Specifications

Glossary-18
PEM
Privacy‐EnhancedMail.Aprotocol,definedinRFC 1422throughRFC 1424,fortransporting
digitalcertificatesandcertificatesigningrequestsovertheInternet.PEMformatencodesthe
certificatesonthebasisofanX.509hierarchyofcertificateauthorities(CAs). Base64encodingis
usedtoconvertthecertificatestoASCIItext,andtheencoded
textisenclosedbetweenBEGIN
CERTIFICATEandENDCERTIFICATEdelimiters.
Per-VLAN Spanning Tree protocol
SeePVST+.
PIM
ProtocolIndependentMulticastprotocol.Aprotocol‐independentmulticastroutingprotocoltha t
supportsthousandsof groups,avarietyofmulticastapplications,andexistingLayer 2subnetwork
technologies.PIMcanbeoperatedintwomodes:denseandsparse.InPIMdensemode(PIM‐DM),
packetsarefloodedonalloutgoinginterfacestomanyreceivers.
PIMsparsemode(PIM‐SM)limits
datadistributiontoaminimalnumberofwidelydistributedrouters.PIM‐SMpacketsaresentonly
iftheyareexplicitlyrequestedatarendezvouspoint(RP ).
PKCS
Public‐KeyCryptographyStandards.Agroupofspecifications producedbyRSALaboratoriesand
securesystemsdevelopers,andfirstpublishedin1991.Amongmanyotherfeaturesandfunctions,
thestandardsdefinesyntaxfordigitalcertificates,certificatesigningrequests,andkey
transportation.
PKI
Public‐keyinfrastructure.Softwarethatenablesusersofaninsecurepublicnetworksuchasthe
Internettoexchangeinformationsecurelyandprivately.ThePKIusespublic‐keycryptography
(alsoknownasasymmetriccryptography)toauthenticatethemessagesenderandencryptthe
messagebymeansofapairofcryptographickeys,
onepublicandoneprivate.Atrustedcertifica te
authority(CA)createsbothkeyssimultaneouslywiththesamealgorithm.Aregistrationauthority
(RA)mustverifythecertificateauthoritybeforeadigitalcertificateisissuedtoarequestor.
ThePKIusesthedigitalcertificatetoidenti fyanindividualoranorganization.Theprivate
keyis
givenonlytotherequestingpartyandisnevershared,andthepublickeyismadepublicly
available(aspartofthedigitalcertificate)inadirectorythatallpartiescanaccess.Youusethe
privatekeytodecrypttextthathasbeenencryptedwithyourpublickey
bysomeoneelse.The
certificatesarestored(and,whennecessary,revoked)bydirectoryservicesandmanagedbya
certificatemanagementsystem.SeealsoCertificateAuthority(CA);RegistrationAuthority(RA).
plenum
Acompartmentorchambertowhichoneormoreairductsareconnected.
plenum-rated cable
Atype ofcableapprovedbyanindependenttestlaboratoryforinstallati oninducts,plenums,and
otherair‐handlingspaces.
PMK
Pairwisemasterkey.AcodederivedfromamastersecretandusedasanencryptionkeyforIEEE
802.11encryptionalgorithms.APMKisalsousedtoderiveapairwisetransientkey(PTK)forIEEE
802.11irobustsecurity.Seealsomastersecret;PTK.