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I was wondering what the main reason was for symmetric keys not being used in this context?

Martin l
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    Stack Overflow is a site for programming and development questions. This question appears to be off-topic because it is not about programming or development. See [What topics can I ask about here](http://stackoverflow.com/help/on-topic) in the Help Center. Perhaps [Cryptography Stack Exchange](http://crypto.stackexchange.com/) or [Information Security Stack Exchange](http://security.stackexchange.com/) would be a better place to ask. – jww Jun 04 '17 at 07:43
  • Verifying the authenticity of the signature without holding the original key would be tricky, for a start. You can't make it generally available as you can with a public key. – Rook Jun 04 '17 at 08:46

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With a symmetric key, anyone who could check the signature could also forge a signature. For most of the use cases of digital signatures, we want untrusted parties to be able to verify the signature. That requires that the key you use to check that a signature is correct be insufficient to generate a valid signature, and that requires asymmetric cryptography by definition.

David Schwartz
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  • Can Hashes be used to provide digital signatures (in HMAC or more complex combinations)? Symmetrical methods may work like hashes in such schemes too. PS: How the "digital signature" is defined and what it should provide. This explains some things: https://crypto.stackexchange.com/a/5647 – osgx Jun 02 '17 at 16:59
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    Sure, but that doesn't change the answer. To check the signature, you need to be able to compare the hash, which means you need to be able to generate it. – David Schwartz Jun 02 '17 at 17:01