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ssh: support rsa-sha2-256/512 on the server side

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This lets clients know we support rsa-sha2-256/512 signatures from
ssh-rsa public keys. OpenSSH prefers to break the connection rather than
attempting trial and error, apparently.

We don't enable support for the "ext-info-s" because we're not
interested in any client->server extensions.

This also replaces isAcceptableAlgo which was rejecting the
rsa-sha2-256/512-cert-v01@openssh.com public key algorithms.

Tested with OpenSSH 9.1 on macOS Ventura.

Fixes golang/go#49269
Updates golang/go#49952

Co-authored-by: Nicola Murino <nicola.murino@gmail.com>
Co-authored-by: Kristin Davidson <kdavidson@atlassian.com>
Change-Id: I4955c3b12bb45575e9977ac657bb5805b49d00c3
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/447757
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Filippo Valsorda
2022-11-12 16:25:23 +00:00
co-authored by Nicola Murino Kristin Davidson
parent 21d60a1521
commit 6fad3dfc18
4 changed files with 38 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ssh/handshake.go
+20 -1
View File
@@ -615,7 +615,8 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
return err
}
if t.sessionID == nil {
firstKeyExchange := t.sessionID == nil
if firstKeyExchange {
t.sessionID = result.H
}
result.SessionID = t.sessionID
@@ -626,6 +627,24 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
if err = t.conn.writePacket([]byte{msgNewKeys}); err != nil {
return err
}
// On the server side, after the first SSH_MSG_NEWKEYS, send a SSH_MSG_EXT_INFO
// message with the server-sig-algs extension if the client supports it. See
// RFC 8308, Sections 2.4 and 3.1.
if !isClient && firstKeyExchange && contains(clientInit.KexAlgos, "ext-info-c") {
extInfo := &extInfoMsg{
NumExtensions: 1,
Payload: make([]byte, 0, 4+15+4+len(supportedPubKeyAuthAlgosList)),
}
extInfo.Payload = appendInt(extInfo.Payload, len("server-sig-algs"))
extInfo.Payload = append(extInfo.Payload, "server-sig-algs"...)
extInfo.Payload = appendInt(extInfo.Payload, len(supportedPubKeyAuthAlgosList))
extInfo.Payload = append(extInfo.Payload, supportedPubKeyAuthAlgosList...)
if err := t.conn.writePacket(Marshal(extInfo)); err != nil {
return err
}
}
if packet, err := t.conn.readPacket(); err != nil {
return err
} else if packet[0] != msgNewKeys {