I wrote this code in a scapy script.
The goal is to generate ICMP v6 Request and get the checksum.
def generate_frame():
eth = Ether()
eth.dst = "00:50:56:9E:7B:BB"
eth.src = "00:50:56:9E:78:AA"
eth.type = 0x8100
ip = IPv6()
ip.src = "2002:c000:0203:0000:0000:0000:0000:00AA"
ip.dst = "2002:c000:0203:0000:0000:0000:0000:00BB"
icmp =ICMPv6EchoRequest(seq=0x1, id=0x792)
icmp.data = "test"
icmp = ICMPv6EchoRequest(icmp.do_build())
ip = IPv6(ip.do_build())
return eth/Dot1Q(vlan=0x185)/ip/icmp
frame = generate_frame()
hexdump(frame)
#frame.pdfdump(layer_shift = 1)
frame.getlayer(ICMPv6EchoRequest).show2()
print "CRC :"+ str(frame['ICMPv6EchoRequest'].cksum)
I get the result :
0000 00 50 56 9E 7B BB 00 50 56 9E 78 AA 81 00 01 85 .PV.{..PV.x.....
0010 86 DD 60 00 00 00 00 00 3B 40 20 02 C0 00 02 03 ..`.....;# .....
0020 00 00 00 00 00 00 00 00 00 AA 20 02 C0 00 02 03 .......... .....
0030 00 00 00 00 00 00 00 00 00 BB 80 00 00 00 07 92 ................
0040 00 01 74 65 73 74 ..test
###[ ICMPv6 Echo Request ]###
type = Echo Request
code = 0
cksum = 0x0
id = 0x792
seq = 0x1
data = 'test'
CRC :0
But the cksum attribute still not evaluated.
I don't understand my mistake.
Many thanks for your help
Don’t use the do_build function. It is a private function that should not be used (it is the second part of a 3-step building process).
Also, it is unnecessary to build each layer. You can just stack them and build the whole packet at the end.
To build an entire packet, call bytes() on it. Building a packet generates the checksums. A good option is to call Ether(bytes(packet)) to get the packet built
Use
def generate_frame():
eth = Ether()
eth.dst = "00:50:56:9E:7B:BB"
eth.src = "00:50:56:9E:78:AA"
eth.type = 0x8100
ip = IPv6()
ip.src = "2002:c000:0203:0000:0000:0000:0000:00AA"
ip.dst = "2002:c000:0203:0000:0000:0000:0000:00BB"
icmp =ICMPv6EchoRequest(seq=0x1, id=0x792)
icmp.data = "test"
packet = eth/Dot1Q(vlan=0x185)/ip/icmp
# Build and recalculate the whole packet
packet = Ether(bytes(packet))
return packet
It should fix your issue
Related
I want to understand why EDNS(0) resource records contains an extra octet? I read RFC 6891 and RFC 1035. It says nothing about case when RDLENGHT == 0 but RDATA == "\0".
To test this here python code
import binascii
import socket
def send_udp_message(message, address, port):
"""send_udp_message sends a message to UDP server
message should be a hexadecimal encoded string
"""
message = message.replace(" ", "").replace("\n", "")
server_address = (address, port)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
try:
sock.sendto(binascii.unhexlify(message), server_address)
data, _ = sock.recvfrom(4096)
finally:
sock.close()
return binascii.hexlify(data).decode("utf-8")
def format_hex(hex):
"""format_hex returns a pretty version of a hex string"""
octets = [hex[i:i+2] for i in range(0, len(hex), 2)]
pairs = [" ".join(octets[i:i+2]) for i in range(0, len(octets), 2)]
return "\n".join(pairs)
message = "AA AA 01 00 00 01 00 00 00 00 00 01 " \
"07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 "
# EDNS(0) resource record
message += "00 00 " # NAME
message += "29 00 " # TYPE
message += "FF 00 00 80 " # TTL
message += "00 00 " # RDLENGTH
# message += "00" # RDATA
response = send_udp_message(message, "8.8.8.8", 53)
print(format_hex(response))
Dns query returns here error. But if uncomment RDATA line it returns success.
You misread section §6.1.2 of RFC 6891, so the RFCs are not "lies".
It says:
+------------+--------------+------------------------------+
| Field Name | Field Type | Description |
+------------+--------------+------------------------------+
| NAME | domain name | MUST be 0 (root domain) |
| TYPE | u_int16_t | OPT (41) |
| CLASS | u_int16_t | requestor's UDP payload size |
| TTL | u_int32_t | extended RCODE and flags |
| RDLEN | u_int16_t | length of all RDATA |
| RDATA | octet stream | {attribute,value} pairs |
+------------+--------------+------------------------------+
so 6 pieces of information while your code has only 5 pieces:
# EDNS(0) resource record
message += "00 00 " # NAME
message += "29 00 " # TYPE
message += "FF 00 00 80 " # TTL
message += "00 00 " # RDLENGTH
# message += "00" # RDATA
You are missing the CLASS between TYPE and TTL, hence things are not interpreted the way you think they are.
You are also misreading how the bytes work for the name.
It is not:
00 00 NAME
29 00 TYPE
FF 00 00 80 TTL
00 00 RDLENGTH
but really:
00 NAME (root domain per EDNS(0) specification, which is a sole zero)
00 29 TYPE (41, per specification)
00 FF CLASS (255, considered as payload)
00 00 80 00 TTL, read as 00 = EXTENDED-CODE, 00 = VERSION (mandatory), 80 = DO set plus everything else 0 as the final 00 byte, per specification
00 RDLENGTH
and the final item RDLENGTH is then not properly formatted per the RFC 1035 specification as it is 2 bytes (16 bits).
Once you comment your last line, RDLENGTH becomes 00 00 and then is valid.
And there is indeed no RDATA part in your message.
What you believe being a 00 value in RDATA is in fact the last byte of RDLENGTH but you did not parse the stream correctly.
Had you used dnspython as advised to you, you would have seen the problem immediately with the proper mapping of fields:
In [1]: import dns
In [2]: import dns.message
In [10]: stream = 'AA AA 01 00 00 01 00 00 00 00 00 01 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 00 00 29 00 FF 00 00 80 00 00 00'
In [11]: data=''.join(chr(int(x, base=16)) for x in stream.split(' '))
In [12]: m = dns.message.from_wire(data)
In [13]: print m
id 43690
opcode QUERY
rcode NOERROR
flags RD
edns 0
eflags DO
payload 255
;QUESTION
example.com. IN A
;ANSWER
;AUTHORITY
;ADDITIONAL
Had you wanted to do that you could have simulated the expected bytes stream that way:
(starting from your message)
In [31]: m = dns.message.from_wire(data)
In [32]: print m
id 43690
opcode QUERY
rcode NOERROR
flags RD
edns 0
eflags DO
payload 255
;QUESTION
example.com. IN A
;ANSWER
;AUTHORITY
;ADDITIONAL
(creating a new one to look like yours)
In [39]: mm = dns.message.make_query('example.com.', 'A', use_edns=0, payload=255, want_dnssec=True)
In [40]: mm.id=43690
In [41]: print mm
id 43690
opcode QUERY
rcode NOERROR
flags RD
edns 0
eflags DO
payload 255
;QUESTION
example.com. IN A
;ANSWER
;AUTHORITY
;ADDITIONAL
(now looking at its wire representation)
In [46]: print ' '.join(hex(ord(d)) for d in mm.to_wire())
0xaa 0xaa 0x1 0x0 0x0 0x1 0x0 0x0 0x0 0x0 0x0 0x1 0x7 0x65 0x78 0x61 0x6d 0x70 0x6c 0x65 0x3 0x63 0x6f 0x6d 0x0 0x0 0x1 0x0 0x1 0x0 0x0 0x29 0x0 0xff 0x0 0x0 0x80 0x0 0x0 0x0
Comparing with your bytestream:
dnspython: AA AA 01 00 00 01 00 00 00 00 00 01 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 00 00 29 00 FF 00 00 80 00 00 00
you: AA AA 01 00 00 01 00 00 00 00 00 01 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 00 00 29 00 FF 00 00 80 00 00
Note the missing final 00 being in your commented line.
This shows that existing good libraries, as dnspython is, really help sometimes better understanding RFCs or other specifications. And in the world of DNS there are many RFCs, sometimes conflicting between each other, with ambiguous parts, etc. So using existing libraries for tests and/or studying their source code really helps, if you want this advice.
I want to generate gp secure channel 01. my trace is:
Send: 80 50 00 00 08 00 00 00 00 00 00 00 00
Recv: 00 00 00 00 00 00 00 00 00 00 FF 02 00 02 0E 5A 8F F4 57 DD 35 5C 49 A6 8B 15 E9 A5 9000
so I have :
Card challenge= 00 02 0E 5A 8F F4 57 DD
Host challenge=00 00 00 00 00 00 00 00
according SPC01: image
Derivation data== 8F F4 57 DD 00 00 00 00 00 02 0E 5A 00 00 00 00
IV=0000000000000000
c_ENC: 404142434445464748494A4B4C4D4E4F
according this image and 3Des online
session s_ENC= C72F032C8BAD55D4D2579295CCF0A6CA
now :
hot-auth_data = card challenge + host challenge + pad
host-auth= 00020E5A8FF457DD00000000000000008000000000000000
s_ENC=C72F032C8BAD55D4D2579295CCF0A6CA
IV=0000000000000000
===========
result= 93CC77E144488A031BFFCCC62EB3B5C233A485F8255FE90E
Host cryptogram= 33A485F8255FE90E
but when I send :
848200000833A485F8255FE90E
I have error 0x6700 in method SDInstruction in line
short len = sc.processSecurity(apdu);
public void process(APDU apdu) throws ISOException {
if (selectingApplet()) {
return;
}
byte[] buffer = apdu.getBuffer();
switch (buffer[ISO7816.OFFSET_INS]) {
case ISO7816.INS_SELECT:
select();
return;
case INS_INIT_UPDATE:
case INS_EXT_AUTH:
SDInstruction(apdu);
break;
}
}
private void SDInstruction(APDU apdu)
{
byte[] buf = apdu.getBuffer();
byte cla = buf[ISO7816.OFFSET_CLA];
byte ins = buf[ISO7816.OFFSET_INS];
apdu.setIncomingAndReceive();
if(ins == INS_INIT_UPDATE)
sc = GPSystem.getSecureChannel();
short len = sc.processSecurity(apdu);
apdu.setOutgoing();
apdu.setOutgoingLength(len);
apdu.sendBytes(ISO7816.OFFSET_CDATA, (short) len);
}
Your card is using SCP02 and not SCP01.
Given the response to the INITIALIZE UPDATE command:
00 00 00 00 00 00 00 00 00 00 FF 02 00 02 0E 5A 8F F4 57 DD 35 5C 49 A6 8B 15 E9 A5 9000
The highlighted part is the "Key Information" which contains:
"Key Version Number" -- in your trace 0xFF
"Secure Channel Protocol Identifier" -- in your trace it is 0x02 indicating SCP02
See the Global Platform Card Specification for further reference (sections describing the INITIALIZE UPDATE command).
So you need to establish the secure channel with the card according to the SCP02.
Some additional (random) notes:
be sure to check the "i" secure channel parameter encoded inside the "Card Recognition Data" (tag '64') as well
you might want to look at the method GlobalPlatform.openSecureChannel() and the inner class GlobalPlatform.SCP0102Wrapper in the GlobalPlatformPro tool source code
Good luck!
According to the GlobalPlatform specification, the EXTERNAL AUTHENTICATE command has to include the host cryptogram as well as the MAC. Both are 8 bytes long, hence, your command should be 16 bytes in total.
If you want to implement the generation of this MAC value yourself, you can follow the description in the GlobalPlatform spec. But I suggest you to make use of available open source implementation. For example: GPJ is a Java implementation of the GlobalPlatform specification and has all commands that you need. You can take a look at the class GlobalPlatformService, where you will find the implementation of the secure channel protocol. GPDroid (github.com/mobilesec/secure-element-gpdroid) is a wrapper for this project on Android.
I'm working to get useful data from a VISA (such as PAN, expiry date...) credit card using a list of AIDs I got stuck.
I have been able to access to all the data manually. Using the next tutorial: http://www.openscdp.org/scripts/tutorial/emv/reademv.html
>>00 A4 04 00 07 A0 00 00 00 03 10 10 00
In ASCII:
<<o<EM>„<BEL> <0><0><0><ETX><DLE><DLE>¥<SO>P<EOT>VISA¿<FF><ENQ>ŸM<STX><VT><LF><0>
In Hexadecimal:
<<6F 19 84 07 A0 00 00 00 03 10 10 A5 0E 50 04 56 49 53 41 BF 0C 05 9F 4D 02 0B 0A 90 00
After that I used:
>>33 00 B2 01 0C 00 //sfi1, rec1
...
...
>>33 00 B2 10 FC 00 //sfi31, rec16
I continued with the tutorial and learned that the proper way to obtain the data was using GPO (Get Processing Options) command. And tried that next:
>>80 A8 00 00 0D 83 0B 00 00 00 00 00 00 00 00 00 00 00 00 // pdo = 83 0B 00 00 00 00 00 00 00 00 00 00 00 which suposse to be the correct one for VISA.
<< 69 85
So the condition of use is not satisfied.
>> 80 A8 00 00 02 83 00 00 //pdo= 83 00 that should work with every non visa card
<< 80 0E 3C 00 08 01 01 00 10 01 04 00 18 01 03 01 90 00
If this response is correct and it looks quite well for me as it starts by 80 and ends by 90 00, I am not able to identify AFL which I think that would make me possible to determine the PAN, expiry date... Can somebody help me?
The FCI that you received in response to the select command (00 A4 0400 07 A0000000031010 00) decodes to
6F 19 (File Control Information (FCI) Template)
84 07 (Dedicated File (DF) Name)
A0000000031010
A5 0E (File Control Information (FCI) Proprietary Template)
50 04 (Application Label)
56495341 ("VISA")
BF0C 05 (File Control Information (FCI) Issuer Discretionary Data)
9F4D 02 (Log Entry)
0B0A (SFI = 11; # of records = 10)
This FCI does not include any PDOL (processing options data list). Consequently, you need to assume a default value for the PDOL (which is an empty list for your card type). Consequently, the PDOL-related data field in the GET PROCESSING OPTIONS command must be empty:
83 00
Where 0x83 is the tag for PDOL-related data and 0x00 is a length of zero bytes.
Thus, the correct GPO command is (as you already found out):
80 A8 0000 02 8300 00
You got the response
800E3C00080101001001040018010301 9000
This decodes to
80 0E (Response Message Template Format 1)
3C00 (Application Interchange Profile)
08010100 10010400 18010301 (Application File Locator)
Consequently, the Application File Locator contains the following three entries:
08010100: SFI = 1, first record = 1, last record = 1, records involved in offline data authentication = 0
10010400: SFI = 2, first record = 1, last record = 4, records involved in offline data authentication = 0
18010301: SFI = 3, first record = 1, last record = 3, records involved in offline data authentication = 1
Consequently, you can read those record with the READ RECORD commands:
00 B2 010C 00
00 B2 0114 00
00 B2 0214 00
00 B2 0314 00
00 B2 0414 00
00 B2 011C 00
00 B2 021C 00
00 B2 031C 00
During a fresh installation, I accidentally formatted a disk containing datas. I have tried using some tools: testdisk, foremost, but I did not get good results. (see my unsuccessful post on superuser).
So I have decided to read some docs about ext2 filesystem structure, and I could get some results:
The deleted partition have a directory tree like that:
dev
|-scripts
|-projects
|-services
|-...
Medias
|-downloads
|-Musique
|-...
backup
...
So, based on the ext2 directory entry format:
Directory Entry
Starting_Byte Ending_Byte Size_in_Bytes Field_Description
0 3 4 Inode
4 5 2 Total size of this entry (Including all subfields)
6 6 1 Name Length least-significant 8 bits
7 7 1 Type indicator (only if the feature bit for "directory entries have file type byte" is set, else this is the most-significant 8 bits of the Name Length)
8 8+N-1 N Name characters
I tried to find some datas matching this structure.
I used this script:
var bindexOf = require('buffer-indexof');
var currentOffset=0;
var deviceReadStream = fs.createReadStream("/dev/sdb");
deviceReadStream.on('error',function(err){
console.log(err);
});
deviceReadStream.on('data',function(data){
var dirs = ["dev","scripts","services","projects","Medias","downloads","Musique","backup"];
dirs.forEach(function(dir){
dirOctetFormat = new Buffer(2);
dirOctetFormat.writeUInt8(dir.length,0);
dirOctetFormat.writeUInt8(2,1);// type is directory
dirOctetFormat= Buffer.concat( [dirOctetFormat, new Buffer(dir)]);
var offset = bindexOf( data, dirOctetFormat );
if( offset >= 0 ){
console.log( dir + " entry found at offset " + (currentOffset + offset) );
}
});
currentOffset += data.length;
});
}
I found data which seems to be the directory entry of the dev directory:
===== Current offset: 233590226944 - 217.5478515625Gio ======
scripts entry found at offset 233590227030
services entry found at offset 233590227014
projects entry found at offset 233590228106
If it is the case, I got the inode numbers of its children directories: scripts, projects, services,...
But I do not know what to do with that!
I tried to deduce the location of these inodes, based on this guide,
but as I was unable to find a superblock of the deleted filesystem, I just have to make guesses about the block size, the number of blocks, ...
and that seems a little bit fuzzy to me to hope obtaining a result.
So could you have some intervals for all values needed to obtain the offset of an inode, and a more formal formula to get this offset?
If you have only erased the partition table (or modified it) you can still get your data, if data has not been reused for something else.
ext2 filesystems have a MAGIC number in superblock, so to recover your partition you have only to search for it. I did this on one machine and was able to recover not one, but seven partitions in one disk. You have some chances to get invalid numbers, but just search for that magic. Magic number is defined in include/uapi/linux/magic.h and value is #define EXT2_SUPER_MAGIC 0xEF53 (it's found at offset #define EXT2_SB_MAGIC_OFFSET 0x38 ---from file include/linux/ext2_fs.h)
To search for the superblock, just try to find 0xef53 at offset 0x38 in one sector of the disk, it will mark the first block of the partition. Be careful, that superblock is replicated several times in one partition, so you'll find all the copies of it.
Good luck! (I had when it happened to me)
Edit (To illustrate with an example)
Just see the magic number in one of my own partitions:
# hd /dev/sda3 | head -20
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000400 40 62 08 00 00 87 21 00 26 ad 01 00 f6 30 15 00 |#b....!.&....0..|
00000410 1d 31 08 00 00 00 00 00 02 00 00 00 02 00 00 00 |.1..............|
00000420 00 80 00 00 00 80 00 00 90 1f 00 00 cf 60 af 55 |.............`.U|
00000430 fc 8a af 55 2d 00 ff ff 53 ef 01 00 01 00 00 00 |...U-...S.......|<- HERE!!!
00000440 36 38 9d 55 00 00 00 00 00 00 00 00 01 00 00 00 |68.U............|
00000450 00 00 00 00 0b 00 00 00 00 01 00 00 3c 00 00 00 |............<...|
00000460 46 02 00 00 7b 00 00 00 5a bf 87 15 12 8f 44 3b |F...{...Z.....D;|
00000470 97 e7 f3 74 4d 75 69 12 72 6f 6f 74 00 00 00 00 |...tMui.root....|
00000480 00 00 00 00 00 00 00 00 2f 00 61 72 67 65 74 00 |......../.arget.|
00000490 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000004c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 18 02 |................|
000004d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000004e0 08 00 00 00 00 00 00 00 00 00 00 00 93 54 99 ab |.............T..|
000004f0 aa 64 46 b3 a6 73 94 34 a3 79 46 28 01 01 00 00 |.dF..s.4.yF(....|
00000500 0c 00 00 00 00 00 00 00 e5 61 92 55 0a f3 02 00 |.........a.U....|
00000510 04 00 00 00 00 00 00 00 00 00 00 00 ff 7f 00 00 |................|
00000520 00 80 10 00 ff 7f 00 00 01 00 00 00 ff ff 10 00 |................|
Remember it is on offset 0x38 counted from the block origin, and assume the super block is the second block (block 0 reserved for bootcode, so it will be block 1, with two sectors per block, to make 1k blocksize) in the partition, so you'll have to rewind 0x438 bytes from the beginning of the magic number to get the partition origin.
I have run the command on my whole disk, getting the following result:
# hd /dev/sda | grep " [0-9a-f][0-9a-f] 53 ef" | sed -e 's/^/ /' | head
006f05f0 ee 00 00 11 66 0a 00 00 53 ef 00 00 11 66 2d 00 |....f...S....f-.|
007c21d0 55 2a aa 7d f4 aa 89 55 53 ef a4 91 70 40 c1 00 |U*.}...US...p#..|
20100430 fc 8a af 55 2d 00 ff ff 53 ef 01 00 01 00 00 00 |...U-...S.......|
2289a910 0f 8f 4f 03 00 00 81 fe 53 ef 00 00 0f 84 ce 04 |..O.....S.......|
230d4c70 0a 00 00 00 1c 00 00 00 53 ef 01 00 00 00 00 00 |........S.......|
231b7e50 a0 73 07 00 00 00 00 00 53 ef 0d 00 00 00 00 00 |.s......S.......|
23dbd230 d5 08 ad 2b ee 71 07 8a 53 ef c2 89 d4 bb 09 1f |...+.q..S.......|
25c0c9e0 06 00 00 00 00 4f 59 c0 53 ef 32 c0 0e 00 00 00 |.....OY.S.2.....|
25d72ca0 b0 b4 7b 3d a4 f7 84 3b 53 ef ba 3c 1f 32 b9 3c |..{=...;S..<.2.<|
25f0eab0 f1 fd 02 be 28 59 67 3c 53 ef 9c bd 04 30 72 bd |....(Yg<S....0r.|
Clearly, there are much more uninteresting lines in this listing than the ones we need. To locate the one interesting here, we have to do some computing with the numbers. We have seen that sectors are 512 bytes long (this is 0x200 in hex) and we can have the superblock magic at offset 0x438, so we expect valid offsets to be at 0xXXXXXX[02468ace]38 only. Just select the lines with offsets ending in that expression, and you'll get the first superblock valid (in the third line) at offset 0x20100430.
Substract 0x430 to give the byte offset of the partition (0x20100000, and then, divide the result by 0x200, giving 0x100800, or 1050624)
# fdisk -l /dev/sda | sed -e 's/^/ /'
Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: DF97DAD4-727D-4BB3-BD7B-3C5A584A2747
Device Start End Sectors Size Type
/dev/sda1 2048 526335 524288 256M EFI System
/dev/sda2 526336 1050623 524288 256M BIOS boot
/dev/sda3 1050624 18628607 17577984 8.4G Linux filesystem <-- HERE!!!
/dev/sda4 18628608 77221887 58593280 28G Linux filesystem
/dev/sda5 77221888 85035007 7813120 3.7G Linux filesystem
/dev/sda6 85035008 104566783 19531776 9.3G Linux filesystem
/dev/sda7 104566784 135817215 31250432 14.9G Linux swap
/dev/sda8 135817216 155348991 19531776 9.3G Linux filesystem
/dev/sda9 155348992 1953523711 1798174720 857.4G Linux filesystem
I am trying to replicate a packet.
This packet:
2C 00 65 00 03 00 00 00 00 00 00 00 42 4C 41 5A
45 00 00 00 00 00 00 00 00 42 4C 41 5A 45......
2c 00 is the size of the packet...
65 00 is the packet id 101...
03 00 is the number of elements in the array...
Now here comes my problem, 42 4C 41 5A 45 is a string... There are exactly 3 Instances of that string in that packet if it is complete... But my problem is it is not just null terminated it has 00 00 00 00 spaces between those instances.
My code:
function channel_list(channels) {
var packet = new SmartBuffer();
packet.writeUInt16LE(101); // response packet for list of channels
packet.writeUInt16LE(channels.length)
channels.forEach(function (key){
console.log(key);
packet.writeStringNT(key);
});
packet.writeUInt16LE(packet.length + 2, 0);
console.log(packet.toBuffer());
}
But how do I add the padding?
I am using this package, https://github.com/JoshGlazebrook/smart-buffer/
Smart-Buffer keeps track of its position for you so you do not need to specify an offset to know where to insert the data to pad your string. You could do something like this with your existing code:
channels.forEach(function (key){
console.log(key);
packet.writeString(key); // This is the string with no padding added.
packet.writeUInt32BE(0); // Four 0x00's are added after the string itself.
});
I'm assuming you want: 42 4C 41 5A 45 00 00 00 00 42 4C 41 5A 45 00 00 00 00 etc.
Editing based on comments:
There is no built in way to do what you want, but you could do something like this:
channels.forEach(function (key){
console.log(key);
packet.writeString(key);
for(var i = 0; i <= (9 - key.length); i++)
packet.writeInt8(0);
});