I'am using JPOS to pack iso8583 messages.
I am using a GenericPackager. In the definition of each field, whatvis the difference between :
IFB_NUMERIC vs IFB_LLNUM ?
IF_CHAR vs IF_LLCHAR ?
Thank you all for time.
Julien
IFB_NUMERIC it's a fixed length field.
IFB_LLNUM it's a field whose length is represented by a byte in BCD.
IF_CHAR vs IF_LLCHAR is analogous but the length is in two decimal digits represented in ascii.
Related
Long story short, I am trying to convert strings of hex values to signed 2's complement integers. I was able to do this in a single line of code in Swift, but for some reason I can't find anything analogous in Kotlin. String.ToInt or String.ToUInt just give the straight base 16 to base 10 conversion. That works for some positive values, but not for any negative numbers.
How do I know I want the signed 2's complement? I've used this online converter and according to its output, what I want is the decimal from signed 2's complement, not the straight base 16 to base 10 conversion that's easy to do by hand.
So, "FFD6" should go to -42 (correct, confirmed in Swift and C#), and "002A" should convert to 42.
I would appreciate any help or even any leads on where to look. Because yes I've searched, I've googled the problem a bunch and, no I haven't found a good answer.
I actually tried writing my own code to do the signed 2's complement but so far it's not giving me the right answers and I'm pretty at a loss. I'd really hope for a built in command that does it instead; I feel like if other languages have that capability Kotlin should too.
For 2's complement, you need to know how big the type is.
Your examples of "FFD6" and "002A" both have 4 hex digits (i.e. 2 bytes). That's the same size as a Kotlin Short. So a simple solution in this case is to parse the hex to an Int and then convert that to a Short. (You can't convert it directly to a Short, as that would give an out-of-range error for the negative numbers.)
"FFD6".toInt(16).toShort() // gives -42
"002A".toInt(16).toShort() // gives 42
(You can then convert back to an Int if needed.)
You could similarly handle 8-digit (4-byte) values as Ints, and 2-digit (1-byte) values as Bytes.
For other sizes, you'd need to do some bit operations. Based on this answer for Java, if you have e.g. a 3-digit hex number, you can do:
("FD6".toInt(16) xor 0x800) - 0x800 // gives -42
(Here 0x800 is the three-digit number with the top bit (i.e. sign bit) set. You'd use 0x80000 for a five-digit number, and so on. Also, for 9–16 digits, you'd need to start with a Long instead of an Int. And if you need >16 digits, it won't fit into a Long either, so you'd need an arbitrary-precision library that handled hex…)
I am using jPOS for creating ISO8583 message, I am using the genericpackager but it seems it only support data fields of fixed length. I want to prepend the length of the field before the field if it has a variable size.
I am using below:
<isofield
id="34"
length="32"
name="Extended Primary Account Number"
class="org.jpos.iso.IF_CHAR"/>
and in .java fileisoMsg.set(34, "12345ABCDE");
What change do I need to make to prepend the length of the field before the field.
For each isofield - you need to modify the class to match the requirements for the appropriate field configuration.
http://jpos.org/doc/javadoc/org/jpos/iso/packager/GenericPackager.html
For instance you can use any of the isofield classes with a Length indicator (L)
such as:
class="org.jpos.iso.IFA_LLCHAR"/>
Or
class="org.jpos.iso.IFB_LLNUM"/>
to support a variable length field.
Where the first example is ASCII 2 byte Length and the second one is Binary 2 byte Length.
you can find a list of sample generic packagers here: https://github.com/jpos/jPOS/tree/master/jpos/src/dist/cfg/packager
you can find a list of isofield classes (start with IF_) here: https://github.com/jpos/jPOS/tree/master/jpos/src/main/java/org/jpos/iso
I am a little confused, with the PUBDEF record in the OMF object format.
My assembler has generated a result which states the record is 4000 bytes, when it clearly is not so why would it do this?
Image of Hex view of OMF
The 0xa0 and 0x0f is the record length in little endian format,
please view the specificaiton: http://pierrelib.pagesperso-orange.fr/exec_formats/OMF_v1.1.pdf
It also appears to state that the strings are zero bytes in length and at one point even has just a zero string length with no string provided. Maybe I am reading the file wrong? I have spent hours now and am struggling.
If anyone can help me with my issue as I am writing a linker and cannot continue without understanding this.
Thanks
There is no PUBDEF record in the file. You seem to have miscalculated the previous record size:
0000:80 THEADR
000e:88 CoMENT
0032:96 LNAMES
0041:98 SEGDEF
004B:98 SEGDEF
0055:88 COMENT
005C:a0 LEDATA
006E:a0 LEDATA
007b:8a MODEND
Learn to use more sofisticated tools for OMF inspection, such as Tdump.exe or ODU.exe.
I am a developer using high level languages. I usually take the lower level details for granted.
I read that standards such as ASCII and Unicode are for character encodings. A character has to be stored as a number. Is this the same for numbers? For example, if I declare a variable in .NET like this:
dim test as integer=5
In this case the value of test (5) will be represented as decimal: 49 according to this table. Is that correct?
If you code Dim test As String = "5" the value will be stored using the Unicode encoding for the character "5". However, Integers (and other numeric types) are not strings and are not encoded in that way, they are represented internally using their numeric value. An Integer is stored as a 32 bit value.
what you are asking about is data representation in memory.The way integers are represented depends on the whether they are signed or unsigned. IF they are signed (usually the case, unless you specify type as unsigned int or something equvalent) they are represented in binary in two's complement form: http://en.wikipedia.org/wiki/Two%27s_complement
When we are using cryptography always we are seeing byte arrays are being used instead of String values. But when we are looking at the techniques of most of the cryptography algorithms they uses hex values to do any operations. Eg. AES: MixColumns, SubBytes all these techniques(I suppose it uses) uses hex values to do those operations.
Can you explain how these byte arrays are used in these operations as hex values.
I have an assignment to develop a encryption algorithm , therefore any related sample codes would be much appropriate.
Every four digits of binary makes a hexadecimal digit, so, you can convert back and forth quite easily (see: http://en.wikipedia.org/wiki/Hexadecimal#Binary_conversion).
I don't think I full understand what you're asking, though.
The most important thing to understand about hexadecimal is that it is a system for representing numeric values, just like binary or decimal. It is nothing more than notation. As you may know, many computer languages allow you to specify numeric literals in a few different ways:
int a = 42;
int a = 0x2A;
These store the same value into the variable 'a', and a compiler should generate identical code for them. The difference between these two lines will be lost very early in the compilation process, because the compiler cares about the value you specified, and not so much about the representation you used to encode it in your source file.
Main takeaway: there is no such thing as "hex values" - there are just hex representations of values.
That all said, you also talk about string values. Obviously 42 != "42" != "2A" != 0x2A. If you have a string, you'll need to parse it to a numeric value before you do any computation with it.
Bytes, byte arrays and/or memory areas are normally displayed within an IDE (integrated development environment) and debugger as hexadecimals. This is because it is the most efficient and clear representation of a byte. It is pretty easy to convert them into bits (in his mind) for the experienced programmer. You can clearly see how XOR and shift works as well, for instance. Those (and addition) are the most common operations when doing symmetric encryption/hashing.
So it's unlikely that the program performs this kind of conversion, it's probably the environment you are in. That, and source code (which is converted to bytes at compile time) probably uses a lot of literals in hexadecimal notation as well.
Cryptography in general except hash functions is a method to convert data from one format to another mostly referred as cipher text using a secret key. The secret key can be applied to the cipher text to get the original data also referred as plain text. In this process data is processed in byte level though it can be bit level as well. The point here the text or strings which we referring to are in limited range of a byte. Example ASCII is defined in certain range in byte value of 0 - 255. In practical when a crypto operation is performed, the character is converted to equivalent byte and the using the key the process is performed. Now the outcome byte or bytes will most probably be out of range of human readable defined text like ASCII encoded etc. For this reason any data to which a crypto function is need to be applied is converted to byte array first. For example the text to be enciphered is "Hello how are you doing?" . The following steps shall be followed:
1. byte[] data = "Hello how are you doing?".getBytes()
2. Process encipher on data using key which is also byte[]
3. The output blob is referred as cipherTextBytes[]
4. Encryption is complete
5. Using Key[], a process is performed over cipherTextBytes[] which returns data bytes
6 A simple new String(data[]) will return string value of Hellow how are you doing.
This is a simple info which might help you to understand reference code and manuals better. In no way I am trying to explain you the core of cryptography here.