HPKP meaning in Academic & Science ?

HTTP Public Key Pinning (HPKP) is a now-deprecated Internet security mechanism delivered via an HTTP header which allows HTTPS websites to resist impersonation by attackers using misissued or otherwise fraudulent digital certificates. A server uses it to deliver to the client (e.g. web browser) a set of hashes of public keys that must appear in the certificate chain of future connections to the same domain name.

For example, attackers might compromise a certificate authority, and then mis-issue certificates for a web origin. To combat this risk, the HTTPS web server serves a list of “pinned” public key hashes valid for a given time; on subsequent connections, during that validity time, clients expect the server to use one or more of those public keys in its certificate chain. If it does not, an error message is shown, which cannot be (easily) bypassed by the user.

The technique does not pin certificates, but public key hashes. This means that one can use the key pair to get a certificate from any certificate authority, when one has access to the private key. Also the user can pin public keys of root or intermediate certificates (created by certificate authorities), restricting site to certificates issued by the said certificate authority.

Due to HPKP mechanism complexity and possibility of accidental misuse, browsers deprecated and removed HPKP support in favor of Certificate Transparency and its Expect-CT header. Certificate Authority Authorization can also be used to restrict which certificate authorities can issue certificates for a particular domain, thus reducing chance of certificate issue errors.