Fix SignedCms certificate collection modification with attribute cert…

…ificates.

When adding or removing certificates from the certificateSet collection, we assumed that the collection would
only contain X.509 certificates. This changes the implementation so that when looking for duplicates, we skip
over choices that are not an X.509 certificate when looking for a duplicate.

The tests peek in to the SignedData ASN.1 to ensure that the attribute certificates are preserved during a round
trip when encoding and decoding a CMS.

src/libraries/System.Security.Cryptography.Pkcs/src/System/Security/Cryptography/Pkcs/SignedCms.cs

@@ -686,7 +686,7 @@ public void AddCertificate(X509Certificate2 certificate)
             {
                 foreach (CertificateChoiceAsn cert in _signedData.CertificateSet!)
                 {
-                    if (cert.Certificate!.Value.Span.SequenceEqual(rawData))
+                    if (cert.Certificate is not null && cert.Certificate.Value.Span.SequenceEqual(rawData))
                     {
                         throw new CryptographicException(SR.Cryptography_Cms_CertificateAlreadyInCollection);
                     }
@@ -721,7 +721,7 @@ public void RemoveCertificate(X509Certificate2 certificate)
 
                 foreach (CertificateChoiceAsn cert in _signedData.CertificateSet!)
                 {
-                    if (cert.Certificate!.Value.Span.SequenceEqual(rawData))
+                    if (cert.Certificate is not null && cert.Certificate.Value.Span.SequenceEqual(rawData))
                     {
                         PkcsHelpers.RemoveAt(ref _signedData.CertificateSet, idx);
                         Reencode();

src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedCmsTests.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Formats.Asn1;
 using System.Linq;
 using System.Security.Cryptography.X509Certificates;
 using System.Security.Cryptography.Xml;
@@ -1611,6 +1612,49 @@ public static void Decode_CanDecodeWithAttributeCertificate()
             cms.CheckSignature(verifySignatureOnly: true);
         }
 
+        [Fact]
+        public static void AddCertificate_CollectionContainsAttributeCertificate()
+        {
+            SignedCms signedCms = new SignedCms();
+
+            signedCms.Decode(SignedDocuments.CmsWithAttributeCertificate);
+            signedCms.CheckSignature(true);
+
+            int countBefore = CountCertificateChoices(SignedDocuments.CmsWithAttributeCertificate);
+            int certCount = signedCms.Certificates.Count;
+
+            using (ECDsa ec = ECDsa.Create(ECCurve.NamedCurves.nistP256))
+            {
+                CertificateRequest req = new("CN=test", ec, HashAlgorithmName.SHA256);
+
+                using (X509Certificate2 cert = req.CreateSelfSigned(DateTimeOffset.Now, DateTimeOffset.Now))
+                {
+                    signedCms.AddCertificate(cert);
+                    byte[] reEncoded = signedCms.Encode();
+                    int countAfter = CountCertificateChoices(reEncoded);
+                    Assert.Equal(countBefore + 1, countAfter);
+
+                    signedCms = new SignedCms();
+                    signedCms.Decode(reEncoded);
+                    signedCms.CheckSignature(true);
+                }
+            }
+        }
+
+        [Fact]
+        public static void RemoveCertificate_CollectionContainsAttributeCertificate()
+        {
+            SignedCms signedCms = new SignedCms();
+
+            signedCms.Decode(SignedDocuments.CmsWithAttributeCertificate);
+            int countBefore = CountCertificateChoices(SignedDocuments.CmsWithAttributeCertificate);
+
+            signedCms.RemoveCertificate(signedCms.Certificates[0]);
+            byte[] reEncoded = signedCms.Encode();
+            int countAfter = CountCertificateChoices(reEncoded);
+            Assert.Equal(countBefore - 1, countAfter);
+        }
+
         private static void CheckNoSignature(byte[] encoded, bool badOid=false)
         {
             SignedCms cms = new SignedCms();
@@ -1630,5 +1674,36 @@ private static void CheckNoSignature(byte[] encoded, bool badOid=false)
                 cms.CheckHash();
             }
         }
+
+        public static int CountCertificateChoices(byte[] encoded)
+        {
+            AsnReader reader = new AsnReader(encoded, AsnEncodingRules.BER);
+            reader = reader.ReadSequence();
+            reader.ReadObjectIdentifier();
+            reader = reader.ReadSequence(new Asn1Tag(TagClass.ContextSpecific, 0));
+            reader = reader.ReadSequence();
+
+            reader.ReadInteger(); // version
+            reader.ReadSetOf(); // digestAlgorithms
+            reader.ReadSequence(); // encapsulatedContentInfo
+
+            Asn1Tag expectedTag = new Asn1Tag(TagClass.ContextSpecific, 0, true); // certificates[0]
+
+            if (reader.PeekTag() == expectedTag)
+            {
+                AsnReader certs = reader.ReadSetOf(expectedTag);
+                int count = 0;
+
+                while (certs.HasData)
+                {
+                    certs.ReadEncodedValue();
+                    count++;
+                }
+
+                return count;
+            }
+
+            return 0;
+        }
     }
 }

src/libraries/System.Security.Cryptography.Pkcs/tests/SignedCms/SignedDocuments.cs

@@ -1626,5 +1626,194 @@ internal static class SignedDocuments
             "6AB46C76047604BA7DF071EE0137B73F4D9DF616095C8F1CA9EB925B6D4C6ABC" +
             "FFEB73A81903169C6B487B316AFC951F696831A4B29B9ABCEA7EBCD243A553D2" +
             "F8B44FDA1B0AC0").HexToByteArray();
+
+        internal static readonly byte[] CmsWithAttributeCertificate = (
+            "3082174e06092a864886f70d010702a082173f3082173b020103310f300d0609" +
+            "608648016503040201050030820161060b2a864886f70d0109100104a0820150" +
+            "0482014c30820148020101060a2b0601040184590a03013031300d0609608648" +
+            "01650304020105000420dffd6021bb2bd5b0af676290809ec3a53191dd81c7f7" +
+            "0a4b28688a362182986f020663a04d30704d1813323032323132323331343430" +
+            "34302e3133375a3004800201f4a081e0a481dd3081da310b3009060355040613" +
+            "025553311330110603550408130a57617368696e67746f6e3110300e06035504" +
+            "0713075265646d6f6e64311e301c060355040a13154d6963726f736f66742043" +
+            "6f72706f726174696f6e31253023060355040b131c4d6963726f736f66742041" +
+            "6d6572696361204f7065726174696f6e7331263024060355040b131d5468616c" +
+            "6573205453532045534e3a424237332d393646442d3737454631353033060355" +
+            "0403132c4d6963726f736f6674205075626c6963205253412054696d65205374" +
+            "616d70696e6720417574686f72697479a08211e6308207823082056aa0030201" +
+            "0202133300000005e5cf0fff662ec987000000000005300d06092a864886f70d" +
+            "01010c05003077310b3009060355040613025553311e301c060355040a13154d" +
+            "6963726f736f667420436f72706f726174696f6e314830460603550403133f4d" +
+            "6963726f736f6674204964656e7469747920566572696669636174696f6e2052" +
+            "6f6f7420436572746966696361746520417574686f726974792032303230301e" +
+            "170d3230313131393230333233315a170d3335313131393230343233315a3061" +
+            "310b3009060355040613025553311e301c060355040a13154d6963726f736f66" +
+            "7420436f72706f726174696f6e31323030060355040313294d6963726f736f66" +
+            "74205075626c6963205253412054696d657374616d70696e6720434120323032" +
+            "3030820222300d06092a864886f70d01010105000382020f003082020a028202" +
+            "01009e7ce75263fde0c59f057d63b50622a31c1ed7e79733d11305bd65464777" +
+            "91c15d706f7fb2ab43970c4aa1521c6aa0dbfa89858a8e431c2e1105c6f24078" +
+            "d70b0324fe5dd3398b60a018f19c6fde5624b8b0ec7ccb8812abc660e3d44401" +
+            "fe61b9784891044a7b7431b3c4a0a74d8a1c0ce711afd2b1a87c9d6a39849335" +
+            "c739e446c14fbbaadf0c7799786d566b5c084af964a4e428a1350b166f34f59d" +
+            "1962543c2e9ee2e45f58722165c802b09faca337f911e1f92ab9459f1a6328a4" +
+            "dabf07c53fa5da199196506f1365a893a20468025a9c7af6e2aa2a14cf562de0" +
+            "544ae773faa2f9d47c036322033d243749e1ed2a883466e6c39388442d04b19d" +
+            "f5585dd4c69dc6819c1eb442b12e6b3bdca1bf67e3247ae6950d042179a9e038" +
+            "4306278a50647e799e02344ddcb56e2ebd20d055e4a9f61d5268f57c51611fc9" +
+            "3c601a33ac46979ec48bde47530f4d57fb82df2163ae1734f3ba8b2506b0482d" +
+            "f1cd8fc45f3b13e08eec0dbc4e98cdab978b8a2ba784a6ead176e390da14e498" +
+            "6d614ae59806e9c518dbf6d4ab78376d002a66deb929c69ec04277672344a1bb" +
+            "f7e4d7fac4de85ac0ea317de38efe347bc28de58b09067733c9607827279e14c" +
+            "5b72417dd7802a1ce88457bc539c3d5aebdc3f513c708c4ba0a483cc20813aed" +
+            "2159d8f328dbbc6394b007596de5d421001632cd1dddc443bf4f52bf055177ad" +
+            "5ebd0203010001a382021b30820217300e0603551d0f0101ff04040302018630" +
+            "1006092b06010401823715010403020100301d0603551d0e041604146b69283a" +
+            "352f486340cf7bd8af49e93ed93ddb2130540603551d20044d304b3049060455" +
+            "1d20003041303f06082b060105050702011633687474703a2f2f7777772e6d69" +
+            "63726f736f66742e636f6d2f706b696f70732f446f63732f5265706f7369746f" +
+            "72792e68746d30130603551d25040c300a06082b06010505070308301906092b" +
+            "0601040182371402040c1e0a00530075006200430041300f0603551d130101ff" +
+            "040530030101ff301f0603551d23041830168014c87ed26a852a1bca19980407" +
+            "27cf50104f68a8a23081840603551d1f047d307b3079a077a075867368747470" +
+            "3a2f2f7777772e6d6963726f736f66742e636f6d2f706b696f70732f63726c2f" +
+            "4d6963726f736f66742532304964656e74697479253230566572696669636174" +
+            "696f6e253230526f6f742532304365727469666963617465253230417574686f" +
+            "72697479253230323032302e63726c30819406082b0601050507010104818730" +
+            "818430818106082b060105050730028675687474703a2f2f7777772e6d696372" +
+            "6f736f66742e636f6d2f706b696f70732f63657274732f4d6963726f736f6674" +
+            "2532304964656e74697479253230566572696669636174696f6e253230526f6f" +
+            "742532304365727469666963617465253230417574686f726974792532303230" +
+            "32302e637274300d06092a864886f70d01010c050003820201005f8876c77e6d" +
+            "b55a1575e74c7868fa4ee1d844992515a5b8b13439afe93bee207bf5c48b35ef" +
+            "86cd18efe2956326f89c796e8017ac9c5a81184742d885a6b4a3324b539622f8" +
+            "b0a672b768be4979dc336de045ecf3b283a2061bf5e1849dd4a967964cef82cd" +
+            "bd5cd8d3f9cf2121f3d17bdaef54230f887ef33d9730e67363b610d0fb30f9eb" +
+            "72359d427acb9f536d75acbb252cab0ef05d9a06cd9c228d64f9a1ce86bc3dc7" +
+            "0e8909638d35ba19e3dee6c185b911f3745b7ccbe6cdda7785ed9bbc8533b523" +
+            "ae17346aacb7c4bec3e4547627bc7d70b58cabb79bd28622a1786a576b6016a6" +
+            "ca1de0e2724f8ff2d1d8205a2f20fed81b86642566a0d47f752a510b1968b748" +
+            "bbf5d28e0a19a838da9b308f26d38b8b6841c0bf8ab0287435bc1cdb57f9c6f3" +
+            "d2c329b4524af8a39b0270c51c4b2e9310feee315f115f4787ff824b1291b269" +
+            "ee8a8bc258839bf87ec34689fd4e5c72762161beef3ca34c37e4990d6c9c5393" +
+            "832117f2a06979f41b1747f1e9446b6226ab8e6069af03fa64e6f0b595c9db78" +
+            "cadc583ff6ea8cde3d0fd359f3572813a6905a6f3c4f021fe11e1865b3a930a3" +
+            "740b27a368f34de352c65c778250c626071dcf90ff000c70f52760abffab63b8" +
+            "e382ced7e9fa8f4d73e66820092951c03f5f681232480700f52f21db684801c4" +
+            "50a881848e89422bd17a9caf59c97e2586d86c187ba668005d5b308207963082" +
+            "057ea00302010202133300000020b001af2f87675c8b000000000020300d0609" +
+            "2a864886f70d01010c05003061310b3009060355040613025553311e301c0603" +
+            "55040a13154d6963726f736f667420436f72706f726174696f6e313230300603" +
+            "55040313294d6963726f736f6674205075626c6963205253412054696d657374" +
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+            "54696d657374616d70696e672043412032303230300d06092a864886f70d0101" +
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     }
 }