Hi,
I'm currently working on my masterthesis and encounter the next problem
with openssl.
I want to generate a bitstring of a given size, constructed on a given
word using SHA1 hash functions. Just by performing SHA1 on the word and
concat to that with the SHA1 of the previous SHA1 result.
for example. I want a 450bit string, generated by the word "test"
> SHA1("test")|SHA(SHA1("test"))|SHA1(SHA(SHA1("test")))
should give me a 480bit string.
When I try to implement and test this,for example 19000bits on
"testphrase", I noticed that something goes wrong with the SHA1 output now
and then. SHA1 outputs 20 bytes almost all time, witch I expect, but
sometimes it output a hash that differs from 20bytes ?
I theire something wrong with my code ? Or is this normal ?
unsigned char* genSha1Key(unsigned char* word, int bitsize)
{
printf("Generating Sha1Key from given string...\n");
unsigned char* hashcode = NULL;
unsigned char* result = NULL;
int sha1_count = ((int) (bitsize/160))+1; // = ceil()
hashcode =(unsigned char*)malloc(20);
result =(unsigned char*)malloc(20*sha1_count);
SHA1((const unsigned char*)word,strlen(word), hashcode);
result = strcpy(result,hashcode);
printf("%i byte code generated\n> Result is now %i bytes
long\n",strlen(hashcode),strlen(result));
while(sha1_count>1)
{
SHA1((const unsigned char*)hashcode,strlen(hashcode), hashcode);
strcat(result,hashcode);
printf("%i byte code generated\n> Result is now %i bytes
long\n",strlen(hashcode),strlen(result));
sha1_count--;
}
free(hashcode);
printf("asked %i bits and generated %i bits\n",bitsize,(strlen(result)*8));
return result;
}
Thanks for your time
Grtz
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