ssldump - dump SSL traffic on a network
SYNOPSIS
ssldump [ -vtaTnsAxXhHVNdq ] [ -r dumpfile ]
[ -i interface ] [ -k keyfile ] [ -p password ] [ expression ]
DESCRIPTION
ssldump is an SSL/TLS network protocol analyzer. It iden-
tifies TCP connections on the chosen network interface and
attempts to interpret them as SSL/TLS traffic. When it
identifies SSL/TLS traffic, it decodes the records and
displays them in a textual form to stdout. If provided
with the appropriate keying material, it will also decrypt
the connections and display the application data traffic.
ssldump has been tested on FreeBSD, Linux, Solaris, and
HP/UX. Since it's based on PCAP, it should work on most
platforms. However, unlike tcpdump, ssldump needs to be
able to see both sides of the data transmission so you may
have trouble using it with network taps such as SunOS nit
that don't permit you to see transmitted data. Under
SunOS with nit or bpf: To run tcpdump you must have read
access to /dev/nit or /dev/bpf*. Under Solaris with dlpi:
You must have read access to the network pseudo device,
e.g. /dev/le. Under HP-UX with dlpi: You must be root or
it must be installed setuid to root. Under IRIX with
snoop: You must be root or it must be installed setuid to
root. Under Linux: You must be root or it must be
installed setuid to root. Under Ultrix and Digital UNIX:
Once the super-user has enabled promiscuous-mode operation
using pfconfig(8), any user may run ssldump Under BSD: You
must have read access to /dev/bpf*.
OPTIONS
-a Print bare TCP ACKs (useful for observing Nagle behav-
ior)
-A Print all record fields (by default ssldump chooses
the most interesting fields)
-d Display the application data traffic. This usually
means decrypting it, but when -d is used ssldump
will also decode application data traffic _before_
the SSL session initiates. This allows you to see
HTTPS CONNECT behavior as well as SMTP STARTTLS. As
a side effect, since ssldump can't tell whether
plaintext is traffic before the initiation of an
SSL connection or just a regular TCP connection,
this allows you to use ssldump to sniff any TCP
connection. ssldump will automatically detect
ASCII data and display it directly to the screen.
-e Print absolute timestamps instead of relative
timestamps
-r Read data from file instead of from the network.
The old -f option still works but is deprecated and
will probably be removed with the next version.
-H
Print the full SSL packet header.
-k Use keyfile as the location of the SSL keyfile
(OpenSSL format) ssldump automatically looks in
./server.pem.
-n Don't try to resolve host names from IP addresses
-N Attempt to parse ASN.1 when it appears, such as in
certificates and DNs.
-p Use password as the SSL keyfile password default is
"password".
-q Don't decode any record fields beyond a single sum-
mary line. (quiet mode).
-x Print each record in hex, as well as decoding it.
-X When the -d option is used, binary data is automat-
ically printed in two columns with a hex dump on
the left and the printable characters on the right.
-X suppresses the display of the printable charac-
ters, thus making it easier to cut and paste the
hext data into some other program. -y Decorate the
output for processing with troff. Not very useful
for the average user.
expression
Selects what packets ssldump will examine. Techni-
cally speaking, ssldump supports the full expres-
sion syntax from PCAP and tcpdump. In fact, the
description here is cribbed from the tcpdump man
page. However, since ssldump needs to examine full
TCP streams, most of the tcpdump expressions will
select traffic mixes that ssldump will simply
ignore. Only the expressions which don't result in
incomplete TCP streams are listed here.
The expression consists of one or more primitives.
Primitives usually consist of an id (name or num-
ber) preceded by one or more qualifiers. There are
three different kinds of qualifier:
are host, net and port. E.g., `host foo',
`net 128.3', `port 20'. If there is no type
qualifier, host is assumed.
dir qualifiers specify a particular transfer
direction to and/or from id. Possible
directions are src, dst, src or dst and src
and dst. E.g., `src foo', `dst net 128.3',
`src or dst port ftp-data'. If there is no
dir qualifier, src or dst is assumed. For
`null' link layers (i.e. point to point pro-
tocols such as slip) the inbound and out-
bound qualifiers can be used to specify a
desired direction.
More complex filter expressions are built up by
using the words and, or and not to combine primi-
tives. E.g., `host foo and not port ftp and not
port ftp-data'. To save typing, identical quali-
fier lists can be omitted. E.g., `tcp dst port ftp
or ftp-data or domain' is exactly the same as `tcp
dst port ftp or tcp dst port ftp-data or tcp dst
port domain'.
Allowable primitives are:
dst host host
True if the IPv4/v6 destination field of the
packet is host, which may be either an
address or a name.
src host host
True if the IPv4/v6 source field of the
packet is host.
host host
True if either the IPv4/v6 source or desti-
nation of the packet is host. Any of the
above host expressions can be prepended with
the keywords, ip, arp, rarp, or ip6 as in:
ip host host
which is equivalent to:
ether proto \ip and host host
If host is a name with multiple IP
addresses, each address will be checked for
a match.
ether dst ehost
True if the ethernet destination address is
ehost. Ehost may be either a name from
/etc/ethers or a number (see ethers(3N) for
numeric format).
True if the ethernet source address is
ehost.
ether host ehost
True if either the ethernet source or desti-
nation address is ehost.
gateway host
True if the packet used host as a gateway.
I.e., the ethernet source or destination
address was host but neither the IP source
nor the IP destination was host. Host must
be a name and must be found in both
/etc/hosts and /etc/ethers. (An equivalent
expression is
ether host ehost and not host host
which can be used with either names or num-
bers for host / ehost.) This syntax does
not work in IPv6-enabled configuration at
this moment.
dst net net
True if the IPv4/v6 destination address of
the packet has a network number of net. Net
may be either a name from /etc/networks or a
network number (see networks(4) for
details).
src net net
True if the IPv4/v6 source address of the
packet has a network number of net.
net net
True if either the IPv4/v6 source or desti-
nation address of the packet has a network
number of net.
net net mask mask
True if the IP address matches net with the
specific netmask. May be qualified with src
or dst. Note that this syntax is not valid
for IPv6 net.
net net/len
True if the IPv4/v6 address matches net a
netmask len bits wide. May be qualified
with src or dst.
dst port port
True if the packet is ip/tcp, ip/udp,
ip6/tcp or ip6/udp and has a destination
port value of port. The port can be a num-
both the port number and protocol are
checked. If a number or ambiguous name is
used, only the port number is checked (e.g.,
dst port 513 will print both tcp/login traf-
fic and udp/who traffic, and port domain
will print both tcp/domain and udp/domain
traffic).
src port port
True if the packet has a source port value
of port.
port port
True if either the source or destination
port of the packet is port. Any of the
above port expressions can be prepended with
the keywords, tcp or udp, as in:
tcp src port port
which matches only tcp packets whose source
port is port.
Primitives may be combined using:
A parenthesized group of primitives and
operators (parentheses are special to the
Shell and must be escaped).
Negation (`!' or `not').
Concatenation (`&&' or `and').
Alternation (`||' or `or').
Negation has highest precedence. Alternation and
concatenation have equal precedence and associate
left to right. Note that explicit and tokens, not
juxtaposition, are now required for concatenation.
If an identifier is given without a keyword, the
most recent keyword is assumed. For example,
not host vs and ace
is short for
not host vs and host ace
which should not be confused with
not ( host vs or ace )
Expression arguments can be passed to ssldump as
either a single argument or as multiple arguments,
whichever is more convenient. Generally, if the
expression contains Shell metacharacters, it is
easier to pass it as a single, quoted argument.
Multiple arguments are concatenated with spaces
To listen to traffic on interface le0 port 443
ssldump -i le0 port 443
To listen to traffic to the server romeo on port 443.
ssldump -i le0 port 443 and host romeo
To decrypt traffic to to host romeo server.pem and the
password foobar
ssldump -Ad -k ~/server.pem -p foobar -i le0 host romeo
OUTPUT FORMAT
All output is printed to standard out.
ssldump prints an indication of every new TCP connection
using a line like the following
New TCP connection #2: iromeo.rtfm.com(2302) <-> sr1.rtfm.com(4433)
The host which send the first SYN is printed on the left
and the host which responded is printed on the right.
Ordinarily, this means that the SSL client will be printed
on the left with the SSL server on the right. In this case
we have a connection from iromeo.rtfm.com (port 2303) to
sr1.rtfm.com (port 4433). To allow the user to disentangle
traffic from different connections, each connection is
numbered. This is connection 2.
The printout of each SSL record begins with a record line.
This line contains the connection and record number, a
timestamp, and the record type, as in the following:
2 3 0.2001 (0.0749) S>C Handshake Certificate
This is record 3 on connection 2. The first timestamp is
the time since the beginning of the connection. The second
is the time since the previous record. Both are in sec-
onds.
The next field in the record line is the direction that
the record was going. C>S indicates records transmitted
from client to server and S>C indicates records transmit-
ted from server to client. ssldump assumes that the host
to transmit the first SYN is the SSL client (this is
nearly always correct).
The next field is the record type, one of Handshake,
IAlert, ChangeCipherSpec, or application_data. Finally,
ssldump may print record-specific data on the rest of the
line. For Handshake records, it prints the handshake mes-
sage. Thus, this record is a Certificate message.
ssldump chooses certain record types for further decoding.
ClientHello - version, offered cipher suites, session id
if provided)
ServerHello - version, session_id, chosen cipher suite,
compression method
Alert - type and level (if obtainable)
Fuller decoding of the various records can be obtained by
using the -A , -d , -k and -p flags.
DECRYPTION
ssldump can decrypt traffic between two hosts if the fol-
lowing two conditions are met:
1. ssldump has the keys.
2. Static RSA was used.
In any other case, once encryption starts, ssldump will
only be able to determine the record type. Consider the
following section of a trace.
1 5 0.4129 (0.1983) C>S Handshake ClientKeyExchange
1 6 0.4129 (0.0000) C>S ChangeCipherSpec
1 7 0.4129 (0.0000) C>S Handshake
1 8 0.5585 (0.1456) S>C ChangeCipherSpec
1 9 0.6135 (0.0550) S>C Handshake
1 10 2.3121 (1.6986) C>S application_data
1 11 2.5336 (0.2214) C>S application_data
1 12 2.5545 (0.0209) S>C application_data
1 13 2.5592 (0.0046) S>C application_data
1 14 2.5592 (0.0000) S>C Alert
Note that the ClientKeyExchange message type is printed
but the rest of the Handshake messages do not have types.
These are the Finished messages, but because they are
encrypted ssldump only knows that they are of type Hand-
shake. Similarly, had the Alert in record 14 happened
during the handshake, it's type and level would have been
printed. However, since it is encrypted we can only tell
that it is an alert.
BUGS
Please send bug reports to ssldump@rtfm.com.
The TCP reassembler is not perfect. No attempt is made to
reassemble IP fragments and the 3-way handshake and close
handshake are imperfectly implemented. In practice, this
turns out not to be much of a problem.
Support is provided for only for Ethernet and loopback
interfaces because that's all that I have. If you have
another kind of network you will need to modify pcap_cb in
base/pcap-snoop.c. If you have direct experience with ssldump
on other networks, please send me patches.
ssldump doesn't implement session caching and therefore
can't decrypt resumed sessions.
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