may you just try my "fix"? At least, it will save me time for searching in completely wrong place.

--- nginx-1.7.10/src/http/modules/ngx_http_ssl_module.c.orig 2015-02-10 15:33:34.000000000 +0100
+++ nginx-1.7.10/src/http/modules/ngx_http_ssl_module.c 2015-03-17 14:55:58.282130993 +0100
@@ -716,7 +716,7 @@
}

/* a temporary 512-bit RSA key is required for export versions of MSIE */
- SSL_CTX_set_tmp_rsa_callback(conf->ssl.ctx, ngx_ssl_rsa512_key_callback);
+ // SSL_CTX_set_tmp_rsa_callback(conf->ssl.ctx, ngx_ssl_rsa512_key_callback);

if (ngx_ssl_dhparam(cf, &conf->ssl, &conf->dhparam) != NGX_OK) {
return NGX_CONF_ERROR;