+Extended Key Usage.
+
+This extensions consists of a list of usages.
+
+These can either be object short names of the dotted numerical form of OIDs.
+While any OID can be used only certain values make sense. In particular the
+following PKIX, NS and MS values are meaningful:
+
+Value Meaning
+----- -------
+serverAuth SSL/TLS Web Server Authentication.
+clientAuth SSL/TLS Web Client Authentication.
+codeSigning Code signing.
+emailProtection E-mail Protection (S/MIME).
+timeStamping Trusted Timestamping
+msCodeInd Microsoft Individual Code Signing (authenticode)
+msCodeCom Microsoft Commercial Code Signing (authenticode)
+msCTLSign Microsoft Trust List Signing
+msSGC Microsoft Server Gated Crypto
+msEFS Microsoft Encrypted File System
+nsSGC Netscape Server Gated Crypto
+
+For example, under IE5 a CA can be used for any purpose: by including a list
+of the above usages the CA can be restricted to only authorised uses.
+
+Note: software packages may place additional interpretations on certificate
+use, in particular some usages may only work for selected CAs. Don't for example
+expect just including msSGC or nsSGC will automatically mean that a certificate
+can be used for SGC ("step up" encryption) otherwise anyone could use it.
+
+Examples:
+
+extendedKeyUsage=critical,codeSigning,1.2.3.4
+extendedKeyUsage=nsSGC,msSGC
+