证书生成流程(OpenSSL篇) - 《Linux笔记》

生成根证书
生成中间 ca
生成服务器证书
- 部署
附录 A 配置文件示范
配置B 配置文件语法
参考文献

:::danger 本文大部分内容参考自[1]。 ::: 我们的目标是生成一个Root CA，两个Intermediate CA, 分别用于服务证书签发和开发证书签发。
一开始我的根证书是依照参考文献[2]生成的，但是参考文献[2]中生成的根证书是不允许签发intermediate ca的，因此我打算重新做一个根证书。

生成根证书

先创建一个工作目录

mkdir /root/ca

创建一个index.txt文件用来追踪已签名的证书
serial文件用来作为证书的序列号
创建证书后index.txt和serial都会更新

cd /root/ca
mkdir certs crl newcerts private
chmod 700 private
touch index.txt
echo 1000 > serial

准备配置文件

CA证书的创建流程
openssl 文件必须有 ca 块，default_ca 告诉 openssl 使用 CA_default 块中的配置

[ ca ]
# `man ca`
default_ca = CA_default

注意这里dir必须与你的工作目录一致

[ CA_default ]
# Directory and file locations.
dir               = /root/ca
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/ca.key.pem
certificate       = $dir/certs/ca.cert.pem

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/ca.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 30

# SHA-1 is deprecated, so use SHA-2 instead.
default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 375
preserve          = no
policy            = policy_strict

由于根证书的唯一作用是创建中间ca，因此我们使用policy_strict

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

由于中间ca需要签server证书或者user证书，而server, user可以来自不同实体，因此中间ca需要更宽松的策略

[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

创建csr(certificate signing request 证书签名请求)时，需要req块

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# Extension to add when the -x509 option is used.
x509_extensions     = v3_ca

req_distinguished_name 块用来存放证书而基本信息

[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = GB
stateOrProvinceName_default     = England
localityName_default            =
0.organizationName_default      = Alice Ltd
#organizationalUnitName_default =
#emailAddress_default           =

v3_ca块作为根证书配置，v3_intermediate_ca块作为中间ca证书配置

[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

pathlen:0 的限制使得中间ca只能签终端证书，不能签ca证书。

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

usr_cert 块作为用户证书配置

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

server_cert 作为服务器证书配置

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth

crl_ext 作为 CRL 证书撤销机制

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always

ocsp 块作为 OCSP 证书撤销机制配置

[ ocsp ]
# Extension for OCSP signing certificates (`man ocsp`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, digitalSignature
extendedKeyUsage = critical, OCSPSigning

生成私钥

genrsa 可以生成私钥，aes256 会用一个密码加密证书，签名时必须要密码才能签名

openssl genrsa -aes256 -out private/ca.key.pem 4096
chmod 400 private/ca.key.pem

生成根证书

根据私钥生成公钥

cd /root/ca
openssl req -config openssl.cnf \
      -key private/ca.key.pem \
      -new -x509 -days 7300 -sha256 -extensions v3_ca \
      -out certs/ca.cert.pem
chmod 444 certs/ca.cert.pem

验证证书
自签名证书的 Subject 和 Issuer 是相同的，因为根证书只能是自签名的。

$ openssl x509 -noout -text -in certs/ca.cert.pem
Signature Algorithm: sha256WithRSAEncryption
    Issuer: C=GB, ST=England,
            O=Alice Ltd, OU=Alice Ltd Certificate Authority,
            CN=Alice Ltd Root CA
    Validity
        Not Before: Apr 11 12:22:58 2015 GMT
        Not After : Apr  6 12:22:58 2035 GMT
    Subject: C=GB, ST=England,
             O=Alice Ltd, OU=Alice Ltd Certificate Authority,
             CN=Alice Ltd Root CA
    Subject Public Key Info:
        Public Key Algorithm: rsaEncryption
            Public-Key: (4096 bit)

这部分可以反映 v3_ca 块配置

X509v3 extensions:
    X509v3 Subject Key Identifier:
        38:58:29:2F:6B:57:79:4F:39:FD:32:35:60:74:92:60:6E:E8:2A:31
    X509v3 Authority Key Identifier:
        keyid:38:58:29:2F:6B:57:79:4F:39:FD:32:35:60:74:92:60:6E:E8:2A:31

    X509v3 Basic Constraints: critical
        CA:TRUE
    X509v3 Key Usage: critical
        Digital Signature, Certificate Sign, CRL Sign

:::info 将根证书设置为系统信任证书时，注意这句话
_/usr/local/share/ca-certificates_
Directory of local CA certificates (with .crt extension). :::

生成中间 ca

先准备一个工作目录

mkdir /root/ca/intermediate

中间CA需要多一个文件夹CSR用来存放证书申请

cd /root/ca/intermediate
mkdir certs crl csr newcerts private
chmod 700 private
touch index.txt
echo 1000 > serial

中间CA的配置与根ca配置有所不同

[ CA_default ]
dir             = /root/ca/intermediate
private_key     = $dir/private/intermediate.key.pem
certificate     = $dir/certs/intermediate.cert.pem
crl             = $dir/crl/intermediate.crl.pem
policy          = policy_loose

生成私钥

中间CA证书仍然用aes256保护

cd /root/ca
openssl genrsa -aes256 \
      -out intermediate/private/intermediate.key.pem 4096
chmod 400 intermediate/private/intermediate.key.pem

生成 CSR 证书签名请求

使用intermediate工作目录中的openssl.conf配置生成 csr
请注意，CommonName必须有别于根ca.

cd /root/ca
openssl req -config intermediate/openssl.cnf -new -sha256 \
      -key intermediate/private/intermediate.key.pem \
      -out intermediate/csr/intermediate.csr.pem

使用根证书生成证书并签名, extension 选择 v3_intermediate_ca 块

cd /root/ca
openssl ca -config openssl.cnf -extensions v3_intermediate_ca \
      -days 3650 -notext -md sha256 \
      -in intermediate/csr/intermediate.csr.pem \
      -out intermediate/certs/intermediate.cert.pem
chmod 444 intermediate/certs/intermediate.cert.pem

签名完成后，intermediate的index.txt就多了一条记录

检查证书

查看证书详情

openssl x509 -noout -text \
      -in intermediate/certs/intermediate.cert.pem

用根证书验证中间ca

openssl verify -CAfile certs/ca.cert.pem \
      intermediate/certs/intermediate.cert.pem

:::info 一般来说用户的浏览器只有根证书，因此服务器证书若是由中间证书签发，必须提供完整的证书链使得浏览器可以查找到证书的issuer。 :::

生成服务器证书

服务端证书的生成和签名和中间CA基本没有区别，但是注意，server证书需要设置 SAN(subjectAltName)。

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName         = @alternate_names

[ alternate_names ]
DNS.1 = clash.dev
DNS.2 = *.clash.dev

另一个问题是证书链，私钥不需要拼接，但是公钥（.cert.pem）需要拼接为一个文件。

cat server.cert.pem intermediate.cert.pem ca.cert.pem > chain.cert.pem

其中server证书必须位于证书文件开头，而不能是中间。 :::info 一般来说用户的浏览器只有根证书，因此服务器证书若是由中间证书签发，必须提供完整的证书链使得浏览器可以查找到证书的issuer。 ::: 完整过程为

# 生成不需要密码的私钥
cd /root/ca
openssl genrsa \
      -out intermediate/private/www.example.com.key.pem 2048
chmod 400 intermediate/private/www.example.com.key.pem
# 生成 csr
cd /root/ca
openssl req -config intermediate/openssl.cnf \
      -key intermediate/private/www.example.com.key.pem \
      -new -sha256 -out intermediate/csr/www.example.com.csr.pem
# 生成证书并签名，extensions 选择 server_cert
cd /root/ca
openssl ca -config intermediate/openssl.cnf \
      -extensions server_cert -days 375 -notext -md sha256 \
      -in intermediate/csr/www.example.com.csr.pem \
      -out intermediate/certs/www.example.com.cert.pem
chmod 444 intermediate/certs/www.example.com.cert.pem
# 查看证书详情
openssl x509 -noout -text \
      -in intermediate/certs/www.example.com.cert.pem
# 对照 ca 验证证书
openssl verify -CAfile intermediate/certs/ca-chain.cert.pem \
      intermediate/certs/www.example.com.cert.pem

部署

使用 Caddy 就可以部署啦

:8081 {
    file_server
  tls chain.cert.pem server.key.pem
}

附录 A 配置文件示范

根证书配置

# OpenSSL root CA configuration file.
# Copy to `/root/ca/openssl.cnf`.

[ ca ]
# `man ca`
default_ca = CA_default

[ CA_default ]
# Directory and file locations.
dir               = /root/ca
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/ca.key.pem
certificate       = $dir/certs/ca.cert.pem

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/ca.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 30

# SHA-1 is deprecated, so use SHA-2 instead.
default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 375
preserve          = no
policy            = policy_strict

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# Extension to add when the -x509 option is used.
x509_extensions     = v3_ca

[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = GB
stateOrProvinceName_default     = England
localityName_default            =
0.organizationName_default      = Alice Ltd
organizationalUnitName_default  =
emailAddress_default            =

[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always

[ ocsp ]
# Extension for OCSP signing certificates (`man ocsp`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, digitalSignature
extendedKeyUsage = critical, OCSPSigning

中间CA配置

# OpenSSL intermediate CA configuration file.
# Copy to `/root/ca/intermediate/openssl.cnf`.

[ ca ]
# `man ca`
default_ca = CA_default

[ CA_default ]
# Directory and file locations.
dir               = /root/ca/intermediate
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/intermediate.key.pem
certificate       = $dir/certs/intermediate.cert.pem

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/intermediate.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 30

# SHA-1 is deprecated, so use SHA-2 instead.
default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 375
preserve          = no
policy            = policy_loose

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# Extension to add when the -x509 option is used.
x509_extensions     = v3_ca

[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = GB
stateOrProvinceName_default     = England
localityName_default            =
0.organizationName_default      = Alice Ltd
organizationalUnitName_default  =
emailAddress_default            =

[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, digitalSignature, cRLSign, keyCertSign

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName         = @alternate_names

[ alternate_names ]
DNS.1 = hello.world
DNS.2 = *.hello.world

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always

[ ocsp ]
# Extension for OCSP signing certificates (`man ocsp`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, digitalSignature
extendedKeyUsage = critical, OCSPSigning

配置B 配置文件语法

openssl 允许你将 basicConstraints=critical,CA:true,pathlen:1 用如下方式重写

basicConstraints=critical,@bs_section

[bs_section]

CA=true
pathlen=1

openssl 允许变量语法，如

dir               = /root/ca/intermediate
certs             = $dir/certs
crl_dir           = $dir/crl

这里dir就是一个变量

参考文献

[1]: https://jamielinux.com/docs/openssl-certificate-authority/create-the-root-pair.html
[2]: https://github.com/laravel/homestead/blob/main/scripts/create-certificate.sh