AssemblySignatureKeyAttribute Class
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Provides migration from an older, simpler strong name key to a larger key with a stronger hashing algorithm.
Assembly: mscorlib (in mscorlib.dll)
The AssemblySignatureKeyAttribute type exposes the following members.
| Name | Description | |
|---|---|---|
 | AssemblySignatureKeyAttribute | Creates a new instance of the AssemblySignatureKeyAttribute class by using the specified public key and countersignature. |
| Name | Description | |
|---|---|---|
 | Countersignature | Gets the countersignature for the strong name for this assembly. |
| PublicKey | Gets the public key for the strong name used to sign the assembly. |
| Name | Description | |
|---|---|---|
| Equals | Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.) |
 | Finalize | Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
| GetHashCode | Returns the hash code for this instance. (Inherited from Attribute.) |
| GetType | Gets the Type of the current instance. (Inherited from Object.) |
| Match | When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.) |
| MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
| ToString | Returns a string that represents the current object. (Inherited from Object.) |
The new larger key is the signature key. In versions before the .NET Framework 4.5, the signature key was identical to the identity key. Starting with the .NET Framework 4.5, the AssemblySignatureKeyAttribute attribute allows the assembly metadata to continue to have the old public key token and binary large object (BLOB) so that existing assembly references continue to work. It also ensures that the mapping comes from an owner of the identity key.
The presence of the attribute does not necessarily mean that strong name validation takes place. In common full-trust scenarios, the attribute is never considered, because strong name signatures are never validated. However, when the strong name signature does have to be validated, both the strong name signature and the countersignature must be validated. The assembly’s identity key does not have to be identical to the signature key (the key used to do the actual signing and validation). The identity key can be mapped to a different (more robust) signing key. This lets you set the identity of an assembly, and update the signing keys and algorithms to more secure versions.
The countersignature addresses security concerns when a malicious assembly claims some other identity. For example, a malicious System.Core.dll assembly could contain the Microsoft public key in its metadata, and use the attribute to tell strong name validation to use the attacker’s signature key if no countersignature is present. Thus, it could masquerade as a strong name-validated Microsoft assembly.
For information about how to sign assemblies for use with this new attribute, see [6cf17a82-62a1-4f6d-8d5a-d7d06dec2bb5].