parsing webpage certificate private key %s failed: %s", key_file, err_buf); ret = -1; goto exit; } /* * Setting SSL parameters */ ret = mbedtls_ssl_config_defaults(&(csp->mbedtls_client_attr.conf), MBEDTLS_SSL_IS_SERVER, MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_config_defaults failed: %s", err_buf); ret = -1; goto exit; } mbedtls_ssl_conf_rng(&(csp->mbedtls_client_attr.conf), mbedtls_ctr_drbg_random, &ctr_drbg); mbedtls_ssl_conf_dbg(&(csp->mbedtls_client_attr.conf), ssl_debug_callback, stdout); #if defined(MBEDTLS_SSL_CACHE_C) mbedtls_ssl_conf_session_cache(&(csp->mbedtls_client_attr.conf), &(csp->mbedtls_client_attr.cache), mbedtls_ssl_cache_get, mbedtls_ssl_cache_set); #endif /* * Setting certificates */ ret = mbedtls_ssl_conf_own_cert(&(csp->mbedtls_client_attr.conf), &(csp->mbedtls_client_attr.server_cert), &(csp->mbedtls_client_attr.prim_key)); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_conf_own_cert failed: %s", err_buf); ret = -1; goto exit; } ret = mbedtls_ssl_setup(&(csp->mbedtls_client_attr.ssl), &(csp->mbedtls_client_attr.conf)); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_setup failed: %s", err_buf); ret = -1; goto exit; } mbedtls_ssl_set_bio(&(csp->mbedtls_client_attr.ssl), &(csp->mbedtls_client_attr.socket_fd), mbedtls_net_send, mbedtls_net_recv, NULL); mbedtls_ssl_session_reset(&(csp->mbedtls_client_attr.ssl)); /* * Setting socket fd in mbedtls_net_context structure. This structure * can't be set by mbedtls functions, because we already have created * a TCP connection when this function is called. */ csp->mbedtls_client_attr.socket_fd.fd = csp->cfd; /* * Handshake with client */ log_error(LOG_LEVEL_CONNECT, "Performing the TLS/SSL handshake with client. Hash of host: %s", csp->http->hash_of_host_hex); while ((ret = mbedtls_ssl_handshake(&(csp->mbedtls_client_attr.ssl))) != 0) { if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "medtls_ssl_handshake with client failed: %s", err_buf); ret = -1; goto exit; } } log_error(LOG_LEVEL_CONNECT, "Client successfully connected over TLS/SSL"); csp->ssl_with_client_is_opened = 1; exit: /* * Freeing allocated paths to files */ freez(cert_file); freez(key_file); /* Freeing structures if connection wasn't created successfully */ if (ret < 0) { free_client_ssl_structures(csp); } return ret; } /********************************************************************* * * Function : close_client_ssl_connection * * Description : Closes TLS/SSL connection with client. This function * checks if this connection is already created. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ extern void close_client_ssl_connection(struct client_state *csp) { int ret = 0; if (csp->ssl_with_client_is_opened == 0) { return; } /* * Notifying the peer that the connection is being closed. */ do { ret = mbedtls_ssl_close_notify(&(csp->mbedtls_client_attr.ssl)); } while (ret == MBEDTLS_ERR_SSL_WANT_WRITE); free_client_ssl_structures(csp); csp->ssl_with_client_is_opened = 0; } /********************************************************************* * * Function : free_client_ssl_structures * * Description : Frees structures used for SSL communication with * client. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ static void free_client_ssl_structures(struct client_state *csp) { /* * We can't use function mbedtls_net_free, because this function * inter alia close TCP connection on setted fd. Instead of this * function, we change fd to -1, which is the same what does * rest of mbedtls_net_free function. */ csp->mbedtls_client_attr.socket_fd.fd = -1; /* Freeing mbedtls structures */ mbedtls_x509_crt_free(&(csp->mbedtls_client_attr.server_cert)); mbedtls_pk_free(&(csp->mbedtls_client_attr.prim_key)); mbedtls_ssl_free(&(csp->mbedtls_client_attr.ssl)); mbedtls_ssl_config_free(&(csp->mbedtls_client_attr.conf)); #if defined(MBEDTLS_SSL_CACHE_C) mbedtls_ssl_cache_free(&(csp->mbedtls_client_attr.cache)); #endif } /********************************************************************* * * Function : create_server_ssl_connection * * Description : Creates TLS/SSL secured connection with server. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : 0 on success, negative value if connection wasn't created * successfully. * *********************************************************************/ extern int create_server_ssl_connection(struct client_state *csp) { int ret = 0; char err_buf[ERROR_BUF_SIZE]; char *trusted_cas_file = NULL; int auth_mode = MBEDTLS_SSL_VERIFY_REQUIRED; csp->server_cert_verification_result = SSL_CERT_NOT_VERIFIED; csp->server_certs_chain.next = NULL; /* Setting path to file with trusted CAs */ trusted_cas_file = csp->config->trusted_cas_file; /* * Initializing mbedtls structures for TLS/SSL connection */ mbedtls_net_init(&(csp->mbedtls_server_attr.socket_fd)); mbedtls_ssl_init(&(csp->mbedtls_server_attr.ssl)); mbedtls_ssl_config_init(&(csp->mbedtls_server_attr.conf)); mbedtls_x509_crt_init(&(csp->mbedtls_server_attr.ca_cert)); /* * Setting socket fd in mbedtls_net_context structure. This structure * can't be set by mbedtls functions, because we already have created * TCP connection when calling this function. */ csp->mbedtls_server_attr.socket_fd.fd = csp->server_connection.sfd; /* * Seed the RNG */ ret = seed_rng(csp); if (ret != 0) { ret = -1; goto exit; } /* * Loading file with trusted CAs */ ret = mbedtls_x509_crt_parse_file(&(csp->mbedtls_server_attr.ca_cert), trusted_cas_file); if (ret < 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Loading trusted CAs file %s failed: %s", trusted_cas_file, err_buf); ret = -1; goto exit; } /* * Set TLS/SSL options */ ret = mbedtls_ssl_config_defaults(&(csp->mbedtls_server_attr.conf), MBEDTLS_SSL_IS_CLIENT, MBEDTLS_SSL_TRANSPORT_STREAM, MBEDTLS_SSL_PRESET_DEFAULT); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_config_defaults failed: %s", err_buf); ret = -1; goto exit; } /* * Setting how strict should certificate verification be and other * parameters for certificate verification */ if (csp->dont_verify_certificate) { auth_mode = MBEDTLS_SSL_VERIFY_NONE; } mbedtls_ssl_conf_authmode(&(csp->mbedtls_server_attr.conf), auth_mode); mbedtls_ssl_conf_ca_chain(&(csp->mbedtls_server_attr.conf), &(csp->mbedtls_server_attr.ca_cert), NULL); /* Setting callback function for certificates verification */ mbedtls_ssl_conf_verify(&(csp->mbedtls_server_attr.conf), ssl_verify_callback, (void *)csp); mbedtls_ssl_conf_rng(&(csp->mbedtls_server_attr.conf), mbedtls_ctr_drbg_random, &ctr_drbg); mbedtls_ssl_conf_dbg(&(csp->mbedtls_server_attr.conf), ssl_debug_callback, stdout); ret = mbedtls_ssl_setup(&(csp->mbedtls_server_attr.ssl), &(csp->mbedtls_server_attr.conf)); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_setup failed: %s", err_buf); ret = -1; goto exit; } /* * Set the hostname to check against the received server certificate */ ret = mbedtls_ssl_set_hostname(&(csp->mbedtls_server_attr.ssl), csp->http->host); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_set_hostname failed: %s", err_buf); ret = -1; goto exit; } mbedtls_ssl_set_bio(&(csp->mbedtls_server_attr.ssl), &(csp->mbedtls_server_attr.socket_fd), mbedtls_net_send, mbedtls_net_recv, NULL); /* * Handshake with server */ log_error(LOG_LEVEL_CONNECT, "Performing the TLS/SSL handshake with the server"); while ((ret = mbedtls_ssl_handshake(&(csp->mbedtls_server_attr.ssl))) != 0) { if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); if (ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED) { log_error(LOG_LEVEL_ERROR, "Server certificate verification failed: %s", err_buf); csp->server_cert_verification_result = mbedtls_ssl_get_verify_result(&(csp->mbedtls_server_attr.ssl)); ret = -1; } else { log_error(LOG_LEVEL_ERROR, "mbedtls_ssl_handshake with server failed: %s", err_buf); ret = -1; } goto exit; } } log_error(LOG_LEVEL_CONNECT, "Server successfully connected over TLS/SSL"); /* * Server certificate chain is valid, so we can clean * chain, because we will not send it to client. */ free_certificate_chain(csp); csp->ssl_with_server_is_opened = 1; csp->server_cert_verification_result = mbedtls_ssl_get_verify_result(&(csp->mbedtls_server_attr.ssl)); exit: /* Freeing structures if connection wasn't created successfully */ if (ret < 0) { free_server_ssl_structures(csp); } return ret; } /********************************************************************* * * Function : close_server_ssl_connection * * Description : Closes TLS/SSL connection with server. This function * checks if this connection is already opened. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ static void close_server_ssl_connection(struct client_state *csp) { int ret = 0; if (csp->ssl_with_server_is_opened == 0) { return; } /* * Notifying the peer that the connection is being closed. */ do { ret = mbedtls_ssl_close_notify(&(csp->mbedtls_server_attr.ssl)); } while (ret == MBEDTLS_ERR_SSL_WANT_WRITE); free_server_ssl_structures(csp); csp->ssl_with_server_is_opened = 0; } /********************************************************************* * * Function : free_server_ssl_structures * * Description : Frees structures used for SSL communication with server * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ static void free_server_ssl_structures(struct client_state *csp) { /* * We can't use function mbedtls_net_free, because this function * inter alia close TCP connection on setted fd. Instead of this * function, we change fd to -1, which is the same what does * rest of mbedtls_net_free function. */ csp->mbedtls_client_attr.socket_fd.fd = -1; mbedtls_x509_crt_free(&(csp->mbedtls_server_attr.ca_cert)); mbedtls_ssl_free(&(csp->mbedtls_server_attr.ssl)); mbedtls_ssl_config_free(&(csp->mbedtls_server_attr.conf)); } /********************************************************************* * * Function : close_client_and_server_ssl_connections * * Description : Checks if client or server should use secured * connection over SSL and if so, closes all of them. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ extern void close_client_and_server_ssl_connections(struct client_state *csp) { if (client_use_ssl(csp) == 1) { close_client_ssl_connection(csp); } if (server_use_ssl(csp) == 1) { close_server_ssl_connection(csp); } } /*====================== Certificates ======================*/ /********************************************************************* * * Function : write_certificate * * Description : Writes certificate into file. * * Parameters : * 1 : crt = certificate to write into file * 2 : output_file = path to save certificate file * 3 : f_rng = mbedtls_ctr_drbg_random * 4 : p_rng = mbedtls_ctr_drbg_context * * Returns : Length of written certificate on success or negative value * on error * *********************************************************************/ static int write_certificate(mbedtls_x509write_cert *crt, const char *output_file, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng) { FILE *f = NULL; size_t len = 0; unsigned char cert_buf[CERTIFICATE_BUF_SIZE + 1]; /* Buffer for certificate in PEM format + terminating NULL */ int ret = 0; char err_buf[ERROR_BUF_SIZE]; memset(cert_buf, 0, sizeof(cert_buf)); /* * Writing certificate into PEM string. If buffer is too small, function * returns specific error and no buffer overflow can happen. */ if ((ret = mbedtls_x509write_crt_pem(crt, cert_buf, sizeof(cert_buf) - 1, f_rng, p_rng)) != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Writing certificate into buffer failed: %s", err_buf); return -1; } len = strlen((char *)cert_buf); /* * Saving certificate into file */ if ((f = fopen(output_file, "w")) == NULL) { log_error(LOG_LEVEL_ERROR, "Opening file %s to save certificate failed", output_file); return -1; } if (fwrite(cert_buf, 1, len, f) != len) { log_error(LOG_LEVEL_ERROR, "Writing certificate into file %s failed", output_file); fclose(f); return -1; } fclose(f); return (int)len; } /********************************************************************* * * Function : write_private_key * * Description : Writes private key into file and copies saved * content into given pointer to string. If function * returns 0 for success, this copy must be freed by * caller. * * Parameters : * 1 : key = key to write into file * 2 : ret_buf = pointer to string with created key file content * 3 : key_file_path = path where to save key file * * Returns : Length of written private key on success or negative value * on error * *********************************************************************/ static int write_private_key(mbedtls_pk_context *key, unsigned char **ret_buf, const char *key_file_path) { size_t len = 0; /* Length of created key */ FILE *f = NULL; /* File to save certificate */ int ret = 0; char err_buf[ERROR_BUF_SIZE]; /* Initializing buffer for key file content */ *ret_buf = zalloc_or_die(PRIVATE_KEY_BUF_SIZE + 1); /* * Writing private key into PEM string */ if ((ret = mbedtls_pk_write_key_pem(key, *ret_buf, PRIVATE_KEY_BUF_SIZE)) != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Writing private key into PEM string failed: %s", err_buf); ret = -1; goto exit; } len = strlen((char *)*ret_buf); /* * Saving key into file */ if ((f = fopen(key_file_path, "wb")) == NULL) { log_error(LOG_LEVEL_ERROR, "Opening file %s to save private key failed: %E", key_file_path); ret = -1; goto exit; } if (fwrite(*ret_buf, 1, len, f) != len) { fclose(f); log_error(LOG_LEVEL_ERROR, "Writing private key into file %s failed", key_file_path); ret = -1; goto exit; } fclose(f); exit: if (ret < 0) { freez(*ret_buf); *ret_buf = NULL; return ret; } return (int)len; } /********************************************************************* * * Function : generate_key * * Description : Tests if private key for host saved in csp already * exists. If this file doesn't exists, a new key is * generated and saved in a file. The generated key is also * copied into given parameter key_buf, which must be then * freed by caller. If file with key exists, key_buf * contain NULL and no private key is generated. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * 2 : key_buf = buffer to save new generated key * * Returns : -1 => Error while generating private key * 0 => Key already exists * >0 => Length of generated private key * *********************************************************************/ static int generate_key(struct client_state *csp, unsigned char **key_buf) { mbedtls_pk_context key; key_options key_opt; int ret = 0; char err_buf[ERROR_BUF_SIZE]; key_opt.key_file_path = NULL; /* * Initializing structures for key generating */ mbedtls_pk_init(&key); /* * Preparing path for key file and other properties for generating key */ key_opt.type = MBEDTLS_PK_RSA; key_opt.rsa_keysize = RSA_KEYSIZE; key_opt.key_file_path = make_certs_path(csp->config->certificate_directory, (char *)csp->http->hash_of_host_hex, KEY_FILE_TYPE); if (key_opt.key_file_path == NULL) { ret = -1; goto exit; } /* * Test if key already exists. If so, we don't have to create it again. */ if (file_exists(key_opt.key_file_path) == 1) { ret = 0; goto exit; } /* * Seed the RNG */ ret = seed_rng(csp); if (ret != 0) { ret = -1; goto exit; } /* * Setting attributes of private key and generating it */ if ((ret = mbedtls_pk_setup(&key, mbedtls_pk_info_from_type(key_opt.type))) != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_pk_setup failed: %s", err_buf); ret = -1; goto exit; } ret = mbedtls_rsa_gen_key(mbedtls_pk_rsa(key), mbedtls_ctr_drbg_random, &ctr_drbg, (unsigned)key_opt.rsa_keysize, RSA_KEY_PUBLIC_EXPONENT); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Key generating failed: %s", err_buf); ret = -1; goto exit; } /* * Exporting private key into file */ if ((ret = write_private_key(&key, key_buf, key_opt.key_file_path)) < 0) { log_error(LOG_LEVEL_ERROR, "Writing private key into file %s failed", key_opt.key_file_path); ret = -1; goto exit; } exit: /* * Freeing used variables */ freez(key_opt.key_file_path); mbedtls_pk_free(&key); return ret; } /********************************************************************* * * Function : generate_webpage_certificate * * Description : Creates certificate file in presetted directory. * If certificate already exists, no other certificate * will be created. Subject of certificate is named * by csp->http->host from parameter. This function also * triggers generating of private key for new certificate. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : -1 => Error while creating certificate. * 0 => Certificate already exists. * >0 => Length of created certificate. * *********************************************************************/ static int generate_webpage_certificate(struct client_state *csp) { mbedtls_x509_crt issuer_cert; mbedtls_pk_context loaded_issuer_key, loaded_subject_key; mbedtls_pk_context *issuer_key = &loaded_issuer_key; mbedtls_pk_context *subject_key = &loaded_subject_key; mbedtls_x509write_cert cert; mbedtls_mpi serial; unsigned char *key_buf = NULL; /* Buffer for created key */ int ret = 0; char err_buf[ERROR_BUF_SIZE]; cert_options cert_opt; /* Paths to keys and certificates needed to create certificate */ cert_opt.issuer_key = NULL; cert_opt.subject_key = NULL; cert_opt.issuer_crt = NULL; cert_opt.output_file = NULL; /* * Create key for requested host */ int subject_key_len = generate_key(csp, &key_buf); if (subject_key_len < 0) { log_error(LOG_LEVEL_ERROR, "Key generating failed"); return -1; } /* * Initializing structures for certificate generating */ mbedtls_x509write_crt_init(&cert); mbedtls_x509write_crt_set_md_alg(&cert, CERT_SIGNATURE_ALGORITHM); mbedtls_pk_init(&loaded_issuer_key); mbedtls_pk_init(&loaded_subject_key); mbedtls_mpi_init(&serial); mbedtls_x509_crt_init(&issuer_cert); /* * Presetting parameters for certificate. We must compute total length * of parameters. */ size_t cert_params_len = strlen(CERT_PARAM_COMMON_NAME) + strlen(CERT_PARAM_ORGANIZATION) + strlen(CERT_PARAM_COUNTRY) + strlen(CERT_PARAM_ORG_UNIT) + 3 * strlen(csp->http->host) + 1; char cert_params[cert_params_len]; memset(cert_params, 0, cert_params_len); /* * Converting unsigned long serial number to char * serial number. * We must compute length of serial number in string + terminating null. */ unsigned long certificate_serial = get_certificate_serial(csp); int serial_num_size = snprintf(NULL, 0, "%lu", certificate_serial) + 1; if (serial_num_size <= 0) { serial_num_size = 1; } char serial_num_text[serial_num_size]; /* Buffer for serial number */ ret = snprintf(serial_num_text, (size_t)serial_num_size, "%lu", certificate_serial); if (ret < 0 || ret >= serial_num_size) { log_error(LOG_LEVEL_ERROR, "Converting certificate serial number into string failed"); ret = -1; goto exit; } /* * Preparing parameters for certificate */ strlcpy(cert_params, CERT_PARAM_COMMON_NAME, cert_params_len); strlcat(cert_params, csp->http->host, cert_params_len); strlcat(cert_params, CERT_PARAM_ORGANIZATION, cert_params_len); strlcat(cert_params, csp->http->host, cert_params_len); strlcat(cert_params, CERT_PARAM_ORG_UNIT, cert_params_len); strlcat(cert_params, csp->http->host, cert_params_len); strlcat(cert_params, CERT_PARAM_COUNTRY, cert_params_len); cert_opt.issuer_crt = csp->config->ca_cert_file; cert_opt.issuer_key = csp->config->ca_key_file; cert_opt.subject_key = make_certs_path(csp->config->certificate_directory, (const char *)csp->http->hash_of_host_hex, KEY_FILE_TYPE); cert_opt.output_file = make_certs_path(csp->config->certificate_directory, (const char *)csp->http->hash_of_host_hex, CERT_FILE_TYPE); if (cert_opt.subject_key == NULL || cert_opt.output_file == NULL) { ret = -1; goto exit; } cert_opt.subject_pwd = CERT_SUBJECT_PASSWORD; cert_opt.issuer_pwd = csp->config->ca_password; cert_opt.subject_name = cert_params; cert_opt.not_before = GENERATED_CERT_VALID_FROM; cert_opt.not_after = GENERATED_CERT_VALID_TO; cert_opt.serial = serial_num_text; cert_opt.is_ca = 0; cert_opt.max_pathlen = -1; /* * Test if certificate exists and private key was already created */ if (file_exists(cert_opt.output_file) == 1 && subject_key_len == 0) { ret = 0; goto exit; } /* * Seed the PRNG */ ret = seed_rng(csp); if (ret != 0) { ret = -1; goto exit; } /* * Parse serial to MPI */ ret = mbedtls_mpi_read_string(&serial, 10, cert_opt.serial); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_mpi_read_string failed: %s", err_buf); ret = -1; goto exit; } /* * Loading certificates */ ret = mbedtls_x509_crt_parse_file(&issuer_cert, cert_opt.issuer_crt); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Loading issuer certificate %s failed: %s", cert_opt.issuer_crt, err_buf); ret = -1; goto exit; } ret = mbedtls_x509_dn_gets(cert_opt.issuer_name, sizeof(cert_opt.issuer_name), &issuer_cert.subject); if (ret < 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_x509_dn_gets failed: %s", err_buf); ret = -1; goto exit; } /* * Loading keys from file or from buffer */ if (key_buf != NULL && subject_key_len > 0) { /* Key was created in this function and is stored in buffer */ ret = mbedtls_pk_parse_key(&loaded_subject_key, key_buf, (size_t)(subject_key_len + 1), (unsigned const char *) cert_opt.subject_pwd, strlen(cert_opt.subject_pwd)); } else { /* Key wasn't created in this function, because it already existed */ ret = mbedtls_pk_parse_keyfile(&loaded_subject_key, cert_opt.subject_key, cert_opt.subject_pwd); } if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Parsing subject key %s failed: %s", cert_opt.subject_key, err_buf); ret = -1; goto exit; } ret = mbedtls_pk_parse_keyfile(&loaded_issuer_key, cert_opt.issuer_key, cert_opt.issuer_pwd); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Parsing issuer key %s failed: %s", cert_opt.issuer_key, err_buf); ret = -1; goto exit; } /* * Check if key and issuer certificate match */ if (!mbedtls_pk_can_do(&issuer_cert.pk, MBEDTLS_PK_RSA) || mbedtls_mpi_cmp_mpi(&mbedtls_pk_rsa(issuer_cert.pk)->N, &mbedtls_pk_rsa(*issuer_key)->N) != 0 || mbedtls_mpi_cmp_mpi(&mbedtls_pk_rsa(issuer_cert.pk)->E, &mbedtls_pk_rsa(*issuer_key)->E) != 0) { log_error(LOG_LEVEL_ERROR, "Issuer key doesn't match issuer certificate"); ret = -1; goto exit; } mbedtls_x509write_crt_set_subject_key(&cert, subject_key); mbedtls_x509write_crt_set_issuer_key(&cert, issuer_key); /* * Setting parameters of signed certificate */ ret = mbedtls_x509write_crt_set_subject_name(&cert, cert_opt.subject_name); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Setting subject name in signed certificate failed: %s", err_buf); ret = -1; goto exit; } ret = mbedtls_x509write_crt_set_issuer_name(&cert, cert_opt.issuer_name); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Setting issuer name in signed certificate failed: %s", err_buf); ret = -1; goto exit; } ret = mbedtls_x509write_crt_set_serial(&cert, &serial); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Setting serial number in signed certificate failed: %s", err_buf); ret = -1; goto exit; } ret = mbedtls_x509write_crt_set_validity(&cert, cert_opt.not_before, cert_opt.not_after); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Setting validity in signed certificate failed: %s", err_buf); ret = -1; goto exit; } /* * Setting the basicConstraints extension for certificate */ ret = mbedtls_x509write_crt_set_basic_constraints(&cert, cert_opt.is_ca, cert_opt.max_pathlen); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "Setting the basicConstraints extension " "in signed certificate failed: %s", err_buf); ret = -1; goto exit; } #if defined(MBEDTLS_SHA1_C) /* Setting the subjectKeyIdentifier extension for certificate */ ret = mbedtls_x509write_crt_set_subject_key_identifier(&cert); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_x509write_crt_set_subject_key_" "identifier failed: %s", err_buf); ret = -1; goto exit; } /* Setting the authorityKeyIdentifier extension for certificate */ ret = mbedtls_x509write_crt_set_authority_key_identifier(&cert); if (ret != 0) { mbedtls_strerror(ret, err_buf, sizeof(err_buf)); log_error(LOG_LEVEL_ERROR, "mbedtls_x509write_crt_set_authority_key_" "identifier failed: %s", err_buf); ret = -1; goto exit; } #endif /* MBEDTLS_SHA1_C */ /* * Writing certificate into file */ ret = write_certificate(&cert, cert_opt.output_file, mbedtls_ctr_drbg_random, &ctr_drbg); if (ret < 0) { log_error(LOG_LEVEL_ERROR, "Writing certificate into file failed"); goto exit; } exit: /* * Freeing used structures */ mbedtls_x509write_crt_free(&cert); mbedtls_pk_free(&loaded_subject_key); mbedtls_pk_free(&loaded_issuer_key); mbedtls_mpi_free(&serial); mbedtls_x509_crt_free(&issuer_cert); freez(cert_opt.subject_key); freez(cert_opt.output_file); freez(key_buf); return ret; } /********************************************************************* * * Function : make_certs_path * * Description : Creates path to file from three pieces. This function * takes parameters and puts them in one new mallocated * char * in correct order. Returned variable must be freed * by caller. This function is mainly used for creating * paths of certificates and keys files. * * Parameters : * 1 : conf_dir = Name/path of directory where is the file. * '.' can be used for current directory. * 2 : file_name = Name of file in conf_dir without suffix. * 3 : suffix = Suffix of given file_name. * * Returns : path => Path was built up successfully * NULL => Path can't be built up * *********************************************************************/ static char *make_certs_path(const char *conf_dir, const char *file_name, const char *suffix) { /* Test if all given parameters are valid */ if (conf_dir == NULL || *conf_dir == '\0' || file_name == NULL || *file_name == '\0' || suffix == NULL || *suffix == '\0') { log_error(LOG_LEVEL_ERROR, "make_certs_path failed: bad input parameters"); return NULL; } char *path = NULL; size_t path_size = strlen(conf_dir) + strlen(file_name) + strlen(suffix) + 2; /* Setting delimiter and editing path length */ #if defined(_WIN32) || defined(__OS2__) char delim[] = "\\"; path_size += 1; #else /* ifndef _WIN32 || __OS2__ */ char delim[] = "/"; #endif /* ifndef _WIN32 || __OS2__ */ /* * Building up path from many parts */ #if defined(unix) if (*conf_dir != '/' && basedir && *basedir) { /* * Replacing conf_dir with basedir. This new variable contains * absolute path to cwd. */ path_size += strlen(basedir) + 2; path = zalloc_or_die(path_size); strlcpy(path, basedir, path_size); strlcat(path, delim, path_size); strlcat(path, conf_dir, path_size); strlcat(path, delim, path_size); strlcat(path, file_name, path_size); strlcat(path, suffix, path_size); } else #endif /* defined unix */ { path = zalloc_or_die(path_size); strlcpy(path, conf_dir, path_size); strlcat(path, delim, path_size); strlcat(path, file_name, path_size); strlcat(path, suffix, path_size); } return path; } /********************************************************************* * * Function : get_certificate_mutex_id * * Description : Computes mutex id from host name hash. This hash must * be already saved in csp structure * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : Mutex id for given host name * *********************************************************************/ static unsigned int get_certificate_mutex_id(struct client_state *csp) { #ifdef LIMIT_MUTEX_NUMBER return (unsigned int)(csp->http->hash_of_host[0] % 32); #else return (unsigned int)(csp->http->hash_of_host[1] + 256 * (int)csp->http->hash_of_host[0]); #endif /* LIMIT_MUTEX_NUMBER */ } /********************************************************************* * * Function : get_certificate_serial * * Description : Computes serial number for new certificate from host * name hash. This hash must be already saved in csp * structure. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : Serial number for new certificate * *********************************************************************/ static unsigned long get_certificate_serial(struct client_state *csp) { unsigned long exp = 1; unsigned long serial = 0; int i = CERT_SERIAL_NUM_LENGTH; /* Length of hash is 16 bytes, we must avoid to read next chars */ if (i > 16) { i = 16; } if (i < 2) { i = 2; } for (; i >= 0; i--) { serial += exp * (unsigned)csp->http->hash_of_host[i]; exp *= 256; } return serial; } /********************************************************************* * * Function : ssl_send_certificate_error * * Description : Sends info about invalid server certificate to client. * Sent message is including all trusted chain certificates, * that can be downloaded in web browser. * * Parameters : * 1 : csp = Current client state (buffers, headers, etc...) * * Returns : N/A * *********************************************************************/ extern void ssl_send_certificate_error(struct client_state *csp) { size_t message_len = 0; int ret = 0; struct certs_chain *cert = NULL; /* Header of message with certificate informations */ const char message_begin[] = "HTTP/1.1 200 OK\r\n" "Content-Type: text/html\r\n" "Connection: close\r\n\r\n" "

Invalid server certificate

Reason: "; const char message_end[] = "\r\n\r\n"; char reason[INVALID_CERT_INFO_BUF_SIZE]; memset(reason, 0, sizeof(reason)); /* Get verification message from verification return code */ mbedtls_x509_crt_verify_info(reason, sizeof(reason), " ", csp->server_cert_verification_result); /* * Computing total length of message with all certificates inside */ message_len = strlen(message_begin) + strlen(message_end) + strlen(reason) + strlen("

") + 1; cert = &(csp->server_certs_chain); while (cert->next != NULL) { size_t base64_len = 4 * ((strlen(cert->file_buf) + 2) / 3) + 1; message_len += strlen(cert->text_buf) + strlen("
\n")
                     +  base64_len + strlen("Download certificate");
      cert = cert->next;
   }

   /*
    * Joining all blocks in one long message
    */
   char message[message_len];
   memset(message, 0, message_len);

   strlcpy(message, message_begin, message_len);
   strlcat(message, reason       , message_len);
   strlcat(message, "
"       , message_len);

   cert = &(csp->server_certs_chain);
   while (cert->next != NULL)
   {
      size_t olen = 0;
      size_t base64_len = 4 * ((strlen(cert->file_buf) + 2) / 3) + 1; /* +1 for terminating null*/
      char base64_buf[base64_len];
      memset(base64_buf, 0, base64_len);

      /* Encoding certificate into base64 code */
      ret = mbedtls_base64_encode((unsigned char*)base64_buf,
               base64_len, &olen, (const unsigned char*)cert->file_buf,
               strlen(cert->file_buf));
      if (ret != 0)
      {
         log_error(LOG_LEVEL_ERROR,
            "Encoding to base64 failed, buffer is to small");
      }

      strlcat(message, "
",        message_len);
      strlcat(message, cert->text_buf, message_len);
      strlcat(message, "
\n",     message_len);

      if (ret == 0)
      {
         strlcat(message, "Download certificate", message_len);
      }

      cert = cert->next;
   }
   strlcat(message, message_end, message_len);

   /*
    * Sending final message to client
    */
   ssl_send_data(&(csp->mbedtls_client_attr.ssl),
      (const unsigned char *)message, strlen(message));
   /*
    * Waiting before closing connection. Some browsers don't show received
    * message if there isn't this delay.
    */
   sleep(1);

   free_certificate_chain(csp);
}


/*********************************************************************
 *
 * Function    :  ssl_verify_callback
 *
 * Description :  This is a callback function for certificate verification.
 *                It's called for all certificates in server certificate
 *                trusted chain and it's preparing information about this
 *                certificates. Prepared informations can be used to inform
 *                user about invalid certificates.
 *
 * Parameters  :
 *          1  :  csp_void = Current client state (buffers, headers, etc...)
 *          2  :  crt   = certificate from trusted chain
 *          3  :  depth = depth in trusted chain
 *          4  :  flags = certificate flags
 *
 * Returns     :  0 on success and negative value on error
 *
 *********************************************************************/
static int ssl_verify_callback(void *csp_void, mbedtls_x509_crt *crt,
   int depth, uint32_t *flags)
{
   struct client_state *csp  = (struct client_state *)csp_void;
   struct certs_chain  *last = &(csp->server_certs_chain);
   size_t olen = 0;
   int ret = 0;

   /*
    * Searching for last item in certificates linked list
    */
   while (last->next != NULL)
   {
      last = last->next;
   }

   /*
    * Preparing next item in linked list for next certificate
    */
   last->next = malloc_or_die(sizeof(struct certs_chain));
   last->next->next = NULL;
   memset(last->next->text_buf, 0, sizeof(last->next->text_buf));
   memset(last->next->file_buf, 0, sizeof(last->next->file_buf));

   /*
    * Saving certificate file into buffer
    */
   if ((ret = mbedtls_pem_write_buffer(PEM_BEGIN_CRT, PEM_END_CRT,
      crt->raw.p, crt->raw.len, (unsigned char *)last->file_buf,
      sizeof(last->file_buf)-1, &olen)) != 0)
   {
      return(ret);
   }

   /*
    * Saving certificate information into buffer
    */
   mbedtls_x509_crt_info(last->text_buf, sizeof(last->text_buf) - 1,
      CERT_INFO_PREFIX, crt);

   return 0;
}


/*********************************************************************
 *
 * Function    :  free_certificate_chain
 *
 * Description :  Frees certificates linked list. This linked list is
 *                used to save informations about certificates in
 *                trusted chain.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  N/A
 *
 *********************************************************************/
static void free_certificate_chain(struct client_state *csp)
{
   struct certs_chain *cert = csp->server_certs_chain.next;

   /* Cleaning buffers */
   memset(csp->server_certs_chain.text_buf, 0,
      sizeof(csp->server_certs_chain.text_buf));
   memset(csp->server_certs_chain.file_buf, 0,
      sizeof(csp->server_certs_chain.file_buf));
   csp->server_certs_chain.next = NULL;

   /* Freeing memory in whole linked list */
   if (cert != NULL)
   {
      do
      {
         struct certs_chain *cert_for_free = cert;
         cert = cert->next;
         freez(cert_for_free);
      } while (cert != NULL);
   }
}


/*********************************************************************
 *
 * Function    :  file_exists
 *
 * Description :  Tests if file exists and is readable.
 *
 * Parameters  :
 *          1  :  path = Path to tested file.
 *
 * Returns     :  1 => File exists and is readable.
 *                0 => File doesn't exist or is not readable.
 *
 *********************************************************************/
static int file_exists(const char *path)
{
   FILE *f;
   if ((f = fopen(path, "r")) != NULL)
   {
      fclose(f);
      return 1;
   }

   return 0;
}


/*********************************************************************
 *
 * Function    :  host_to_hash
 *
 * Description :  Creates MD5 hash from host name. Host name is loaded
 *                from structure csp and saved again into it.
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     :  1 => Error while creating hash
 *                0 => Hash created successfully
 *
 *********************************************************************/
static int host_to_hash(struct client_state *csp)
{
   int ret = 0;

#if !defined(MBEDTLS_MD5_C)
   log_error(LOG_LEVEL_ERROR, "MBEDTLS_MD5_C is not defined. Can't create"
      "MD5 hash for certificate and key name.");
   return -1;
#else
   memset(csp->http->hash_of_host, 0, sizeof(csp->http->hash_of_host));
   mbedtls_md5((unsigned char *)csp->http->host, strlen(csp->http->host),
      csp->http->hash_of_host);

   /* Converting hash into string with hex */
   size_t i = 0;
   for (; i < 16; i++)
   {
      if ((ret = sprintf((char *)csp->http->hash_of_host_hex + 2 * i, "%02x",
         csp->http->hash_of_host[i])) < 0)
      {
         log_error(LOG_LEVEL_ERROR, "Sprintf return value: %d", ret);
         return -1;
      }
   }

   return 0;
#endif /* MBEDTLS_MD5_C */
}


/*********************************************************************
 *
 * Function    :  tunnel_established_successfully
 *
 * Description :  Check if parent proxy server response contains
 *                informations about successfully created connection with
 *                destination server. (HTTP/... 2xx ...)
 *
 * Parameters  :
 *          1  :  server_response = Buffer with parent proxy server response
 *          2  :  response_len = Length of server_response
 *
 * Returns     :  1 => Connection created successfully
 *                0 => Connection wasn't created successfully
 *
 *********************************************************************/
extern int tunnel_established_successfully(const char *server_response,
   unsigned int response_len)
{
   unsigned int pos = 0;

   if (server_response == NULL)
   {
      return 0;
   }

   /* Tests if "HTTP/" string is at the begin of received response */
   if (strncmp(server_response, "HTTP/", 5) != 0)
   {
      return 0;
   }

   for (pos = 0; pos < response_len; pos++)
   {
      if (server_response[pos] == ' ')
      {
         break;
      }
   }

   /*
    * response_len -3 because of buffer end, response structure and 200 code.
    * There must be at least 3 chars after space.
    * End of buffer: ... 2xx'\0'
    *             pos = |
    */
   if (pos >= (response_len - 3))
   {
      return 0;
   }

   /* Test HTTP status code */
   if (server_response[pos + 1] != '2')
   {
      return 0;
   }

   return 1;
}


/*********************************************************************
 *
 * Function    :  seed_rng
 *
 * Description :  Seeding the RNG for all SSL uses
 *
 * Parameters  :
 *          1  :  csp = Current client state (buffers, headers, etc...)
 *
 * Returns     : -1 => RNG wasn't seed successfully
 *                0 => RNG is seeded successfully
 *
 *********************************************************************/
static int seed_rng(struct client_state *csp)
{
   int ret = 0;
   char err_buf[ERROR_BUF_SIZE];

   if (rng_seeded == 0)
   {
      privoxy_mutex_lock(&rng_mutex);
      if (rng_seeded == 0)
      {
         mbedtls_ctr_drbg_init(&ctr_drbg);
         mbedtls_entropy_init(&entropy);
         ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func,
            &entropy, NULL, 0);
         if (ret != 0)
         {
            mbedtls_strerror(ret, err_buf, sizeof(err_buf));
            log_error(LOG_LEVEL_ERROR,
               "mbedtls_ctr_drbg_seed failed: %s", err_buf);
            privoxy_mutex_unlock(&rng_mutex);
            return -1;
         }
         rng_seeded = 1;
      }
      privoxy_mutex_unlock(&rng_mutex);
   }
   return 0;
}