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I did the following:

Server A:

ssh-keygen -t rsa
(did not enter any passphrase)

cat ~/.ssh/

Server B:

mkdir ~/.ssh
chmod 0700 ~/.ssh
touch ~/.ssh/authorized_keys
chmod 0644 ~/.ssh/authorized_keys

placed the content of ~/.ssh/ file into ~/.ssh/authorized_keys

tried to login from server B into server A but can not. I am being asked for password:

$ ssh -p custom_port -v username@serverA
OpenSSH_5.5p1 Debian-6+squeeze3, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to serverA [XXX.XXX.XXX.XXX] port custom_port.
debug1: Connection established.
debug1: identity file /var/username/.ssh/id_rsa type -1
debug1: identity file /var/username/.ssh/id_rsa-cert type -1
debug1: identity file /var/username/.ssh/id_dsa type -1
debug1: identity file /var/username/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze2
debug1: match: OpenSSH_5.5p1 Debian-6+squeeze2 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr 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 '[serverA]:custom_port' is known and matches the RSA host key.
debug1: Found key in /var/username/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /var/username/.ssh/id_rsa
debug1: Trying private key: /var/username/.ssh/id_dsa
debug1: Next authentication method: password
username@serverA's password:

Any ideas?

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up vote 2 down vote accepted

It looks as though you have the roles reversed.

The public key should be in authorized_keys on the server you are attempting to login to.

Also note: SSH version 2 uses the file authorized_keys2 while version 1 uses authorized_keys

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The authorized_keys file has to be on server A when you login from B to A.

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