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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssh
import (
"encoding/asn1"
"errors"
)
var krb5OID []byte
func init() {
krb5OID, _ = asn1.Marshal(krb5Mesh)
}
// GSSAPIClient provides the API to plug-in GSSAPI authentication for client logins.
type GSSAPIClient interface {
// InitSecContext initiates the establishment of a security context for GSS-API between the
// ssh client and ssh server. Initially the token parameter should be specified as nil.
// The routine may return a outputToken which should be transferred to
// the ssh server, where the ssh server will present it to
// AcceptSecContext. If no token need be sent, InitSecContext will indicate this by setting
// needContinue to false. To complete the context
// establishment, one or more reply tokens may be required from the ssh
// server;if so, InitSecContext will return a needContinue which is true.
// In this case, InitSecContext should be called again when the
// reply token is received from the ssh server, passing the reply
// token to InitSecContext via the token parameters.
// See RFC 2743 section 2.2.1 and RFC 4462 section 3.4.
InitSecContext(target string, token []byte, isGSSDelegCreds bool) (outputToken []byte, needContinue bool, err error)
// GetMIC generates a cryptographic MIC for the SSH2 message, and places
// the MIC in a token for transfer to the ssh server.
// The contents of the MIC field are obtained by calling GSS_GetMIC()
// over the following, using the GSS-API context that was just
// established:
// string session identifier
// byte SSH_MSG_USERAUTH_REQUEST
// string user name
// string service
// string "gssapi-with-mic"
// See RFC 2743 section 2.3.1 and RFC 4462 3.5.
GetMIC(micFiled []byte) ([]byte, error)
// Whenever possible, it should be possible for
// DeleteSecContext() calls to be successfully processed even
// if other calls cannot succeed, thereby enabling context-related
// resources to be released.
// In addition to deleting established security contexts,
// gss_delete_sec_context must also be able to delete "half-built"
// security contexts resulting from an incomplete sequence of
// InitSecContext()/AcceptSecContext() calls.
// See RFC 2743 section 2.2.3.
DeleteSecContext() error
}
// GSSAPIServer provides the API to plug in GSSAPI authentication for server logins.
type GSSAPIServer interface {
// AcceptSecContext allows a remotely initiated security context between the application
// and a remote peer to be established by the ssh client. The routine may return a
// outputToken which should be transferred to the ssh client,
// where the ssh client will present it to InitSecContext.
// If no token need be sent, AcceptSecContext will indicate this
// by setting the needContinue to false. To
// complete the context establishment, one or more reply tokens may be
// required from the ssh client. if so, AcceptSecContext
// will return a needContinue which is true, in which case it
// should be called again when the reply token is received from the ssh
// client, passing the token to AcceptSecContext via the
// token parameters.
// The srcName return value is the authenticated username.
// See RFC 2743 section 2.2.2 and RFC 4462 section 3.4.
AcceptSecContext(token []byte) (outputToken []byte, srcName string, needContinue bool, err error)
// VerifyMIC verifies that a cryptographic MIC, contained in the token parameter,
// fits the supplied message is received from the ssh client.
// See RFC 2743 section 2.3.2.
VerifyMIC(micField []byte, micToken []byte) error
// Whenever possible, it should be possible for
// DeleteSecContext() calls to be successfully processed even
// if other calls cannot succeed, thereby enabling context-related
// resources to be released.
// In addition to deleting established security contexts,
// gss_delete_sec_context must also be able to delete "half-built"
// security contexts resulting from an incomplete sequence of
// InitSecContext()/AcceptSecContext() calls.
// See RFC 2743 section 2.2.3.
DeleteSecContext() error
}
var (
// OpenSSH supports Kerberos V5 mechanism only for GSS-API authentication,
// so we also support the krb5 mechanism only.
// See RFC 1964 section 1.
krb5Mesh = asn1.ObjectIdentifier{1, 2, 840, 113554, 1, 2, 2}
)
// The GSS-API authentication method is initiated when the client sends an SSH_MSG_USERAUTH_REQUEST
// See RFC 4462 section 3.2.
type userAuthRequestGSSAPI struct {
N uint32
OIDS []asn1.ObjectIdentifier
}
func parseGSSAPIPayload(payload []byte) (*userAuthRequestGSSAPI, error) {
n, rest, ok := parseUint32(payload)
if !ok {
return nil, errors.New("parse uint32 failed")
}
s := &userAuthRequestGSSAPI{
N: n,
OIDS: make([]asn1.ObjectIdentifier, n),
}
for i := 0; i < int(n); i++ {
var (
desiredMech []byte
err error
)
desiredMech, rest, ok = parseString(rest)
if !ok {
return nil, errors.New("parse string failed")
}
if rest, err = asn1.Unmarshal(desiredMech, &s.OIDS[i]); err != nil {
return nil, err
}
}
return s, nil
}
// See RFC 4462 section 3.6.
func buildMIC(sessionID string, username string, service string, authMethod string) []byte {
out := make([]byte, 0, 0)
out = appendString(out, sessionID)
out = append(out, msgUserAuthRequest)
out = appendString(out, username)
out = appendString(out, service)
out = appendString(out, authMethod)
return out
}
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