int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs,
               X509_STORE *store, BIO *dcont, BIO *out, unsigned int flags)
{
    CMS_SignerInfo *si;
    STACK_OF(CMS_SignerInfo) *sinfos;
    STACK_OF(X509) *cms_certs = NULL;
    STACK_OF(X509_CRL) *crls = NULL;
    X509 *signer;
    int i, scount = 0, ret = 0;
    BIO *cmsbio = NULL, *tmpin = NULL;

    if (!dcont && !check_content(cms))
        return 0;

    /* Attempt to find all signer certificates */

    sinfos = CMS_get0_SignerInfos(cms);

    if (sk_CMS_SignerInfo_num(sinfos) <= 0) {
        CMSerr(CMS_F_CMS_VERIFY, CMS_R_NO_SIGNERS);
        goto err;
    }

    for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
        si = sk_CMS_SignerInfo_value(sinfos, i);
        CMS_SignerInfo_get0_algs(si, NULL, &signer, NULL, NULL);
        if (signer)
            scount++;
    }

    if (scount != sk_CMS_SignerInfo_num(sinfos))
        scount += CMS_set1_signers_certs(cms, certs, flags);

    if (scount != sk_CMS_SignerInfo_num(sinfos)) {
        CMSerr(CMS_F_CMS_VERIFY, CMS_R_SIGNER_CERTIFICATE_NOT_FOUND);
        goto err;
    }

    /* Attempt to verify all signers certs */

    if (!(flags & CMS_NO_SIGNER_CERT_VERIFY)) {
        cms_certs = CMS_get1_certs(cms);
        if (!(flags & CMS_NOCRL))
            crls = CMS_get1_crls(cms);
        for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
            si = sk_CMS_SignerInfo_value(sinfos, i);
            if (!cms_signerinfo_verify_cert(si, store,
                                            cms_certs, crls, flags))
                goto err;
        }
    }

    /* Attempt to verify all SignerInfo signed attribute signatures */

    if (!(flags & CMS_NO_ATTR_VERIFY)) {
        for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
            si = sk_CMS_SignerInfo_value(sinfos, i);
            if (CMS_signed_get_attr_count(si) < 0)
                continue;
            if (CMS_SignerInfo_verify(si) <= 0)
                goto err;
        }
    }

    /*
     * Performance optimization: if the content is a memory BIO then store
     * its contents in a temporary read only memory BIO. This avoids
     * potentially large numbers of slow copies of data which will occur when
     * reading from a read write memory BIO when signatures are calculated.
     */

    if (dcont && (BIO_method_type(dcont) == BIO_TYPE_MEM)) {
        char *ptr;
        long len;
        len = BIO_get_mem_data(dcont, &ptr);
        tmpin = BIO_new_mem_buf(ptr, len);
        if (tmpin == NULL) {
            CMSerr(CMS_F_CMS_VERIFY, ERR_R_MALLOC_FAILURE);
            goto err2;
        }
    } else
        tmpin = dcont;

    cmsbio = CMS_dataInit(cms, tmpin);
    if (!cmsbio)
        goto err;

    if (!cms_copy_content(out, cmsbio, flags))
        goto err;

    if (!(flags & CMS_NO_CONTENT_VERIFY)) {
        for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
            si = sk_CMS_SignerInfo_value(sinfos, i);
            if (CMS_SignerInfo_verify_content(si, cmsbio) <= 0) {
                CMSerr(CMS_F_CMS_VERIFY, CMS_R_CONTENT_VERIFY_ERROR);
                goto err;
            }
        }
    }

    ret = 1;

 err:

    if (dcont && (tmpin == dcont))
        do_free_upto(cmsbio, dcont);
    else
        BIO_free_all(cmsbio);

 err2:
    if (cms_certs)
        sk_X509_pop_free(cms_certs, X509_free);
    if (crls)
        sk_X509_CRL_pop_free(crls, X509_CRL_free);

    return ret;
}