Convert ASCII To Characters Manually?

JockVSJock · 08-12-2016, 02:31 PM

Is there a method or manual way to convert ASCII to characters without using a table?

dugan · 08-12-2016, 04:03 PM

You mean the numeric ASCII codes?

In C or C++, you just assign the number to a char variable.

JockVSJock · 08-12-2016, 06:00 PM

This is in reference to a blind sql injection attack example, where the sql statement is trying to determine if the first character of the database user is less than or equal to the letter B.

Code:

if (ascii(substring(user,1,1))<=66) waitfor delay '00:00:15'

Without looking at a chart like the following:

http://www.asciitable.com/

How can someone determine that the 66 correlates to the letter B?

dugan · 08-12-2016, 06:50 PM

Some ideas:

http://unix.stackexchange.com/a/92448
http://stackoverflow.com/q/890262/240515

The search term you want to use is "ordinal value to character" or something similar.

Or, just use the following Python 2 script:

Code:

#!/usr/bin/env python
import sys
print chr(int(sys.argv[1]))

Save it as "chr" and make it executable:

Then:

Code:

> chr 66
B

ntubski · 08-12-2016, 07:25 PM

Quote:

Originally Posted by JockVSJock

Without looking at a chart like the following:

http://www.asciitable.com/

How can someone determine that the 66 correlates to the letter B?

You can memorize the chart, or automate the lookup with a program as dugan suggested.

JockVSJock · 08-15-2016, 07:52 AM

Quote:

Originally Posted by ntubski

You can memorize the chart

That is what I'm after. Is there a way to work it out, say like convert ip address to binary and vice versa?

thanks

rtmistler · 08-15-2016, 08:47 AM

If you're talking about converting ASCII numbers to binary, why not:

Code:

input &= 0xdf; // optional for small letters
input -= 0x30;
if(input > 15) { input -= 7; }

I don't see any point to converting ASCII other values to binary. SPACE is 0x20, the value is "the value", what conversion would you do to that? Same thing for ASCII G, that is 0x47, what does G represent otherwise though? Meanwhile things like AF could be HEX AF which are ASCII { 0x41, 0x46 }, or in binary as decimal values they could be { A, F } or { 10, 15 }.

The other issue is what language? Because strictly C is one thing, and yes there are library functions, there are also very many library functions for C++, or C#, or Objective-C, or Java, ...

My example is me thinking from the perspective the code running without library support, no OS.

dugan · 08-15-2016, 09:36 AM

Quote:

Originally Posted by JockVSJock

That is what I'm after. Is there a way to work it out, say like convert ip address to binary and vice versa?

thanks

Paste them into a web app that does the conversion?

BTW, your "that's what I'm after" is completely different from what you were asking up until now. If you're trying to steer the answers by strategically omitting information, you should know that never works.

grail · 08-15-2016, 10:01 AM

My first question would be like some of the others, what language?

keefaz · 08-15-2016, 10:05 AM

Quote:

Originally Posted by JockVSJock

That is what I'm after. Is there a way to work it out, say like convert ip address to binary and vice versa?

thanks

You mean decompose the numbers into powers of two?

rtmistler · 08-15-2016, 10:37 AM

Quote:

Originally Posted by JockVSJock

That is what I'm after. Is there a way to work it out, say like convert ip address to binary and vice versa?

thanks

Missed this from earlier. I thought that was already in the inet library. For instance the sin_addr_t or addr_t structures I forget and not bothering to look it up, but one version requires a long which means you need it in binary, and another version takes is in w.x.y.z form. I recall something like inet_ntoa() and stuff like that. Just searching for example network code and viewing different examples will show these conversions or how to use a version that starts with an ASCII IP address and accepts it in that form. And I may be wrong about it being inet, if you just look at the various include files you need to add to do networking, it's in one or more of those include files.

ntubski · 08-15-2016, 01:44 PM

Quote:

Originally Posted by JockVSJock

Quote:

You can memorize the chart

That is what I'm after. Is there a way to work it out, say like convert ip address to binary and vice versa?

Converting IP addresses is essentially decimal <-> binary conversion. You have to memorize the meaning of 10 digits for that.

ASCII encoding is pretty much base-128, so you have to memorize 128 "digits". There are some patterns in the chart that can help you memorize it.

PTrenholme · 08-19-2016, 05:37 PM

Of course most modern system use UFT-8 encoding, not ASCII. So there are several different ways to represent, e.g., "B"

And your proposed test, even in an ASCII world, would not accomplish your stated goal. A test for N < 66 would accept a "B" and anything that followed B in the ASCII code table.

If you're really in an ASCII world, and the computer language you're using permits it, consider just using 'B' to represent 'B', and ignore the binary (or decimal, or ...) equivalents to that symbol. (I.e., What's the point in switching from one encoding scheme to some other one if the meaning of the symbol is all you care about?)

JockVSJock · 08-20-2016, 07:16 AM

Quote:

Originally Posted by dugan

BTW, your "that's what I'm after" is completely different from what you were asking up until now. If you're trying to steer the answers by strategically omitting information, you should know that never works.

I'm not trying to omit any information, it my lack of experience and understanding of the topic, which is why I'm not able to ask the question clearly.

At one time you were new to learning something too, so you probably weren't sure how to go about asking the right question either.

JockVSJock · 08-20-2016, 07:29 AM

Quote:

Originally Posted by grail

My first question would be like some of the others, what language?

One of the examples I'm seeing online pertain to using SQL, like the following:

Code:

1 and  
(
  select top 1 ascii(lower(substring(name, 1, 1))) from sysobjects where id=(
    select top 1 id from (
      select top 1 id from sysobjects where xtype='u' order by id
    ) sq order by id desc
  )
) > 109

https://www.troyhunt.com/everything-...now-about-sql/