Problem - Kevin Tafuro

HMAC_CTX c;
unsigned long ctr = 0, nbo_ctr;
size_t tl, i;
unsigned char last[HMAC_OUT_LEN];
while (ol >= HMAC_OUT_LEN) {
HMAC_Init(&c, base, bl, EVP_sha1( ));
HMAC_Update(&c, dist, dl);
nbo_ctr = htonl(ctr++);
HMAC_Update(&c, (unsigned char *)&nbo_ctr, sizeof(nbo_ctr));
HMAC_Final(&c, out, &tl);
out += HMAC_OUT_LEN;
ol -= HMAC_OUT_LEN;
}
if (!ol) return;
HMAC_Init(&c, base, bl, EVP_sha1( ));
HMAC_Update(&c, dist, dl);
nbo_ctr = htonl(ctr);
HMAC_Update(&c, (unsigned char *)&nbo_ctr, sizeof(nbo_ctr));
HMAC_Final(&c, last, &tl);
for (i = 0; i < ol; i++)
out[i] = last[i];
}
Here is an example implementation of a PRF based on HMAC-SHA1, using the Windows
CryptoAPI for HMAC (discussed in Recipe 6.10). The code presented here also
requires SpcGetExportableContext( ) and SpcImportKeyData( ) from Recipe 5.26.
#include
#include
#define HMAC_OUT_LEN 20 /* SHA1 specific */
static DWORD SwapInt32(DWORD dwInt32) {
__asm mov eax, dwInt32
__asm bswap eax
}
BOOL SpcMakeDerivedKey(BYTE *pbBase, DWORD cbBase, BYTE *pbDist, DWORD cbDist,
BYTE *pbOut, DWORD cbOut) {
BYTE pbLast[HMAC_OUT_LEN];
DWORD cbData, dwCounter = 0, dwBigCounter;
HCRYPTKEY hKey;
HMAC_INFO HMACInfo;
HCRYPTHASH hHash;
HCRYPTPROV hProvider;
if (!(hProvider = SpcGetExportableContext( ))) return FALSE;
if (!(hKey = SpcImportKeyData(hProvider, CALG_RC4, pbBase, cbBase))) {
CryptReleaseContext(hProvider, 0);
return FALSE;
}
HMACInfo.HashAlgid = CALG_SHA1;
HMACInfo.pbInnerString = HMACInfo.pbOuterString = 0;
HMACInfo.cbInnerString = HMACInfo.cbOuterString = 0;
Algorithmically Generating Symmetric Keys from One Base Secret | 145
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