数字签名(PKCS#7-延迟签名）/自应用签名以来文档已被更改或损坏

Question

我已经研究了所有类似的问题，但找不到一个应用itextsharp延迟签名的案例。

基本上，我的应用程序使用pkcs#7签名对pdf文档进行签名，该签名是由远程web服务创建的。

我的应用程序向这个web服务发送原始文档的哈希（添加空签名字段后可签名字节的哈希），并接收一个Base64编码的签名文件。

我将此签名嵌入到先前生成的临时pdf文件中，该文件具有空签名字段。

最后，我的签名未被验证，因为Adobe Reader指出文档已更改或已损坏。

添加空签名字段并获得Pdf可签名字节的代码

public static string GetBytesToSign(string unsignedPdf, string tempPdf, string signatureFieldName)
{
    if (File.Exists(tempPdf))
        File.Delete(tempPdf);

    using (PdfReader reader = new PdfReader(unsignedPdf))
    {
        using (FileStream os = File.OpenWrite(tempPdf))
        {
            PdfStamper stamper = PdfStamper.CreateSignature(reader, os, '\0');
            PdfSignatureAppearance appearance = stamper.SignatureAppearance;
            appearance.SetVisibleSignature(new Rectangle(36, 748, 250, 400), 1, signatureFieldName);

            IExternalSignatureContainer external = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);

            MakeSignature.SignExternalContainer(appearance, external, 8192);

            byte[] array = SHA256Managed.Create().ComputeHash(appearance.GetRangeStream());

            return Convert.ToBase64String(array);
        }
    }
}

打开临时Pdf并嵌入接收到的签名的代码

public static void EmbedSignature(string tempPdf, string signedPdf, string signatureFieldName, string signature)
{
    byte[] signedBytes = Convert.FromBase64String(signature);

    using (PdfReader reader = new PdfReader(tempPdf))
    {
        using (FileStream os = File.OpenWrite(signedPdf))
        {
            IExternalSignatureContainer external = new MyExternalSignatureContainer(signedBytes);
            MakeSignature.SignDeferred(reader, signatureFieldName, os, external);
        }
    }
}

此操作的结果是生成最终的signedpdf。但是，Adobe表示，由于更改或损坏，签名无效。

我的原始文件

Z9QIYVTP4CRBZ1SSCQ+P0JVRINZ5LVJYJXK3L7YP/IE=

我从web服务收到的签名是：

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

我比较了tempFile和signedFile的字节，只有tempFile的0（我想是用于临时签名文件）被替换为signedFile中的实际签名。

Answer 1

在您从web服务收到的签名中有：

  39   59: . . . SEQUENCE {
  41    9: . . . . OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
         : . . . . . (PKCS #7)
  52   46: . . . . [0] {
  54   44: . . . . . OCTET STRING    
         : . . . . . . 7A 39 71 49 79 76 74 70    z9qIyvtp
         : . . . . . . 34 63 52 42 5A 31 53 53    4cRBZ1SS
         : . . . . . . 43 51 2B 50 30 4A 56 52    CQ+P0JVR
         : . . . . . . 69 6E 7A 35 6C 76 6A 59    inz5lvjY
         : . . . . . . 6A 58 6B 33 4C 37 59 50    jXk3L7YP
         : . . . . . . 2F 49 45 3D                /IE=
         : . . . . . }
         : . . . . }
[...]
1955    9: . . . . . SEQUENCE {
1957    5: . . . . . . OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
         : . . . . . . . (OIW)
1964    0: . . . . . . NULL
         : . . . . . . }
1966   93: . . . . . [0] {
1968   24: . . . . . . SEQUENCE {
1970    9: . . . . . . . OBJECT IDENTIFIER contentType (1 2 840 113549 1 9 3)
         : . . . . . . . . (PKCS #9)
1981   11: . . . . . . . SET {
1983    9: . . . . . . . . OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
         : . . . . . . . . . (PKCS #7)
         : . . . . . . . . }
         : . . . . . . . }
1994   28: . . . . . . SEQUENCE {
1996    9: . . . . . . . OBJECT IDENTIFIER signingTime (1 2 840 113549 1 9 5)
         : . . . . . . . . (PKCS #9)
2007   15: . . . . . . . SET {
2009   13: . . . . . . . . UTCTime 22/09/2017 13:18:38 GMT
         : . . . . . . . . }
         : . . . . . . . }
2024   35: . . . . . . SEQUENCE {
2026    9: . . . . . . . OBJECT IDENTIFIER messageDigest (1 2 840 113549 1 9 4)
         : . . . . . . . . (PKCS #9)
2037   22: . . . . . . . SET {
2039   20: . . . . . . . . OCTET STRING    
         : . . . . . . . . . EF 37 38 3B B1 31 AB 96    .78;.1..
         : . . . . . . . . . CE FC 47 1E 32 A7 79 73    ..G.2.ys
         : . . . . . . . . . 5D 95 15 04                ]...
         : . . . . . . . . }
         : . . . . . . . }
         : . . . . . . }
2061   13: . . . . . SEQUENCE {
2063    9: . . . . . . OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1 1)
         : . . . . . . . (PKCS #1)
2074    0: . . . . . . NULL
         : . . . . . . }

在此，您的base64编码散列显示为嵌入的有符号数据（偏移56..99)。此外，哈希算法被选择为“SHA-1”（offsets 1955.1965)，并且签名的文档哈希是与SHA-1哈希值的大小匹配的20字节值。此外，如PKCS#1 1.5（偏移量2061.2075)中所述，RSA用于签名。

因此，您的签名服务看起来不是将您的输入用作base64编码的预先计算的文档哈希值，而是用作使用SHA1WITHRSA/2048进行签名的普通数据。

因此错误不在iText使用代码中,而在签名服务调用代码中。