int ssl3_check_cert_and_algorithm(SSL *s)
{
    int i, idx;
    long alg_k, alg_a;
    EVP_PKEY *pkey = NULL;
    int pkey_bits;
    SESS_CERT *sc;
#ifndef OPENSSL_NO_RSA
    RSA *rsa;
#endif
#ifndef OPENSSL_NO_DH
    DH *dh;
#endif
    int al = SSL_AD_HANDSHAKE_FAILURE;

    alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
    alg_a = s->s3->tmp.new_cipher->algorithm_auth;

    /* we don't have a certificate */
    if ((alg_a & (SSL_aNULL | SSL_aKRB5)) || (alg_k & SSL_kPSK))
        return (1);

    sc = s->session->sess_cert;
    if (sc == NULL) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);
        goto err;
    }
#ifndef OPENSSL_NO_RSA
    rsa = s->session->sess_cert->peer_rsa_tmp;
#endif
#ifndef OPENSSL_NO_DH
    dh = s->session->sess_cert->peer_dh_tmp;
#endif

    /* This is the passed certificate */

    idx = sc->peer_cert_type;
#ifndef OPENSSL_NO_ECDH
    if (idx == SSL_PKEY_ECC) {
        if (ssl_check_srvr_ecc_cert_and_alg(sc->peer_pkeys[idx].x509, s) == 0) {
            /* check failed */
            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_BAD_ECC_CERT);
            goto f_err;
        } else {
            return 1;
        }
    } else if (alg_a & SSL_aECDSA) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
               SSL_R_MISSING_ECDSA_SIGNING_CERT);
        goto f_err;
    } else if (alg_k & (SSL_kECDHr | SSL_kECDHe)) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_MISSING_ECDH_CERT);
        goto f_err;
    }
#endif
    pkey = X509_get_pubkey(sc->peer_pkeys[idx].x509);
    pkey_bits = EVP_PKEY_bits(pkey);
    i = X509_certificate_type(sc->peer_pkeys[idx].x509, pkey);
    EVP_PKEY_free(pkey);

    /* Check that we have a certificate if we require one */
    if ((alg_a & SSL_aRSA) && !has_bits(i, EVP_PK_RSA | EVP_PKT_SIGN)) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
               SSL_R_MISSING_RSA_SIGNING_CERT);
        goto f_err;
    }
#ifndef OPENSSL_NO_DSA
    else if ((alg_a & SSL_aDSS) && !has_bits(i, EVP_PK_DSA | EVP_PKT_SIGN)) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
               SSL_R_MISSING_DSA_SIGNING_CERT);
        goto f_err;
    }
#endif
#ifndef OPENSSL_NO_RSA
    if (alg_k & SSL_kRSA) {
        if (!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) &&
            !has_bits(i, EVP_PK_RSA | EVP_PKT_ENC)) {
            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                   SSL_R_MISSING_RSA_ENCRYPTING_CERT);
            goto f_err;
        } else if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher)) {
            if (pkey_bits <= SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)) {
                if (!has_bits(i, EVP_PK_RSA | EVP_PKT_ENC)) {
                    SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                           SSL_R_MISSING_RSA_ENCRYPTING_CERT);
                    goto f_err;
                }
                if (rsa != NULL) {
                    /* server key exchange is not allowed. */
                    al = SSL_AD_INTERNAL_ERROR;
                    SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);
                    goto f_err;
                }
            }
        }
    }
#endif
#ifndef OPENSSL_NO_DH
    if ((alg_k & SSL_kEDH) && dh == NULL) {
        al = SSL_AD_INTERNAL_ERROR;
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);
        goto f_err;
    }
    if ((alg_k & SSL_kDHr) && !SSL_USE_SIGALGS(s) &&
               !has_bits(i, EVP_PK_DH | EVP_PKS_RSA)) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
               SSL_R_MISSING_DH_RSA_CERT);
        goto f_err;
    }
# ifndef OPENSSL_NO_DSA
    if ((alg_k & SSL_kDHd) && !SSL_USE_SIGALGS(s) &&
        !has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {
        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
               SSL_R_MISSING_DH_DSA_CERT);
        goto f_err;
    }
# endif

    if (alg_k & (SSL_kDHE | SSL_kDHr | SSL_kDHd)) {
        int dh_size;
        if (alg_k & SSL_kDHE) {
            dh_size = BN_num_bits(dh->p);
        } else {
            DH *dh_srvr = get_server_static_dh_key(sc);
            if (dh_srvr == NULL)
                goto f_err;
            dh_size = BN_num_bits(dh_srvr->p);
            DH_free(dh_srvr);
        }

        if ((!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 768)
            || (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 512)) {
            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_DH_KEY_TOO_SMALL);
            goto f_err;
        }
    }
#endif  /* !OPENSSL_NO_DH */

    if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) &&
        pkey_bits > SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)) {
#ifndef OPENSSL_NO_RSA
        if (alg_k & SSL_kRSA) {
            if (rsa == NULL) {
                SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                       SSL_R_MISSING_EXPORT_TMP_RSA_KEY);
                goto f_err;
            } else if (BN_num_bits(rsa->n) >
                SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)) {
                /* We have a temporary RSA key but it's too large. */
                al = SSL_AD_EXPORT_RESTRICTION;
                SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                       SSL_R_MISSING_EXPORT_TMP_RSA_KEY);
                goto f_err;
            }
        } else
#endif
#ifndef OPENSSL_NO_DH
        if (alg_k & SSL_kDHE) {
            if (BN_num_bits(dh->p) >
                SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)) {
                /* We have a temporary DH key but it's too large. */
                al = SSL_AD_EXPORT_RESTRICTION;
                SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                       SSL_R_MISSING_EXPORT_TMP_DH_KEY);
                goto f_err;
            }
        } else if (alg_k & (SSL_kDHr | SSL_kDHd)) {
            /* The cert should have had an export DH key. */
            al = SSL_AD_EXPORT_RESTRICTION;
            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                   SSL_R_MISSING_EXPORT_TMP_DH_KEY);
                goto f_err;
        } else
#endif
        {
            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,
                   SSL_R_UNKNOWN_KEY_EXCHANGE_TYPE);
            goto f_err;
        }
    }
    return (1);
 f_err:
    ssl3_send_alert(s, SSL3_AL_FATAL, al);
 err:
    return (0);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.