SHA256 Loop

Task

Implement the main function

• Read strings from stdin in a loop (one per line) and print the SHA256 hash of each string in lowercase hexadecimal format
• The loop should continue until EOF (end of file)

IMPORTANT

Must compile with the -lcrypto flag to link the OpenSSL library

gcc sha256_loop.c -o sha256_loop -lcrypto

Using SHA256

#include <openssl/sha.h>
 
unsigned char hash[32];  // SHA256 produces 32 bytes
SHA256((unsigned char*)my_string, strlen(my_string), hash);
 
// Print as lowercase hex (2 hex digits per byte = 64 characters total)
for(int i = 0; i < 32; i++) {
    printf("%02x", hash[i]);
}
printf("\n");

---

Test

$ gcc sha256_loop.c -o sha256_loop -lcrypto
$ ./sha256_loop
password
5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8
hello
2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
CSE29
8c0d6f3f5bcfed5043c0b854560dfcc3f2857a5c2d0d98d0b8f5d64c35b44aef
<Press Ctrl-D for end of input>
$ ./sha256_loop < small_input.txt
5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8
2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824
8c0d6f3f5bcfed5043c0b854560dfcc3f2857a5c2d0d98d0b8f5d64c35b44aef
$ # The next command is how you should create the output files
$ # It will result in a new file with the output from running ./sha256_loop, which
$ # the grader will check for
$ ./sha256_loop < small_input.txt > small_result.txt
$ ./sha256_loop < input.txt > result.txt

---

Code

#include <stdio.h>
#include <string.h>
#include <openssl/sha.h>
 
int main() {
    char buffer[1000];
    while(1){
        char* maybe_eof = fgets(buffer, sizeof(buffer), stdin);
        if(maybe_eof == NULL) { break; }
 
        size_t len = strlen(buffer);
        if(len > 0 && buffer[len - 1] == '\n') { buffer[len - 1] = 0; }
 
        unsigned char hash[32];
        SHA256((unsigned char*) buffer, strlen(buffer), hash);
        for(int i = 0; i < 32; i++){
            printf("%02x", hash[i]);
        }
        printf("\n");
    }
 
    return 0;
}