diff --git a/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.cs b/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.cs
index 79ecb125bbcd2..90ffa1454feeb 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/ref/System.Security.Cryptography.Pkcs.cs
@@ -48,6 +48,7 @@ public AlgorithmIdentifier(System.Security.Cryptography.Oid oid) { }
         public AlgorithmIdentifier(System.Security.Cryptography.Oid oid, int keyLength) { }
         public int KeyLength { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public System.Security.Cryptography.Oid Oid { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        public byte[] Parameters { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
     }
     public sealed partial class CmsRecipient
     {
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/src/System/Security/Cryptography/Pkcs/AlgorithmIdentifier.cs b/src/libraries/System.Security.Cryptography.Pkcs/src/System/Security/Cryptography/Pkcs/AlgorithmIdentifier.cs
index 4d0526dc472af..3f57bc67f5ca7 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/src/System/Security/Cryptography/Pkcs/AlgorithmIdentifier.cs
+++ b/src/libraries/System.Security.Cryptography.Pkcs/src/System/Security/Cryptography/Pkcs/AlgorithmIdentifier.cs
@@ -30,6 +30,8 @@ public AlgorithmIdentifier(Oid oid, int keyLength)
         public Oid Oid { get; set; }
 
         public int KeyLength { get; set; }
+
+        public byte[] Parameters { get; set; } = Array.Empty<byte>();
     }
 }
 
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/AlgorithmIdentifierTest.cs b/src/libraries/System.Security.Cryptography.Pkcs/tests/AlgorithmIdentifierTest.cs
new file mode 100644
index 0000000000000..f7647d7207ce4
--- /dev/null
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/AlgorithmIdentifierTest.cs
@@ -0,0 +1,113 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Test.Cryptography;
+using Xunit;
+
+namespace System.Security.Cryptography.Pkcs.Tests
+{
+    public static class AlgorithmIdentifierTest
+    {
+        [Fact]
+        public static void ParameterlessConstructor()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier();
+            Assert.Equal(0, ai.KeyLength);
+            Assert.Equal(Oids.TripleDesCbc, ai.Oid.Value);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void ConstructorTakesOid()
+        {
+            Oid o = new Oid(Oids.Rsa);
+            AlgorithmIdentifier ai = new AlgorithmIdentifier(o);
+            Assert.Equal(0, ai.KeyLength);
+            Assert.Equal(Oids.Rsa, ai.Oid.Value);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void ConstructorTakesNullOid()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier(null);
+            Assert.Null(ai.Oid);
+            Assert.Equal(0, ai.KeyLength);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void ConstructorTakesOidAndKeyLength()
+        {
+            Oid o = new Oid(Oids.Rsa);
+            AlgorithmIdentifier ai = new AlgorithmIdentifier(o, 128);
+            Assert.Equal(128, ai.KeyLength);
+            Assert.Equal(Oids.Rsa, ai.Oid.Value);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void ConstructorTakesNullOidAndKeyLength()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier(null, 128);
+            Assert.Null(ai.Oid);
+            Assert.Equal(128, ai.KeyLength);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void ConstructorTakesOidAndNegativeKeyLength()
+        {
+            Oid o = new Oid(Oids.Rsa);
+            AlgorithmIdentifier ai = new AlgorithmIdentifier(o, -1);
+            Assert.Equal(-1, ai.KeyLength);
+            Assert.Equal(Oids.Rsa, ai.Oid.Value);
+            Assert.NotNull(ai.Parameters);
+            Assert.Equal(0, ai.Parameters.Length);
+        }
+
+        [Fact]
+        public static void KeyLength()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier
+            {
+                KeyLength = int.MaxValue
+            };
+            Assert.Equal(int.MaxValue, ai.KeyLength);
+            ai.KeyLength = 0;
+            Assert.Equal(0, ai.KeyLength);
+            ai.KeyLength = int.MinValue;
+            Assert.Equal(int.MinValue, ai.KeyLength);
+        }
+
+        [Fact]
+        public static void Oid()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier
+            {
+                Oid = new Oid(Oids.Rsa)
+            };
+            Assert.Equal(Oids.Rsa, ai.Oid.Value);
+            ai.Oid = null;
+            Assert.Null(ai.Oid);
+        }
+
+        [Fact]
+        public static void Parameters()
+        {
+            AlgorithmIdentifier ai = new AlgorithmIdentifier
+            {
+                Parameters = new byte[2] { 0x05, 0x00 } // ASN.1 NULL
+            };
+            Assert.Equal("0500", ai.Parameters.ByteArrayToHex());
+            ai.Parameters = null;
+            Assert.Null(ai.Parameters);
+        }
+    }
+}
diff --git a/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj b/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
index db9a8da869c69..334489aa5e7a3 100644
--- a/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
+++ b/src/libraries/System.Security.Cryptography.Pkcs/tests/System.Security.Cryptography.Pkcs.Tests.csproj
@@ -12,6 +12,7 @@
     <Compile Include="$(CommonTestPath)\System\Security\Cryptography\ByteUtils.cs">
       <Link>CommonTest\System\Security\Cryptography\ByteUtils.cs</Link>
     </Compile>
+    <Compile Include="AlgorithmIdentifierTest.cs" />
     <Compile Include="Certificates.cs" />
     <Compile Include="CertLoader.cs" />
     <Compile Include="CertLoader.Settings.cs" />