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自己CAを構築し、自己CAで署名付けした中間証明書とサーバ証明書を作成する

Last updated at 2020-03-12Posted at 2020-02-18

目的

いろんな状況のサーバ証明書(revoke、期限切れ、署名連鎖不正 etc..)を検証するために証明書作成環境が必要
ルート証明書は自己署名だが、中間証明書、サーバ証明書として「正常な連鎖状態にある」証明書を使いたい。
汎用的でどこでも使えるopensslのみで構築したい。
嵌る原因となるCA.sh、CA.plを一切使わない
嵌る原因となるopenssl.cnfも既定の暗黙参照のみ
久しぶりに構築しようとすると必ず嵌っているので整理

概要

構築しようとするCA環境は以下の通り
- ルートCAは自己署名
- 中間証明書はルートCAで署名
- サーバ証明書は中間CAで署名　結果：自己署名ではないサーバ証明書の出来上がり

構築・作成手順
1. 自己署名によるルートCAを構築
2. ↑のルートCAで署名付けした中間証明書と中間CAを構築
3. ↑の中間CAで署名付けしたサーバ証明書を作成
証明書の検証
作成された証明書の利用、特別な証明書(有効期限切れ、SAN、AIA拡張、CRL/OCSP連携)については別途

環境

OS :Linux推奨

$ uname -a
Linux vUbuntuLTS 5.3.0-28-generic #30~18.04.1-Ubuntu SMP Fri Jan 17 06:14:09 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

openssl（2020/02/18時点最新)

$ openssl
OpenSSL> version
OpenSSL 1.1.1  11 Sep 2018

構築手順

共通コマンド環境の作成

任意の作業ディレクトリ(self_ca)を作成し、RCA, ICA, serverの３ディレクトリを作成
- RCA: ルートCA作業環境
- ICA: 中間CA作業環境
- server: サーバ証明書作業環境
```
$ mkdir ~/self_ca
$ mkdir ~/self_ca/RCA
$ mkdir ~/self_ca/ICA
$ mkdir ~/self_ca/server
```

自己ルートCAを構築

ルートCAディレクトリ ~/self_ca/RCAに移動

CAディレクトリとdatabaseを作成

$ mkdir -p demoCA
$ mkdir -p demoCA/certs
$ mkdir -p demoCA/crl
$ mkdir -p demoCA/newcerts
$ mkdir -p demoCA/private
$ touch demoCA/index.txt

証明書要求(careq.pem)と秘密キー(demoCA/private/cakey.pem)を作成

x.509/Organization Nameには、作成する中間証明書、サーバ証明書と同じ組織名を入力する (ex. my)
x.509/Common Nameには、ルートCA（=本サーバ）にアクセス可能なFQDNを入力する。(ex. rca.vubuntults.mydomain)

$ openssl req -new -keyout demoCA/private/cakey.pem -out demoCA/careq.pem
Generating a RSA private key
...............................................+++++
..........................+++++
writing new private key to 'demoCA/private/cakey.pem'
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
-----
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) [AU]:JP
State or Province Name (full name) [Some-State]:Tokyo
Locality Name (eg, city) []:Shinjuku-ku
Organization Name (eg, company) [Internet Widgits Pty Ltd]:my
Organizational Unit Name (eg, section) []:room
Common Name (e.g. server FQDN or YOUR name) []:rca.vubuntults.mydomain                
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

証明書要求に自己署名し、ルート証明書(demoCA/cacert.pem)を作成する。

有効期限：-days 1095
「Can't open ./demoCA/index.txt.attr for reading, No such file or directory」は無視しても良い

$ openssl ca -create_serial -out demoCA/cacert.pem -days 1095 -batch -keyfile demoCA/private/cakey.pem -selfsign -extensions v3_ca -infiles demoCA/careq.pem 
Using configuration from /usr/lib/ssl/openssl.cnf
Enter pass phrase for demoCA/private/cakey.pem:
Can't open ./demoCA/index.txt.attr for reading, No such file or directory
140363278688704:error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:72:fopen('./demoCA/index.txt.attr','r')
140363278688704:error:2006D080:BIO routines:BIO_new_file:no such file:../crypto/bio/bss_file.c:79:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number:
            19:e7:a9:be:65:1e:a5:93:6b:bf:40:81:e1:0b:dd:d2:0b:46:e0:46
        Validity
            Not Before: Feb 18 06:41:23 2020 GMT
            Not After : Feb 17 06:41:23 2023 GMT
        Subject:
            countryName               = JP
            stateOrProvinceName       = Tokyo
            organizationName          = my
            organizationalUnitName    = room
            commonName                = rca.vubuntults.mydomain
        X509v3 extensions:
            X509v3 Subject Key Identifier: 
                EE:07:B4:FE:82:93:76:BB:F6:EE:AF:63:DC:20:D7:E9:EE:BC:79:0C
            X509v3 Authority Key Identifier: 
                keyid:EE:07:B4:FE:82:93:76:BB:F6:EE:AF:63:DC:20:D7:E9:EE:BC:79:0C

            X509v3 Basic Constraints: critical
                CA:TRUE
Certificate is to be certified until Feb 17 06:41:23 2023 GMT (1095 days)

Write out database with 1 new entries
Data Base Updated

中間CAを構築

証明書要求(newreq.pem)と秘密キー(newkey.pem)を作成する。

中間CAディレクトリ ~/self_ca/ICAに移動

証明書要求コマンド(openssl req)を実行

x.509/Organization Nameには、ルート証明書、サーバ証明書と同じ組織名を入力する (ex. my)
x.509/Common Nameには、中間CA（=本サーバ）にアクセス可能なFQDNを入力する。(ex. ica.vubuntults.mydomain)

$ openssl req -new -keyout newkey.pem -out newreq.pem -days 1095
Ignoring -days; not generating a certificate
Generating a RSA private key
..........+++++
...........................................................+++++
writing new private key to 'newkey.pem'
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
-----
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) [AU]:JP
State or Province Name (full name) [Some-State]:Tokyo 
Locality Name (eg, city) []:Shinjuku-ku
Organization Name (eg, company) [Internet Widgits Pty Ltd]:my
Organizational Unit Name (eg, section) []:room
Common Name (e.g. server FQDN or YOUR name) []:ica.vubuntults.mydomain
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

証明書要求に対してルートCAで署名をし、中間証明書(../ICA/newcert.pem)を作成する

ルートCAディレクトリ ~/self_ca/RCAに移動

署名コマンド(openssl ca)を実行

$ openssl ca -policy policy_anything -out ../ICA/newcert.pem -extensions v3_ca -infiles ../ICA/newreq.pem 
Using configuration from /usr/lib/ssl/openssl.cnf
Enter pass phrase for ./demoCA/private/cakey.pem:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number:
            19:e7:a9:be:65:1e:a5:93:6b:bf:40:81:e1:0b:dd:d2:0b:46:e0:48
        Validity
            Not Before: Feb 18 09:09:40 2020 GMT
            Not After : Feb 17 09:09:40 2021 GMT
        Subject:
            countryName               = JP
            stateOrProvinceName       = Tokyo
            localityName              = Shinjuku-ku
            organizationName          = my
            organizationalUnitName    = room
            commonName                = ica.vubuntults.mydomain
        X509v3 extensions:
            X509v3 Subject Key Identifier: 
                D1:8B:4F:7B:FE:14:FA:AB:92:80:3C:D4:63:E5:F2:A9:67:CA:EB:31
            X509v3 Authority Key Identifier: 
                keyid:EE:07:B4:FE:82:93:76:BB:F6:EE:AF:63:DC:20:D7:E9:EE:BC:79:0C

            X509v3 Basic Constraints: critical
                CA:TRUE
Certificate is to be certified until Feb 17 09:09:40 2021 GMT (365 days)
Sign the certificate? [y/n]:y

1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated

中間CAを構築する

中間CAディレクトリ ~/self_ca/ICAに移動

CAディレクトリとdatabaseを作成

$ mkdir -p demoCA
$ mkdir -p demoCA/certs
$ mkdir -p demoCA/crl
$ mkdir -p demoCA/newcerts
$ mkdir -p demoCA/private
$ touch demoCA/index.txt

公開キー、秘密キーを所定のディレクトリに移動

$ mv newkey.pem demoCA/private/cakey.pem
$ mv cacert.pem demoCA/cacert.pem

公開キーのシリアルを作成し、所定のファイル(demoCA/serial)に保存する
```
$ openssl x509 -in demoCA/cacert.pem -noout -next_serial -out demoCA/serial
```

証明書チェインを作成

ここまででルート証明書と中間証明書が出来ており、その証明書チェインを作成しとく
証明書チェインはTLSサーバ等で必要になるケースがあり、またサーバ証明書を作成した後の検証に使われる
文字通りルート証明書、中間証明書を連結(cat)したもの。

自己CAディレクトリ(~/self_ca)に移動

ルート証明書、中間証明書から不要な情報（CERTIFICATEブロック以外)を削除する。

$ openssl x509 -outform pem -in RCA/demoCA/cacert.pem -out rca.pem
$ openssl x509 -outform pem -in ICA/demoCA/cacert.pem -out ica.pem

[option] ルート証明書と中間証明書のチェインを確認
```
$ openssl verify -CAfile rca.pem ica.pem 
ica.pem: OK
```
連結して証明書チェイン(cert_chain.pem)を作成
```
$ cat rca.pem ica.pem >> cert_chain.pem
```

サーバ証明書を作成

秘密キーを作成

2048bitのRSAキーを作成し、キーをAES256で暗号化する。

$ openssl genrsa -aes256 2048 > server_key.pem
Generating RSA private key, 2048 bit long modulus (2 primes)
..+++++
.................................................................................................+++++
e is 65537 (0x010001)
Enter pass phrase:
Verifying - Enter pass phrase:

パスフレーズをクリアするためopenssl rsaで上書きする

$ openssl rsa -in server_key.pem -out server_key.pem 
Enter pass phrase for server_key.pem:
writing RSA key

証明書要求(server_req.pem)を作成

x.509/Organization Nameには、ルート証明書、中間証明書と同じ組織名を入力する (ex. my)

$ openssl req -new -key server_key.pem -out server_req.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) [AU]:JP
State or Province Name (full name) [Some-State]:Tokyo
Locality Name (eg, city) []:Shinjuku-ku
Organization Name (eg, company) [Internet Widgits Pty Ltd]:my
Organizational Unit Name (eg, section) []:room
Common Name (e.g. server FQDN or YOUR name) []:www.vubuntults.mydomain
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

中間CAで証明書要求に署名し、サーバ証明書(www_vubuntults_mydomain.crt)を発行する

中間CA作業ディレクトリ(~/self_ca/ICA)で実行しないとエラーとなる。
サーバ証明書は~/self_ca/server/www_vubuntults_mydomain.crtに生成

$ openssl ca -batch -in ../server/server_req.pem -keyfile demoCA/private/cakey.pem -cert demoCA/cacert.pem -out ../server/www_vubuntults_mydomain.crt -days 1095
Using configuration from /usr/lib/ssl/openssl.cnf
Enter pass phrase for demoCA/private/cakey.pem:
Can't open ./demoCA/index.txt.attr for reading, No such file or directory
140058091311552:error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:72:fopen('./demoCA/index.txt.attr','r')
140058091311552:error:2006D080:BIO routines:BIO_new_file:no such file:../crypto/bio/bss_file.c:79:
Check that the request matches the signature
Signature ok
Certificate Details:
        Serial Number:
            19:e7:a9:be:65:1e:a5:93:6b:bf:40:81:e1:0b:dd:d2:0b:46:e0:49
        Validity
            Not Before: Feb 18 09:28:33 2020 GMT
            Not After : Feb 17 09:28:33 2023 GMT
        Subject:
            countryName               = JP
            stateOrProvinceName       = Tokyo
            organizationName          = my
            organizationalUnitName    = room
            commonName                = www.vubuntults.mydomain
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                27:D5:91:6B:5E:50:43:B5:1E:3A:74:F3:D0:F0:84:52:9F:E2:73:AD
            X509v3 Authority Key Identifier: 
                keyid:D1:8B:4F:7B:FE:14:FA:AB:92:80:3C:D4:63:E5:F2:A9:67:CA:EB:31

Certificate is to be certified until Feb 17 09:28:33 2023 GMT (1095 days)

Write out database with 1 new entries
Data Base Updated

サーバ証明書を検証

証明書チェインを作成で作成した証明書チェインを使って、サーバ証明書を検証する。

コマンド出力でOKとなればOK

$ cd ~/self_ca
$ openssl verify -CAfile cert_chain.pem server/www_vubuntults_mydomain.crt 
server/www_vubuntults_mydomain.crt: OK

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