// Check is called during the handshake to check the server's public key for
// unexpected changes. The key argument is in SSH wire format. It can be parsed
// using ssh.ParsePublicKey. The address before DNS resolution is passed in the
// addr argument, so the key can also be checked against the hostname.
// It returns any error encountered while checking the public key. A nil return
// value indicates that the key was either successfully verified (against an
// existing known_hosts entry), or accepted by the user as a new key.
func (kc *HostKeyChecker) Check(addr string, remote net.Addr, key gossh.PublicKey) error {
remoteAddr, err := kc.addrToHostPort(remote.String())
if err != nil {
return err
}
algoStr := algoString(key.Type())
keyFingerprintStr := md5String(md5.Sum(key.Marshal()))
hostKeys, err := kc.m.GetHostKeys()
_, ok := err.(*os.PathError)
if err != nil && !ok {
log.Errorf("Failed to read known_hosts file %v: %v", kc.m.String(), err)
}
mismatched := false
for pattern, keys := range hostKeys {
if !matchHost(remoteAddr, pattern) {
continue
}
for _, hostKey := range keys {
// Any matching key is considered a success, irrespective of previous failures
if hostKey.Type() == key.Type() && bytes.Compare(hostKey.Marshal(), key.Marshal()) == 0 {
return nil
}
// TODO(jonboulle): could be super friendly like the OpenSSH client
// and note exactly which key failed (file + line number)
mismatched = true
}
}
if mismatched {
fmt.Fprintf(os.Stderr, warningRemoteHostChanged, algoStr, keyFingerprintStr, kc.m.String())
return ErrUnmatchKey
}
// If we get this far, we haven't matched on any of the hostname patterns,
// so it's considered a new key. Prompt the user to trust it.
if !kc.trustHost(remoteAddr, algoStr, keyFingerprintStr) {
fmt.Fprintln(os.Stderr, "Host key verification failed.")
return ErrUntrustHost
}
if err := kc.m.PutHostKey(remoteAddr, key); err != nil {
fmt.Fprintf(os.Stderr, "Failed to add the host to the list of known hosts (%v).\n", kc.m)
return nil
}
fmt.Fprintf(os.Stderr, "Warning: Permanently added '%v' (%v) to the list of known hosts.\n", remoteAddr, algoStr)
return nil
}
// Check is called during the handshake to check server's
// public key for unexpected changes. The hostKey argument is
// in SSH wire format. It can be parsed using
// ssh.ParsePublicKey. The address before DNS resolution is
// passed in the addr argument, so the key can also be checked
// against the hostname.
func (kc *HostKeyChecker) Check(addr string, remote net.Addr, key gossh.PublicKey) error {
remoteAddr := remote.String()
algoStr := algoString(key.Type())
keyFingerprintStr := md5String(md5.Sum(key.Marshal()))
// get existing host keys
hostKeys, err := kc.m.GetHostKeys()
_, ok := err.(*os.PathError)
if err != nil && !ok {
kc.errLog.Println("Warning: read host file with", err)
}
// check existing host keys
hostKey, ok := hostKeys[remoteAddr]
if !ok {
if kc.trustHost == nil {
return ErrUnsetTrustFunc
}
if !kc.trustHost(remoteAddr, algoStr, keyFingerprintStr) {
kc.errLog.Println("Host key verification failed.")
return ErrUntrustHost
}
if err := kc.m.PutHostKey(remoteAddr, key); err != nil {
kc.errLog.Printf("Failed to add the host to the list of known hosts (%v).\n", kc.m)
return nil
}
kc.errLog.Printf("Warning: Permanently added '%v' (%v) to the list of known hosts.\n", remoteAddr, algoStr)
return nil
}
if hostKey.Type() != key.Type() || bytes.Compare(hostKey.Marshal(), key.Marshal()) != 0 {
kc.errLog.Printf(`%s
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the %v key sent by the remote host is
%v.
Please contact your system administrator.
Add correct host key in %v to get rid of this message.
Host key verification failed.%c`,
warningRemoteHostChanged, algoStr, keyFingerprintStr, kc.m.String(), '\n')
return ErrUnmatchKey
}
return nil
}
