Recommendations for SHA1. (#2840)

* Recommendations for SHA1.

* Update xml/System.Security.Cryptography/MD5.xml

Co-Authored-By: Jeremy Barton <[email protected]>

* Update xml/System.ServiceModel.Security/Basic128SecurityAlgorithmSuite.xml

Co-Authored-By: Andy De George <[email protected]>

* Implement input.

Author: TimShererWithAquent

xml/System.Security.Cryptography/MD5.xml

@@ -47,7 +47,7 @@
  The <xref:System.Security.Cryptography.HashAlgorithm.ComputeHash%2A> methods of the <xref:System.Security.Cryptography.MD5> class return the hash as an array of 16 bytes.  Note that some MD5 implementations produce a 32-character, hexadecimal-formatted hash.  To interoperate with such implementations, format the return value of the <xref:System.Security.Cryptography.HashAlgorithm.ComputeHash%2A> methods as a hexadecimal value.  
   
 > [!NOTE]
->  Newer hash functions, such as the Secure Hash Algorithms SHA-256 and SHA-512, are available. Consider using the <xref:System.Security.Cryptography.SHA256> class or the <xref:System.Security.Cryptography.SHA512> class instead of the <xref:System.Security.Cryptography.MD5> class. Use <xref:System.Security.Cryptography.MD5> only for compatibility with legacy applications and data.  
+>  Due to collision problems with MD5/SHA1, Microsoft recommends SHA256 or SHA512. Consider using the <xref:System.Security.Cryptography.SHA256> class or the <xref:System.Security.Cryptography.SHA512> class instead of the <xref:System.Security.Cryptography.MD5> class. Use <xref:System.Security.Cryptography.MD5> only for compatibility with legacy applications and data.  
   
    
   
@@ -213,4 +213,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>

xml/System.ServiceModel.Security/Basic128SecurityAlgorithmSuite.xml

@@ -79,7 +79,7 @@
       <Docs>
         <summary>Gets the default asymmetric signature algorithm, RsaSha1Signature.</summary>
         <value>The default asymmetric signature algorithm, RsaSha1Signature.</value>
-        <remarks>To be added.</remarks>
+        <remarks>Due to collision problems with SHA1, Microsoft recommends a security model based on SHA256 or better.</remarks>
       </Docs>
     </Member>
     <Member MemberName="DefaultCanonicalizationAlgorithm">
@@ -121,7 +121,7 @@
       <Docs>
         <summary>Gets the default digest algorithm, Sha1Digest.</summary>
         <value>The default digest algorithm, Sha1Digest.</value>
-        <remarks>To be added.</remarks>
+        <remarks>Due to collision problems with SHA1, Microsoft recommends a security model based on SHA256 or better.</remarks>
       </Docs>
     </Member>
     <Member MemberName="DefaultEncryptionAlgorithm">
@@ -247,7 +247,7 @@
       <Docs>
         <summary>Gets the default symmetric signature algorithm, HmacSha1Signature.</summary>
         <value>The default symmetric signature algorithm, HmacSha1Signature.</value>
-        <remarks>To be added.</remarks>
+        <remarks>Due to collision problems with SHA1, Microsoft recommends a security model based on SHA256 or better.</remarks>
       </Docs>
     </Member>
     <Member MemberName="IsAsymmetricKeyLengthSupported">
@@ -325,4 +325,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>

xml/System.Web.Configuration/AuthenticationSection.xml

@@ -47,6 +47,8 @@
   </forms>  
 </authentication>  
 ```  
+
+ This example uses SHA1. Due to collision problems with SHA1, Microsoft recommends SHA256.
   
  The following code example demonstrates how to use the <xref:System.Web.Configuration.AuthenticationSection> class.