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Suppose I've got a response from a website using https. Is it possible to store the certificate and keys exchange to prove to a third-party that the response came from that domain?

msbrogli
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  • Exact dupe https://crypto.stackexchange.com/questions/29751/are-https-web-sessions-non-repudiable?rq=1 and https://crypto.stackexchange.com/questions/60233/does-the-server-signs-message-body-after-ssl-handshake and crossdupe https://security.stackexchange.com/questions/187577/can-you-use-https-to-prove-document-was-sent-from-domain and more – dave_thompson_085 Aug 30 '18 at 00:32

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No, at least for standard ciphersuites, TLS/https does not allow proving to a third party that an https payload was received from a certain domain.

Problem is, the initial TLS handshake leads to symmetric keys known by both parties, used to secure the rest of the exchange. Thus each party can forge messages and pretend the other side sent them.

fgrieu
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  • That's exactly what I first thought about it. The private/public keys are used only to verify the identity, then a symmetric key is exchanged, and the remaining payload is encrypted with the symmetric key. – msbrogli Aug 29 '18 at 05:01