Problem - Kevin Tafuro

Here’s a pair of functions that do all-in-one wrapping of the OpenSSLEVP message
digest interface:
#include
#include
#include
unsigned char *spc_create_nonced_digest(EVP_MD *type, unsigned char *in,
unsigned long n, unsigned int *outlen) {
int bsz, dlen;
EVP_MD_CTX ctx;
unsigned char *pad, *ret;
EVP_DigestInit(&ctx, type);
dlen = EVP_MD_CTX_size(&ctx);
if (!(ret = (unsigned char *)malloc(dlen * 2))) return 0;
RAND_bytes(ret, dlen);
EVP_DigestUpdate(&ctx, ret, dlen);
bsz = EVP_MD_CTX_block_size(&ctx);
if (!(pad = (unsigned char *)malloc(bsz - dlen))) {
free(ret);
return 0;
}
memset(pad, 0, bsz - dlen);
EVP_DigestUpdate(&ctx, pad, bsz - dlen);
EVP_DigestUpdate(&ctx, in, n);
EVP_DigestUpdate(&ctx, ret, dlen);
EVP_DigestUpdate(&ctx, pad, bsz - dlen);
free(pad);
EVP_DigestFinal(&ctx, ret + dlen, outlen);
*outlen *= 2;
return ret;
}
int spc_verify_nonced_digest(EVP_MD *type, unsigned char *in, unsigned long n,
unsigned char *toverify) {
int dlen, outlen, bsz, i;
EVP_MD_CTX ctx;
unsigned char *pad, *vfy;
EVP_DigestInit(&ctx, type);
bsz = EVP_MD_CTX_block_size(&ctx);
dlen = EVP_MD_CTX_size(&ctx);
EVP_DigestUpdate(&ctx, toverify, dlen);
if (!(pad = (unsigned char *)malloc(bsz - dlen))) return 0;
memset(pad, 0, bsz - dlen);
EVP_DigestUpdate(&ctx, pad, bsz - dlen);
EVP_DigestUpdate(&ctx, in, n);
EVP_DigestUpdate(&ctx, toverify, dlen);
EVP_DigestUpdate(&ctx, pad, bsz - dlen);
free(pad);
272 | Chapter 6: Hashes and Message Authentication
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