gokrb5.v7

gokrb5

This is work in progress and does not yet fully work...

Implemented Encryption & Checksum Types

The currently implemented encrytion types are:

Implementation	Encryption ID	Checksum ID
aes128-cts-hmac-sha1-96	17	15
aes256-cts-hmac-sha1-96	18	16

Usage

Configuration

The gokrb5 libraries use the same krb5.conf configuration file format as MIT Kerberos, described here. Config instances can be created by loading from a file path or by passing a string, io.Reader or bufio.Scanner to the relevant method:

import "github.com/jcmturner/gokrb5/config"
cfg, err := config.Load("/path/to/config/file")
cfg, err := config.NewConfigFromString(krb5Str) //String must have appropriate newline separations
cfg, err := config.NewConfigFromReader(reader)
cfg, err := config.NewConfigFromScanner(scanner)

Keytab files

Standard keytab files can be read from a file or from a slice of bytes:

import 	"github.com/jcmturner/gokrb5/keytab"
ktFromFile, err := keytab.Load("/path/to/file.keytab")
ktFromBytes, err := keytab.Parse(b)

Kerberos Client

Create a client instance with either a password or a keytab:

import 	"github.com/jcmturner/gokrb5/client"
cl := client.NewClientWithPassword("username", "REALM.COM", "password")
cl := client.NewClientWithKeytab("username", "REALM.COM", kt)

Provide configuration to the client:

cl.WithConfig(cfg)

Login:

err := cl.Login

(Optional) Enable automatic refresh of Kerberos Ticket Granting Ticket (TGT):

cl.EnableAutoSessionRenewal()

Request a Serivce ticket for a Service Principal Name (SPN). This method will use the client's cache either returning a valid cached ticket, renewing a cached ticket with the KDC or requesting a new ticket from the KDC. Therefore the GetServiceTicket method can be continually used for the most efficient interation with the KDC.

tkt, err := cl.GetServiceTicket("HTTP/host.test.gokrb5")

References

RFCs

• RFC 4120 The Kerberos Network Authentication Service (V5) text html
• RFC 3961 Encryption and Checksum Specifications for Kerberos 5 text html
• RFC 3962 Advanced Encryption Standard (AES) Encryption for Kerberos 5 text html
• The Simple and Protected Generic Security Service Application Program Interface (GSS-API) Negotiation Mechanism text html
• SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows text html
• RFC 6806 Kerberos Principal Name Canonicalization and Cross-Realm Referrals text html
• RFC 6113 A Generalized Framework for Kerberos Pre-Authentication text html
• IANA Assigned Kerberos Numbers
• Microsoft PAC Validation
• Microsoft Kerberos Protocol Extensions

Useful Links

• https://en.wikipedia.org/wiki/Ciphertext_stealing#CBC_ciphertext_stealing

Thanks

• Greg Hudson from the MIT Consortium for Kerberos and Internet Trust for providing useful advice.

Known Issues

Issue	Worked around?	References
Golang's ASN1 package cannot unmarshal into slice of asn1.RawValue	Yes	https://github.com/golang/go/issues/17321
Golang's ASN1 package cannot marshal into a GeneralString	Yes - using https://github.com/jcmturner/asn1	https://github.com/golang/go/issues/18832
Golang's ASN1 package cannot marshal into slice of strings and pass stringtype parameter tags to members	Yes - using https://github.com/jcmturner/asn1	https://github.com/golang/go/issues/18834
Golang's ASN1 package cannot marshal with application tags	Yes