Verify Application Base 64 Encoded public key

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http://stackoverflow.com – i am going to build an SDK in which developer will enter his application base64 encoded public key. So need to verify his public key. As i am very poor in security's. Can any one tell me how to verify correctness of this key. I went through this. but couldn't understand it and i think this is just to verify signed data and not the signature key. Please let me know if i can do this? and if yes then how? (HowTos)