main
1// Copyright 2011 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package ssh
6
7import (
8 "encoding/asn1"
9 "errors"
10)
11
12var krb5OID []byte
13
14func init() {
15 krb5OID, _ = asn1.Marshal(krb5Mesh)
16}
17
18// GSSAPIClient provides the API to plug-in GSSAPI authentication for client logins.
19type GSSAPIClient interface {
20 // InitSecContext initiates the establishment of a security context for GSS-API between the
21 // ssh client and ssh server. Initially the token parameter should be specified as nil.
22 // The routine may return a outputToken which should be transferred to
23 // the ssh server, where the ssh server will present it to
24 // AcceptSecContext. If no token need be sent, InitSecContext will indicate this by setting
25 // needContinue to false. To complete the context
26 // establishment, one or more reply tokens may be required from the ssh
27 // server;if so, InitSecContext will return a needContinue which is true.
28 // In this case, InitSecContext should be called again when the
29 // reply token is received from the ssh server, passing the reply
30 // token to InitSecContext via the token parameters.
31 // See RFC 2743 section 2.2.1 and RFC 4462 section 3.4.
32 InitSecContext(target string, token []byte, isGSSDelegCreds bool) (outputToken []byte, needContinue bool, err error)
33 // GetMIC generates a cryptographic MIC for the SSH2 message, and places
34 // the MIC in a token for transfer to the ssh server.
35 // The contents of the MIC field are obtained by calling GSS_GetMIC()
36 // over the following, using the GSS-API context that was just
37 // established:
38 // string session identifier
39 // byte SSH_MSG_USERAUTH_REQUEST
40 // string user name
41 // string service
42 // string "gssapi-with-mic"
43 // See RFC 2743 section 2.3.1 and RFC 4462 3.5.
44 GetMIC(micFiled []byte) ([]byte, error)
45 // Whenever possible, it should be possible for
46 // DeleteSecContext() calls to be successfully processed even
47 // if other calls cannot succeed, thereby enabling context-related
48 // resources to be released.
49 // In addition to deleting established security contexts,
50 // gss_delete_sec_context must also be able to delete "half-built"
51 // security contexts resulting from an incomplete sequence of
52 // InitSecContext()/AcceptSecContext() calls.
53 // See RFC 2743 section 2.2.3.
54 DeleteSecContext() error
55}
56
57// GSSAPIServer provides the API to plug in GSSAPI authentication for server logins.
58type GSSAPIServer interface {
59 // AcceptSecContext allows a remotely initiated security context between the application
60 // and a remote peer to be established by the ssh client. The routine may return a
61 // outputToken which should be transferred to the ssh client,
62 // where the ssh client will present it to InitSecContext.
63 // If no token need be sent, AcceptSecContext will indicate this
64 // by setting the needContinue to false. To
65 // complete the context establishment, one or more reply tokens may be
66 // required from the ssh client. if so, AcceptSecContext
67 // will return a needContinue which is true, in which case it
68 // should be called again when the reply token is received from the ssh
69 // client, passing the token to AcceptSecContext via the
70 // token parameters.
71 // The srcName return value is the authenticated username.
72 // See RFC 2743 section 2.2.2 and RFC 4462 section 3.4.
73 AcceptSecContext(token []byte) (outputToken []byte, srcName string, needContinue bool, err error)
74 // VerifyMIC verifies that a cryptographic MIC, contained in the token parameter,
75 // fits the supplied message is received from the ssh client.
76 // See RFC 2743 section 2.3.2.
77 VerifyMIC(micField []byte, micToken []byte) error
78 // Whenever possible, it should be possible for
79 // DeleteSecContext() calls to be successfully processed even
80 // if other calls cannot succeed, thereby enabling context-related
81 // resources to be released.
82 // In addition to deleting established security contexts,
83 // gss_delete_sec_context must also be able to delete "half-built"
84 // security contexts resulting from an incomplete sequence of
85 // InitSecContext()/AcceptSecContext() calls.
86 // See RFC 2743 section 2.2.3.
87 DeleteSecContext() error
88}
89
90var (
91 // OpenSSH supports Kerberos V5 mechanism only for GSS-API authentication,
92 // so we also support the krb5 mechanism only.
93 // See RFC 1964 section 1.
94 krb5Mesh = asn1.ObjectIdentifier{1, 2, 840, 113554, 1, 2, 2}
95)
96
97// The GSS-API authentication method is initiated when the client sends an SSH_MSG_USERAUTH_REQUEST
98// See RFC 4462 section 3.2.
99type userAuthRequestGSSAPI struct {
100 N uint32
101 OIDS []asn1.ObjectIdentifier
102}
103
104func parseGSSAPIPayload(payload []byte) (*userAuthRequestGSSAPI, error) {
105 n, rest, ok := parseUint32(payload)
106 if !ok {
107 return nil, errors.New("parse uint32 failed")
108 }
109 s := &userAuthRequestGSSAPI{
110 N: n,
111 OIDS: make([]asn1.ObjectIdentifier, n),
112 }
113 for i := 0; i < int(n); i++ {
114 var (
115 desiredMech []byte
116 err error
117 )
118 desiredMech, rest, ok = parseString(rest)
119 if !ok {
120 return nil, errors.New("parse string failed")
121 }
122 if rest, err = asn1.Unmarshal(desiredMech, &s.OIDS[i]); err != nil {
123 return nil, err
124 }
125
126 }
127 return s, nil
128}
129
130// See RFC 4462 section 3.6.
131func buildMIC(sessionID string, username string, service string, authMethod string) []byte {
132 out := make([]byte, 0, 0)
133 out = appendString(out, sessionID)
134 out = append(out, msgUserAuthRequest)
135 out = appendString(out, username)
136 out = appendString(out, service)
137 out = appendString(out, authMethod)
138 return out
139}