Problem - Kevin Tafuro

free(out);
out = 0;
goto err;
}
bytes_remaining -= b_per_ct;
ptr += b_per_ct;
/* Remember, output is larger than the input. */
p += RSA_size(recip_pub_key);
}
err:
if (sig) free(sig);
if (tmp) free(tmp);
if (to_encrypt) free(to_encrypt);
return out;
}
Once the message generated by this function is received on the server side, the following
code will validate the signature on the message and retrieve the secret:
#include
#include
#include
#include
#include
#define MIN(x,y) ((x) > (y) ? (y) : (x))
/* recip_key must contain both the public and private key. */
int validate_and_retreive_secret(RSA *recip_key, RSA *signers_pub_key,
unsigned char *encr, unsigned int inlen,
unsigned char *secret) {
int result = 0;
BN_CTX *tctx;
unsigned int ctlen, stlen, i, l;
unsigned char *decrypt, *signedtext, *p, hash[20];
if (inlen % RSA_size(recip_key)) return 0;
if (!(p = decrypt = (unsigned char *)malloc(inlen))) return 0;
if (!(tctx = BN_CTX_new( ))) {
free(decrypt);
return 0;
}
RSA_blinding_on(recip_key, tctx);
for (ctlen = i = 0; i < inlen / RSA_size(recip_key); i++) {
if (!(l = RSA_private_decrypt(RSA_size(recip_key), encr, p, recip_key,
RSA_PKCS1_OAEP_PADDING))) goto err;
encr += RSA_size(recip_key);
p += l;
ctlen += l;
}
if (ctlen != 16 + RSA_size(signers_pub_key)) goto err;
stlen = 16 + BN_num_bytes(recip_key->n) + BN_num_bytes(recip_key->e);
if (!(signedtext = (unsigned char *)malloc(stlen))) goto err;
346 | Chapter 7: Public Key Cryptography
This is the Title of the Book, eMatter Edition
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