解密SAML 2 Assertion报Data decryption key may not be null错误如何解决

待解密SAML响应 #

<saml:EncryptedAssertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
    <xenc:EncryptedData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="ED-13b5261b-6429-4fc6-9df4-00ba4c956df4" Type="http://www.w3.org/2001/04/xmlenc#Element">
        <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes256-cbc"/>
        <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
            <xenc:EncryptedKey Id="EK-cde830f3-5741-440c-a6a3-03d7fc29bec7">
                <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p">
                    <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
                </xenc:EncryptionMethod>
                <ds:KeyInfo>
                    <wsse:SecurityTokenReference
                            xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd">
                        <ds:X509Data>
                            <ds:X509IssuerSerial>
                                <ds:X509IssuerName>CN=Foo,OU=Ba,O=Foobaa,C=AU
                                </ds:X509IssuerName>
                                <ds:X509SerialNumber>161...39233</ds:X509SerialNumber>
                            </ds:X509IssuerSerial>
                        </ds:X509Data>
                    </wsse:SecurityTokenReference>
                </ds:KeyInfo>
                <xenc:CipherData>
                    <xenc:CipherValue>
                        OrjesuK...lOQ==
                    </xenc:CipherValue>
                </xenc:CipherData>
            </xenc:EncryptedKey>
        </ds:KeyInfo>
        <xenc:CipherData>
            <xenc:CipherValue>
                RHkpDrgRX0AJprMr...k62Q==
            </xenc:CipherValue>
        </xenc:CipherData>
    </xenc:EncryptedData>
</saml:EncryptedAssertion>

现有解密代码 #

// Given here a EncryptedAssertion type populated from the above xml

// Open and initialise the Keystore
KeyStore ks = KeyStore.getInstance("PKCS12");
try (FileInputStream fileInputStream = new FileInputStream("keystoreUrl")) {
    ks.load(fileInputStream, config.getBAMKeystorePassword().toCharArray());
}
PrivateKey certificate= (PrivateKey) ks.getKey("privateKeyAlias", null);

// Decrypt the encrypted assertion
BasicX509Credential cred = new BasicX509Credential();
cred.setPrivateKey(certificate);
StaticKeyInfoCredentialResolver resolver = new StaticKeyInfoCredentialResolver(cred);
Decrypter decrypter = new Decrypter(resolver, resolver, new InlineEncryptedKeyResolver());
decrypter.setRootInNewDocument(true);
Assertion decrypted = decrypter.decrypt(encryptedAssertion);

报错信息 #

java.lang.IllegalArgumentException: Data decryption key may not be null

问题原因与修复方案 #

Data decryption key may not be null报错的核心原因是OpenSAML的解密器未能成功获取到可用的解密密钥，无法解密响应中内嵌的AES256加密密钥，最终没有密钥可用于解密断言本身。具体问题排查和修复步骤如下：

• 核心错误：BasicX509Credential仅填充了私钥，缺少对应的X509证书实体。OpenSAML的密钥匹配逻辑会校验SAML响应中X509IssuerSerial信息和传入凭证的证书信息是否匹配，仅传私钥的凭证会直接被匹配逻辑过滤，导致解密器拿不到可用密钥。
  修复代码如下：

// 从keystore同时取出私钥和对应证书
KeyStore ks = KeyStore.getInstance("PKCS12");
char[] storePass = config.getBAMKeystorePassword().toCharArray();
// 如果私钥有单独密码替换为对应密码即可
char[] keyPass = storePass;
try (FileInputStream fileInputStream = new FileInputStream("keystoreUrl")) {
    ks.load(fileInputStream, storePass);
}
PrivateKey privateKey = (PrivateKey) ks.getKey("privateKeyAlias", keyPass);
X509Certificate cert = (X509Certificate) ks.getCertificate("privateKeyAlias");

// 完整填充凭证
BasicX509Credential cred = new BasicX509Credential();
cred.setPrivateKey(privateKey);
cred.setEntityCertificate(cert);
// 多证书场景下建议补充填充证书链
// cred.setEntityCertificateChain(Collections.singletonList(cert));

StaticKeyInfoCredentialResolver resolver = new StaticKeyInfoCredentialResolver(cred);
Decrypter decrypter = new Decrypter(null, resolver, new InlineEncryptedKeyResolver());
decrypter.setRootInNewDocument(true);
Assertion decrypted = decrypter.decrypt(encryptedAssertion);

• 其他排查点：
  • 确认JRE开启了无限制加密权限：AES256加密需要JCE无限制权限策略支持，JDK8u151及以上版本可通过代码Security.setProperty("crypto.policy", "unlimited")开启，更低版本需要下载对应JDK的JCE无限制权限包替换JRE目录下的policy文件。
  • 确认keystore中对应证书的颁发者名称、序列号和SAML响应中X509IssuerName、X509SerialNumber的取值完全一致，否则匹配逻辑会过滤掉传入的凭证。
  • 确认私钥密码正确：如果私钥设置了独立于keystore的密码，ks.getKey方法的第二个参数需要传入私钥的密码，不能传null，否则取到的私钥为null。

内容的提问来源于stack exchange，提问作者Michael Betterton