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Send ext-info-c with kex algorithms (#622)

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Some SSH servers will not honor the negotiated rsa-sha2-256 algorithms
if the client does not indicate support for SSH_MSG_EXT_INFO messages.
Since we only need to accept these messages, but are free to ignore
their contents, adding support amounts to sending "ext-info-c" with our
kex algorithm proposal.
This commit is contained in:
Fabian Henneke
2020-07-20 15:54:28 +02:00
committed by GitHub
parent a5efdf1f0d
commit 64f448d438
4 changed files with 43 additions and 1 deletions
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36
src/main/java/com/hierynomus/sshj/transport/kex/ExtInfoClientFactory.java Normal file
View File

@@ -0,0 +1,36 @@
/*
* Copyright (C)2009 - SSHJ Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hierynomus.sshj.transport.kex;
import net.schmizz.sshj.transport.kex.KeyExchange;
/**
* Stub kex algorithm factory that indicates support for SSH2_MSG_EXT_INFO.
* Some servers will not send `rsa-sha2-*` signatures if the client doesn't indicate support.
*
* Note: Since the server sends `ext-info-s` to indicate support, this fake kex algorithm is never negotiated.
*/
public class ExtInfoClientFactory implements net.schmizz.sshj.common.Factory.Named<KeyExchange> {
@Override
public String getName() {
return "ext-info-c";
}
@Override
public KeyExchange create() {
return null;
}
}

4
src/main/java/net/schmizz/sshj/DefaultConfig.java
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@@ -20,6 +20,7 @@ import com.hierynomus.sshj.key.KeyAlgorithms;
import com.hierynomus.sshj.transport.cipher.BlockCiphers;
import com.hierynomus.sshj.transport.cipher.StreamCiphers;
import com.hierynomus.sshj.transport.kex.DHGroups;
import com.hierynomus.sshj.transport.kex.ExtInfoClientFactory;
import com.hierynomus.sshj.transport.kex.ExtendedDHGroups;
import com.hierynomus.sshj.transport.mac.Macs;
import com.hierynomus.sshj.userauth.keyprovider.OpenSSHKeyV1KeyFile;
@@ -125,7 +126,8 @@ public class DefaultConfig
ExtendedDHGroups.Group16SHA256(),
ExtendedDHGroups.Group16SHA384AtSSH(),
ExtendedDHGroups.Group16SHA512AtSSH(),
ExtendedDHGroups.Group18SHA512AtSSH());
ExtendedDHGroups.Group18SHA512AtSSH(),
new ExtInfoClientFactory());
} else {
setKeyExchangeFactories(DHGroups.Group1SHA1(), new DHGexSHA1.Factory());
}

1
src/main/java/net/schmizz/sshj/common/Message.java
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@@ -25,6 +25,7 @@ public enum Message {
DEBUG(4),
SERVICE_REQUEST(5),
SERVICE_ACCEPT(6),
EXT_INFO(7),
KEXINIT(20),
NEWKEYS(21),

3
src/main/java/net/schmizz/sshj/transport/TransportImpl.java
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@@ -529,6 +529,9 @@ public final class TransportImpl
case SERVICE_ACCEPT:
gotServiceAccept();
break;
case EXT_INFO:
log.debug("Received SSH_MSG_EXT_INFO");
break;
case USERAUTH_BANNER:
log.debug("Received USERAUTH_BANNER");
break;