Problem - Kevin Tafuro

BIGNUM *dP, *dQ, *qInv;
} RSA_PRIVATE;
void spc_keypair_from_primes(BIGNUM *p, BIGNUM *q, unsigned long e,
RSA_PUBKEY *pubkey, RSA_PRIVATE *privkey)
{
BN_CTX *x = BN_CTX_new( );
BIGNUM p_minus_1, q_minus_1, one, tmp, bn_e;
pubkey->n = privkey->n = BN_new( );
privkey->d = BN_new( );
pubkey->e = e;
privkey->p = p;
privkey->q = q;
BN_mul(pubkey->n, p, q, x);
BN_init(&p_minus_1);
BN_init(&q_minus_1);
BN_init(&one);
BN_init(&tmp);
BN_init(&bn_e);
BN_set_word(&bn_e, e);
BN_one(&one);
BN_sub(&p_minus_1, p, &one);
BN_sub(&q_minus_1, q, &one);
BN_mul(&tmp, &p_minus_1, &q_minus_1, x);
BN_mod_inverse(privkey->d, &bn_e, &tmp, x);
/* Compute extra values. */
privkey->dP = BN_new( );
privkey->dQ = BN_new( );
privkey->qInv = BN_new( );
BN_mod(privkey->dP, privkey->d, &p_minus_1, x);
BN_mod(privkey->dQ, privkey->d, &q_minus_1, x);
BN_mod_inverse(privkey->qInv, q, p, x);
}
See Also
Recipes 7.1, 7.2, 7.5
7.7 Disentangling the Public and Private Keys
in OpenSSL
Problem
You are using OpenSSLand have a filled RSA object. You wish to remove the private
parts of the key, leaving only the public key, so that you can serialize the data structure
and send it off to a party who should not have the private information.
Disentangling the Public and Private Keys in OpenSSL | 329
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