CentOS8で「TLS暗号設定ガイドライン」に準拠したSSLの暗号設定を行う


#はじめに
IPAの「TLS暗号設定ガイドライン～安全なウェブサイトのために（暗号設定対策編）～」に沿って、CentOS8のSSLの設定を行ってみた。

#実施範囲
今回は、ローカル環境において**オレオレ証明書**を使ったため、「TLS暗号設定ガイドライン チェックリスト」における②プロトコルバージョン設定、④暗号スイート設定を対象とし、③サーバ証明書設定は対象外とした。

また、「推奨セキュリティ型」、「高セキュリティ型」、「セキュリティ例外型」のうち**「推奨セキュリティ型]**を**「TLSv1.3あり」**で実施した。

さらにローカル環境ということで、設定内容の確認として、SSL Server Test (https://www.ssllabs.com/ssltest/) は使わずに、フリーソフトウェア  **testssl.sh** (https://github.com/drwetter/testssl.sh) を用いた確認を実施した。

#環境
- CentOS 8.1
- Apache+mod_ssl 2.4.37　
- OpenSSL 1.1.1

#手順


## プロトコルバージョンの設定

今回、TLS1.2と1.3を使うため、以下のようにする。

```/etc/httpd/conf.d/ssl.conf
SSLProtocol  TLSv1.2 +TLSv1.3
```

## 暗号スイート設定

TLS1.2、1.3の推奨セキュリティ型設定を以下のように追加する(TLS暗号設定 暗号スイートの設定例参照)。

```/etc/httpd/conf.d/ssl.conf
SSLCipherSuite "ECDHE+AESGCM:DHE+aRSA+AESGCM:ECDHE+AESCCM:DHE+aRSA+AESCCM:+AES256:ECDHE+CHACHA20:DHE+aRSA+CHACHA20:+DHE:ECDHE+AES128:ECDHE+CAMELLIA128:ECDHE+AES:ECDHE+CAMELLIA:+ECDHE+SHA:DHE+aRSA+AES128:DHE+aRSA+CAMELLIA128:DHE+aRSA+AES:DHE+aRSA+CAMELLIA:+DHE+aRSA+SHA"

SSLCipherSuite TLSv1.3 "TLS_AES_128_GCM_SHA256:TLS_AES_128_CCM_SHA256:TLS_AES_128_CCM_8_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256"
```


##  暗号スイート順序サーバ優先設定
以下を追加する

```/etc/httpd/conf.d/ssl.conf
<VirtualHost _default_:443>
（中略）
SSLHonorCipherOrder On
<VirtualHost>
```

## 鍵交換パラメータの設定

###OpenSSL による DHE パラメータファイルの生成
以下により生成する。結構時間がかかる。

```
openssl dhparam -out dh2048.pem -outform PEM 2048
```

###DHE 鍵交換で使用するグループのパラメータファイルによる指定
SSLCertificateFileで指定したファイルに、dh2048.pemを追加する。

```
cat /etc/httpd/conf.d/ssl.cert/server.crt dh2048.pem > /etc/httpd/conf.d/ssl.cert/server_dh2048.crt
```

SSLCertificateFileの設定を上の出力ファイルに変更する。

```/etc/httpd/conf/httpd.conf
SSLCertificateFile /etc/httpd/conf.d/ssl.cert/server_dh2048.crt
```

###ECDHE 鍵交換で使用するグループの設定
以下を追加する

```/etc/httpd/conf/httpd.conf
SSLOpenSSLConfCmd Groups "X25519:X448:P-256:P-384:P-521"
```

## HTTP Strict Transport Security（HSTS）の設定
以下を追加する

```/etc/httpd/conf/httpd.conf
Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains"
```


## OCSP stapling の設定
以下を追加する

```/etc/httpd/conf.d/ssl.conf
SSLStaplingCache "shmcb:/var/run/httpd/stapling_cache(32768)"
<VirtualHost *:443>
（中略）
SSLUseStapling on
</VirtualHost>
```


## 設定内容の確認

### testssl.shのインストール
```
git clone https://github.com/drwetter/testssl.sh
```

### testssl.shによる確認
以下コマンドを実行

```bash
$cd testssl.sh
$./testssl.sh localhost
```

### 確認結果

```
[root@localhost testssl.sh]# ./testssl.sh localhost

###########################################################
    testssl.sh       3.1dev from https://testssl.sh/dev/
    (b4c9437 2020-10-03 10:21:31 -- )

      This program is free software. Distribution and
             modification under GPLv2 permitted.
      USAGE w/o ANY WARRANTY. USE IT AT YOUR OWN RISK!

       Please file bugs @ https://testssl.sh/bugs/

###########################################################

 Using "OpenSSL 1.0.2-chacha (1.0.2k-dev)" [~183 ciphers]
 on localhost:./bin/openssl.Linux.x86_64
 (built: "Jan 18 17:12:17 2019", platform: "linux-x86_64")


 Start 2020-09-29 01:42:44        -->> 127.0.0.1:443 (localhost) <<--

 rDNS (127.0.0.1):       localhost.
 Service detected:       HTTP


 Testing protocols via sockets except NPN+ALPN

 SSLv2      not offered (OK)
 SSLv3      not offered (OK)
 TLS 1      not offered
 TLS 1.1    not offered
 TLS 1.2    offered (OK)
 TLS 1.3    offered (OK): final
 NPN/SPDY   not offered
 ALPN/HTTP2 http/1.1 (offered)

 Testing cipher categories

 NULL ciphers (no encryption)                      not offered (OK)
 Anonymous NULL Ciphers (no authentication)        not offered (OK)
 Export ciphers (w/o ADH+NULL)                     not offered (OK)
 LOW: 64 Bit + DES, RC[2,4], MD5 (w/o export)      not offered (OK)
 Triple DES Ciphers / IDEA                         not offered
 Obsoleted CBC ciphers (AES, ARIA etc.)            offered
 Strong encryption (AEAD ciphers) with no FS       not offered
 Forward Secrecy strong encryption (AEAD ciphers)  offered (OK)


 Testing server's cipher preferences

 Has server cipher order?     yes (OK) -- TLS 1.3 and below
 Negotiated protocol          TLSv1.3
 Negotiated cipher            TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Cipher per protocol

Hexcode  Cipher Suite Name (OpenSSL)       KeyExch.   Encryption  Bits     Cipher Suite Name (IANA/RFC)
-----------------------------------------------------------------------------------------------------------------------------
SSLv2
 -
SSLv3
 -
TLSv1
 -
TLSv1.1
 -
TLSv1.2 (server order)
 xc02f   ECDHE-RSA-AES128-GCM-SHA256       ECDH 253   AESGCM      128      TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
 xc030   ECDHE-RSA-AES256-GCM-SHA384       ECDH 253   AESGCM      256      TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
 xcca8   ECDHE-RSA-CHACHA20-POLY1305       ECDH 253   ChaCha20    256      TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
 x9e     DHE-RSA-AES128-GCM-SHA256         DH 2048    AESGCM      128      TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 
 xc0a2   DHE-RSA-AES128-CCM8               DH 2048    AESCCM8     128      TLS_DHE_RSA_WITH_AES_128_CCM_8      
 xc09e   DHE-RSA-AES128-CCM                DH 2048    AESCCM      128      TLS_DHE_RSA_WITH_AES_128_CCM        
 x9f     DHE-RSA-AES256-GCM-SHA384         DH 2048    AESGCM      256      TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 
 xc0a3   DHE-RSA-AES256-CCM8               DH 2048    AESCCM8     256      TLS_DHE_RSA_WITH_AES_256_CCM_8      
 xc09f   DHE-RSA-AES256-CCM                DH 2048    AESCCM      256      TLS_DHE_RSA_WITH_AES_256_CCM        
 xccaa   DHE-RSA-CHACHA20-POLY1305         DH 2048    ChaCha20    256      TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256
 xc027   ECDHE-RSA-AES128-SHA256           ECDH 253   AES         128      TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
 xc076   ECDHE-RSA-CAMELLIA128-SHA256      ECDH 253   Camellia    128      TLS_ECDHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
 xc028   ECDHE-RSA-AES256-SHA384           ECDH 253   AES         256      TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
 xc077   ECDHE-RSA-CAMELLIA256-SHA384      ECDH 253   Camellia    256      TLS_ECDHE_RSA_WITH_CAMELLIA_256_CBC_SHA384
 xc013   ECDHE-RSA-AES128-SHA              ECDH 253   AES         128      TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA  
 xc014   ECDHE-RSA-AES256-SHA              ECDH 253   AES         256      TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA  
 x67     DHE-RSA-AES128-SHA256             DH 2048    AES         128      TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 
 xbe     DHE-RSA-CAMELLIA128-SHA256        DH 2048    Camellia    128      TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
 x6b     DHE-RSA-AES256-SHA256             DH 2048    AES         256      TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 
 xc4     DHE-RSA-CAMELLIA256-SHA256        DH 2048    Camellia    256      TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA256
 x33     DHE-RSA-AES128-SHA                DH 2048    AES         128      TLS_DHE_RSA_WITH_AES_128_CBC_SHA    
 x45     DHE-RSA-CAMELLIA128-SHA           DH 2048    Camellia    128      TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA
 x39     DHE-RSA-AES256-SHA                DH 2048    AES         256      TLS_DHE_RSA_WITH_AES_256_CBC_SHA    
 x88     DHE-RSA-CAMELLIA256-SHA           DH 2048    Camellia    256      TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA
TLSv1.3 (server order)
 x1301   TLS_AES_128_GCM_SHA256            ECDH 253   AESGCM      128      TLS_AES_128_GCM_SHA256              
 x1304   TLS_AES_128_CCM_SHA256            ECDH 253   AESCCM      128      TLS_AES_128_CCM_SHA256              
 x1305   TLS_AES_128_CCM_8_SHA256          ECDH 253   AESCCM8     128      TLS_AES_128_CCM_8_SHA256            
 x1302   TLS_AES_256_GCM_SHA384            ECDH 253   AESGCM      256      TLS_AES_256_GCM_SHA384              
 x1303   TLS_CHACHA20_POLY1305_SHA256      ECDH 253   ChaCha20    256      TLS_CHACHA20_POLY1305_SHA256        


 Testing robust forward secrecy (FS) -- omitting Null Authentication/Encryption, 3DES, RC4

 FS is offered (OK)           TLS_AES_256_GCM_SHA384 TLS_CHACHA20_POLY1305_SHA256 ECDHE-RSA-AES256-GCM-SHA384
                              ECDHE-RSA-AES256-SHA384 ECDHE-RSA-AES256-SHA DHE-RSA-AES256-GCM-SHA384
                              ECDHE-RSA-CHACHA20-POLY1305 DHE-RSA-CHACHA20-POLY1305 DHE-RSA-AES256-CCM8
                              DHE-RSA-AES256-CCM DHE-RSA-AES256-SHA256 DHE-RSA-AES256-SHA
                              ECDHE-RSA-CAMELLIA256-SHA384 DHE-RSA-CAMELLIA256-SHA256 DHE-RSA-CAMELLIA256-SHA
                              TLS_AES_128_GCM_SHA256 TLS_AES_128_CCM_SHA256 TLS_AES_128_CCM_8_SHA256
                              ECDHE-RSA-AES128-GCM-SHA256 ECDHE-RSA-AES128-SHA256 ECDHE-RSA-AES128-SHA
                              DHE-RSA-AES128-GCM-SHA256 DHE-RSA-AES128-CCM8 DHE-RSA-AES128-CCM
                              DHE-RSA-AES128-SHA256 DHE-RSA-AES128-SHA ECDHE-RSA-CAMELLIA128-SHA256
                              DHE-RSA-CAMELLIA128-SHA256 DHE-RSA-CAMELLIA128-SHA
 Elliptic curves offered:     prime256v1 secp384r1 secp521r1 X25519 X448
 DH group offered:            Unknown DH group (2048 bits)

 Testing server defaults (Server Hello)

 TLS extensions (standard)    "renegotiation info/#65281" "EC point formats/#11" "session ticket/#35"
                              "supported versions/#43" "key share/#51" "supported_groups/#10"
                              "max fragment length/#1" "application layer protocol negotiation/#16"
                              "encrypt-then-mac/#22" "extended master secret/#23"
 Session Ticket RFC 5077 hint 300 seconds, session tickets keys seems to be rotated < daily
 SSL Session ID support       yes
 Session Resumption           Tickets: yes, ID: yes
 TLS clock skew               Random values, no fingerprinting possible
 Signature Algorithm          SHA256 with RSA
 Server key size              RSA 2048 bits (exponent is 65537)
 Server key usage             --
 Server extended key usage    --
 Serial / Fingerprints        10E4C9CA96C8D66CDBEBA985B85AFF1CC115E500 / SHA1 6719A785AAFC505E5B2B0247DB30C66D2971288A
                              SHA256 B1552EA11105499B23708A1902EA781EC8BB2DF16A05C6ED7EB871E1A7E02812
 Common Name (CN)             (no CN field in subject)
 subjectAltName (SAN)         missing (NOT ok) -- Browsers are complaining
 Trust (hostname)             certificate does not match supplied URI (same w/o SNI)
 Chain of trust               NOT ok (self signed)
 EV cert (experimental)       no
 Certificate Validity (UTC)   28 >= 60 days (2020-09-27 11:34 --> 2020-10-27 11:34)
 ETS/"eTLS", visibility info  not present
 Certificate Revocation List  --
 OCSP URI                     --
                              NOT ok -- neither CRL nor OCSP URI provided
 OCSP stapling                not offered
 OCSP must staple extension   --
 DNS CAA RR (experimental)    not offered
 Certificate Transparency     --
 Certificates provided        1
 Issuer                        (Default Company Ltd from XX)
 Intermediate Bad OCSP (exp.) Ok


 Testing HTTP header response @ "/"

 HTTP Status Code             200 OK
 HTTP clock skew              0 sec from localtime
 Strict Transport Security    365 days=31536000 s, includeSubDomains
 Public Key Pinning           --
 Server banner                Apache
 Application banner           --
 Cookie(s)                    (none issued at "/")
 Security headers             --
 Reverse Proxy banner         --


 Testing vulnerabilities

 Heartbleed (CVE-2014-0160)                not vulnerable (OK), no heartbeat extension
 CCS (CVE-2014-0224)                       not vulnerable (OK)
 Ticketbleed (CVE-2016-9244), experiment.  not vulnerable (OK)
 ROBOT                                     Server does not support any cipher suites that use RSA key transport
 Secure Renegotiation (RFC 5746)           supported (OK)
 Secure Client-Initiated Renegotiation     not vulnerable (OK)
 CRIME, TLS (CVE-2012-4929)                not vulnerable (OK)
 BREACH (CVE-2013-3587)                    no gzip/deflate/compress/br HTTP compression (OK)  - only supplied "/" tested
 POODLE, SSL (CVE-2014-3566)               not vulnerable (OK), no SSLv3 support
 TLS_FALLBACK_SCSV (RFC 7507)              No fallback possible (OK), no protocol below TLS 1.2 offered
 SWEET32 (CVE-2016-2183, CVE-2016-6329)    not vulnerable (OK)
 FREAK (CVE-2015-0204)                     not vulnerable (OK)
 DROWN (CVE-2016-0800, CVE-2016-0703)      not vulnerable on this host and port (OK)
                                           make sure you don't use this certificate elsewhere with SSLv2 enabled services
                                           https://censys.io/ipv4?q=B1552EA11105499B23708A1902EA781EC8BB2DF16A05C6ED7EB871E1A7E02812 could help you to find out
 LOGJAM (CVE-2015-4000), experimental      not vulnerable (OK): no DH EXPORT ciphers, no common prime detected
 BEAST (CVE-2011-3389)                     not vulnerable (OK), no SSL3 or TLS1
 LUCKY13 (CVE-2013-0169), experimental     potentially VULNERABLE, uses cipher block chaining (CBC) ciphers with TLS. Check patches
 Winshock (CVE-2014-6321), experimental    not vulnerable (OK)
 RC4 (CVE-2013-2566, CVE-2015-2808)        no RC4 ciphers detected (OK)


 Running client simulations (HTTP) via sockets

 Android 4.4.2                TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Android 5.0.0                TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Android 6.0                  TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Android 7.0 (native)         TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Android 8.1 (native)         TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 253 bit ECDH (X25519)
 Android 9.0 (native)         TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Android 10.0 (native)        TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Chrome 74 (Win 10)           TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Chrome 79 (Win 10)           TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Firefox 66 (Win 8.1/10)      TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Firefox 71 (Win 10)          TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 IE 6 XP                      No connection
 IE 8 Win 7                   No connection
 IE 8 XP                      No connection
 IE 11 Win 7                  TLSv1.2 DHE-RSA-AES128-GCM-SHA256, 2048 bit DH
 IE 11 Win 8.1                TLSv1.2 DHE-RSA-AES128-GCM-SHA256, 2048 bit DH
 IE 11 Win Phone 8.1          TLSv1.2 ECDHE-RSA-AES128-SHA256, 256 bit ECDH (P-256)
 IE 11 Win 10                 TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Edge 15 Win 10               TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 253 bit ECDH (X25519)
 Edge 17 (Win 10)             TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 253 bit ECDH (X25519)
 Opera 66 (Win 10)            TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Safari 9 iOS 9               TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Safari 9 OS X 10.11          TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Safari 10 OS X 10.12         TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Safari 12.1 (iOS 12.2)       TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Safari 13.0 (macOS 10.14.6)  TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Apple ATS 9 iOS 9            TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Java 6u45                    No connection
 Java 7u25                    No connection
 Java 8u161                   TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 Java 11.0.2 (OpenJDK)        TLSv1.3 TLS_AES_128_GCM_SHA256, 256 bit ECDH (P-256)
 Java 12.0.1 (OpenJDK)        TLSv1.3 TLS_AES_128_GCM_SHA256, 256 bit ECDH (P-256)
 OpenSSL 1.0.2e               TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 256 bit ECDH (P-256)
 OpenSSL 1.1.0l (Debian)      TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256, 253 bit ECDH (X25519)
 OpenSSL 1.1.1d (Debian)      TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)
 Thunderbird (68.3)           TLSv1.3 TLS_AES_128_GCM_SHA256, 253 bit ECDH (X25519)


 Rating (experimental)

 Rating specs (not complete)  SSL Labs's 'SSL Server Rating Guide' (version 2009q from 2020-01-30)
 Specification documentation  https://github.com/ssllabs/research/wiki/SSL-Server-Rating-Guide
 Protocol Support (weighted)  0 (0)
 Key Exchange     (weighted)  0 (0)
 Cipher Strength  (weighted)  0 (0)
 Final Score                  0
 Overall Grade                T
 Grade cap reasons            Grade capped to T. Issues with the chain of trust (self signed)
                              Grade capped to M. Domain name mismatch

 Done 2020-09-29 01:44:26 [ 103s] -->> 127.0.0.1:443 (localhost) <<--
```

### 考察
- 証明書関連、ドメイン名のミスマッチの脆弱性が残っているが、暗号系はOKっぽい？
- OCSP stapling 関連が not OK、not offeredとなっている。オレオレ証明書が原因くさい。
- DH group offered が"Unknown DH group (2048 bits)"となっているが、"鍵交換パラメータの設定"の設定をしなかった場合、何等かのグループ名が設定されており2048ビットになっている。"鍵交換パラメータの設定"はあえて設定する必要はない？
- LUCKY13 (CVE-2013-0169), experimental の脆弱性がでているが、これはTLS1.2の暗号スイートを「高セキュリティ型設定」に変更すると消える。

#参考
- [TLS暗号設定ガイドライン～安全なウェブサイトのために（暗号設定対策編）～](https://www.ipa.go.jp/security/vuln/ssl_crypt_config.html)

- [SSL Server Test](https://www.ssllabs.com/ssltest/)  

- [testssl.sh](https://github.com/drwetter/testssl.sh)