static BIO *PKCS7_find_digest(EVP_MD_CTX **pmd, BIO *bio, int nid)
{
    for (;;) {
        bio = BIO_find_type(bio, BIO_TYPE_MD);
        if (bio == NULL) {
            PKCS7err(PKCS7_F_PKCS7_FIND_DIGEST,
                     PKCS7_R_UNABLE_TO_FIND_MESSAGE_DIGEST);
            return NULL;
        }
        BIO_get_md_ctx(bio, pmd);
        if (*pmd == NULL) {
            PKCS7err(PKCS7_F_PKCS7_FIND_DIGEST, ERR_R_INTERNAL_ERROR);
            return NULL;
        }
        if (EVP_MD_CTX_type(*pmd) == nid)
            return bio;
        bio = BIO_next(bio);
    }
    return NULL;
}

Unknown