/0 char within a char array?

bryon · 05-02-2009, 08:42 PM

I am working on converting this C++ code into C so that I can optimize it with the CUDA architecture. Long story short I am running into problems with strings.

The PBKDF2 spec section I am having trouble with is below

Code:

where

     U_1 = PRF (P, S || INT (i)) ,
     U_2 = PRF (P, U_1) ,
     ...
     U_c = PRF (P, U_{c-1}) .

     Here, INT (i) is a four-octet encoding of the integer i, mostsignificant octet first.

So in the first round given a salt of "mysalt" the resulting 'key' passed to the HMAC function should be "mysalt0001" except the numbers 0001 are characters (and the char 0 is the same thing as'\0') which cases the end of the string prematurly. This worked fine with the C++ implementation using strings that accepted the '\0' and did not truncate the string. In my C implementation the char array is passed to HMAC and the trailing char's are lost.

I tried using other values, like '0' which didnt work because its value was not actually 0. Thank you for any help.

Some of the code.

Code:

     char U[14+5];  // my test salt is 14 characters
     char appended[] = {(char)0, (char)0, (char)0, (char)i, '\0'};

     strcpy(U,S);
     for (j=0;j<5;++j)
     {
          U[14+j] = appended[j];
     }

Then later HMAC is called...

Code:

     HMAC(U,P);

HMAC's header...

Code:

void HMAC(char* text, char* key)

I have verified and tested my versions of HMAC and SHA1
hmac_sha1.c

quzah · 05-02-2009, 08:49 PM

You can have null characters in your arrays of characters, if you treat them as that: arrays of charaters, and not as strings. That means no using string functions, and passing the actual size of the array along to whatever function uses it.

So stop treating them as strings, and start treating them as arrays of characters of a specified size, and you should be fine.

Quzah.

bryon · 05-02-2009, 11:03 PM

Thank you!

That and a few corrected wrong turns made it all work.
Also, thanks for your quick reply, I've been working feverishly since your post and it all works now.

05-02-2009, 08:42 PM	#1
bryon Registered User Join Date: May 2009 Posts: 2	/0 char within a char array? I am working on converting this C++ code into C so that I can optimize it with the CUDA architecture. Long story short I am running into problems with strings. The PBKDF2 spec section I am having trouble with is below Code: where U_1 = PRF (P, S \|\| INT (i)) , U_2 = PRF (P, U_1) , ... U_c = PRF (P, U_{c-1}) . Here, INT (i) is a four-octet encoding of the integer i, mostsignificant octet first. So in the first round given a salt of "mysalt" the resulting 'key' passed to the HMAC function should be "mysalt0001" except the numbers 0001 are characters (and the char 0 is the same thing as'\0') which cases the end of the string prematurly. This worked fine with the C++ implementation using strings that accepted the '\0' and did not truncate the string. In my C implementation the char array is passed to HMAC and the trailing char's are lost. I tried using other values, like '0' which didnt work because its value was not actually 0. Thank you for any help. Some of the code. Code: char U[14+5]; // my test salt is 14 characters char appended[] = {(char)0, (char)0, (char)0, (char)i, '\0'}; strcpy(U,S); for (j=0;j<5;++j) { U[14+j] = appended[j]; } Then later HMAC is called... Code: HMAC(U,P); HMAC's header... Code: void HMAC(char* text, char* key) I have verified and tested my versions of HMAC and SHA1 hmac_sha1.c Last edited by bryon; 05-02-2009 at 08:46 PM.
bryon is offline

05-02-2009, 08:49 PM	#2
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 10,259	You can have null characters in your arrays of characters, if you treat them as that: arrays of charaters, and not as strings. That means no using string functions, and passing the actual size of the array along to whatever function uses it. So stop treating them as strings, and start treating them as arrays of characters of a specified size, and you should be fine. Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

05-02-2009, 11:03 PM	#3
bryon Registered User Join Date: May 2009 Posts: 2	Thank you! That and a few corrected wrong turns made it all work. Also, thanks for your quick reply, I've been working feverishly since your post and it all works now.
bryon is offline

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