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2007/08/24

網路穿牆術:使用VPN來突破網路限制(三) - stunnel篇

STunnel的作用是將在個人的電腦要送到外部SOCKS伺服器的資料,經過加密的步驟送出,在送給SOCKS伺服器前才解密。


如第一篇的圖所示,SOCKS伺服器本身並不直接接收個人電腦的資料,而是接收stunnel解密後的資料。Stunnel分二部份,一部份是伺服器端,在此次的實作中,STunnel伺服器和SOCKS伺服器是裝在同一台,這表示SOCKS伺服器只接受Stunnel伺服器的要求,故SOCKS只允許127.0.0.1來的資料即可。
而在個人電腦端的STunnel,則扮演著Client端的角色。負責將資料送出去前加密。加密的動作是透過SSL而且在此實作中,我們在Stunnel的伺服器和用戶端,皆產生一個新的私鑰,以確保資料的保密性。
STunnel最重要的就是私鑰,下載時附的私鑰是一點安全性也沒有的,故我們要用OpenSSL先產生私鑰。以下的例子為產生10年期的私鑰:


d:\openssl\>openssl req -new -x509 -days 3650 -nodes -config ./openssl.cnf -out s
em -keyout stunnel.pem
Loading 'screen' into random state - done
Generating a 1024 bit RSA private key
.........++++++
....................++++++
unable to write 'random state'
writing new private key to 'stunnel.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [CA]:TW
State or Province Name (full name) [Quebec]:Taipei
Locality Name (eg, city) [Montreal]:Taipei
Organization Name (eg, company) [Open Network Architecture]:Private Use
Organizational Unit Name (eg, section) [Internet Department]:N/A
Common Name (eg, YOUR name) [www.openna.com]:localhost
Email Address [admin@openna.com]:root@localhost


OpenSSL要一個設定檔openssl.cnf才能運作,Windows版的OpenSSL並沒有這個檔案,以下是該設定檔的例子:


# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

RANDFILE = D:\openssl\rnd
oid_file = D:\openssl\oid
oid_section = new_oids

# To use this configuration file with the "-extfile" option of the
# "openssl x509" utility, name here the section containing the
# X.509v3 extensions to use:
# extensions =
# (Alternatively, use a configuration file that has only
# X.509v3 extensions in its main [= default] section.)

[ new_oids ]

# We can add new OIDs in here for use by 'ca' and 'req'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

####################################################################
[ ca ]
default_ca = CA_default # The default ca section

####################################################################
[ CA_default ]

dir = D:\openssl\ # Where everything is kept
certs = $dir/certs # Where the issued certs are kept
crl_dir = $dir/crl # Where the issued crl are kept
database = $dir/ca.db.index # database index file.
new_certs_dir = $dir/ca.db.certs # default place for new certs.

certificate = $dir/certs/ca.crt # The CA certificate
serial = $dir/ca.db.serial # The current serial number
crl = $dir/crl.pem # The current CRL
private_key = $dir/private/ca.key # The private key
RANDFILE = $dir/ca.db.rand # private random number file

x509_extensions = usr_cert # The extentions to add to the cert

# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crl_extensions = crl_ext

default_days = 365 # how long to certify for
default_crl_days = 30 # how long before next CRL
default_md = md5 # which md to use.
Preserve = no # keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy = policy_match

# For the CA policy
[ policy_match ]
countryName = match
stateOrProvinceName = match
organizationName = match
organizationalUnitName = optional
commonName = supplied
emailAddress = optional

# For the 'anything' policy
# At this point in time, you must list all acceptable 'object'
# types.
[ policy_anything ]
countryName = optional
stateOrProvinceName = optional
localityName = optional
organizationName = optional
organizationalUnitName = optional
commonName = supplied
emailAddress = optional

####################################################################
[ req ]
default_bits = 1024
default_keyfile = privkey.pem
distinguished_name = req_distinguished_name
attributes = req_attributes
x509_extensions = v3_ca # The extentions to add to the self signed cert

[ req_distinguished_name ]
countryName = Country Name (2 letter code)
countryName_default = CA
countryName_min = 2
countryName_max = 2

stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = Quebec

localityName = Locality Name (eg, city)
localityName_default = Montreal

0.organizationName = Organization Name (eg, company)
0.organizationName_default = Open Network Architecture

# we can do this but it is not needed normally :-)
#1.organizationName = Second Organization Name (eg, company)
#1.organizationName_default = World Wide Web Pty Ltd

organizationalUnitName = Organizational Unit Name (eg, section)
organizationalUnitName_default = Internet Department

commonName = Common Name (eg, YOUR name)
commonName_default = www.openna.com
commonName_max = 64

emailAddress = Email Address
emailAddress_default = admin@openna.com
emailAddress_max = 40

# SET-ex3 = SET extension number 3

[ req_attributes ]
challengePassword = A challenge password
challengePassword_min = 4
challengePassword_max = 20

unstructuredName = An optional company name

[ usr_cert ]

# These extensions are added when 'ca' signs a request.

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer:always

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

[ v3_ca]

# Extensions for a typical CA


# PKIX recommendation.

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer:always

# This is what PKIX recommends but some broken software chokes on critical
# extensions.
#basicConstraints = critical,CA:true
# So we do this instead.
basicConstraints = CA:true

# Key usage: this is typical for a CA certificate. However since it will
# prevent it being used as an test self-signed certificate it is best
# left out by default.
# keyUsage = cRLSign, keyCertSign

# Some might want this also
# nsCertType = sslCA, emailCA

# Include email address in subject alt name: another PKIX recommendation
# subjectAltName=email:copy
# Copy issuer details
# issuerAltName=issuer:copy

# RAW DER hex encoding of an extension: beware experts only!
# 1.2.3.5=RAW:02:03
# You can even override a supported extension:
# basicConstraints= critical, RAW:30:03:01:01:FF

[ crl_ext ]
# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always,issuer:always


產生好二個私鑰,分別放在伺服器和用戶端的STunnel目錄的中。
再來就是STunnel伺服器端的設定STunnel.conf:


; cert後面接著放私鑰的檔名
cert = stunnel.pem
socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1
; rle壓縮,不用zip是因為zip較吃CPU
compression = rle
; 除錯開到最大
debug = 7
output = stunnel.log
[socks2ssl]
;接受8080 Port
accept = 8080
;連到1080 Port出去
connect = 127.0.0.1:1080



STunnel用戶端的設定STunnel.conf:


cert = stunnel.pem
socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1

compression = rle
debug = 7
output = stunnel.log

; 用戶端模式,此例子為有經過公司的Proxy出去的狀況,並且在公司的Web Proxy並不用密碼的情況下所設計,如果Web Proxy要密碼(例如要NT的帳號認證),那就要在PC端,再架一台二級代理,例如NTLMAPS代理伺服器。
client = yes
[socks2ssl]
;接受SocksCap從1081 Port
accept = localhost:1081

;Proxy Server的IP和Port
connect = 192.168.0.250:80

;遠端電腦的IP和STunnelPort
protocolHost = 10.1.1.250:8080
protocol = connect
delay = yes

;下方為3proxy中設定的帳號密碼
protocolPassword = abc123
protocolUsername = user1

; 下方為簡易模式
;[socks2ssl]
;accept = localhost:1081
;connect = 172.20.254.225:8080



設定好後,執行二端的STunnel,這部份就算完成。

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