[转]Certificate Authorities & Intermediate CAs

Certificate Authorities & Intermediate CAs

 

Self-signed CA

• keyUsage: cRLSign, digitalSignature, keyCertSign
• Should not contain any other KUs or EKUs
• V3 Profile:

• [ v3_ca ]
• basicConstraints        = critical, CA:TRUE
• subjectKeyIdentifier    = hash
• authorityKeyIdentifier  = keyid:always, issuer:always
• keyUsage                = critical, cRLSign, digitalSignature, keyCertSign
• subjectAltName          = @alt_ca

Intermediate CA

• keyUsage: cRLSign, digitalSignature, keyCertSign
• Should not contain any other KUs or EKUs
• V3 Profile:

• [ v3_ica ]
• basicConstraints        = critical, CA:TRUE, pathlen:1
• subjectKeyIdentifier    = hash
• authorityKeyIdentifier  = keyid:always, issuer:always
• keyUsage                = critical, cRLSign, digitalSignature, keyCertSign
• subjectAltName          = @alt_ica

• Where pathlen: is equal to the number of CAs/ICAs it can sign
• Can not sign other CAs/ICAs if pathlen: is set to 0

 

 

Non-CA Certificates

 

VPN Server

• keyUsage: nonRepudiation, digitalSignature, keyEncipherment, keyAgreement
• V3 Profile:

• [ v3_vpn_server ]
• basicConstraints        = critical, CA:FALSE
• subjectKeyIdentifier    = hash
• authorityKeyIdentifier  = keyid:always, issuer:always
• keyUsage                = critical, nonRepudiation, digitalSignature, keyEncipherment, keyAgreement
• extendedKeyUsage        = critical, serverAuth
• subjectAltName          = @alt_vpn_server

VPN Client

• keyUsage: nonRepudiation, digitalSignature, keyEncipherment
• V3 Profile:

• [ v3_vpn_client ]
• basicConstraints        = critical, CA:FALSE
• subjectKeyIdentifier    = hash
• authorityKeyIdentifier  = keyid:always, issuer:always
• keyUsage                = critical, nonRepudiation, digitalSignature, keyEncipherment
• extendedKeyUsage        = critical, clientAuth
• subjectAltName          = @alt_vpn_client

 

 

keyUsage

 

CA ONLY

keyCertSign

• Subject public key is used to verify signatures on certificates
• This extension must only be used for CA certificates

cRLSign

• Subject public key is to verify signatures on revocation information, such as a CRL
• This extension must only be used for CA certificates

 

digitalSignature

• Certificate may be used to apply a digital signature
• Digital signatures are often used for entity authentication & data origin authentication with integrity

nonRepudiation

• Certificate may be used to sign data as above but the certificate public key may be used to provide non-repudiation services
• This prevents the signing entity from falsely denying some action

keyEncipherment

• Certificate may be used to encrypt a symmetric key which is then transferred to the target
• Target decrypts key, subsequently using it to encrypt & decrypt data between the entities

dataEncipherment

• Certificate may be used to encrypt & decrypt actual application data

keyAgreement

• Certificate enables use of a key agreement protocol to establish a symmetric key with a target
• Symmetric key may then be used to encrypt & decrypt data sent between the entities

encipherOnly

• Public key used only for enciphering data while performing key agreement
• Req. KU: keyAgreement

decipherOnly

• Public key used only for deciphering data while performing key agreement
• Req. KU: keyAgreement

 

RFC 5280 [4.2.1.3]

id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }

• Bitstring is hexadecimal

• KeyUsage ::= BIT STRING {
• digitalSignature    (0),
• nonRepudiation      (1),
• keyEncipherment     (2),
• dataEncipherment    (3),
• keyAgreement        (4),
• keyCertSign         (5),
• cRLSign             (6),
• encipherOnly        (7),
• decipherOnly        (8)
• }

 

 

extendedKeyUsage

 

serverAuth

• All VPN servers should be signed with this EKU present
• SSL/TLS Web/VPN Server authentication EKU, distinguishing a server which clients can authenticate against
• This supersedes nscertype options (ns in nscertype stands for NetScape [browser])
• Req. KU: digitalSignature, keyEncipherment or keyAgreement

clientAuth

• All VPN clients must be signed with this EKU present
• SSL/TLS Web/VPN Client authentication EKU distinguishing a client as a client only
• Req. KU: digitalSignature and/or keyAgreement

codeSigning

• Code Signing
• Req. KU: digitalSignature, nonRepudiation, and/or keyEncipherment or keyAgreement

emailProtection

• Email Protection via S/MIME, allows you to send and receive encrypted emails
• Req. KU: digitalSignature, keyEncipherment or keyAgreement

timeStamping

• Trusted Timestamping
• Req. KU: digitalSignature, nonRepudiation

OCSPSigning

• OCSP Signing
• Req. KU: digitalSignature, nonRepudiation

msCodeInd

• Microsoft Individual Code Signing (authenticode)
• Req. KU: digitalSignature, keyEncipherment or keyAgreement

msCodeCom

• Microsoft Commerical Code Signing (authenticode)
• Req. KU: digitalSignature, keyEncipherment or keyAgreement

mcCTLSign

• Microsoft Trust List Signing
• Req. KU: digitalSignature, nonRepudiation

msEFS

• Microsoft Encrypted File System Signing
• Req. KU: digitalSignature, keyEncipherment or keyAgreement

 

!!! SHOULD NOT BE UTILIZED !!!

ipsecEndSystem, ipsecTunnel, & ipsecUser

• Assigned in 1999, the semantics of these values were never clearly defined
• RFC 4945: The use of these three EKU values is obsolete and explicitly deprecated by this specification [5.1.3.12]

ipsecIKE

• IPSec Internet Key Exchange
• I believe this is in the same boat as the three above
• Research needs to be performed to determine if this EKU should also no longer be utilized
• clientAuth can be utilized in an IPSec VPN client cert

 

RFC 5280 [4.2.1.12]

anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

• id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
• id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 }
• TLS server authentication
• KU bits for:
  digitalSignature, keyEncipherment or keyAgreement
• id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 }
• TLS client authentication
• KU bits for:
  digitalSignature and/or keyAgreement
• id-kp-codeSigning OBJECT IDENTIFIER ::= { id-kp 3 }
• Signing of downloadable executable code
• KU bits for:
  digitalSignature
• id-kp-emailProtection OBJECT IDENTIFIER ::= { id-kp 4 }
• Email protection
• KU bits for:
  digitalSignature, nonRepudiation, and/or keyEncipherment or keyAgreement
• id-kp-timeStamping OBJECT IDENTIFIER ::= { id-kp 8 }
• Binding the hash of an object to a time
• KU bits for:
  digitalSignature and/or nonRepudiation
• id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 }
• Signing OCSP responses
• KU bits for:
  digitalSignature and/or nonRepudiation