How to get last 64 bits of SHA1 function?

Question

I am working on project which requires distribution of files on different servers. For the distribution scheme I chose to use SHA1 algorithm and take the last 64 bits (out of 160 bits hash) to identify the file.

I am not sure if it is my fault or not but I am not able to get as an int a stable value of the last 64 bit of the hash.

What I tried is this:

   char *plaintext = "file";
   size_t len = strlen(plaintext);
   char hash[41];

   /*hash contains the hash of the file as char* */
   plaintext_to_sha1(hash, plaintext, len);

   /*get last 64 bits of the hash*/
   uint64_t  value = (uint64_t)(hash + (24 * sizeof(char)));
   printk(LOG_LEVEL "value: %llu\n", value);

The value contained by value is sometimes different and I do not understand what I am doing wrong. I am taking the last 64 bits by casting to int the hash shifted 24 bytes to the right.

Any suggestions are appreciated.

Answer 1

Use following :

memcpy(&value,hash+12,8);