Problem - Kevin Tafuro

#define MIN(x,y) ((x) > (y) ? (y) : (x))
unsigned char *generate_and_package_128_bit_secret(RSA *recip_pub_key,
RSA *signers_key, unsigned char *sec, unsigned int *olen) {
unsigned char *tmp = 0, *to_encrypt = 0, *sig = 0, *out = 0, *p, *ptr;
unsigned int len, ignored, b_per_ct;
int bytes_remaining; /* MUST NOT BE UNSIGNED. */
unsigned char hash[20];
/* Generate the secret. */
if (!RAND_bytes(sec, 16)) return 0;
/* Now we need to sign the public key and the secret both.
* Copy the secret into tmp, then the public key and the exponent.
*/
len = 16 + RSA_size(recip_pub_key) + BN_num_bytes(recip_pub_key->e);
if (!(tmp = (unsigned char *)malloc(len))) return 0;
memcpy(tmp, sec, 16);
if (!BN_bn2bin(recip_pub_key->n, tmp + 16)) goto err;
if (!BN_bn2bin(recip_pub_key->e, tmp + 16 + RSA_size(recip_pub_key))) goto err;
/* Now sign tmp (the hash of it), again mallocing space for the signature. */
if (!(sig = (unsigned char *)malloc(BN_num_bytes(signers_key->n)))) goto err;
if (!SHA1(tmp, len, hash)) goto err;
if (!RSA_sign(NID_sha1, hash, 20, sig, &ignored, signers_key)) goto err;
/* How many bytes we can encrypt each time, limited by the modulus size
* and the padding requirements.
*/
b_per_ct = RSA_size(recip_pub_key) - (2 * 20 + 2);
if (!(to_encrypt = (unsigned char *)malloc(16 + RSA_size(signers_key))))
goto err;
/* The calculation before the mul is the number of encryptions we're
* going to make. After the mul is the output length of each
* encryption.
*/
*olen = ((16 + RSA_size(signers_key) + b_per_ct - 1) / b_per_ct) *
RSA_size(recip_pub_key);
if (!(out = (unsigned char *)malloc(*olen))) goto err;
/* Copy the data to encrypt into a single buffer. */
ptr = to_encrypt;
bytes_remaining = 16 + RSA_size(signers_key);
memcpy(to_encrypt, sec, 16);
memcpy(to_encrypt + 16, sig, RSA_size(signers_key));
p = out;
while (bytes_remaining > 0) {
/* encrypt b_per_ct bytes up until the last loop, where it may be fewer. */
if (!RSA_public_encrypt(MIN(bytes_remaining,b_per_ct), ptr, p,
recip_pub_key, RSA_PKCS1_OAEP_PADDING)) {
Securely Signing and Encrypting with RSA | 345
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