XMLDSig：我是否必须在封装的签名中指定引用 URI

Question

假设我有这样的xml：

<?xml version="1.0" encoding="UTF-8"?>
<CATALOG>
    <CD>
        <TITLE>Empire Burlesque</TITLE>                    
        <ARTIST>Bob Dylan</ARTIST>
        <COUNTRY id="123">USA</COUNTRY>
        <COMPANY>Columbia</COMPANY>
        <PRICE>10.90</PRICE>
        <YEAR>1985</YEAR>
    </CD>    
    <CD>
        <TITLE>Hide your heart</TITLE>
        <ARTIST>Bonnie Tyler</ARTIST>
        <COUNTRY>UK</COUNTRY>
        <COMPANY>CBS Records</COMPANY>
        <PRICE>9.90</PRICE>
        <YEAR>1988</YEAR>
    </CD>
    <CD>
        <TITLE>Greatest Hits</TITLE>
        <ARTIST>Dolly Parton</ARTIST>
        <COUNTRY>USA</COUNTRY>
        <COMPANY>RCA</COMPANY>
        <PRICE>9.90</PRICE>
        <YEAR>1982</YEAR>
    </CD>   
</CATALOG>

签名后我得到：

<?xml version="1.0" encoding="UTF-8"?>
<CATALOG>
    <CD>
        <TITLE>Empire Burlesque</TITLE>                    
        <ARTIST>Bob Dylan</ARTIST>
        <COUNTRY id="123">USA</COUNTRY>
        <COMPANY>Columbia</COMPANY>
        <PRICE>10.90</PRICE>
        <YEAR>1985</YEAR>
        <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
            <ds:SignedInfo>
                <ds:CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
                <ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-md5"/>
                <ds:Reference URI="">
                    <ds:Transforms>
                        <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
                        <ds:Transform Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
                    </ds:Transforms>
                    <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#md5"/>
                    <ds:DigestValue>C6i9GSNZ8seoXxfuFc482Q==</ds:DigestValue>
                </ds:Reference>
            </ds:SignedInfo>
            <ds:SignatureValue>
d/ufAnYK35PKUdi+O6DUytV+36OGAr5meHXq2qoOUp+zO1Q5HbJvIs01qlPT9oKiBEi2QiAF3Sya
ZVwi4hEI9xHkLiewmOxPo1KgVfJ1Ir2RPpkdegFYFx9QCMR4Z1M7zTkijCKv9ncWR4MYjOAfDrKf
fbvUX3AbRHlUYJj6M4QcrQUuBPhSqo4TcxtfblNqmKUT+141+sLSsuM2xy24YeyF7NUff9tirCiP
KgBHpFGtiJAdxugAlzqHaR9CP2kRA2Sg046NBo2yO/nTDfUKqquZm4aaZsLWbvKJYvrgqD4YgH4M
FFpK5ChgYa4oi7f9BAYxOFcY9f1OCHsvpdCbpw==
            </ds:SignatureValue>
            <ds:KeyInfo>
                <ds:KeyValue>
                    <ds:RSAKeyValue>
                        <ds:Modulus>
1Bphf/ypmjIyIbWKBS39IaBpUn/e7oylpexMhTtsKYnbKuufzDhReR15oJ9cavVa9BkSSmLjaLxt
jIzIswaoW0SnTR4VySpbkujoeCSzoIGTlQ2ae96vT4sZURferQ8GpS/iExpblSX5knD8TBDCt+MK
UNTpJzPy6HdYGBtKfcc5C0STt07WGnhnOYYrIht1y/blne2Ec90dCt3hQmInqbBUbp1Ngl4V7xXH
rSifvQ6X+Dzg10l/vx92vFwBM3we+7p8jbDey9KLWS44W/AXmcxmuBo4kTN4fS9Ld/ctMR7ATbP2
frjcHJoecsQs3tnK1VZjrnnQUsZxDqjWhYDx2w==
                        </ds:Modulus>
                        <ds:Exponent>AQAB</ds:Exponent>
                    </ds:RSAKeyValue>
                </ds:KeyValue>
                <ds:X509Data>
                    <ds:X509Certificate>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                    </ds:X509Certificate>
                </ds:X509Data>
            </ds:KeyInfo>
        </ds:Signature>
    </CD>    
    <CD>
        <TITLE>Hide your heart</TITLE>
        <ARTIST>Bonnie Tyler</ARTIST>
        <COUNTRY>UK</COUNTRY>
        <COMPANY>CBS Records</COMPANY>
        <PRICE>9.90</PRICE>
        <YEAR>1988</YEAR>
    </CD>
    <CD>
        <TITLE>Greatest Hits</TITLE>
        <ARTIST>Dolly Parton</ARTIST>
        <COUNTRY>USA</COUNTRY>
        <COMPANY>RCA</COMPANY>
        <PRICE>9.90</PRICE>
        <YEAR>1982</YEAR>
    </CD>   
</CATALOG>

<Signature> 被包裹在 <CD> 下是否意味着它准确地标记了元素，或者因为 <ds:Reference URI=""> 这意味着整个 XML签署了吗？通过阅读规范 http://www.w3.org/TR/xmldsig-core/ 我留下的印象是封装的签名不需要引用 URI。这是正确的吗？

Answer 1

如果 Reference URI 为空，则表示将对哪个元素进行签名，并且签名将被封装为该元素的子元素。如果签署文档的一部分，则封装签名可能具有引用 URI，但签名由文档中的另一元素封装。例如签署一个或所有 <CD> 元素，但 ds:signature 本身被 <CATALOG> 元素包围。在你的文档中只有第一个 CD 元素用于计算摘要和签名值，但其他 CD 可以更改而不会使签名失效。

Answer 2

我想我明白了。

根据specification URI=""

Identifies the node-set (minus any comment nodes) of the XML resource containing the signature

我理解为 "Identifies all nodes (the node-set) of the XML document that contains the <ds:Signature> element. That would mean that URI="" <=> 签名是整个文档。

此声明得到另一个 resource - Apache Santuario 常见问题解答的支持：

3.1. What is the enveloped transform? The enveloped transform is a special transform that enables the use of so-called enveloped signatures.

Enveloped signatures are signatures over an entire XML document, for which the element is included in the document itself. An example could be:
<![CDATA[
<?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?>
   <Root>
     <SomeContent>
       ... 
     </SomeContent>
       <ds:Signature>
         <ds:SignedInfo>
           <ds:Reference URI="">
             <ds:Transforms>
               <ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
             </ds:Transforms>
           </ds:Reference>
         </ds:SignedInfo>
         ....
       </ds:Signature>
   </Root>
]]>
The Reference indicates that Root and it's descendants (except for comments) are signed, but the Transform element says to throw out the Signature element (that is the parent of this Reference) from the stream that is to be signed. Note that if there are other Signature elements in Root, they will remain untouched.

... 翻译成 "The URI="" 已签名的是包含 <ds:Signature> 的整个文档，我们有一个 <ds:Transform> 表示此签名已被封装，因此应该验证前删除

因此，结论是：URI=""和签名类型（detached, enveloped, enveloping）是完全不同的两个东西。 URI 是指向 XML 文档的一部分的指针，说明哪些已签名，哪些未签名。 URI="" 表示正在对整个当前文档（包含 <ds:Signature> 的文档）进行签名。签名类型（分离的、封装的、封装的）otoh 影响在验证之前应应用哪些转换。如有包封，必须整个<ds:Signature>取出后方可验证。

XMLDSig：我是否必须在封装的签名中指定引用 URI

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