Cygwin sshd key auth doesn't work (seteuid 500: Permission denied)

[Tomàs Núñez]

Hi

I am trying to connect to a Cygwin sshd server using key authentication, 
but I can't. When I use password authentication, it works great, but I 
need to run some unattended processes, so key auth is mandatory.

When I try to connect, I get that:
user@workstation:~/.ssh$ ssh administrator@server -o 
PreferredAuthentications=publickey -v
OpenSSH_5.1p1 Debian-3, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to server [1.1.1.1] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/identity type -1
debug1: identity file /home/user/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.1
debug1: match: OpenSSH_5.1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.1p1 Debian-3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'server' is known and matches the RSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:27
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: 
publickey,password,keyboard-interactive
debug1: Next authentication method: publickey
debug1: Trying private key: /home/user/.ssh/identity
debug1: Offering public key: /home/user/.ssh/id_rsa
Connection closed by 10.7.0.62

When I run ssh daemon as a windows service, the event viewer shows this 
error:
The description for Event ID ( 0 ) in Source ( sshd ) cannot be found. 
The local computer may not have the necessary registry information or 
message DLL files to display messages from a remote computer. You may be 
able to use the /AUXSOURCE= flag to retrieve this description; see Help 
and Support for details. The following information is part of the event: 
sshd: PID 8272: fatal: seteuid 500: Permission denied.


When I run ssh daemon as a user, in order to debug, I get that:
user@server ~/$ /usr/sbin/sshd.exe -d
debug1: sshd version OpenSSH_5.1p1
debug1: read PEM private key done: type RSA
debug1: private host key: #0 type 1 RSA
debug1: read PEM private key done: type DSA
debug1: private host key: #1 type 2 DSA
debug1: rexec_argv[0]='/usr/sbin/sshd'
debug1: rexec_argv[1]='-d'
debug1: Bind to port 22 on 0.0.0.0.
Server listening on 0.0.0.0 port 22.
debug1: fd 4 clearing O_NONBLOCK
debug1: Server will not fork when running in debugging mode.
debug1: rexec start in 4 out 4 newsock 4 pipe -1 sock 7
debug1: inetd sockets after dupping: 3, 3
Connection from 1.1.1.1 port 39396
debug1: Client protocol version 2.0; client software version 
OpenSSH_5.1p1 Debian-3
debug1: match: OpenSSH_5.1p1 Debian-3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.1
debug1: list_hostkey_types: ssh-rsa,ssh-dss
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST received
debug1: SSH2_MSG_KEX_DH_GEX_GROUP sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_INIT
debug1: SSH2_MSG_KEX_DH_GEX_REPLY sent
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: KEX done
debug1: userauth-request for user administrator service ssh-connection 
method none
debug1: attempt 0 failures 0
Failed none for administrator from 1.1.1.1 port 39396 ssh2
debug1: userauth-request for user administrator service ssh-connection 
method publickey
debug1: attempt 1 failures 0
debug1: test whether pkalg/pkblob are acceptable
debug1: temporarily_use_uid: 500/513 (e=400/401)
seteuid 500: Permission denied
debug1: do_cleanup

I've also tried to run sshd with strace, but I've found nothing (logs 
are 412KB, that's why I don't attach them).

Does anyone use key auth with cygwin sshd server?
Any hint about this issue?

Thanks in advance!
Tomà s

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