On 09/01/2010 11:38 AM, Benjamin GIGON via RT wrote:
> Hello,
> I used SHA1 functions to create HMAC fingerprint
> It is a very simple prog:
>[snip]
> while( !feof(fh) ) {
> retval = fread((char*)content, 1, 4096, fh);
> printf("Read:%d\n", retval);
> SHA1_Update(&ctx, content, retval);
> }
>
> SHA1_Final(message_digest, &ctx);
> puts((char *)message_digest);
This is the problem. puts prints zero terminated string of ASCII.
SHA1_Final returns a unsigned char buffer of non-ASCII data.
Use fwrite(message_digest, SHA_DIGEST_LENGTH, 1, stdout) to write
the binary data, or something like:
for (i = 0; i < SHA_DIGEST_LENGTH; i++)
printf("%02x", message_digest[i]);
printf("\n");
To print the hex dump of the hash (which is likely what you wanted).
> I read file and I create a message digest with SHA1_Final;
> For 99,99% of files, I have a good message digest
I'm pretty sure you get other weird results too. Likely the number
of bytes the fputs prints can vary depending if the hash a zero byte
in it. It can also print random characters under certain
non-deterministic circumstances.
> But, recently I tried to create a message digest for a file and my software
> doesn't work.
> I've tried to understand and I've seen that SHA1_Final gives an empty
> message_digest
>
> File available here: http://team.lea-linux.org/prae/fichier.bin
> MD5SUM: 9bda8cfe9fef3a6fb94cc3836e0ad993
And the sha1sum starts with '00...'. Your program interprets it as zero
length strings due to bad usage of fputs.
- Timo
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