CryptDecryptMessage

[DllImport("Crypt32.dll", SetLastError = true)]
public static extern bool CryptDecryptMessage(
   ref CRYPT_DECRYPT_MESSAGE_PARA pDecryptPara,
   byte[] pbEncryptedBlob,
   uint cbEncryptedBlob,
   byte[] pbDecrypted,
   ref uint pcbDecrypted,
   ref IntPtr ppXchgCert
);

Microsoft documentation: Link

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