Last active
August 5, 2024 06:34
-
-
Save lockie/7dff60ee12c0a51f4cfafe5e55ad8972 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
/* compilation: gcc -o client client.c -lssl -lcrypto */ | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include <string.h> | |
#include <openssl/bio.h> /* BasicInput/Output streams */ | |
#include <openssl/err.h> /* errors */ | |
#include <openssl/ssl.h> /* core library */ | |
#define BuffSize 1024 | |
void report_and_exit(const char* msg) { | |
perror(msg); | |
ERR_print_errors_fp(stderr); | |
exit(-1); | |
} | |
void init_ssl() { | |
SSL_load_error_strings(); | |
SSL_library_init(); | |
} | |
void cleanup(SSL_CTX* ctx, BIO* bio) { | |
SSL_CTX_free(ctx); | |
BIO_free_all(bio); | |
} | |
void secure_connect(const char* hostname) { | |
char request[BuffSize]; | |
char response[BuffSize]; | |
const SSL_METHOD* method = TLS_client_method(); | |
if (NULL == method) report_and_exit("TLS_client_method..."); | |
SSL_CTX* ctx = SSL_CTX_new(method); | |
if (NULL == ctx) report_and_exit("SSL_CTX_new..."); | |
BIO* bio = BIO_new_ssl_connect(ctx); | |
if (NULL == bio) report_and_exit("BIO_new_ssl_connect..."); | |
SSL* ssl = NULL; | |
/* link bio channel, SSL session, and server endpoint */ | |
BIO_get_ssl(bio, &ssl); /* session */ | |
SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY); /* robustness */ | |
BIO_set_conn_hostname(bio, hostname); /* prepare to connect */ | |
/* try to connect */ | |
if (BIO_do_connect(bio) <= 0) { | |
cleanup(ctx, bio); | |
report_and_exit("BIO_do_connect..."); | |
} | |
/* verify truststore, check cert */ | |
if (!SSL_CTX_load_verify_locations(ctx, | |
"/etc/ssl/certs/ca-certificates.crt", /* truststore */ | |
"/etc/ssl/certs/")) /* more truststore */ | |
report_and_exit("SSL_CTX_load_verify_locations..."); | |
long verify_flag = SSL_get_verify_result(ssl); | |
if (verify_flag != X509_V_OK) | |
fprintf(stderr, | |
"##### Certificate verification error (%i) but continuing...\n", | |
(int) verify_flag); | |
/* now fetch the homepage as sample data */ | |
sprintf(request, | |
"GET / HTTP/1.1\x0D\x0AHost: %s\x0D\x0A\x43onnection: Close\x0D\x0A\x0D\x0A", | |
hostname); | |
BIO_puts(bio, request); | |
/* read HTTP response from server and print to stdout */ | |
while (1) { | |
memset(response, '\0', sizeof(response)); | |
int n = BIO_read(bio, response, BuffSize); | |
if (n <= 0) break; /* 0 is end-of-stream, < 0 is an error */ | |
puts(response); | |
} | |
cleanup(ctx, bio); | |
} | |
int main() { | |
init_ssl(); | |
const char* hostname = "www.google.com:443"; | |
fprintf(stderr, "Trying an HTTPS connection to %s...\n", hostname); | |
secure_connect(hostname); | |
return 0; | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment