How does the ECDSA in C# work

I'm looking at this example: http://msdn.microsoft.com/en-us/library/system.security.cryptography.ecdsacng.aspx开发者_如何学Go and I'm trying to understand how is it possible that a man-in-the-middle attack would not work against this? Also, how would this differ from using a Certificate like SSL does?

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this cryptosystem alone is not immune to MITM attacks

all public key cryptosystems are prone to MITM regardless of their design

you need a public key infrastructure or common trusted third party to make sure an attacker can not provide his own keys as the keys of alice and/or bob