diff --git a/src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonClaimSet.cs b/src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonClaimSet.cs
index 5f95a34a41..2862fd258f 100644
--- a/src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonClaimSet.cs
+++ b/src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonClaimSet.cs
@@ -22,10 +22,10 @@ internal class JsonClaimSet
 
         internal static JsonClaimSet Empty { get; } = new JsonClaimSet("{}"u8.ToArray());
         internal object _claimsLock = new();
-        internal IDictionary<string, object> _jsonClaims;
-        private IList<Claim> _claims;
+        internal readonly Dictionary<string, object> _jsonClaims;
+        private List<Claim> _claims;
 
-        internal JsonClaimSet(IDictionary<string, object> jsonClaims)
+        internal JsonClaimSet(Dictionary<string, object> jsonClaims)
         {
             _jsonClaims = jsonClaims;
         }
@@ -34,7 +34,7 @@ internal JsonClaimSet(byte[] jsonUtf8Bytes)
             _jsonClaims = JwtTokenUtilities.CreateClaimsDictionary(jsonUtf8Bytes, jsonUtf8Bytes.Length);
         }
 
-        internal IList<Claim> Claims(string issuer)
+        internal List<Claim> Claims(string issuer)
         {
             if (_claims == null)
                 lock (_claimsLock)
@@ -43,16 +43,16 @@ internal IList<Claim> Claims(string issuer)
             return _claims;
         }
 
-        internal IList<Claim> CreateClaims(string issuer)
+        internal List<Claim> CreateClaims(string issuer)
         {
-            IList<Claim> claims = new List<Claim>();
+            var claims = new List<Claim>();
             foreach (KeyValuePair<string, object> kvp in _jsonClaims)
                 CreateClaimFromObject(claims, kvp.Key, kvp.Value, issuer);
 
             return claims;
         }
 
-        internal static void CreateClaimFromObject(IList<Claim> claims, string claimType, object value, string issuer)
+        internal static void CreateClaimFromObject(List<Claim> claims, string claimType, object value, string issuer)
         {
             // Json.net recognized DateTime by default.
             if (value is string str)
diff --git a/src/Microsoft.IdentityModel.JsonWebTokens/JwtTokenUtilities.cs b/src/Microsoft.IdentityModel.JsonWebTokens/JwtTokenUtilities.cs
index 568cbbfcb3..771375d194 100644
--- a/src/Microsoft.IdentityModel.JsonWebTokens/JwtTokenUtilities.cs
+++ b/src/Microsoft.IdentityModel.JsonWebTokens/JwtTokenUtilities.cs
@@ -533,7 +533,7 @@ internal static string GetStringClaimValueType(string str)
         // We need a shared model for adding claims from object for JsonWebToken and JwtSecurityToken
         // From getting ClaimValueTypes to setting object types
 
-        internal static IDictionary<string, object> CreateClaimsDictionary(byte[] bytes, int length)
+        internal static Dictionary<string, object> CreateClaimsDictionary(byte[] bytes, int length)
         {
             Dictionary<string, object> claims = new();
             Span<byte> utf8Span = bytes;
@@ -575,9 +575,9 @@ internal static IDictionary<string, object> CreateClaimsDictionary(byte[] bytes,
         /// <param name="startIndex"></param>
         /// <param name="length"></param>
         /// <returns></returns>
-        internal static IDictionary<string,object> ParseJsonBytes(string rawString, int startIndex, int length)
+        internal static Dictionary<string,object> ParseJsonBytes(string rawString, int startIndex, int length)
         {
-            return Base64UrlEncoding.Decode<IDictionary<string,object>>(rawString, startIndex, length, CreateClaimsDictionary);
+            return Base64UrlEncoding.Decode(rawString, startIndex, length, CreateClaimsDictionary);
         }
     }
 }
diff --git a/src/Microsoft.IdentityModel.Protocols.OpenIdConnect/OpenIdConnectProtocolValidator.cs b/src/Microsoft.IdentityModel.Protocols.OpenIdConnect/OpenIdConnectProtocolValidator.cs
index b7384698f5..7ada8ec1b9 100644
--- a/src/Microsoft.IdentityModel.Protocols.OpenIdConnect/OpenIdConnectProtocolValidator.cs
+++ b/src/Microsoft.IdentityModel.Protocols.OpenIdConnect/OpenIdConnectProtocolValidator.cs
@@ -27,7 +27,7 @@ namespace Microsoft.IdentityModel.Protocols.OpenIdConnect
     /// </summary>
     public class OpenIdConnectProtocolValidator
     {
-        private IDictionary<string, string> _hashAlgorithmMap =
+        private readonly Dictionary<string, string> _hashAlgorithmMap =
             new Dictionary<string, string>
             {
                 { SecurityAlgorithms.EcdsaSha256, "SHA256" },
diff --git a/src/Microsoft.IdentityModel.Protocols/AuthenticationProtocolMessage.cs b/src/Microsoft.IdentityModel.Protocols/AuthenticationProtocolMessage.cs
index 96fa9eb75e..dd9f0892fb 100644
--- a/src/Microsoft.IdentityModel.Protocols/AuthenticationProtocolMessage.cs
+++ b/src/Microsoft.IdentityModel.Protocols/AuthenticationProtocolMessage.cs
@@ -20,7 +20,7 @@ public abstract class AuthenticationProtocolMessage
         private string _scriptButtonText = "Submit";
         private string _scriptDisabledText = "Script is disabled. Click Submit to continue.";
 
-        private IDictionary<string, string> _parameters = new Dictionary<string, string>();
+        private readonly Dictionary<string, string> _parameters = new Dictionary<string, string>();
         private string _issuerAddress = string.Empty;
 
         /// <summary>
diff --git a/src/Microsoft.IdentityModel.Tokens.Saml/Saml2/Saml2Evidence.cs b/src/Microsoft.IdentityModel.Tokens.Saml/Saml2/Saml2Evidence.cs
index 7282ba3ea7..dfd5b4e6f0 100644
--- a/src/Microsoft.IdentityModel.Tokens.Saml/Saml2/Saml2Evidence.cs
+++ b/src/Microsoft.IdentityModel.Tokens.Saml/Saml2/Saml2Evidence.cs
@@ -18,9 +18,9 @@ namespace Microsoft.IdentityModel.Tokens.Saml2
     /// </remarks>
     public class Saml2Evidence
     {
-        private ICollection<Saml2Id> _assertionIdReferences = new List<Saml2Id>();
-        private ICollection<Saml2Assertion> _assertions = new List<Saml2Assertion>();
-        private AbsoluteUriCollection _assertionUriReferences = new AbsoluteUriCollection();
+        private readonly List<Saml2Id> _assertionIdReferences = new List<Saml2Id>();
+        private readonly List<Saml2Assertion> _assertions = new List<Saml2Assertion>();
+        private readonly AbsoluteUriCollection _assertionUriReferences = new AbsoluteUriCollection();
 
         /// <summary>
         /// Initializes a new instance of <see cref="Saml2Evidence"/> class.
diff --git a/src/Microsoft.IdentityModel.Tokens/AsymmetricSignatureProvider.cs b/src/Microsoft.IdentityModel.Tokens/AsymmetricSignatureProvider.cs
index 0bfa7b3d4e..e4c2f3534b 100644
--- a/src/Microsoft.IdentityModel.Tokens/AsymmetricSignatureProvider.cs
+++ b/src/Microsoft.IdentityModel.Tokens/AsymmetricSignatureProvider.cs
@@ -16,9 +16,8 @@ public class AsymmetricSignatureProvider : SignatureProvider
         private DisposableObjectPool<AsymmetricAdapter> _asymmetricAdapterObjectPool;
         private CryptoProviderFactory _cryptoProviderFactory;
         private bool _disposed;
-        private Lazy<bool> _keySizeIsValid;
-        private IReadOnlyDictionary<string, int> _minimumAsymmetricKeySizeInBitsForSigningMap;
-        private IReadOnlyDictionary<string, int> _minimumAsymmetricKeySizeInBitsForVerifyingMap;
+        private Dictionary<string, int> _minimumAsymmetricKeySizeInBitsForSigningMap;
+        private Dictionary<string, int> _minimumAsymmetricKeySizeInBitsForVerifyingMap;
 
         /// <summary>
         /// Mapping from algorithm to minimum <see cref="AsymmetricSecurityKey"/>.KeySize when creating signatures.
@@ -131,7 +130,6 @@ public AsymmetricSignatureProvider(SecurityKey key, string algorithm, bool willC
                 throw LogHelper.LogExceptionMessage(new NotSupportedException(LogHelper.FormatInvariant(LogMessages.IDX10634, LogHelper.MarkAsNonPII((algorithm)), key)));
 
             WillCreateSignatures = willCreateSignatures;
-            _keySizeIsValid = new Lazy<bool>(ValidKeySize);
             _asymmetricAdapterObjectPool = new DisposableObjectPool<AsymmetricAdapter>(CreateAsymmetricAdapter, _cryptoProviderFactory.SignatureProviderObjectPoolCacheSize);
         }
 
diff --git a/src/Microsoft.IdentityModel.Tokens/BaseConfigurationManager.cs b/src/Microsoft.IdentityModel.Tokens/BaseConfigurationManager.cs
index 2ae21b827f..042f69ba5c 100644
--- a/src/Microsoft.IdentityModel.Tokens/BaseConfigurationManager.cs
+++ b/src/Microsoft.IdentityModel.Tokens/BaseConfigurationManager.cs
@@ -94,7 +94,7 @@ public virtual Task<BaseConfiguration> GetBaseConfigurationAsync(CancellationTok
         /// Gets all valid last known good configurations.
         /// </summary>
         /// <returns>A collection of all valid last known good configurations.</returns>
-        internal ICollection<BaseConfiguration> GetValidLkgConfigurations()
+        internal BaseConfiguration[] GetValidLkgConfigurations()
         {
             return _lastKnownGoodConfigurationCache.ToArray().Where(x => x.Value.Value > DateTime.UtcNow).Select(x => x.Key).ToArray();
         }
diff --git a/src/Microsoft.IdentityModel.Tokens/JsonWebKey.cs b/src/Microsoft.IdentityModel.Tokens/JsonWebKey.cs
index b9504122a1..40f98ebc20 100644
--- a/src/Microsoft.IdentityModel.Tokens/JsonWebKey.cs
+++ b/src/Microsoft.IdentityModel.Tokens/JsonWebKey.cs
@@ -19,9 +19,9 @@ public class JsonWebKey : SecurityKey
     {
         internal const string ClassName = "Microsoft.IdentityModel.Tokens.JsonWebKey";
         private Dictionary<string, object> _additionalData;
-        private IList<string> _keyOps;
-        private IList<string> _oth;
-        private IList<string> _x5c;
+        private List<string> _keyOps;
+        private List<string> _oth;
+        private List<string> _x5c;
         private string _kid;
 
         /// <summary>
diff --git a/src/Microsoft.IdentityModel.Tokens/JsonWebKeySet.cs b/src/Microsoft.IdentityModel.Tokens/JsonWebKeySet.cs
index fa46dc58c0..be3d3306ba 100644
--- a/src/Microsoft.IdentityModel.Tokens/JsonWebKeySet.cs
+++ b/src/Microsoft.IdentityModel.Tokens/JsonWebKeySet.cs
@@ -19,7 +19,7 @@ namespace Microsoft.IdentityModel.Tokens
     public class JsonWebKeySet
     {
         internal const string ClassName = "Microsoft.IdentityModel.Tokens.JsonWebKeySet";
-        private IDictionary<string, object> _additionalData;
+        private Dictionary<string, object> _additionalData;
 
         /// <summary>
         /// Returns a new instance of <see cref="JsonWebKeySet"/>.
diff --git a/src/Microsoft.IdentityModel.Tokens/TokenUtilities.cs b/src/Microsoft.IdentityModel.Tokens/TokenUtilities.cs
index 8f75b45125..fc1b29f4c2 100644
--- a/src/Microsoft.IdentityModel.Tokens/TokenUtilities.cs
+++ b/src/Microsoft.IdentityModel.Tokens/TokenUtilities.cs
@@ -41,7 +41,7 @@ internal class TokenUtilities
         /// </summary>
         /// <param name="claims"> A list of claims.</param>
         /// <returns> A Dictionary representing claims.</returns>
-        internal static IDictionary<string, object> CreateDictionaryFromClaims(IEnumerable<Claim> claims)
+        internal static Dictionary<string, object> CreateDictionaryFromClaims(IEnumerable<Claim> claims)
         {
             var payload = new Dictionary<string, object>();
 
diff --git a/src/Microsoft.IdentityModel.Tokens/TokenValidationResult.cs b/src/Microsoft.IdentityModel.Tokens/TokenValidationResult.cs
index 347e087c09..6714c71b9e 100644
--- a/src/Microsoft.IdentityModel.Tokens/TokenValidationResult.cs
+++ b/src/Microsoft.IdentityModel.Tokens/TokenValidationResult.cs
@@ -35,8 +35,8 @@ public class TokenValidationResult
         private volatile bool _claimsIdentityInitialized;
         private object _claimsIdentitySyncObj;
         private ClaimsIdentity _claimsIdentity;
-        private IDictionary<string, object> _claims;
-        private IDictionary<string, object> _propertyBag;
+        private Dictionary<string, object> _claims;
+        private Dictionary<string, object> _propertyBag;
 
         /// <summary>
         /// Creates an instance of <see cref="TokenValidationResult"/>
diff --git a/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs b/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs
index 80a6bed605..f78738d453 100644
--- a/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs
+++ b/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs
@@ -663,7 +663,7 @@ private static bool TryConvertToInt(object value, ref int outVal)
 #pragma warning restore CS0162 // Unreachable code detected
         }
 
-        internal IList<string> GetIListClaims(string claimType)
+        internal List<string> GetIListClaims(string claimType)
         {
             List<string> claimValues = new List<string>();
 
diff --git a/src/System.IdentityModel.Tokens.Jwt/JwtSecurityTokenHandler.cs b/src/System.IdentityModel.Tokens.Jwt/JwtSecurityTokenHandler.cs
index 220eab73f0..8819fa8630 100644
--- a/src/System.IdentityModel.Tokens.Jwt/JwtSecurityTokenHandler.cs
+++ b/src/System.IdentityModel.Tokens.Jwt/JwtSecurityTokenHandler.cs
@@ -32,7 +32,7 @@ public class JwtSecurityTokenHandler : SecurityTokenHandler
         private const string _namespace = "http://schemas.xmlsoap.org/ws/2005/05/identity/claimproperties";
         private const string _className = "System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler";
         private IDictionary<string, string> _outboundClaimTypeMap;
-        private IDictionary<string, string> _outboundAlgorithmMap = null;
+        private Dictionary<string, string> _outboundAlgorithmMap = null;
         private static string _shortClaimType = _namespace + "/ShortTypeName";
         private bool _mapInboundClaims = DefaultMapInboundClaims;
 
@@ -741,7 +741,7 @@ private IEnumerable<Claim> OutboundClaimTypeTransform(IEnumerable<Claim> claims)
             }
         }
 
-        private IDictionary<string, object> OutboundClaimTypeTransform(IDictionary<string, object> claimCollection)
+        private Dictionary<string, object> OutboundClaimTypeTransform(IDictionary<string, object> claimCollection)
         {
             var claims = new Dictionary<string, object>();
 
diff --git a/test/Microsoft.IdentityModel.Protocols.OpenIdConnect.Tests/ConfigurationManagerTests.cs b/test/Microsoft.IdentityModel.Protocols.OpenIdConnect.Tests/ConfigurationManagerTests.cs
index 0196bd7103..404318e6f5 100644
--- a/test/Microsoft.IdentityModel.Protocols.OpenIdConnect.Tests/ConfigurationManagerTests.cs
+++ b/test/Microsoft.IdentityModel.Protocols.OpenIdConnect.Tests/ConfigurationManagerTests.cs
@@ -443,19 +443,19 @@ public void TestConfigurationComparer()
             configWithSameKidDiffKeyMaterial.SigningKeys.Add(new SymmetricSecurityKey(KeyingMaterial.DefaultSymmetricSecurityKey_128.Key) { KeyId = KeyingMaterial.DefaultSymmetricSecurityKey_256.KeyId });
 
             var configurationManager = new MockConfigurationManager<OpenIdConnectConfiguration>(config, config);
-            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Count, 1, context);
+            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Length, 1, context);
 
             configurationManager.LastKnownGoodConfiguration = configWithSameKeysDiffOrder;
-            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Count, 1, context);
+            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Length, 1, context);
 
             configurationManager.LastKnownGoodConfiguration = configWithOverlappingKey;
-            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Count, 2, context);
+            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Length, 2, context);
 
             configurationManager.LastKnownGoodConfiguration = configWithOverlappingKeyDiffissuer;
-            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Count, 3, context);
+            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Length, 3, context);
 
             configurationManager.LastKnownGoodConfiguration = configWithSameKidDiffKeyMaterial;
-            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Count, 4, context);
+            IdentityComparer.AreEqual(configurationManager.GetValidLkgConfigurations().Length, 4, context);
 
             TestUtilities.AssertFailIfErrors(context);
         }