1.2. 生成 RSA CA 根证书

calendar Sep 22, 2024 · 3 min read · pki tls ssl rsa ca certificates x509 openssl  ·
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本文地址：https://fenying.net/book/pki-tutorials/1.2.generate-rsa-ca-root/

本章节介绍如何使用 OpenSSL 生成 RSA CA 根证书。

初始化工作目录

假定 RSA CA 的工作目录在 /data/ca/RSA/Root，那么执行如下脚本：

 1export MY_CA_WORKDIR=/data/ca
 2mkdir -p $MY_CA_WORKDIR
 3
 4MY_CA_ROOT_DIR=$MY_CA_WORKDIR/RSA/Root
 5
 6mkdir -p $MY_CA_ROOT_DIR
 7
 8cd $MY_CA_ROOT_DIR
 9
10MY_CA_RAND_FILE=$MY_CA_ROOT_DIR/.rand
11
12mkdir -p issued_certs crl
13touch index.txt
14
15openssl rand -out $MY_CA_RAND_FILE 65535
16md5sum $MY_CA_RAND_FILE | grep -Po '^\w+' > serial
17
18openssl rand -out $MY_CA_RAND_FILE 1048576

生成 CA 根证书的 RSA 私钥

1MY_CA_ROOT_KEY_PATH=$MY_CA_ROOT_DIR/key.pem
2
3openssl genrsa \
4    -rand $MY_CA_RAND_FILE \
5    -aes-256-cfb \
6    -out $MY_CA_ROOT_KEY_PATH \
7    4096

生成证书签名申请表文件

 1MY_CA_ROOT_REQ_PATH=$MY_CA_ROOT_DIR/req.cnf
 2
 3cat > $MY_CA_ROOT_REQ_PATH << EOL
 4[ req ]
 5
 6distinguished_name  = req_distinguished_name
 7string_mask         = utf8only
 8prompt              = no
 9
10# SHA-1 is deprecated, so use SHA-2 instead.
11default_md          = sha384
12
13# Extension to add when the -x509 option is used.
14x509_extensions     = v3_ca
15req_extensions     = v3_ca
16
17[ req_distinguished_name ]
18# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
19countryName                     = CN
200.organizationName              = Demo ORG
21organizationalUnitName          = www.demo.org
22commonName                      = Demo CA RSA Root
23
24[ v3_ca ]
25
26subjectKeyIdentifier = hash
27authorityKeyIdentifier = keyid:always,issuer:always
28basicConstraints = critical, CA:true
29keyUsage = critical, digitalSignature, cRLSign, keyCertSign
30EOL

签发自签名 CA 根证书

 1MY_CA_ROOT_CERT_PATH=$MY_CA_ROOT_DIR/ca.pem
 2
 3# 生成一个有效期为 30 年的自签名 CA 根证书
 4openssl req -config $MY_CA_ROOT_REQ_PATH \
 5    -new \
 6    -x509 \
 7    -extensions v3_ca \
 8    -days 10950 \
 9    -key $MY_CA_ROOT_KEY_PATH \
10    -out $MY_CA_ROOT_CERT_PATH

然后可以通过如下命令查看生成证书的详细信息。

1openssl x509 -noout -text -in $MY_CA_ROOT_CERT_PATH

通过如下命令验证自签名 CA 证书是否可以自验证。

1openssl verify -CAfile $MY_CA_ROOT_CERT_PATH $MY_CA_ROOT_CERT_PATH

配置 CA

最后对 CA 进行配置，以用于签发其他证书。

  1MY_CA_ROOT_CONF_PATH=$MY_CA_ROOT_DIR/ca.cnf
  2
  3cat > $MY_CA_ROOT_CONF_PATH << EOL
  4[ ca ]
  5default_ca = CA_default
  6
  7[ CA_default ]
  8# Directory and file locations.
  9dir               = $MY_CA_ROOT_DIR
 10certs             = \$dir/certs
 11crl_dir           = \$dir/crl
 12new_certs_dir     = \$dir/issued_certs
 13database          = \$dir/index.txt
 14serial            = \$dir/serial
 15RANDFILE          = \$dir/.rand
 16
 17# The root key and root certificate.
 18private_key       = \$dir/key.pem
 19certificate       = \$dir/ca.pem
 20
 21# For certificate revocation lists.
 22crlnumber         = \$dir/crlnumber
 23crl               = \$dir/crl/ca.crl.pem
 24crl_extensions    = crl_ext
 25default_crl_days  = 30
 26copy_extensions   = copy
 27
 28# SHA-1 is deprecated, so use SHA-2 instead.
 29default_md        = sha256
 30
 31name_opt          = ca_default
 32cert_opt          = ca_default
 33default_days      = 375
 34preserve          = no
 35policy            = policy_strict
 36
 37[ policy_strict ]
 38# The root CA should only sign intermediate certificates that match.
 39countryName             = match
 40stateOrProvinceName     = optional
 41organizationName        = match
 42organizationalUnitName  = optional
 43commonName              = supplied
 44emailAddress            = optional
 45
 46[ policy_loose ]
 47# Allow the intermediate CA to sign a more diverse range of certificates.
 48countryName             = optional
 49stateOrProvinceName     = optional
 50localityName            = optional
 51organizationName        = optional
 52organizationalUnitName  = optional
 53commonName              = supplied
 54emailAddress            = optional
 55
 56[ req ]
 57default_bits        = 4096
 58distinguished_name  = req_distinguished_name
 59string_mask         = utf8only
 60prompt              = no
 61
 62# SHA-1 is deprecated, so use SHA-2 instead.
 63default_md          = sha384
 64
 65# Extension to add when the -x509 option is used.
 66x509_extensions     = v3_ca
 67
 68[ req_distinguished_name ]
 69# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
 70countryName                     = CN
 710.organizationName              = Demo ORG
 72organizationalUnitName          = www.demo.org
 73commonName                      = Demo CA RSA Root
 74
 75[ v3_ca ]
 76subjectKeyIdentifier = hash
 77authorityKeyIdentifier = keyid:always,issuer:always
 78basicConstraints = critical, CA:true
 79keyUsage = critical, digitalSignature, cRLSign, keyCertSign
 80
 81[ v3_intermediate_ca ]
 82keyUsage = critical, digitalSignature, cRLSign, keyCertSign
 83extendedKeyUsage = critical, clientAuth, serverAuth
 84basicConstraints = critical, CA:true, pathlen:0
 85subjectKeyIdentifier = hash
 86authorityKeyIdentifier = keyid:always,issuer:always
 87# authorityInfoAccess = caIssuers;URI:http://demo.org/ca.html
 88# crlDistributionPoints = URI:http://demo.org/ca.crl
 89# certificatePolicies = 2.23.140.1.2.1,@policy_issuer_info
 90
 91# [ policy_issuer_info ]
 92# policyIdentifier = 1.3.6.1.4.1.44947.1.2.3.4.5.6.7.8
 93
 94[ crl_ext ]
 95authorityKeyIdentifier=keyid:always
 96
 97[ ocsp ]
 98basicConstraints = CA:FALSE
 99subjectKeyIdentifier = hash
100authorityKeyIdentifier = keyid:always,issuer:always
101keyUsage = critical, digitalSignature
102extendedKeyUsage = critical, OCSPSigning
103EOL

注意，此时的 CA 不允许重复对同一个 commonName 签发证书，需要改成可以对同一个主体重复颁发证书：

1echo 'unique_subject = no' > $MY_CA_ROOT_DIR/index.txt.attr

至此，RSA CA 根证书已经生成完毕。

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