Add managed Composite ML-KEM implementation

[PranavSenthilnathan]

Managed Composite ML-KEM. This implementation is just for OpenSSL. Windows will have a native implementation added in a future PR.

Contributes to #129633

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[Copilot]

Pull request overview

Adds a managed implementation of Composite ML-KEM (hybrid ML-KEM + traditional KEM) for the OpenSSL-backed build, wiring it into System.Security.Cryptography and extending the shared test suite with IETF test vectors.

Changes:

• Add managed Composite ML-KEM implementation (CompositeMLKemManaged*) and route OpenSSL implementation entrypoints to it.
• Extend Composite ML-KEM tests with implementation tests, base test coverage, and IETF vector data.
• Expand supporting infrastructure (RSA PKCS#1 decode rule set parameter, BER DER utilities, new SR string).

Reviewed changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/System.Security.Cryptography/tests/System.Security.Cryptography.Tests.csproj	Includes shared Composite ML-KEM test files in the System.Security.Cryptography test project.
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/MLKemImplementation.OpenSsl.cs	Adds per-algorithm support probing for OpenSSL ML-KEM.
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/CompositeMLKemImplementation.OpenSsl.cs	Routes Composite ML-KEM OpenSSL implementation hooks to the managed implementation.
src/libraries/System.Security.Cryptography/src/System.Security.Cryptography.csproj	Adds Composite ML-KEM managed sources and swaps in OpenSSL composite implementation file.
src/libraries/System.Security.Cryptography/src/Resources/Strings.resx	Adds an SR string for RSA-OAEP decapsulation length mismatch.
src/libraries/Microsoft.Bcl.Cryptography/tests/Microsoft.Bcl.Cryptography.Tests.csproj	Includes shared Composite ML-KEM test vector/types in the BCL test project.
src/libraries/Common/tests/System/Security/Cryptography/AsnUtils.cs	Updates DER→BER helper to take ReadOnlySpan<byte> and use Slice.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemTestVector.cs	Adds a test-vector wrapper that parses SPKI from a certificate.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemTestsBase.cs	Adds a shared behavioral test base covering encapsulate/decapsulate and import/export failure modes.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemTestData.cs	Adds vector-driven MemberData helpers and component metadata used by tests.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemTestData.Raw.cs	Adds IETF test vectors (generated) used by Composite ML-KEM tests.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemImplementationTests.cs	Adds tests asserting returned runtime types are internal and validating import/export behavior against vectors.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemFactoryTests.cs	Updates support checks and adds successful import tests and PKCS#8/Encrypted PKCS#8 coverage.
src/libraries/Common/tests/System/Security/Cryptography/AlgorithmImplementations/CompositeMLKem/CompositeMLKemContractTests.cs	Strengthens contract tests to ensure secrets are cleared on exceptions and call counts are correct.
src/libraries/Common/src/System/Security/Cryptography/RSAKeyFormatHelper.Pkcs1.cs	Adds an AsnEncodingRules parameter to PKCS#1 decode helpers (default BER).
src/libraries/Common/src/System/Security/Cryptography/MLKemImplementation.Windows.cs	Adds IsAlgorithmSupported helper for Windows implementation.
src/libraries/Common/src/System/Security/Cryptography/MLKemImplementation.NotSupported.cs	Adds IsAlgorithmSupported helper for NotSupported implementation.
src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.XDiffieHellman.cs	Implements the X25519-based traditional KEM portion for the managed composite KEM.
src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.RSA.cs	Implements the RSA-OAEP traditional KEM portion and adds a dedicated decapsulation failure SR message.
src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.ECDiffieHellman.cs	Implements the ECDH traditional KEM portion and DER-only key import/export logic.
src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs	Implements the managed composite KEM logic (support probing, key gen/import, encaps/decaps, combiner).
src/libraries/Common/src/System/Security/Cryptography/CompositeMLKem.cs	Clears shared-secret buffers on exceptions in encapsulate/decapsulate wrapper methods.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 22 changed files in this pull request and generated 1 comment.

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:488

• The X25519 algorithm metadata uses a 6-byte label value that doesn’t match the ASCII label style used for the other Composite ML-KEM algorithms in this table (e.g., "MLKEM768-RSAOAEP2048", "MLKEM1024-X448"). Since the label is part of the combiner input (and should be stable / spec-defined), this looks like an accidental placeholder and would change the derived shared secret.

 CompositeMLKemAlgorithm.MLKem768WithX25519,
new(MLKemAlgorithm.MLKem768, new XDiffieHellmanKemAlgorithm(IsX25519: true), [0x5C, 0x2E, 0x2F, 0x2F, 0x5E, 0x5C])
},

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:443

• TraditionalKem declares abstract members but is declared with the non-existent keyword closed, which will not compile. This should be an abstract base type (matching the pattern used by CompositeMLDsaManaged.ComponentAlgorithm).

 private closed class TraditionalKem : IDisposable

[Copilot]

Pull request overview

Copilot reviewed 21 out of 22 changed files in this pull request and generated no new comments.

Suppressed comments (2)

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:443

• TraditionalKem declares abstract members but the type itself is not abstract. This won’t compile (non-abstract types can’t contain abstract members).

 private closed class TraditionalKem : IDisposable

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:537

• TraditionalKemAlgorithm has an abstract member (SharedSecretSizeInBytes) but the record itself is not abstract. This won’t compile.

 private closed record TraditionalKemAlgorithm

[Copilot]

Pull request overview

Copilot reviewed 21 out of 22 changed files in this pull request and generated no new comments.

Suppressed comments (3)

Previously missed (1) — in code that hasn't changed since the last review.

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:488

• The X25519 label is currently hard-coded to the byte sequence \ . / / ^ \ ([0x5C, 0x2E, 0x2F, 0x2F, 0x5E, 0x5C]), which is inconsistent with the other labels (UTF-8 text) and is very likely incorrect per the composite KEM spec label inputs. Use a UTF-8 string label consistent with the other algorithms (e.g., "MLKEM768-X25519").

 {
CompositeMLKemAlgorithm.MLKem768WithX25519,
new(MLKemAlgorithm.MLKem768, new XDiffieHellmanKemAlgorithm(IsX25519: true), [0x5C, 0x2E, 0x2F, 0x2F, 0x5E, 0x5C])
},

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:450

• TraditionalKem declares abstract members but is currently declared as closed class, which is not a valid C# modifier and will not compile. This should be abstract (or sealed with no abstract members).

 private closed class TraditionalKem : IDisposable
{
private bool _disposed;
internal abstract void Encapsulate(Span<byte> ciphertext, Span<byte> sharedSecret);
internal abstract void Decapsulate(ReadOnlySpan<byte> ciphertext, Span<byte> sharedSecret);
internal abstract int ExportPublicKey(Span<byte> destination);
internal abstract int ExportPrivateKey(Span<byte> destination);

src/libraries/Common/src/System/Security/Cryptography/CompositeMLKemManaged.cs:540

• TraditionalKemAlgorithm has an abstract member but is declared as closed record, which is not a valid C# modifier and will not compile. Make the base record abstract so derived algorithm records can override the abstract property.

 private closed record TraditionalKemAlgorithm
{
internal abstract int SharedSecretSizeInBytes { get; }
}

[PranavSenthilnathan]

/ba-g all the failures are either #132830 or #132831