X-Git-Url: http://git.code-monkey.de/?a=blobdiff_plain;f=src%2Fssl.c;h=62257d0c59667e130b99e68d71de1212f22966a0;hb=8299f488088878d38ccf7ba9bbccc4743e48bd13;hp=44fa0c9378d07a0eda9aaa5f7542adcb9154f3c7;hpb=0f7364c13546d3e674da3827eeb2f00a307f4b73;p=umurmur.git diff --git a/src/ssl.c b/src/ssl.c index 44fa0c9..62257d0 100644 --- a/src/ssl.c +++ b/src/ssl.c @@ -1,5 +1,5 @@ -/* Copyright (C) 2009-2011, Martin Johansson - Copyright (C) 2005-2011, Thorvald Natvig +/* Copyright (C) 2009-2014, Martin Johansson + Copyright (C) 2005-2014, Thorvald Natvig All rights reserved. @@ -30,6 +30,7 @@ */ #include #include +#include #include "conf.h" #include "log.h" @@ -40,33 +41,62 @@ * PolarSSL interface */ +#include #include #include #include #include #include -#define CA_CRT_FILENAME "ca.crt" - +#ifdef POLARSSL_API_V1_2_ABOVE +int ciphers[] = +{ + TLS_DHE_RSA_WITH_AES_256_CBC_SHA, + TLS_RSA_WITH_AES_256_CBC_SHA, + TLS_RSA_WITH_AES_128_CBC_SHA, + 0 +}; +#else int ciphers[] = { SSL_EDH_RSA_AES_256_SHA, - SSL_EDH_RSA_CAMELLIA_256_SHA, - SSL_EDH_RSA_DES_168_SHA, SSL_RSA_AES_256_SHA, - SSL_RSA_CAMELLIA_256_SHA, SSL_RSA_AES_128_SHA, - SSL_RSA_CAMELLIA_128_SHA, - SSL_RSA_DES_168_SHA, - SSL_RSA_RC4_128_SHA, - SSL_RSA_RC4_128_MD5, 0 }; +#endif + +#ifdef POLARSSL_API_V1_3_ABOVE +static x509_crt certificate; +static inline int x509parse_keyfile(rsa_context *rsa, const char *path, + const char *pwd) +{ + int ret; + pk_context pk; + + pk_init(&pk); + ret = pk_parse_keyfile(&pk, path, pwd); + if (ret == 0 && !pk_can_do( &pk, POLARSSL_PK_RSA)) + ret = POLARSSL_ERR_PK_TYPE_MISMATCH; + if (ret == 0) + rsa_copy(rsa, pk_rsa(pk)); + else + rsa_free(rsa); + pk_free(&pk); + return ret; +} +#else static x509_cert certificate; +#endif + static rsa_context key; bool_t builtInTestCertificate; -havege_state hs; /* exported to crypt.c */ +#ifdef USE_POLARSSL_HAVEGE +havege_state hs; +#else +int urandom_fd; +#endif /* DH prime */ char *my_dhm_P = @@ -79,31 +109,35 @@ char *my_dhm_P = "DEF409C08E8AC24D1732A6128D2220DC53"; char *my_dhm_G = "4"; +#ifdef USE_POLARSSL_TESTCERT static void initTestCert() { int rc; builtInTestCertificate = true; +#ifdef POLARSSL_API_V1_3_ABOVE + rc = x509_crt_parse_rsa(&certificate, (unsigned char *)test_srv_crt, + strlen(test_srv_crt)); +#else rc = x509parse_crt(&certificate, (unsigned char *)test_srv_crt, - strlen(test_srv_crt)); + strlen(test_srv_crt)); +#endif if (rc != 0) Log_fatal("Could not parse built-in test certificate"); - rc = x509parse_crt(&certificate, (unsigned char *)test_ca_crt, - strlen(test_ca_crt)); - if (rc != 0) - Log_fatal("Could not parse built-in test CA certificate"); } static void initTestKey() { int rc; - - rc = x509parse_key(&key, (unsigned char *)test_srv_key, - strlen(test_srv_key), NULL, 0); + + rc = x509parse_key_rsa(&key, (unsigned char *)test_srv_key, + strlen(test_srv_key), NULL, 0); if (rc != 0) Log_fatal("Could not parse built-in test RSA key"); } +#endif /* + * How to generate a self-signed cert with openssl: * openssl genrsa 1024 > host.key * openssl req -new -x509 -nodes -sha1 -days 365 -key host.key > host.cert */ @@ -111,44 +145,30 @@ static void initCert() { int rc; char *crtfile = (char *)getStrConf(CERTIFICATE); - char *ca_file, *p; - + if (crtfile == NULL) { - Log_warn("No certificate file specified"); +#ifdef USE_POLARSSL_TESTCERT + Log_warn("No certificate file specified. Falling back to test certificate."); initTestCert(); +#else + Log_fatal("No certificate file specified"); +#endif return; } +#ifdef POLARSSL_API_V1_3_ABOVE + rc = x509_crt_parse_file(&certificate, crtfile); +#else rc = x509parse_crtfile(&certificate, crtfile); +#endif if (rc != 0) { - Log_warn("Could not read certificate file %s", crtfile); +#ifdef USE_POLARSSL_TESTCERT + Log_warn("Could not read certificate file '%s'. Falling back to test certificate.", crtfile); initTestCert(); +#else + Log_fatal("Could not read certificate file '%s'", crtfile); +#endif return; } - - /* Look for CA certificate file in same dir */ - ca_file = malloc(strlen(crtfile) + strlen(CA_CRT_FILENAME) + 1); - strcpy(ca_file, crtfile); - p = strrchr(ca_file, '/'); - if (p != NULL) - strcpy(p + 1, CA_CRT_FILENAME); - else - strcpy(ca_file, CA_CRT_FILENAME); - - rc = x509parse_crtfile(&certificate, ca_file); - if (rc != 0) { /* No CA certifiacte found. Assume self-signed. */ - Log_info("CA certificate file %s not found. Assuming self-signed certificate.", ca_file); - } - - /* - * PolarSSL 0.11 - 0.12,1 has a bug; it ignores the last certificate in the chain. - * Read the certificate again so that it gets last in chain. Later releases like 0.14.0 works - * fine with the extra certificate, so I don't see any harm in doing so. - */ - rc = x509parse_crtfile(&certificate, crtfile); - if (rc != 0) - Log_fatal("Could not read certificate file %s", crtfile); - - free(ca_file); } static void initKey() @@ -157,69 +177,138 @@ static void initKey() char *keyfile = (char *)getStrConf(KEY); if (keyfile == NULL) - Log_fatal("No key file specified"); + Log_fatal("No key file specified"); rc = x509parse_keyfile(&key, keyfile, NULL); if (rc != 0) Log_fatal("Could not read RSA key file %s", keyfile); } +#ifndef USE_POLARSSL_HAVEGE +int urandom_bytes(void *ctx, unsigned char *dest, size_t len) +{ + int cur; + + while (len) { + cur = read(urandom_fd, dest, len); + if (cur < 0) + continue; + len -= cur; + } + return 0; +} +#endif + #define DEBUG_LEVEL 0 static void pssl_debug(void *ctx, int level, const char *str) { if (level <= DEBUG_LEVEL) - Log_debug("PolarSSL [level %d]: %s", level, str); + Log_info("PolarSSL [level %d]: %s", level, str); } void SSLi_init(void) { + char verstring[12]; + initCert(); +#ifdef USE_POLARSSL_TESTCERT if (builtInTestCertificate) { Log_warn("*** Using built-in test certificate and RSA key ***"); - Log_warn("*** This is not secure! Please use a CA-signed certificate or create a self-signed certificate ***"); + Log_warn("*** This is not secure! Please use a CA-signed certificate or create a key and self-signed certificate ***"); initTestKey(); } else initKey(); +#else + initKey(); +#endif + + /* Initialize random number generator */ +#ifdef USE_POLARSSL_HAVEGE havege_init(&hs); - Log_info("PolarSSL library initialized"); +#else + urandom_fd = open("/dev/urandom", O_RDONLY); + if (urandom_fd < 0) + Log_fatal("Cannot open /dev/urandom"); +#endif + + version_get_string(verstring); + Log_info("PolarSSL library version %s initialized", verstring); } void SSLi_deinit(void) { +#ifdef POLARSSL_API_V1_3_ABOVE + x509_crt_free(&certificate); +#else x509_free(&certificate); +#endif rsa_free(&key); } +/* Create SHA1 of last certificate in the peer's chain. */ +bool_t SSLi_getSHA1Hash(SSL_handle_t *ssl, uint8_t *hash) +{ +#ifdef POLARSSL_API_V1_3_ABOVE + x509_crt const *cert; +#else + x509_cert const *cert; +#endif +#ifdef POLARSSL_API_V1_2_ABOVE + cert = ssl_get_peer_cert(ssl); +#else + cert = ssl->peer_cert; +#endif + if (!cert) { + return false; + } + sha1(cert->raw.p, cert->raw.len, hash); + return true; +} + SSL_handle_t *SSLi_newconnection(int *fd, bool_t *SSLready) { ssl_context *ssl; ssl_session *ssn; int rc; - + ssl = malloc(sizeof(ssl_context)); ssn = malloc(sizeof(ssl_session)); if (!ssl || !ssn) Log_fatal("Out of memory"); memset(ssl, 0, sizeof(ssl_context)); memset(ssn, 0, sizeof(ssl_session)); - + rc = ssl_init(ssl); if (rc != 0 ) - Log_fatal("Failed to initalize: %d", rc); - - ssl_set_endpoint(ssl, SSL_IS_SERVER); - ssl_set_authmode(ssl, SSL_VERIFY_OPTIONAL); + Log_fatal("Failed to initialize: %d", rc); - ssl_set_rng(ssl, havege_rand, &hs); - ssl_set_dbg(ssl, pssl_debug, NULL); - ssl_set_bio(ssl, net_recv, fd, net_send, fd); + ssl_set_endpoint(ssl, SSL_IS_SERVER); + ssl_set_authmode(ssl, SSL_VERIFY_OPTIONAL); - ssl_set_ciphers(ssl, ciphers); +#ifdef USE_POLARSSL_HAVEGE + ssl_set_rng(ssl, HAVEGE_RAND, &hs); +#else + ssl_set_rng(ssl, urandom_bytes, NULL); +#endif + + ssl_set_dbg(ssl, pssl_debug, NULL); + ssl_set_bio(ssl, net_recv, fd, net_send, fd); + + ssl_set_ciphersuites(ssl, ciphers); + +#ifdef POLARSSL_API_V1_2_ABOVE + ssl_set_session(ssl, ssn); +#else ssl_set_session(ssl, 0, 0, ssn); +#endif - ssl_set_ca_chain(ssl, certificate.next, NULL, NULL); - ssl_set_own_cert(ssl, &certificate, &key); - ssl_set_dh_param(ssl, my_dhm_P, my_dhm_G); + ssl_set_ca_chain(ssl, &certificate, NULL, NULL); +#ifdef POLARSSL_API_V1_3_ABOVE + ssl_set_own_cert_rsa(ssl, &certificate, &key); +#else + ssl_set_own_cert(ssl, &certificate, &key); +#endif + ssl_set_dh_param(ssl, my_dhm_P, my_dhm_G); return ssl; } @@ -227,10 +316,12 @@ SSL_handle_t *SSLi_newconnection(int *fd, bool_t *SSLready) int SSLi_nonblockaccept(SSL_handle_t *ssl, bool_t *SSLready) { int rc; - + rc = ssl_handshake(ssl); if (rc != 0) { - if (rc == POLARSSL_ERR_NET_TRY_AGAIN) { + if (rc == POLARSSL_ERR_NET_WANT_READ || rc == POLARSSL_ERR_NET_WANT_WRITE) { + return 0; + } else if (rc == POLARSSL_ERR_X509_CERT_VERIFY_FAILED) { /* Allow this (selfsigned etc) */ return 0; } else { Log_warn("SSL handshake failed: %d", rc); @@ -244,8 +335,9 @@ int SSLi_nonblockaccept(SSL_handle_t *ssl, bool_t *SSLready) int SSLi_read(SSL_handle_t *ssl, uint8_t *buf, int len) { int rc; + rc = ssl_read(ssl, buf, len); - if (rc == POLARSSL_ERR_NET_TRY_AGAIN) + if (rc == POLARSSL_ERR_NET_WANT_READ) return SSLI_ERROR_WANT_READ; return rc; } @@ -253,8 +345,9 @@ int SSLi_read(SSL_handle_t *ssl, uint8_t *buf, int len) int SSLi_write(SSL_handle_t *ssl, uint8_t *buf, int len) { int rc; + rc = ssl_write(ssl, buf, len); - if (rc == POLARSSL_ERR_NET_TRY_AGAIN) + if (rc == POLARSSL_ERR_NET_WANT_WRITE) return SSLI_ERROR_WANT_WRITE; return rc; } @@ -277,7 +370,10 @@ void SSLi_shutdown(SSL_handle_t *ssl) void SSLi_free(SSL_handle_t *ssl) { Log_debug("SSLi_free"); - free(ssl->session); /* XXX - Hmmm. */ +#if (POLARSSL_VERSION_MINOR <= 2 && POLARSSL_VERSION_PATCH < 6) + free(ssl->session); /* Workaround for memory leak in PolarSSL < 1.2.6 */ + ssl->session = NULL; +#endif ssl_free(ssl); free(ssl); } @@ -296,6 +392,8 @@ static RSA *rsa; static SSL_CTX *context; static EVP_PKEY *pkey; +static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx); + static int SSL_add_ext(X509 * crt, int nid, char *value) { X509_EXTENSION *ex; X509V3_CTX ctx; @@ -314,17 +412,17 @@ static X509 *SSL_readcert(char *certfile) { FILE *fp; X509 *x509; - - /* open the private key file */ + + /* open the certificate file */ fp = fopen(certfile, "r"); if (fp == NULL) { Log_warn("Unable to open the X509 file %s for reading.", certfile); return NULL; } - - /* allocate memory for the cert structure */ + + /* allocate memory for the cert structure */ x509 = X509_new(); - + if (PEM_read_X509(fp, &x509, NULL, NULL) == 0) { /* error reading the x509 information - check the error stack */ Log_warn("Error trying to read X509 info."); @@ -347,13 +445,13 @@ static RSA *SSL_readprivatekey(char *keyfile) Log_warn("Unable to open the private key file %s for reading.", keyfile); return NULL; } - + /* allocate memory for the RSA structure */ rsa = RSA_new(); - + /* assign a callback function for the password */ - - /* read a private key from file */ + + /* read a private key from file */ if (PEM_read_RSAPrivateKey(fp, &rsa, NULL, NULL) <= 0) { /* error reading the key - check the error stack */ Log_warn("Error trying to read private key."); @@ -368,23 +466,15 @@ static RSA *SSL_readprivatekey(char *keyfile) static void SSL_writecert(char *certfile, X509 *x509) { FILE *fp; - BIO *err_output; - - /* prepare a BIO for outputting error messages */ - - err_output = BIO_new_fp(stderr,BIO_NOCLOSE); - + /* open the private key file */ fp = fopen(certfile, "w"); if (fp == NULL) { - BIO_printf(err_output, "Unable to open the X509 file for writing.\n"); - BIO_free(err_output); + Log_warn("Unable to open the X509 file %s for writing", certfile); return; } - if (PEM_write_X509(fp, x509) == 0) { - BIO_printf(err_output, "Error trying to write X509 info.\n"); - ERR_print_errors(err_output); + Log_warn("Error trying to write X509 info."); } fclose(fp); } @@ -392,29 +482,24 @@ static void SSL_writecert(char *certfile, X509 *x509) static void SSL_writekey(char *keyfile, RSA *rsa) { FILE *fp; - BIO *err_output; - /* prepare a BIO for outputing error messages */ - err_output = BIO_new_fp(stderr, BIO_NOCLOSE); - + /* open the private key file for reading */ fp = fopen(keyfile, "w"); if (fp == NULL) { - BIO_printf(err_output, "Unable to open the private key file %s for writing.\n", keyfile); - BIO_free(err_output); + Log_warn("Unable to open the private key file %s for writing.", keyfile); return; } - + if (PEM_write_RSAPrivateKey(fp, rsa, NULL, NULL, 0, NULL, NULL) == 0) { - /* error reading the key - check the error stack */ - BIO_printf(err_output, "Error trying to write private key\n"); - ERR_print_errors(err_output); + Log_warn("Error trying to write private key"); } fclose(fp); } static void SSL_initializeCert() { + char *crt, *key, *pass; - + crt = (char *)getStrConf(CERTIFICATE); key = (char *)getStrConf(KEY); pass = (char *)getStrConf(PASSPHRASE); @@ -424,11 +509,12 @@ static void SSL_initializeCert() { if (rsa != NULL) { pkey = EVP_PKEY_new(); EVP_PKEY_assign_RSA(pkey, rsa); - } - + } + + #if 0 /* Later ... */ - if (key && !x509) { + if (key && !x509) { qscCert = QSslCertificate(key); if (! qscCert.isNull()) { logthis("Using certificate from key."); @@ -456,38 +542,35 @@ static void SSL_initializeCert() { } #endif - + if (!rsa || !x509) { - logthis("Generating new server certificate."); + Log_info("Generating new server certificate."); + - BIO *bio_err; - CRYPTO_mem_ctrl(CRYPTO_MEM_CHECK_ON); - - bio_err=BIO_new_fp(stderr, BIO_NOCLOSE); - + x509 = X509_new(); pkey = EVP_PKEY_new(); rsa = RSA_generate_key(1024,RSA_F4,NULL,NULL); EVP_PKEY_assign_RSA(pkey, rsa); - + X509_set_version(x509, 2); ASN1_INTEGER_set(X509_get_serialNumber(x509),1); X509_gmtime_adj(X509_get_notBefore(x509),0); X509_gmtime_adj(X509_get_notAfter(x509),60*60*24*365); X509_set_pubkey(x509, pkey); - + X509_NAME *name=X509_get_subject_name(x509); - + X509_NAME_add_entry_by_txt(name, "CN", MBSTRING_ASC, (const uint8_t *)"Murmur Autogenerated Certificate v2", -1, -1, 0); X509_set_issuer_name(x509, name); SSL_add_ext(x509, NID_basic_constraints, "critical,CA:FALSE"); SSL_add_ext(x509, NID_ext_key_usage, "serverAuth,clientAuth"); SSL_add_ext(x509, NID_subject_key_identifier, "hash"); SSL_add_ext(x509, NID_netscape_comment, "Generated from umurmur"); - + X509_sign(x509, pkey, EVP_md5()); - + SSL_writecert(crt, x509); SSL_writekey(key, rsa); } @@ -498,22 +581,29 @@ void SSLi_init(void) { const SSL_METHOD *method; SSL *ssl; - int i, offset = 0; + int i, offset = 0, cipherstringlen = 0; STACK_OF(SSL_CIPHER) *cipherlist = NULL, *cipherlist_new = NULL; SSL_CIPHER *cipher; - char cipherstring[1024]; - + char *cipherstring, tempstring[128]; + SSL_library_init(); - OpenSSL_add_all_algorithms(); /* load & register all cryptos, etc. */ - SSL_load_error_strings(); /* load all error messages */ - ERR_load_crypto_strings(); /* load all error messages */ - method = SSLv23_server_method(); /* create new server-method instance */ - context = SSL_CTX_new(method); /* create new context from method */ - if (context == NULL) - { - ERR_print_errors_fp(stderr); - abort(); - } + OpenSSL_add_all_algorithms(); /* load & register all cryptos, etc. */ + SSL_load_error_strings(); /* load all error messages */ + ERR_load_crypto_strings(); /* load all error messages */ + method = SSLv23_server_method(); /* create new server-method instance */ + context = SSL_CTX_new(method); /* create new context from method */ + if (context == NULL) + { + ERR_print_errors_fp(stderr); + abort(); + } + + char* sslCAPath = getStrConf(CAPATH); + if(sslCAPath != NULL) + { + SSL_CTX_load_verify_locations(context, NULL, sslCAPath); + } + SSL_initializeCert(); if (SSL_CTX_use_certificate(context, x509) <= 0) Log_fatal("Failed to initialize cert"); @@ -523,10 +613,10 @@ void SSLi_init(void) } /* Set cipher list */ - ssl = SSL_new(context); + ssl = SSL_new(context); cipherlist = (STACK_OF(SSL_CIPHER) *) SSL_get_ciphers(ssl); cipherlist_new = (STACK_OF(SSL_CIPHER) *) sk_SSL_CIPHER_new_null(); - + for ( i = 0; (cipher = sk_SSL_CIPHER_value(cipherlist, i)) != NULL; i++) { if (SSL_CIPHER_get_bits(cipher, NULL) >= 128) { sk_SSL_CIPHER_push(cipherlist_new, cipher); @@ -534,23 +624,32 @@ void SSLi_init(void) } Log_debug("List of ciphers:"); if (cipherlist_new) { - for ( i = 0; (cipher = sk_SSL_CIPHER_value(cipherlist_new, i)) != NULL; i++) { + for (i = 0; (cipher = sk_SSL_CIPHER_value(cipherlist_new, i)) != NULL; i++) { Log_debug("%s", SSL_CIPHER_get_name(cipher)); - offset += snprintf(cipherstring + offset, 1024 - offset, "%s:", SSL_CIPHER_get_name(cipher)); + cipherstringlen += strlen(SSL_CIPHER_get_name(cipher)) + 1; + } + cipherstring = malloc(cipherstringlen + 1); + if (cipherstring == NULL) + Log_fatal("Out of memory"); + for (i = 0; (cipher = sk_SSL_CIPHER_value(cipherlist_new, i)) != NULL; i++) { + offset += sprintf(cipherstring + offset, "%s:", SSL_CIPHER_get_name(cipher)); } - cipherstring[offset - 1] = '\0'; } - + if (cipherlist_new) sk_SSL_CIPHER_free(cipherlist_new); - + if (strlen(cipherstring) == 0) Log_fatal("No suitable ciphers found!"); - + if (SSL_CTX_set_cipher_list(context, cipherstring) == 0) Log_fatal("Failed to set cipher list!"); - - + + free(cipherstring); + + SSL_CTX_set_verify(context, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE, + verify_callback); + SSL_free(ssl); Log_info("OpenSSL library initialized"); @@ -583,7 +682,7 @@ int SSLi_nonblockaccept(SSL_handle_t *ssl, bool_t *SSLready) SSL_handle_t *SSLi_newconnection(int *fd, bool_t *SSLready) { SSL *ssl; - + *SSLready = false; ssl = SSL_new(context); SSL_set_fd(ssl, *fd); @@ -594,6 +693,32 @@ SSL_handle_t *SSLi_newconnection(int *fd, bool_t *SSLready) return ssl; } +/* Create SHA1 of last certificate in the peer's chain. */ +bool_t SSLi_getSHA1Hash(SSL_handle_t *ssl, uint8_t *hash) +{ + X509 *x509; + uint8_t *buf, *p; + int len; + + x509 = SSL_get_peer_certificate(ssl); + if (!x509) { + return false; + } + + len = i2d_X509(x509, NULL); + buf = malloc(len); + if (buf == NULL) { + Log_fatal("malloc"); + } + + p = buf; + i2d_X509(x509, &p); + + SHA1(buf, len, hash); + free(buf); + return true; +} + void SSLi_closeconnection(SSL_handle_t *ssl) { SSL_free(ssl); @@ -629,4 +754,38 @@ void SSLi_free(SSL_handle_t *ssl) SSL_free(ssl); } +static int verify_callback(int preverify_ok, X509_STORE_CTX *ctx) +{ + char buf[256]; + X509 *err_cert; + int err, depth; + SSL *ssl; + + err_cert = X509_STORE_CTX_get_current_cert(ctx); + err = X509_STORE_CTX_get_error(ctx); + depth = X509_STORE_CTX_get_error_depth(ctx); + + ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx()); + X509_NAME_oneline(X509_get_subject_name(err_cert), buf, 256); + + if (depth > 5) { + preverify_ok = 0; + err = X509_V_ERR_CERT_CHAIN_TOO_LONG; + X509_STORE_CTX_set_error(ctx, err); + } + if (!preverify_ok) { + Log_warn("SSL: verify error:num=%d:%s:depth=%d:%s\n", err, + X509_verify_cert_error_string(err), depth, buf); + } + /* + * At this point, err contains the last verification error. We can use + * it for something special + */ + if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) { + X509_NAME_oneline(X509_get_issuer_name(ctx->current_cert), buf, 256); + Log_warn("issuer= %s", buf); + } + return 1; +} + #endif