sign_and_send_pubkey: signing failed: agent refused operation

I login on a server (fpirisp) without problems with connectbot. But if I try to ssh to it again from the command prompt (having agent enabled on connectbot) it refuses to login using the agent with the error

sign_and_send_pubkey: signing failed: agent refused operation

The ssh keypair is configured correctly (if it weren’t it would not let me login from connectbot). And the agent in connectbot is also correct, because it lets me login to other servers (that have lower versions of OpenSSH: OpenSSH_6.7p1 Debian-5+deb8u2 on a debian stable, for example).

The server in question that gives me problems has OpenSSH_7.2p2 Debian-5.

This is the output when trying to ssh back into the server from the connectbot session:

$ ssh -vvv fpirisp

OpenSSH_7.2p2 Debian-5, OpenSSL 1.0.2h  3 May 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: /etc/ssh/ssh_config line 69: Applying options for fpirisp
debug3: kex names ok: [diffie-hellman-group1-sha1]
debug2: resolving "fpirisp" port 9614
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to fpirisp [127.0.1.1] port 9614.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/kiko/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2p2 Debian-5
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Debian-5
debug1: match: OpenSSH_7.2p2 Debian-5 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to fpirisp:9614 as 'kiko'
debug3: put_host_port: [fpirisp]:9614
debug3: hostkeys_foreach: reading file "/home/kiko/.ssh/known_hosts"
debug3: hostkeys_foreach: reading file "/etc/ssh/ssh_known_hosts"
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: [e-mail],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,ext-info-c
debug2: host key algorithms: [e-mail],[e-mail],[e-mail],[e-mail],[e-mail],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: [e-mail],aes128-ctr,aes192-ctr,aes256-ctr,[e-mail],[e-mail],aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc
debug2: ciphers stoc: [e-mail],aes128-ctr,aes192-ctr,aes256-ctr,[e-mail],[e-mail],aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc
debug2: MACs ctos: [e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: [e-mail],zlib,none
debug2: compression stoc: [e-mail],zlib,none
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: [e-mail],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: ssh-rsa,rsa-sha2-512,rsa-sha2-256
debug2: ciphers ctos: [e-mail],aes128-ctr,aes192-ctr,aes256-ctr,[e-mail],[e-mail]
debug2: ciphers stoc: [e-mail],aes128-ctr,aes192-ctr,aes256-ctr,[e-mail],[e-mail]
debug2: MACs ctos: [e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[e-mail]
debug2: compression stoc: none,[e-mail]
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug1: kex: algorithm: [e-mail]
debug1: kex: host key algorithm: rsa-sha2-512
debug1: kex: server->client cipher: [e-mail] MAC: <implicit> compression: [e-mail]
debug1: kex: client->server cipher: [e-mail] MAC: <implicit> compression: [e-mail]
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ssh-rsa SHA256:1u68rDFU6bC7+xFdMlC8BMcg/X3LTLDng5Jpzvo6j7o
debug3: verify_host_key_dns
DNS lookup error: name does not exist
debug3: put_host_port: [127.0.1.1]:9614
debug3: put_host_port: [fpirisp]:9614
debug3: hostkeys_foreach: reading file "/home/kiko/.ssh/known_hosts"
debug3: hostkeys_foreach: reading file "/etc/ssh/ssh_known_hosts"
debug1: checking without port identifier
debug3: hostkeys_foreach: reading file "/home/kiko/.ssh/known_hosts"
debug3: hostkeys_foreach: reading file "/etc/ssh/ssh_known_hosts"
debug3: record_hostkey: found key type RSA in file /etc/ssh/ssh_known_hosts:53
debug3: load_hostkeys: loaded 1 keys from fpirisp
debug1: Host 'fpirisp' is known and matches the RSA host key.
debug1: Found key in /etc/ssh/ssh_known_hosts:53
debug1: found matching key w/out port
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug2: set_newkeys: mode 0
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug2: key: kiko@phonew (0x55e563e1c670), agent
debug2: key: /home/kiko/.ssh/id_rsa ((nil))
debug2: key: /home/kiko/.ssh/id_dsa ((nil))
debug2: key: /home/kiko/.ssh/id_ecdsa ((nil))
debug2: key: /home/kiko/.ssh/id_ed25519 ((nil))
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: kiko@phonew
debug3: send_pubkey_test
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 60
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug2: input_userauth_pk_ok: fp SHA256:eAOGXFvhRKGQuwGrCQT6lGFZkp8F7DtdAQClj/CboP8
debug3: sign_and_send_pubkey: RSA SHA256:eAOGXFvhRKGQuwGrCQT6lGFZkp8F7DtdAQClj/CboP8
sign_and_send_pubkey: signing failed: agent refused operation
debug1: Trying private key: /home/kiko/.ssh/id_rsa
debug3: no such identity: /home/kiko/.ssh/id_rsa: No such file or directory
debug1: Trying private key: /home/kiko/.ssh/id_dsa
debug3: no such identity: /home/kiko/.ssh/id_dsa: No such file or directory
debug1: Trying private key: /home/kiko/.ssh/id_ecdsa
debug3: no such identity: /home/kiko/.ssh/id_ecdsa: No such file or directory
debug1: Trying private key: /home/kiko/.ssh/id_ed25519
debug3: no such identity: /home/kiko/.ssh/id_ed25519: No such file or directory
debug2: we did not send a packet, disable method
debug1: No more authentication methods to try.
Permission denied (publickey).

[vorburger]

@kruton (and anyone else reading along here) just wanted to let you know that using auth agent with ConnectBot 1.9.6 to a host with e.g. OpenSSH 8.1 (which includes the bug released with openssh-8.0) with a ssh-rsa key with 4096 bits works fine now.

I did however just encounter the same sign_and_send_pubkey: signing failed: agent refused operation with a ssh-ed25519 key (same host); not a biggie, but thought worth mentioning here, just to let you know.

[kruton]

The SSH agent is entirely dependent on ConnectBot source code, so not adding ed25519 is just an oversight.