Warm$-$Up $9\mathrm{.}1$: Hashing Strings

Start Assignment

Due Oct $27$ by $11$:$59$pm

Points $0$

Submitting a text entry box or a file upload

File Types c

Available until Dec $1$ at $11$:$59$pm

Introduction

For this program you will be generating MD$5$ hashes of strings. This program will make use of concepts we have been learning:

Command line arguments

Reading and writing files

Linking to libraries

Multi$-$file compilation

We will be using the MD$5$ hashing algorithm which, as discussed in the live session, creates $128-$bit hashes. By convention, the hashes are represented as a string of $32$ hexadecimal digits.

Specification

The program, called makehash, will accept two command line arguments:

The source file name to read plaintext from

The destination file name to write hashes to

If the user doesn't supply these two filenames, an appropriate error message should be displayed and the program exits with status code $1.$

Each line in the source file is read in$,$ hashed, and the hash written to the destination file. Each input line should have its newline, if present, trimmed off before hashing.

Using the md$5$ function

The md$5$ function is contained in the md$5.$c file. A corresponding function prototype is in the md$5.$h header file. To use the md$5$ function in your program, #include the md$5.$h header file to make the function prototype available. For most people viewing this page, the contents of the files can be found in the tabs below.

To generate an MD$5$ hash, call the md$5$ function, passing in two parameters:

The string to be hashed;

The length of the string.

The function returns to the caller a string containing the $32-$character hexadecimal hash. The character array is malloc'd by the md$5$ function; it is the caller's responsibility to free the memory when it is no longer needed.

Compiling your program

Your program will consist of two source files that need to be compiled together to make an executable. Neither of them, individually, is a complete program. Additionally, the md$5$ function internally calls additional functions from the libcrypto library. This will need to be linked in to your program.

To compile your program, use this command line:

clang makehash.c md$5.$c $-$l crypto

Note: the crypto library is included in your Theia environment. In other environments $($for example, Ubuntu Linux or Mac OS X$),$ the libraries you need may be different.

What to Turn In

For this assignment, just submit your makehash.c file. You don't need to submit any of the other files that were needed to compile this program.

Files

Test File $1$

Use this short text file a source for strings to hash.

dinosaur pineapple SpongeBob rockstar Burger King May the Force be with you.

When run through your$$program$,$ the output should appear as below.

$03318769$a$5$ee$1354$f$7479$acc$69755$e$7$c $9$dee$45$a$24$efffc$78483$a$02$cfcfd$834335703038$ffb$5$c$1$a$34$b$391111460$c$74586$ d$2$feb$9$b$6718$bb$374$dfdd$68938067695469489$b$9$a$664$e$43$bf$088$e$8$ccea$3$e$545869$c$1$bd$15$cd$9811$efab$188647$a$1323$abb$7$

Test File $2$

I ate a clock yesterday, it was very time$-$consuming. Did you hear about the monkeys who shared an Amazon account? They were Prime mates. Two guys stole a calendar. They got six months each. What do you call a thieving alligator? A Crookodile.

Here are the resulting hashes:

$1074$e$0$e$8021422$f$759204$f$5$b$7$b$35$cb$3$e $69$f$3$d$9$e$428$eec$55$d$73$d$851395413$bb$9$e $80349245$c$053$a$9$a$85956852$ffce$248$dd c$7$feb$25$f$95$ff$7630$bd$528983$fd$82$da$5$e $32$c$7620215$eeeae$8946$efae$725$cbf$342$

md$5.$c

#include #include #include #include char $*$md$5($const char $*$str$,$ int length$)\{$ EVP$\_$MD$\_$CTX $*$mdctx; unsigned int md$5\_$digest$\_$len $=$ EVP$\_$MD$\_$size$($EVP$\_$md$5())$; uint$8\_$t md$5\_$digest$[$md$5\_$digest$\_$len$]$; char $*$hexdigest $=($char $*)$ malloc$($md$5\_$digest$\_$len $*2+1)$; $//$ MD$5\_$Init mdctx $=$ EVP$\_$MD$\_$CTX$\_$new$()$; EVP$\_$DigestInit$\_$ex$($mdctx$,$ EVP$\_$md$5(),$ NULL$)$; $//$ MD$5\_$Update while $($length $>0)\{$ if $($length $>512)\{$ EVP$\_$DigestUpdate$($mdctx$,$ str$,512)$; $\}$ else $\{$ EVP$\_$DigestUpdate$($mdctx$,$ str$,$ length$)$; $\}$ length $-=512$; str $+=512$; $\}//$ MD$5\_$Final EVP$\_$DigestFinal$\_$ex$($mdctx$,$ md$5\_$digest, &md$5\_$digest$\_$len$)$; EVP$\_$MD$\_$CTX$\_$free$($mdctx$)$; for $($int n $=0$; n $<$ md$5\_$digest$\_$len; $++$n$)\{$ snprintf$($hexdigest $+$ n$*2,3,"\%02$x$",$ md$5\_$digest$[$n$])$; $\}$ hexdigest$[$md$5\_$digest$\_$len $*2]=\text{'}\backslash 0\text{'}$; return hexdigest; $\}$

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md$5.$h

$/**$ Create an MD$5$ hex digest from a string. $*33-$byte string is malloc'd by this function. The caller must free it$.*$ When compiling, link to: $-$l crypto $*/$ char $*$md$5($const char $*$str$,$ int length$)$;

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