Re: RSACryptoServiceProvider or similar

hula wrote:
but the should not be able to generate a new
modified message.

If you're trying to prevent attackers from generating "messages" that would be recognized as valid by the recipient, then you could use digital signatures generated using the master's private key. You would need to keep that private key private, which, since it's only used at one central location, is not that hard. And you would have to ensure that the recipient verifies the digital signature using the corresponding public key, and that's no harder than any other license-checking provision in the software running at the customer site.

--Mike Amling
.

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