subjectAltName 的作用
subjectAltName 在 RFC 5280 4.2.1.6. 中提供了详细的说明，subjectAltName 是 X.509 version 3 的一个扩展项，该扩展项用于标记和界定证书持有者的身份。
在 X.509 格式的证书中，一般使用 Issuer 项标记证书的颁发者信息，该项必须是一个非空的 Distinguished Name 名称。除此之外还可以使用扩展项 issuerAltName 来标记颁发者的其他名称，这是一个非关键的扩展项。
对于证书持有者，一般使用 Subject 项标记，并使用 subjectAltName 扩展项提供更详细的持有者身份信息。 subjectAltName 全称为 Subject Alternative Name，缩写为 SAN。它可以包括一个或者多个的电子邮件地址，域名，IP地址和 URI 等，详细定义如下：
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SubjectAltName ::= GeneralNames
GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
GeneralName ::= CHOICE {
otherName [0] OtherName,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER
}
当颁发的证书不存在 Subject 项的时候，证书必须包含扩展项 subjectAltName，并且标记为关键（critical）的。当颁发的证书存在 Subject 项的时候，必须将扩展项 subjectAltName 标记为非关键（no-critical）的。注意：用于颁发证书的 CA 证书是必须包含 Subject 项的。
根据 RFC 6125 中的规定，当一个网站使用证书标记自己的身份时，如果证书中包含 subjectAltName，在识别证书持有者时会忽略 Subject 子项，而是通过 subjectAltName 来识别证书持有者。在早期颁发的证书中一般通过 Subject 的 CommonName 来识别持有者的身份，不包含 subjectAltName 扩展项。这会导致最新版本的浏览器Chrome、Firefox 等在通过 HTTPS 访问 web 网站时，触发 NET::ERR_CERT_COMMON_NAME_INVALID 错误。
Java TLS 中的检查过程
Java 在 TLS 建立的过程中，默认通过 sun.security.util.HostnameChecker 进行证书持有者身份检查。检查流程如下：
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从 SSLSession 中获取到服务端的地址信息
SSLSession#getPeerHost()，这个地址实际上是 Socket 建立连接的时候指定的 IP 地址或域名地址。 -
判断该地址是 IP 地址还是域名地址。
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public void match(String host, X509Certificate serverCert) throws CertificateException { if (isIpAddress(host)) { matchIP(host, serverCert); } else { this.matchDNS(host, serverCert); } }
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如果是 IP 地址，则在 subjectAltName 中寻找 IP 进行匹配，根据 RFC 5280 4.2.1.6. 中对 GeneralName 的定义 IP 为类型 7。
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private static void matchIP(String host, X509Certificate certificate) throws CertificateException { Collection san = certificate.getSubjectAlternativeNames(); if (san == null) { throw new CertificateException("No subject alternative names present"); } else { Iterator generalNames = san.iterator(); while(generalNames.hasNext()) { List var4 = (List)generalNames.next(); if ((Integer)var4.get(0) == 7) { String generalName = (String)var4.get(1); if (host.equalsIgnoreCase(generalName)) { return; } try { if (InetAddress.getByName(host).equals(InetAddress.getByName(generalName))) { return; } } catch (UnknownHostException var7) { } catch (SecurityException var8) { } } } throw new CertificateException("No subject alternative names matching IP address " + host + " found"); } }
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如果是域名地址，则在 subjectAltName 中寻找域名进行匹配，根据 RFC 5280 4.2.1.6. 中对 GeneralName 的定义域名为类型 2。注意：当使用域名的时候，除了检查 subjectAltName 中是否存在匹配的域名之外，还会检查 Subject 中的 commonName 是否和域名匹配。
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private void matchDNS(String host, X509Certificate certificate) throws CertificateException { try { new SNIHostName(host); } catch (IllegalArgumentException e) { throw new CertificateException("Illegal given domain name: " + host, e); } Collection san = certificate.getSubjectAlternativeNames(); if (san != null) { boolean unMatched = false; Iterator generalNames = san.iterator(); while(generalNames.hasNext()) { List generalName = (List)generalNames.next(); if ((Integer)generalName.get(0) == 2) { unMatched = true; String var7 = (String)generalName.get(1); if (this.isMatched(host, var7)) { return; } } } if (unMatched) { throw new CertificateException("No subject alternative DNS name matching " + host + " found."); } } X500Name DN = getSubjectX500Name(certificate); DerValue commonName = DN.findMostSpecificAttribute(X500Name.commonName_oid); if (var11 != null) { try { if (this.isMatched(host, commonName.getAsString())) { return; } } catch (IOException e) { } } String err = "No name matching " + host + " found"; throw new CertificateException(err); }
配置和脚本
自签发 CA 证书配置文件 ca-openssl.cnf：
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[req]
distinguished_name = req_distinguished_name
req_extensions = v3_req
[req_distinguished_name]
countryName = Country Name (2 letter code)
countryName_default = CN
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = Some-State
organizationName = Organization Name (eg, company)
organizationName_default = Internet Widgits Pty Ltd
commonName = Common Name (eg, YOUR name)
commonName_default = testca
[v3_req]
basicConstraints = CA:true
keyUsage = critical, keyCertSign
服务端证书配置文件 server-openssl.cnf：
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[req]
distinguished_name = req_distinguished_name
req_extensions = v3_req
[req_distinguished_name]
countryName = Country Name (2 letter code)
countryName_default = CN
stateOrProvinceName = State or Province Name (full name)
stateOrProvinceName_default = Beijing
localityName = Locality Name (eg, city)
localityName_default = Beijing
organizationName = Organization Name (eg, company)
organizationName_default = Example, Co.
commonName = Common Name (eg, YOUR name)
commonName_max = 64
####################################################################
[ ca ]
default_ca = CA_default # The default ca section
####################################################################
[ CA_default ]
dir = . # Where everything is kept
certs = $dir # Where the issued certs are kept
crl_dir = $dir # Where the issued crl are kept
database = $dir/index.txt # database index file.
#unique_subject = no # Set to 'no' to allow creation of
# several ctificates with same subject.
new_certs_dir = $dir # default place for new certs.
certificate = $dir/ca.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
RANDFILE = $dir/private/.rand # private random number file
x509_extensions = usr_cert # The extentions 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
# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crlnumber must also be commented out to leave a V1 CRL.
# crl_extensions = crl_ext
default_days = 365 # how long to certify for
default_crl_days= 30 # how long before next CRL
default_md = default # use public key default MD
preserve = no # keep passed DN ordering
# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy = policy_anything
[ policy_anything ]
countryName = optional
stateOrProvinceName = optional
localityName = optional
organizationName = optional
organizationalUnitName = optional
commonName = supplied
emailAddress = optional
[v3_req]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names
[alt_names]
IP.1 = 10.0.2.70
这里的 [alt_names] 域中即为我们需要指定的 subjectAltName，可以配置多个 IP，DNS 或其他值。
下面是一个用于证书签发，证书文件转换的脚本 certificate-gen.sh。使用该脚本前需要确认有 Java 的 keytool 命令和 openssl 命令。该脚本会生成一张 CA 自签发证书，然后使用该证书签发一张客户端证书和服务端证书。该脚本运行时会要求输入一个服务端 IP 的地址，这个地址会替换 [alt_names] 域的 IP.1 的值。下面是脚本内容：
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#! /bin/bash
echo "INFO: 清理环境"
rm *.rsa
rm *.jks
rm *.p12
rm *.key
rm *.csr
rm *.srl
echo "INFO: 生成自签发证书"
openssl req -x509 -new -newkey rsa:2048 -nodes -keyout ca.key -out ca.pem -config ca-openssl.cnf -days 3650 -extensions v3_req
echo "INFO: 将 ca.pem 转换为 ca.jks, KeyStore 密码为 123456"
keytool -importcert -trustcacerts -file ca.pem -keystore ca.jks -storepass 123456
echo "INFO: 签发客户端证书"
openssl genrsa -out client.key.rsa 2048
openssl pkcs8 -topk8 -in client.key.rsa -out client.key -nocrypt
openssl req -new -key client.key -out client.csr
openssl x509 -req -CA ca.pem -CAkey ca.key -CAcreateserial -in client.csr -out client.pem -days 3650
echo "INFO: 将私钥和对应的证书链合成 PKCS#12 格式，KeyStore 密码和私钥密码均为 123456"
openssl pkcs12 -export -CAfile ca.pem -in client.pem -inkey client.key -out client.p12 -passout pass:123456
echo "INFO: 签发服务端证书"
echo "INFO: 填写主机名"
read -p "请输入服务器域名或者主机名：" server
echo "INFO: set alt_names $server"
old_server=$(grep "IP.1 = " server-openssl.cnf|awk -F " " '{print $3}')
echo "INFO: 将 alt_names 从 $old_server 修改为 $server"
sed -i "s/$old_server/$server/g" server-openssl.cnf
openssl genrsa -out server.key.rsa 2048
openssl pkcs8 -topk8 -in server.key.rsa -out server.key -nocrypt
openssl req -new -key server.key -out server.csr -config server-openssl.cnf
openssl x509 -req -CA ca.pem -CAkey ca.key -CAcreateserial -in server.csr -out server.pem -extensions v3_req -extfile server-openssl.cnf -days 3650
echo "INFO: 将私钥和对应的证书链合成 PKCS#12 格式，KeyStore 密码和私钥密码均为 123456"
openssl pkcs12 -export -CAfile ca.pem -in server.pem -inkey server.key -out server.p12 -passout pass:123456
echo "INFO：清理无用的文件"
rm *.rsa
rm *.csr
rm ca.srl
运行脚本前的目录结构：
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certificates
├── ca-openssl.cnf
├── certificate-gen.sh
└── server-openssl.cnf
运行脚本后的目录结构：
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certificates
├── ca-openssl.cnf
├── ca.jks
├── ca.key
├── ca.pem
├── certificate-gen.sh
├── client.key
├── client.p12
├── client.pem
├── server-openssl.cnf
├── server.key
├── server.p12
└── server.pem
0 directories, 12 files
