Question

I am able to generate SHA-1 hash for a whole file. I did this using Open SSL through the following C++ code.

file_buffer = mmap(0, file_size, PROT_READ, MAP_SHARED, file_name, 0); 
SHA1((unsigned char*) file_buffer, file_size, hash_value);

But I want to create separate hash values for smaller chunks of the file.

Consider,

File Size  = 10KB and 
Chunk Size = 2KB

In this case, I want to generate 5 hash values for each chunk of the file. How can I do this?

Answer 1

file_buffer = mmap(0, file_size, PROT_READ, MAP_SHARED, file_name, 0); 

SHA1((unsigned char*) file_buffer, 2048, hash_value_1);
SHA1((unsigned char*) (file_buffer+2048), 2048, hash_value_2);
//...