Non-repudiation
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def
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assurance that the sender of information cannot deny having sent it, because the recipient can verify the source — adds a different perspective to cryptography beyond confidentiality
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example
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a signed digital contract — the sender cannot later claim they never sent it; others can see the signature
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two components
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proof of integrity — verifying the data has not changed; in cryptography, done with a hash (a message digest/fingerprint); if the data changes, the hash changes; on its own this does NOT associate the data with a specific individual
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proof of origin — proving both the source of the message (authentication) and that the signature isn't fake (non-repudiation); achieved by signing with the sender's Private Key (the message itself doesn't need to be encrypted) and verifying with the sender's Public Key — any change to the message invalidates the signature
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