I am trying to create a simple encryptation scheme for strings. Each character of the string is given another ascii value.
It entails writing ascii characters upto 246 to a simple file on disk.
I want to find out if it is safe to write these special characters to the disk or can it cause untoward results. Thanks for your help.
Edit: I am considering algorithm similar to following:
* Convert each character of string to its integer number (hence 110 for 'n' and 122 for 'z')
* Double that number (get 220 and 244)
* Convert this to character (will get extended ascii codes)
* Save these characters to file.
Is it safe to save these extended ascii characters to disk files using usual text file writing functions?
There is only a limited set of ASCII characters. There are 95 printable characters such as 'A' but also the space character. There are 33 printable characters such as Line Feed, Carriage Return, NUL but also DELETE. So you cannot use 246 characters of ASCII as there are only 128 total available. ASCII is strictly 7 bits giving you 2^7 = 128 possible values.
Even if you would use the ISO 8859 Latin character set or the Windows-1252 character set you would still have the unprintable control characters to deal with, leaving you with 256 - 33 - 5 characters or 218 characters. Windows-1252 still has 5 undefined characters.
What you can do is of course save your data as bytes. Each byte has 256 possible values (usually 0 to 255 or -128 to 127). As long as you open files as binary this pose no problem.
You can of course store as many characters in a file as you want, up to the file system or operating system limit. So I presume you didn't ask that.
Related
I have a 1.2 GB .csv file on my disk. I use R's filename = read.csv(path)-function and then I check the object size via object.size(filename) and it turns out, that it's 3721MB large. Why is this difference?
A CSV file is a plain text file and might look like this:
1,2,3,4
3,2,3,2
3,4,2,1
each character (ie digit and comma) is a byte. This file is 24 bytes big (there's an invisible "new line" character at the end of each row).
When read into R each number is stored as a floating point decimal number, which is 8 bytes. The file above would then be 8*24 (values) = 96 bytes big.
It can go the other way. If the above file was instead written:
1.0000000000, 2.0000000000, 3.00000000000, 4.000000000
[etc]
then in the CSV each number is taking about 12 bytes - each digit, decimal point, command and zero takes a byte - and when read in to R would still only take 8 bytes as floating point decimal values.
How do I know exactly what characters are used for the encrypted output using jasypt? Can I force that my output does not contain certain characters or are always all ASCII characters used?
Reason I am asking is that the encrypted text is part of a file with delimiters and I would like to avoid that this delimiter is part of the encrypted text. The delimiter should also not be a hidden character, like SOH, because the file can be edited manually.
"Base64 only uses 6 bits (corresponding to 2^6 = 64 characters) to ensure encoded data is printable and humanly readable. None of the special characters available in ASCII are used. The 64 characters (hence the name Base64) are 10 digits, 26 lowercase characters, 26 uppercase characters as well as '+' and '/'."
So, looks like I can use ASCII special characters as a delimiter.
I noticed that the symbol . doesn't represent the same hexadecimal number when I tried to tune my YARA rules that I run on VirusTotal. When I tried to exclude the false positive-generating text string .sample., it would not get excluded because . converted from text representation was 2E in this case, meanwhile in the string, that was actually contained in the false positives, . represented 00.
I assume that when the files are matched, text is converted to hex, the hex string is then matched in a hexdump of a file and the whole hexdump is converted to text in the VT preview.
Then I noticed that there were actually more hexadecimal numbers that were represented as . in VirusTotal's text preview. For example, 0A, 99, 09 (screenshot).
I tried seeing the text representation of these hex numbers using an online converter (http://www.unit-conversion.info/texttools/hexadecimal/) and some of them were represented as � or a blank symbol (not a space symbol, as the number 20, but just a blank space).
So my questions are - why do different numbers seem to represent the same symbol? In addition, what do the "blank spaces" represent in a file's hexdump?
The 0A characters are line feed characters, as can be seen from the table in this doc, while the 2E characters are actual periods.
As per this answer on the same issue:
These are whitespace characters, and if included literally would mess up the ASCII table. That's why they (as well as the unprintable control characters below 32, and any binary values above 127, which aren't defined by ASCII and would need another character set to be interpreted correctly) are represented by .
Essentially, the '.' character is a catch-all for things which can't be shown properly in the table.
As for the online converter, it appears to generate characters until 7F, after which ASCII's 128 bit implementation is no longer defined and the translator provides a � symbol. Even from 00 to 7F we find the translator has issues with a few hex values including the line feed character 0A.
The ASCII table linked earlier hints at a few characters which the translator might have trouble with, such the DEL character (7F), the bell (07), and ENQ (05).
I would expect that blank spaces are whitespace characters, this should be possible to verify in the ASCII table.
I'm having an encoding problem related to cookies on one of my websites.
A user is inputing Usuário, which has an acute accent, and that's being put in a cookie. The raw HEX for the cookie response is (for the Usuário string):
55 73 75 C3 A1 72 69 6F
When I see it in the browser, it looks like this:
...which is really messy. I need to fix this up.
Then I went to this website: http://www.rapidtables.com/convert/number/hex-to-ascii.htm and converted the HEX value to see how it would look like. And I got the same output:
Right. This means the HEX code is wrong. Then I tried to convert Usuário to ASCII to see how it should be. I used this WebSite: http://www.asciitohex.com/ and this is the result:
For my surprise, the HEX is exactly the one that is showing up messy. Why???
And how do I represent Usuário in ASCII so I can put it in a cookie? Should I manually encode it?
PS: I'm using ASP.NET, just in case it matters.
As of 2015 the standard of the web to store character data is UTF-8 and not ASCII. ASCII actually only contains the first 128 characters of the codepage, and does not include any kind of accented characters. To add accented characters to this 128 characters there were many legacy solutions: codepages. They each added 128 different characters to the default ASCII list thereby allowing representing 256 different characters.
The problem was, that this didn't properly solve the issue: ASCII based codepages were more or less incomatible with each other (except for the first 128 characters), and there was usually no way of programatically knowing which codepage was in used.
One of the solutions was UTF-8, which is a way to encode the unocde character set (containing most of the characters used around the world, and more) while trying to remain compatible with ASCII. The first 128 characters are actually the same in both cases, but afterwards UTF-8 characters become multi-byte: one character is encoded using a series of bytes (usually 2-3, depends on which character needs to be encoded)
The problem is if you are using some kind of ASCII based single byte codebase (like ISO-8859-1), which encodes supported characters in single bytes, but your input is actually UTF-8, which will encode accented characters in multiple bytes (you can see this in your HEX example. á is encoded as C3 A1: two bytes). If you try to read these two bytes in an ASCII based codepage, which uses single bytes for every characters (in West-Europe this codepage is usually ISO-8859-1), then each of this two bytes will be reprensented with two different characters.
In the web world the default encoding is UTF-8, so your clients will usually send their requests using UTF-8. ASP.NET is Unicode aware, so it can handle these requests. However somewere in your code this UTF-8 is converted acccidentally into ISO-8859-1, and then back into UTF-8. This might happen on various layers. As you have issues it probably happens at the cookie layer, which is sometimes problematic (here is how it worked in 2009). You should also double check your application that it uses UTF-8 everywhere else though (views, database, etc.), if you want to properly support accented characters.
What is the cause of certain characters to be blank when using XOR encryption? Furthermore, how can this be compensated for when decrypting?
For instance:
....
void basic_encrypt(char *to_encrypt) {
char c;
while (*to_encrypt) {
*to_encrypt = *to_encrypt ^ 20;
to_encrypt++;
}
}
will return "nothing" for the character k. Clearly, character decay is problematic for decryption.
I assume this is caused by the bit operator, but I am not very good with binary so I was wondering if anyone could explain.
Is it converting an element, k, in this case, to some spaceless ASCII character? Can this be compensated for by choosing some y < x < z operator where x is the operator?
Lastly, if it hasn't been compensated for, is there a realistic decryption strategy for filling in blanks besides guess and check?
'k' has the ASCII value 107 = 0x6B. 20 is 0x14, so
'k' ^ 20 == 0x7F == 127
if your character set is ASCII compatible. 127 is \DEL in ASCII, which is a non-printable character, so won't be displayed if you print it out.
You will have to know the difference between bytes and characters to understand which is happening. On the one hand you have the C char type, which is simply a presentation of a byte, not a character.
In the old days each character was mapped to one byte or octet value in a character encoding table, or code page. Nowadays we have encodings that take more bytes for certain characters, e.g. UTF-8, or even encodings that always take more than one byte such as UTF-16. The last two are unicode encodings, which means that each character has a certain number value and the encoding is used to encode this number into bytes.
Many computers will interpret bytes in ISO/IEC 8859-1 or Latin-1, sometimes extended by Windows-1252. These code pages have holes for control characters, or byte values that are simply not used. Now it depends on the runtime system how these values are handled. Java by default substitutes an ? character in place of the missing character. Other runtimes will simply drop the value or - of course - execute the control code. Some terminals may use the ESC control code to set the color or to switch to another code page (making a mess of the screen).
This is why ciphertext should be converted to another encoding, such as hexadecimals or Base64. These encodings should make sure that the result is readable text. This takes care of the cipher text. You will have to choose a character set for your plain text too, e.g. simply perform ASCII or UTF-8 encoding before encryption.
Getting a zero value from encryption does not matter because once you re-xor with the same xor key you get the original value.
value == value
value XOR value == 0 [encryption]
( value XOR value ) XOR value == value [decryption]
If you're using a zero-terminated string mechanism, then you have two main strategies for preventing 'character degradation'
store the length of the string before encryption and make sure to decrypt at least that number of characters on decryption
check for a zero character after decoding the character