Key is correct, but refused :: Support Forum

WhiteTiger-IT
Joined:: 2018-07-10
Posts:: 2
Location:: Italia

Key is correct, but refused

2020-06-18 10:30

I generated an SSH key with PuTTYGen.
I copied authorized_keys to the debian server and the private .ppk key to the PC.
If from the linux terminal I launch an SSH session I can connect without errors.
If instead I try to connect from PuTTY (both from Win10 and Linux) I get the error

Server refused our key

I have tried several times, even generating different keys, with length 2048 and 4096.
I don't understand where I'm wrong.
Until I am sure that the key is always accepted, I obviously cannot block access with passwords.

This is the log of the last session.
PuTTY didn't accept the key, but he accepted the user's login.

2020-06-18 10:51:53   Looking up host "192.168.201.11" for SSH connection
2020-06-18 10:51:53   Connecting to 192.168.201.11 port 1022
2020-06-18 10:51:53   We claim version: SSH-2.0-PuTTY_Release_0.73
2020-06-18 10:51:53   Remote version: SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
2020-06-18 10:51:53   Using SSH protocol version 2
2020-06-18 10:51:53   No GSSAPI security context available
2020-06-18 10:51:53   Doing ECDH key exchange with curve Curve25519 and hash SHA-256 (unaccelerated)
2020-06-18 10:51:53   Server also has ecdsa-sha2-nistp256/ssh-rsa host keys, but we don't know any of them
2020-06-18 10:51:53   Host key fingerprint is:
2020-06-18 10:51:53   ssh-ed25519 255 d8:8f:87:27:ca:87:01:86:20:6e:9e:a0:14:b7:d4:21
2020-06-18 10:51:53   Initialised AES-256 SDCTR (unaccelerated) outbound encryption
2020-06-18 10:51:53   Initialised HMAC-SHA-256 (unaccelerated) outbound MAC algorithm
2020-06-18 10:51:53   Initialised AES-256 SDCTR (unaccelerated) inbound encryption
2020-06-18 10:51:53   Initialised HMAC-SHA-256 (unaccelerated) inbound MAC algorithm
2020-06-18 10:51:53   Reading key file "L:\Chiavi-SSH\LS-ULHQ-1-PuTTY-Private-Key.ppk"
2020-06-18 10:51:53   Writing new session log (raw mode) to file: putty.log
2020-06-18 10:52:04   Offered public key
2020-06-18 10:52:04   Server refused our key
2020-06-18 10:52:04   Attempting keyboard-interactive authentication
2020-06-18 10:52:18   Access granted
2020-06-18 10:52:18   Opening main session channel
2020-06-18 10:52:18   Opened main channel
2020-06-18 10:52:18   Allocated pty
2020-06-18 10:52:18   Started a shell/command

This is the sshd-config

Port 1022
ListenAddress 0.0.0.0
PermitRootLogin no
PubkeyAuthentication yes
AuthorizedKeysFile   .ssh/authorized_keys .ssh/authorized_keys2
PasswordAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication yes
UsePAM yes
X11Forwarding yes
PrintMotd no
AcceptEnv LANG LC_*
Subsystem   sftp   /usr/lib/openssh/sftp-server

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martin◆ Site Admin
Joined:: 2002-12-10
Posts:: 41,441
Location:: Prague, Czechia

Re: Key is correct, but refused

2020-06-19

How do you authenticate "from the linux terminal"?

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WhiteTiger-IT
Joined:: 2018-07-10
Posts:: 2
Location:: Italia

2020-06-20 09:08

Simply by using ssh.
I created a config file with the indications of the various servers and where the private key is located on my PC, then I type ssh Host-Name
For example (in this Host-Name=server1):

Host server1
     HostName 192.168.100.100
     User user1
     IdentityFile ~/.ssh/server1.key

In this way, with ssh server1 first I have to type the key password; then I have to type the password of user1; then, if I need it, I type su - and I have to type the password for the root.
Obviously without any error.

Instead, if I connect to the same server from PuTTY (using the ppk key), it first gives me an error Server refused our key, then immediately asks me for the password of user1.

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martin◆ Site Admin

2020-06-23

Can you authenticate using server1.key (or its .ppk equivalent) using any SSH/SFTP client on that Windows machine?

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Uwe
Joined:: 2021-12-15
Posts:: 2
Location:: California

2021-12-15 01:48

Per https://winscp.net/tracker/1952:

OpenSSH 8.8 disabled ssh-rsa by default. Until WinSCP 5.20 is released, add this to server's sshd_config to re-enable it:
PubkeyAcceptedAlgorithms +ssh-rsa

You might also need to add:

PubkeyAuthentication yes

See also: https://winscp.net/forum/viewtopic.php?t=31767

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martin◆ Site Admin

2021-12-16

@Uwe: Note that WinSCP 5.20 beta was released already.

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Uwe

2021-12-16 17:57

@martin: That might well be so, but as of 2021-12-16 the main download at https://winscp.net/eng/download.php is still 5.19, so presumably that's what most folks run.

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