Auditing SSH logs

Hi folks, good morning/afternoon/evening ;)

I'll try explain my doubt, but sorry for my english..

Can someone tell me if has a way to do SSHD log shows me "which" key
has been accepted when logged as root ?

"May 31 15:15:17 lazlo sshd[12583]: Accepted publickey for root from port 1835 ssh2"

But ... which key has been accepted ? how can i audit something like
it, if i have more than a single key on authorized_keys for root

More info about one of my boxes:

lazlo:~# cat /etc/debian_version
lazlo:~# uname -a
Linux lazlo 2.6.18-4-amd64 #1 SMP Mon Mar 26 11:36:53 CEST 2007 x86_64 GNU/Linux
lazlo:~# dpkg -l | grep ssh
ii openssh-client 4.3p2-9
Secure shell client, an rlogin/rsh/rcp repla
ii openssh-server 4.3p2-9
Secure shell server, an rshd replacement
lazlo:~# telnet localhost 22
Connected to localhost.
Escape character is '^]'.
SSH-2.0-OpenSSH_4.3p2 Debian-9

Connection closed by foreign host.
lazlo:~# grep -Ev '^$|^#' /etc/ssh/sshd_config
Port 22
Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
UsePrivilegeSeparation yes
KeyRegenerationInterval 3600
ServerKeyBits 768
SyslogFacility AUTH
LogLevel INFO
LoginGraceTime 120
PermitRootLogin without-password
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
UsePAM yes

Best regards,

Flávio do Carmo Junior