Problem - Kevin Tafuro

#include
int main(int argc, char *argv[ ]) {
int i, ol;
EVP_MD_CTX ctx;
unsigned char result[EVP_MAX_MD_SIZE]; /* enough for any hash function */
unsigned char *s1 = "Testing";
unsigned char *s2 = "...1...2...3...";
/* Note the extra parameter */
EVP_DigestInit(&ctx, EVP_sha1( ));
EVP_DigestUpdate(&ctx, s1, strlen(s1));
EVP_DigestUpdate(&ctx, s2, strlen(s2));
/* Here, the context object is first. Notice the pointer to the output length */
EVP_DigestFinal(&ctx, result, &ol);
printf("SHA1(\"%s%s\") = ", s1, s2);
for (i = 0; i < ol; i++) printf("%02x", result[i]);
printf("\n");
return 0;
}
Note particularly that EVP_DigestFinal( ) requires you to pass in a pointer to an integer,
into which the output length is stored. You should use this value in your computations
instead of hardcoding SHA1’s digest size, under the assumption that you
might someday have to replace crypto algorithms in a hurry, in which case the digest
size may change. For that reason, allocate EVP_MAX_MD_SIZE bytes for any buffer into
which you store a message digest, even if some of that space may go unused.
Alternatively, if you’d like to allocate a buffer of the correct size for output dynamically
(which is a good idea if you’re space-constrained, because if SHA-512 is ever
added to OpenSSL, EVP_MAX_MD_SIZE will become 512 bits), you can use the function
EVP_MD_CTX_size( ), which takes a context object and returns the size of the digest.
For example:
#include
#include
#include
#include
int main(int argc, char *argv[ ]) {
int i, ol;
EVP_MD_CTX ctx;
unsigned char *result;
unsigned char *s1 = "Testing";
unsigned char *s2 = "...1...2...3...";
EVP_DigestInit(&ctx, EVP_sha1( ));
EVP_DigestUpdate(&ctx, s1, strlen(s1));
EVP_DigestUpdate(&ctx, s2, strlen(s2));
if (!(result = (unsigned char *)malloc(EVP_MD_CTX_block_size(&ctx))))abort();
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