.TH AUTH 6.SH NAMEauth \- authentication using station-to-station protocol.SH DESCRIPTIONThe following protocol,based on the Station-to-Stationprotocol, is used for mutual authentication of two parties,each possessing a certificate from the same certifying authority (CA)..PPIn the description below:.TF CERTx.PD.TP.I alphais a Diffie-Hellman base used system wide.TP.I pis a Diffie-Hellman modulus used system wide.TP.I Rxis a random number of the same order as.IR p ..TP.BI PK xthe public key of.I x.TP.BI SK xthe private key of.I x.TP.BI CERT xthe public keyof.I xsigned by the certifying authority.TP.BI sig n ( x )represents.I xsigned with.IR n 'sprivate key.PPIn the following, the parties are labelled 0 and 1..PPEach sends its public key and certificate to the other together witha computation.IR "alpha**r0 mod p".RI ( "alpha**r1 mod p" )based on the Diffie-Hellman parameters contained in the certificate:.IP.EX0 → 1  alpha**r0 mod p, CERTu0, PKu01 → 0  alpha**r1 mod p, CERTu1, PKu1.EE.PPEach can now use the CA's public key and the certificate received to checkthat each has the other's public key..PPFinally, each user signs values known to both that each can then verify:.IP.EX0 → 1  sig0(alpha**r0 mod p, alpha**r1 mod p)1 → 0  sig1(alpha**r0 mod p, alpha**r1 mod p).EE.PPAt this point 0 and 1 can calculate the shared secret.BR "alpha**(r0*r1)" ,and can use it to encrypt later communications..SH SEE ALSO.IR keyring-auth (2),.IR keytext (6),.IR login (6)