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The following commit(s) were added to refs/heads/master by this push:
new 72224fa6f Improved documentation + HOWTO for strict KEX management
72224fa6f is described below
commit 72224fa6f76ef33fd80eebc46a8661866e6f7f62
Author: Lyor Goldstein <lgoldst...@apache.org>
AuthorDate: Sat Jan 6 10:20:27 2024 +0200
Improved documentation + HOWTO for strict KEX management
---
docs/howto.md | 38 ++++++++++++++++++++++++++++++++++++++
docs/standards.md | 18 ++++++++++++++++--
2 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/docs/howto.md b/docs/howto.md
index 70f0b64e4..af3aad189 100644
--- a/docs/howto.md
+++ b/docs/howto.md
@@ -23,3 +23,41 @@ In order to achieve this one needs to use a
`ReservedSessionMessagesHandler` on
The idea is to prevent the normal session establish flow by taking over the
initial handshake identification and blocking the initial KEX message from the
server.
A sample implementation can be found in the
`EndlessTarpitSenderSupportDevelopment` class in the *sshd-contrib* package
*test* section.
+
+## Disabling strict KEX
+
+The current code implements the
[strict-kex](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL)
extension by default. If users want/need to disable it, then
+this can be done *programmatically* as follows (the example is for the client,
but a similar approach can be implemented for the server):
+
+
+```java
+class NoStrictKexSession extends ClientSessionImpl {
+ NoStrictKexSession(ClientFactoryManager client, IoSession ioSession)
throws Exception {
+ super(client, ioSession);
+ }
+
+ @Override
+ protected Map<KexProposalOption, String>
doStrictKexProposal(Map<KexProposalOption, String> proposal) {
+ return proposal;
+ }
+}
+
+class NoStrictKexSessionFactory extends SessionFactory {
+ NoStrictKexSessionFactory(ClientFactoryManager client) {
+ super(client);
+ }
+
+ @Override
+ protected ClientSessionImpl doCreateSession(IoSession ioSession) throws
Exception {
+ return new NoStrictKexSession(getClient(), ioSession);
+ }
+}
+
+SshClient client = ...;
+SessionFactory factory = new NoStrictKexSessionFactory(client);
+client.setSessionFactory(factory);
+client.start();
+```
+
+If one needs to disable the protocol on a per-session basis, then it is
possible to examine the peer's address (e.g., or anything else for that matter)
in the `doCreateSession`
+or the `doStrictKexProposal` overrides and then invoke the super-class (for
continuing with strict KEX) or return immediately (for disabling it).
\ No newline at end of file
diff --git a/docs/standards.md b/docs/standards.md
index d223bda4c..c2d8f28f8 100644
--- a/docs/standards.md
+++ b/docs/standards.md
@@ -35,7 +35,22 @@
* [OpenSSH support for U2F/FIDO security
keys](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.u2f)
* **Note:** the server side supports these keys by default. The client
side requires specific initialization
* [OpenSSH public-key certificate authentication system for use by
SSH](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.certkeys)
-* [OpenSSH strict key exchange
extension](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL)
+* [OpenSSH 1.9 transport: strict key exchange
extension](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL)
+* [(Some) OpenSSH SFTP
extensions](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL)
+
+**Note:** some implementations may be limited to client-side - i.e., we
provide a capability for the client to detect if the server
+supports the extension and then use it, but our server does not publish it as
being supported.
+
+| Section | Extension | Client | Server |
+| ------- | -------------------------- | ------ | ------ |
+| 4.3 | `posix-ren...@openssh.com` | Yes | Yes |
+| 4.4 | `stat...@openssh.com` | Yes | Yes |
+| 4.4 | `fstat...@openssh.com` | Yes | Yes |
+| 4.5 | `hardl...@openssh.com` | Yes | Yes |
+| 4.6 | `fs...@openssh.com` | Yes | Yes |
+| 4.7 | `lsets...@openssh.com` | Yes | Yes |
+| 4.8 | `lim...@openssh.com` | Yes | Yes |
+| 4.10 | `copy-data` | Yes | Yes |
### SFTP version 3-6 + extensions
@@ -50,7 +65,6 @@
* `copy-file`, `copy-data` - [DRAFT 00 - sections 6,
7](https://tools.ietf.org/id/draft-ietf-secsh-filexfer-extensions-00.txt)
* `space-available` - [DRAFT 09 - section
9.2](https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-09#section-9.2)
* `filename-charset`, `filename-translation-control` - [DRAFT 13 - section
6](https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-6) - only
client side
-* Several [OpenSSH SFTP
extensions](https://github.com/openssh/openssh-portable/blob/master/PROTOCOL)
### Miscellaneous
