[Breaking change]: CoseSigner.Key may now be null #46999
Description
Description
CoseSigner.Key may now be null. If CoseSigner is backed by an RSA or ECDSA key then CoseSigner.Key will continue to return the key and it will be non-null. However, when CoseSigner is backed by a key that doesn't derive from AsymmetricAlgorithm, like MLDsa (a new Post-Quantum Cryptography (PQC) signing algorithm), CoseSigner.Key will be null.
Version
.NET 10 Preview 7
Previous behavior
CoseSigner.Key cannot be null. It had type AsymmetricAlgorithm.
New behavior
CoseSigner.Key can be null. It now has type AsymmetricAlgorithm?.
using RSA rsaKey = RSA.Create();
CoseSigner signer = new CoseSigner(rsaKey, RSASignaturePadding.Pss, HashAlgorithmName.SHA512);
// signer.Key is rsaKey here
// CoseKey is a new abstraction for all keys used in COSE
CoseKey coseKey = new CoseKey(rsaKey, RSASignaturePadding.Pss, HashAlgorithmName.SHA512);
signer = new CoseSigner(coseKey);
// signer.Key is rsaKey here
using MLDsa mldsa = MLDsa.GenerateKey(MLDsaAlgorithm.MLDsa44);
coseKey = new CoseKey(mldsa);
signer = new CoseSigner(coseKey);
// signer.Key is null hereType of breaking change
- Binary incompatible: Existing binaries might encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
- Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code might require source changes to compile successfully.
- Behavioral change: Existing binaries might behave differently at run time.
Reason for change
With the introduction of new signing algorithms such as ML-DSA, .NET has moved away from using AsymmetricAlgorithm as the universal base class for all asymmetric algorithms. Likewise, CoseSigner can now be constructed with a key that doesn't derive from AsymmetricAlgorithm. In this case CoseSigner.Key can't return a AsymmetricAlgorithm representing the underlying key and thus returns null instead.
This change was introduced in dotnet/runtime#115158.
Recommended action
CoseSigner.Key can still be used, but callers should handle null values.
Feature area
Cryptography
Affected APIs
namespace System.Security.Cryptography.Cose
{
public partial class CoseSigner
{
- public System.Security.Cryptography.AsymmetricAlgorithm Key { get; }
+ public System.Security.Cryptography.AsymmetricAlgorithm? Key { get; }
}
}