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Seed Lab PKI Writeup

Luke
Author
Luke
Currently a master student in NYCU High Speed Lab
Table of Contents

Motivation
#

公開金鑰加密是當前通訊安全的基礎，但在雙方傳送公開金鑰時，也成為中間人攻擊的目標之一，其根本的問題在於 驗證公開金鑰的擁有者 不是件容易的事情，換句話說，如何驗證送過來的公開金鑰就如它聲稱的是來自於該擁有者，而 公開金鑰基礎設施 (Public Key Infrastructure, PKI) 就是此問題的有效解法

Lab Environment
#

Get Corresponding Files
#

至 Seed Labs 2.0 > Crypto > PKI Lab 下載相關檔案，包含 [題目說明] (https://seedsecuritylabs.org/Labs_20.04/Files/Crypto_PKI/Crypto_PKI.pdf )與 lab 環境

DNS Set Up
#

在這個 lab 當中，會以 www.bank32.com 作為設定 HTTPS server 的範例，因此需特別針對 DNS 做設定

# 打開 /etc/hosts，新增下面一行資訊
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ sudo vim /etc/hosts

10.9.0.80 www.bank32.com

Lab Tasks
#

Task 1: Becoming a Certificate Authority (CA)
#

:::success 憑證管理中心、憑證頒發機構 (Certificate Authority, CA) 是具公信力第三方，可對個人及機關團體提供認證及憑證簽發管理等服務，而數位憑證 (digital certificates) 可以用來證明一把公開金鑰的擁有性。有些商業類型的 CAs 被稱作根憑證頒發機構 (root CAs)，例如 VeriSign ，一般用戶可以透過 CA 獲取數位憑證，而 CA 的憑證可能是由另一間 CA 所頒發，不斷追溯源頭就會找到一間最大的 CA，即 root CA，而 root CA 的憑證是自行頒發的 (self-signed)，也理所當然的被相信，通常 root CA 憑證都是先裝在大多數的作業系統、網路瀏覽器或其他需要 PKI 的軟體

這個 task 的目標就是假扮 root CA 產生一張數位憑證，並在之後的 task 頒發憑證給其他 server :::

要使用 OpenSSL 產生憑證會需要一份設定檔 (configuration file)，通常設定檔會以 .cnf 後綴結尾，供三個 OpenSSL 指令所使用： ca, req 以及 x509。預設上 OpenSSL 會使用 /usr/lib/ssl/openssl.cnf 作為設定檔，但因為我會需要對它做一些修正，所以先將它複製到當前目錄，並告訴 OpenSSL 要使用這份新的配置檔。

在配置檔中的預設設定提到，所有東西會放在 ./demoCA 底下，頒發的 certs 會放在 $dir/certs，頒發的 crl 會放在 $dir/crl，新憑證會放在 $dir/newcerts，index file 的資料庫為 $dir/index.txt，serial number 會放在 $dir/derial 中。因此先根據上述設定建立環境

# 把預設的 conf 檔從 /usr/lib/ssl/openssl.cnf 複製過來，重新命名成 myCA_openssl.cnf
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ cp /usr/lib/ssl/openssl.cnf myCA_openssl.cnf

# 創建資料夾 demoCA
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ mkdir demoCA

# 進到 demoCA
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ cd demoCA/

# 再創建三個資料夾 certs, crl 和 newcerts
[02/13/25]seed@VM:~/.../demoCA$ mkdir certs crl newcerts

# 創建兩個空白檔案 index.txt 和 serial
[02/13/25]seed@VM:~/.../demoCA$ touch index.txt serial

# serial 裡面要放 serial number，假設放 1000
[02/13/25]seed@VM:~/.../demoCA$ echo 1000 > serial

又因為這個 lab 可能會對同一個 subject 創建很多次憑證，所以需要特別把 #unique_subject = no 這行取消註解

# 編輯 myCA_openssl.cnf，將 unique_subject = no 那行取消註解
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ vim myCA_openssl.cnf

# 節錄 myCA_openssl.cnf 內容
[ CA_default ]

dir		= ./demoCA		# 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/index.txt	# database index file.
unique_subject	= no			# Set to 'no' to allow creation of
					# several certs with same subject.
new_certs_dir	= $dir/newcerts	# default place for new certs.

certificate	= $dir/cacert.pem 	# The CA certificate
serial		= $dir/serial 		# The current serial number
crlnumber	= $dir/crlnumber	# the current crl number
					# must be commented out to leave a V1 CRL
crl		= $dir/crl.pem 	# The current CRL
private_key	= $dir/private/cakey.pem# The private key

x509_extensions	= usr_cert	# The extensions to add to the cert

完成設定檔後，即可透過 openssl 指令產生憑證，又因為這個 lab 是假設為 root CA，因此簽出來的憑證會是自簽憑證，指令如下

# 使用以下指令產生憑證
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -keyout ca.key -out ca.crt -subj "/CN=www.modelCA.com/O=Model CA LTD./C=US" -passout pass:dees
Generating a RSA private key
....................................................................................................................................................................................................................++++
.......................................++++
writing new private key to 'ca.key'
-----
指令、參數說明
openssl req向 root CA 發送憑證簽署要求或自前憑證
-x509告訴 OpenSSL 這是自簽憑證，而不是簽給別人
-newkey rsa:4096產生一組大小為 4096 bits 用來簽署憑證的 RSA key-pair
-sha256指定要用 sha256 簽署該憑證
-days 3650設定有效日期為 3650 天
-keyout ca.keyCA private key 儲存於 ca.key 中
-out ca.crt公鑰憑證 (public key certificate) 存放於 ca.crt 中
-subj "/CN=www.modelCA.com/O=Model CA LTD./C=US"subject information
/CN: Common Name
/O: Organization
/C: Country
-passout pass:dees密碼，每次使用此 CA 為他人簽憑證時都需輸入一次

可以透過以下指令查看憑證

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl x509 -in ca.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            74:cd:b2:fb:e0:15:b2:1f:12:e1:4a:41:39:8d:7b:31:26:9f:b8:44
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN = www.modelCA.com, O = Model CA LTD., C = US
        Validity
            Not Before: Feb 13 07:38:24 2025 GMT
            Not After : Feb 11 07:38:24 2035 GMT
        Subject: CN = www.modelCA.com, O = Model CA LTD., C = US
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (4096 bit)
                Modulus:
                    00:e4:6f:76:32:94:48:4d:c4:e1:18:23:d9:c7:cb:...
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier: 
                A5:E9:74:99:52:6F:A3:D7:0E:8A:A6:C1:F6:E6:24:5B:BE:C6:A4:03
            X509v3 Authority Key Identifier: 
                keyid:A5:E9:74:99:52:6F:A3:D7:0E:8A:A6:C1:F6:E6:24:5B:BE:C6:A4:03

            X509v3 Basic Constraints: critical
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         03:e3:a7:4f:b2:e2:6b:df:66:f0:bc:32:1d:3d:c1:25:fb:e3:...
指令、參數說明
openssl x509告訴 OpenSSL 要解讀 X509 憑證
-in ca.crt指定 input file
-text以人類讀得懂的方式顯示該憑證的完整資訊
包含擁有者 (Subject) 資訊、發佈人資訊、驗證期限、公鑰資訊、簽章所用演算法等等
-noout不要顯示 base64 編碼版本
如果沒加這行則會同時印出編碼版與文字版

另外，可以透過以下指令查看私鑰

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl rsa -in ca.key -text -noout
Enter pass phrase for ca.key:
RSA Private-Key: (4096 bit, 2 primes)
modulus:
    00:e4:6f:76:32:94:48:4d:c4:e1:18:23:d9:c7:cb:...
publicExponent: 65537 (0x10001)
privateExponent:
    00:84:df:d4:e7:fc:da:c5:e9:d4:68:ff:49:89:6e:...
prime1:
    00:f4:53:7e:98:01:5e:0d:f3:86:90:c1:4c:bd:5f:...
prime2:
    00:ef:59:98:f5:44:32:bf:8f:ad:43:8d:21:8a:e4:...
exponent1:
    0d:71:82:a7:ae:7b:94:5c:ef:ec:8b:16:43:dd:38:...
exponent2:
    00:80:cb:d3:f5:57:67:7f:91:8f:08:e4:af:02:10:...
coefficient:
    00:8f:2f:26:4b:4e:27:5f:bf:17:39:fe:e4:3f:1f:...
指令、參數說明
openssl rsa告訴 OpenSSL 要做與 RSA 私鑰相關的事情
-in ca.key指定 input file
-text以人類讀得懂的方式顯示該憑證的完整資訊
包含私鑰組成以及公鑰推導等等
-noout不要顯示 base64 編碼版本
如果沒加這行則會同時印出編碼版與文字版
  1. What part of the certificate indicates this is a CA’s certificate?

    CA:TRUE

  2. What part of the certificate indicates this is a self-signed certificate?

    Issuer 與 Subject 皆相同

  3. In the RSA algorithm, we have a public exponent e, a private exponent d, a modulus n, and two secret numbers p and q, such that n = pq. Please identify the values for these elements in your certificate and key files.
    參數值
    eca.crt 中的 Exponent
    ca.key 中的 publicExponent
    dca.key 中的 privateExponent
    nca.crt 中的 Modulus
    ca.key 中的 Modulus
    pca.key 中的 prime1
    qca.key 中的 prime2

Task 2: Generating a Certificate Request for Your Web Server
#

接下來要幫一間叫做 bank32.com 的公司簽憑證，流程是 bank32.com 發送一個憑證簽署請求 (Certificate Signing Request, CSR)，CSR 會被送到 CA 那邊，再由 CA 驗證提交的身分資訊是否正確，最後產生憑證。在 Task 2 中，會模擬 bank32.com 發送 CSR 至 CA 端

與 Task 1 十分類似，只是這次不需要加上 -x509，因為這次不是自簽憑證

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -newkey rsa:2048 -sha256 -keyout server.key -out server.csr -subj "/CN=www.bank32.com/O=Bank32 Inc./C=US" -passout pass:dees
Generating a RSA private key
.....................................................................+++++
......................+++++
writing new private key to 'server.key'
-----

查看一下 CSR

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -in server.csr -text -noout
Certificate Request:
    Data:
        Version: 1 (0x0)
        Subject: CN = www.bank32.com, O = Bank32 Inc., C = US
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:c9:fc:7a:a2:0e:c3:f8:a1:4c:b6:ee:1c:c9:07:...
                Exponent: 65537 (0x10001)
        Attributes:
            a0:00
    Signature Algorithm: sha256WithRSAEncryption
         28:78:1e:30:e9:ff:21:48:6a:cb:26:4c:d0:98:ca:48:9a:38:...

不過現今很多網站會有不同的 URL，但都可以連到同一個伺服器，這是因為瀏覽器的 hostname matching policy，可以透過 X509 的延伸套件 (extension) Subject Alternative Name (SAN) 幫主機指定不同 URL 別名，如此提交的 CSR 就會告訴 CA 這些別名都可以使用

這邊要透過指令 -addext "subjectAltName = DNS:<URL>" 做到，不過需要注意 subjectAltName 中還是必須包含 common name (CN)，否則 CN 會變成 invalid name

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -newkey rsa:2048 -sha256 -keyout server.key -out server.csr -subj "/CN=www.bank32.com/O=Bank32 Inc./C=US" -passout pass:dees -addext "subjectAltName = DNS:www.bank32.com, DNS:www.bank32A.com, DNS:www.bank32B.com"
Generating a RSA private key
.................+++++
....+++++
writing new private key to 'server.key'
-----

查看一下更新後的 CSR，就看到有多一段 Requested Extension 指出 URL alias

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -in server.csr -text -noout
Certificate Request:
    Data:
        Version: 1 (0x0)
        Subject: CN = www.bank32.com, O = Bank32 Inc., C = US
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:ec:2a:5a:ac:70:e0:f6:99:20:e0:22:17:cd:f7:...
                Exponent: 65537 (0x10001)
        Attributes:
        Requested Extensions:
            X509v3 Subject Alternative Name: 
                DNS:www.bank32.com, DNS:www.bank32A.com, DNS:www.bank32B.com
    Signature Algorithm: sha256WithRSAEncryption
         20:ae:80:70:aa:ad:e5:b7:23:62:2f:c8:c5:04:60:34:37:44:...

Task 3: Generating a Certificate for your server
#

延續 Task 2，在 Task 3 中，要扮演回 CA 的角色，拿著 CSR 幫助 bank32.com 產生憑證。

要注意的是，因為安全性的考量，OpenSSL 預設不讓 openssl ca 從 request 中複製 extension field 至最終的憑證，但這次先把這個預設打開，從 myCA_openssl.cnf 中取消註解 # copy_extensions = copy

# 編輯 myCA_openssl.cnf，將 copy_extensions = copy 那行取消註解
[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ vim myCA_openssl.cnf

# 節錄 myCA_openssl.cnf 內容
[ CA_default ]

dir		= ./demoCA		# 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/index.txt	# database index file.
unique_subject	= no			# Set to 'no' to allow creation of
					# several certs with same subject.
new_certs_dir	= $dir/newcerts		# default place for new certs.

certificate	= $dir/cacert.pem 	# The CA certificate
serial		= $dir/serial 		# The current serial number
crlnumber	= $dir/crlnumber	# the current crl number
					# must be commented out to leave a V1 CRL
crl		= $dir/crl.pem 		# The current CRL
private_key	= $dir/private/cakey.pem# The private key

x509_extensions	= usr_cert		# The extensions to add to the cert

# Comment out the following two lines for the "traditional"
# (and highly broken) format.
name_opt 	= ca_default		# Subject Name options
cert_opt 	= ca_default		# Certificate field options

# Extension copying option: use with caution.
copy_extensions = copy

接著透過下面的指令產生憑證

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl ca -config myCA_openssl.cnf -policy policy_anything -md sha256 -days 3650 -in server.csr -out server.crt -batch -cert ca.crt -keyfile ca.key
Using configuration from myCA_openssl.cnf
Enter pass phrase for ca.key:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 4096 (0x1000)
        Validity
            Not Before: Feb 13 09:25:04 2025 GMT
            Not After : Feb 11 09:25:04 2035 GMT
        Subject:
            countryName               = US
            organizationName          = Bank32 Inc.
            commonName                = www.bank32.com
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                A7:DB:BB:3C:41:57:FD:0F:32:07:B5:25:71:5C:C1:C4:C6:CE:CF:D5
            X509v3 Authority Key Identifier: 
                keyid:A5:E9:74:99:52:6F:A3:D7:0E:8A:A6:C1:F6:E6:24:5B:BE:C6:A4:03

            X509v3 Subject Alternative Name: 
                DNS:www.bank32.com, DNS:www.bank32A.com, DNS:www.bank32B.com
Certificate is to be certified until Feb 11 09:25:04 2035 GMT (3650 days)

Write out database with 1 new entries
Data Base Updated
指令、參數說明
openssl ca告訴 OpenSSL 現在要簽核一張 CSR
-config myCA_openssl.cnf告訴 OpenSSL 使用 myCA_openssl.cnf 這個設定檔
-policy policy_anything指定憑證使用的政策
policy_anything 在 myCA_openssl.cnf 中有提及
-md sha256使用 sha256 簽署憑證
-days 3650設定有效日期為 3650 天
-in server.csr指定 input CSR 為 server.csr
-out server.crt指定產出的憑證名為 server.crt
-batch執行 batch mode，這樣就不會中途停下來要求手動許可簽屬程序
-cert ca.crt指定使用 CA 的憑證 ca.crt 簽署 CSR
-keyfile ca.key使用 ca.key 作為 CA 的私鑰簽署 CSR

確認簽署的憑證，應該包含 CSR 中指定的 DNS alias

[02/13/25]seed@VM:~/.../SEEDLAB-PKI$ openssl x509 -in server.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 4096 (0x1000)
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN = www.modelCA.com, O = Model CA LTD., C = US
        Validity
            Not Before: Feb 13 09:25:04 2025 GMT
            Not After : Feb 11 09:25:04 2035 GMT
        Subject: C = US, O = Bank32 Inc., CN = www.bank32.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:ec:2a:5a:ac:70:e0:f6:99:20:e0:22:17:cd:f7:...
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                A7:DB:BB:3C:41:57:FD:0F:32:07:B5:25:71:5C:C1:C4:C6:CE:CF:D5
            X509v3 Authority Key Identifier: 
                keyid:A5:E9:74:99:52:6F:A3:D7:0E:8A:A6:C1:F6:E6:24:5B:BE:C6:A4:03

            X509v3 Subject Alternative Name: 
                DNS:www.bank32.com, DNS:www.bank32A.com, DNS:www.bank32B.com
    Signature Algorithm: sha256WithRSAEncryption
         df:0b:02:78:52:d2:b8:9e:d7:23:56:1e:b5:11:81:ac:40:a6:...

Task 4: Deploying Certificate in an Apache-Based HTTPS Website
#

Task 4 要實際將產生的憑證放入瀏覽器中，使其能夠辨識並使用 HTTPS 安全瀏覽信任的網頁。概念上來說，對於 CA 而言，需要將先前產生的憑證 ca.crt 提交給瀏覽器，跟瀏覽器說我相信這個 CA 簽出來的憑證；對 bank32 這間公司而言，瀏覽器會跟它要屬於它的憑證，即 server.crt，又因為 server.crt 是 CA 簽出來的，所以瀏覽器會相信，並讓用戶成功瀏覽 https://www.bank32.com 網頁。

這個 task 會需要建置基於 HTTPS 的 apache server，Seed lab 已經將它安裝於 container，只需要根據先前 tasks 產生的內容作一些設定上的調整即可

第一個是要修改 apache server 的設定檔，位於 image_www/bank32_apache_ssl.conf，需要調整 bank32 的資訊，包含 SSLCertificateFile 會從 /certs/server.crt 抓，相似地，SSLCertificateKeyFile 會從 /certs/server.key 取得，結果如下：

<VirtualHost *:443> 
    DocumentRoot /var/www/bank32
    ServerName www.bank32.com
    ServerAlias www.bank32A.com
    ServerAlias www.bank32B.com
    ServerAlias www.bank32W.com
    DirectoryIndex index.html
    SSLEngine On 
    SSLCertificateFile /certs/server.crt
    SSLCertificateKeyFile /certs/server.key
</VirtualHost>

<VirtualHost *:80> 
    DocumentRoot /var/www/bank32
    ServerName www.bank32.com
    DirectoryIndex index_red.html
</VirtualHost>

# Set the following gloal entry to suppress an annoying warning message
ServerName localhost

接著是 Dockerfile，建置 container 時要把 server.crt 和 server.key 複製到 container 的 /certs/ 中

FROM handsonsecurity/seed-server:apache-php

ARG WWWDIR=/var/www/bank32

COPY ./index.html ./index_red.html $WWWDIR/
COPY ./bank32_apache_ssl.conf /etc/apache2/sites-available
COPY ./certs/server.crt ./certs/server.key  /certs/

RUN  chmod 400 /certs/server.key \
     && chmod 644 $WWWDIR/index.html \
     && chmod 644 $WWWDIR/index_red.html \
     && asenmod ssl \
     && a2ensite bank32_apache_ssl   

CMD  tail -f /dev/null

根據上面調整的內容，把 server.crt 以及 server.key 移到 image_www/certs/ 中

使用 dcbuild 建置環境，並以 dcup 將 container 啟動

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dcbuild
Building web-server
Step 1/7 : FROM handsonsecurity/seed-server:apache-php
 ---> 2365d0ed3ad9
Step 2/7 : ARG WWWDIR=/var/www/bank32
 ---> Using cache
 ---> 16a0763ac43d
Step 3/7 : COPY ./index.html ./index_red.html $WWWDIR/
 ---> Using cache
 ---> 718a24968c38
Step 4/7 : COPY ./bank32_apache_ssl.conf /etc/apache2/sites-available
 ---> Using cache
 ---> 844a04cc06cf
Step 5/7 : COPY ./certs/server.crt ./certs/server.key  /certs/
 ---> d81c4562174e
Step 6/7 : RUN  chmod 400 /certs/server.key      && chmod 644 $WWWDIR/index.html      && chmod 644 $WWWDIR/index_red.html      && a2ensite bank32_apache_ssl
 ---> Running in 6e1c1867ea71
Enabling site bank32_apache_ssl.
To activate the new configuration, you need to run:
  service apache2 reload
Removing intermediate container 6e1c1867ea71
 ---> 7ed73be4cc19
Step 7/7 : CMD  tail -f /dev/null
 ---> Running in a8c9a1796b6f
Removing intermediate container a8c9a1796b6f
 ---> 362809e7726b

Successfully built 362809e7726b
Successfully tagged seed-image-www-pki:latest
[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dcup -d
Creating network "net-10.9.0.0" with the default driver
Creating www-10.9.0.80 ... done

透過 dockps 可查看 container ID，以 docksh <id> 連線進去

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dockps
0cc4d835efca  www-10.9.0.80
[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ docksh 0c
root@0cc4d835efca:/#

進到 container 後，要開啟 apache service，使用指令 service apache2 start，它會要求輸入 server.key 的密碼，密碼為 dees

root@0cc4d835efca:/# service apache2 start
 * Starting Apache httpd web server apache2                                 Enter passphrase for SSL/TLS keys for www.bank32.com:443 (RSA):
 * 
root@0cc4d835efca:/#

打開 firefox 瀏覽器，嘗試連線 https://www.bank32.com ，會發現還是無法連線，這是因為我們還沒告知瀏覽器我們的 CA 是可以信任的 Task4-1

在網址列輸入 about:preferences#private，找到憑證的區域，點擊 View Certificate Task4-2

在 Authorities 標籤內，點擊 Import Task4-3

匯入 ca.crt 這張憑證 Task4-4

這邊要選擇 “Trust this CA to identify websites”，這樣瀏覽器就會信任這個 CA 所頒發的憑證的網站 Task4-5

重新瀏覽 https://www.bank32.com ，看到綠色的 Hello World 代表成功連線 Task4-6

Task 5: Launching a Man-In-The-Middle Attack
#

Task 5 會說明 PKI 可以阻擋中間人攻擊，先簡單說明這個 Task 的攻擊場景：接下來有三個人物：用戶 (Alice)、中間人 (MITM)、伺服器 (server)，Alice 打算使用 server 的服務，MITM 打算從中作梗，讓 Alice 存取的服務有問題，在這個 task 中，假設 server 是師大資工 www.csie.ntnu.edu.tw ，Alice 想要瀏覽該網頁，而中間人（也就是自己）打算將該網站導到別的地方，如果成功導向其他地方，那代表 MITM 攻擊成功，否則表示 PKI 成功阻擋了 MITM 攻擊。

接著要思考如何進行攻擊，有兩個方法可以做到，一個是直接攻擊路由，另一個方法是攻擊 DNS，這個 task 中會以後者作為範例。假設中間人有方法修改 Alice 本機上的 /etc/hosts（VM 上的 /etc/hosts/），並新增 10.9.0.80 www.csie.ntnu.edu.tw，如此當 Alice 瀏覽 https://www.csie.ntnu.edu.tw 時，就會被導到 10.9.0.80，也就是 MITM 自架的服務

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ sudo vim /etc/hosts

10.9.0.80 www.csie.ntnu.edu.tw

打開 firefox 瀏覽器，嘗試連線 https://www.csie.ntnu.edu.tw ，會發現並沒有如 Task 4 一樣顯示綠色的 Hello World 頁面，表示 PKI 有成功擋下 MITM 攻擊 Task5-1

進到 Task 6 之前稍微說明一下原因：原因就是因為 https://www.csie.ntnu.edu.tw 並無法提交合格的憑證，所以 PKI 將它擋了下來

Task 6: Launching a Man-In-The-Middle Attack with a Compromised CA
#

Task 6 就是要幫假服務偽造假憑證，使 MITM 攻擊成功，過程基本上就是仿造 Task 1-4

首先建立向 CA 發出憑證簽署要求的 CSR (ntnu.csr) 及私鑰 (ntnu.key)，再讓 CA 簽署該 CSR，產生憑證 ntnu.crt

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ openssl req -newkey rsa:2048 -sha256 -keyout ntnu.key -out ntnu.csr -subj "/CN=www.csie.ntnu.edu.tw/O=NTNU CSIE/C=TW" -passout pass:dees
Generating a RSA private key
..........................................................................................+++++
.............................................................................................................................................................................+++++
writing new private key to 'ntnu.key'
-----
[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ openssl ca -config myCA_openssl.cnf -policy policy_anything -md sha256 -days 3650 -in ntnu.csr -out ntnu.crt -batch -cert ca.crt -keyfile ca.key
Using configuration from myCA_openssl.cnf
Enter pass phrase for ca.key:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number: 4097 (0x1001)
        Validity
            Not Before: Feb 14 15:08:24 2025 GMT
            Not After : Feb 12 15:08:24 2035 GMT
        Subject:
            countryName               = TW
            organizationName          = NTNU CSIE
            commonName                = www.csie.ntnu.edu.tw
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                53:48:8B:B3:ED:7F:8C:1E:19:7C:FA:84:F7:05:BC:59:69:6E:3F:51
            X509v3 Authority Key Identifier: 
                keyid:D6:9E:DC:28:B8:0B:6E:67:00:F1:F3:C2:83:AC:7C:66:89:AC:D4:FF

Certificate is to be certified until Feb 12 15:08:24 2035 GMT (3650 days)

Write out database with 1 new entries
Data Base Updated

接著修改 container 設定，Dockerfile 設定如下

FROM handsonsecurity/seed-server:apache-php

ARG WWWDIR=/var/www/bank32

COPY ./index.html ./index_red.html $WWWDIR/
COPY ./bank32_apache_ssl.conf /etc/apache2/sites-available
COPY ./ntnu_apache_ssl.conf /etc/apache2/sites-available
COPY ./certs/server.crt ./certs/server.key  /certs/
COPY ./certs/ntnu.crt ./certs/ntnu.key  /certs/

RUN  chmod 400 /certs/server.key \
     && chmod 400 /certs/ntnu.key \
     && chmod 644 $WWWDIR/index.html \
     && chmod 644 $WWWDIR/index_red.html \
     && a2enmod ssl \
     && a2ensite bank32_apache_ssl \
     && a2ensite ntnu_apache_ssl   

CMD  tail -f /dev/null

apache server 也要新增 https://www.csie.ntnu.edu.tw

[02/14/25]seed@VM:~/.../image_www$ cp bank32_apache_ssl.conf ntnu_apache_ssl.conf
[02/14/25]seed@VM:~/.../image_www$ vim ntnu_apache_ssl.conf

ntnu_apache_ssl.conf 設定如下

<VirtualHost *:443> 
    DocumentRoot /var/www/bank32
    ServerName www.csie.ntnu.edu.tw
    DirectoryIndex index.html
    SSLEngine On 
    SSLCertificateFile /certs/ntnu.crt
    SSLCertificateKeyFile /certs/ntnu.key
</VirtualHost>

<VirtualHost *:80> 
    DocumentRoot /var/www/bank32
    ServerName www.csie.ntnu.edu.tw
    DirectoryIndex index_red.html
</VirtualHost>

# Set the following gloal entry to suppress an annoying warning message
ServerName localhost

一樣根據 Dockerfile 的設定，將 ntnu.crt、ntnu.key 複製到 image_www/certs 中

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ cp ntnu.crt ntnu.key ./image_www/certs/

最後 dcbuild 建置 container，dcup 啟動

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dcbuild
Building web-server
Step 1/9 : FROM handsonsecurity/seed-server:apache-php
 ---> 2365d0ed3ad9
Step 2/9 : ARG WWWDIR=/var/www/bank32
 ---> Using cache
 ---> 16a0763ac43d
Step 3/9 : COPY ./index.html ./index_red.html $WWWDIR/
 ---> Using cache
 ---> 718a24968c38
Step 4/9 : COPY ./bank32_apache_ssl.conf /etc/apache2/sites-available
 ---> Using cache
 ---> 844a04cc06cf
Step 5/9 : COPY ./ntnu_apache_ssl.conf /etc/apache2/sites-available
 ---> 4f12dd172ab3
Step 6/9 : COPY ./certs/server.crt ./certs/server.key  /certs/
 ---> 72f13efc4133
Step 7/9 : COPY ./certs/ntnu.crt ./certs/ntnu.key  /certs/
 ---> cff8cc3d7e59
Step 8/9 : RUN  chmod 400 /certs/server.key      && chmod 400 /certs/ntnu.key      && chmod 644 $WWWDIR/index.html      && chmod 644 $WWWDIR/index_red.html      && a2ensite bank32_apache_ssl      && a2ensite ntnu_apache_ssl
 ---> Running in baafc9959d27
Enabling site bank32_apache_ssl.
To activate the new configuration, you need to run:
  service apache2 reload
Enabling site ntnu_apache_ssl.
To activate the new configuration, you need to run:
  service apache2 reload
Removing intermediate container baafc9959d27
 ---> b781c9decb84
Step 9/9 : CMD  tail -f /dev/null
 ---> Running in afe500be0d41
Removing intermediate container afe500be0d41
 ---> a79c3a37a3b6

Successfully built a79c3a37a3b6
Successfully tagged seed-image-www-pki:latest
[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dcup -d
Creating network "net-10.9.0.0" with the default driver
Creating www-10.9.0.80 ... done

docksh <id> 連進 container 後，使用指令 service apache2 start 啟用 apache 服務

[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ dockps
5b31c4d5ea6f  www-10.9.0.80
[02/14/25]seed@VM:~/.../SEEDLAB-PKI$ docksh 5b
root@5b31c4d5ea6f:/# service apache2 start
 * Starting Apache httpd web server apache2                                                                                                                                                                Enter passphrase for SSL/TLS keys for www.csie.ntnu.edu.tw:443 (RSA):
 * 
root@5b31c4d5ea6f:/#

重新瀏覽 https://www.csie.ntnu.edu.tw ，發現成功顯示 Hello World 頁面，表示 MITM 攻擊成功 Task6-1