The ter­ror­ists who killed at least 129 people in Par­is likely used en­cryp­tion tools to plot their at­tacks without alert­ing gov­ern­ment in­tel­li­gence agen­cies, two key sen­at­ors said Tues­day.

Sen­ate In­tel­li­gence Com­mit­tee Chair­man Richard Burr and rank­ing mem­ber Di­anne Fein­stein said they plan to con­sider pro­pos­als to en­sure gov­ern­ment in­tel­li­gence agen­cies can ac­cess com­mu­nic­a­tions.

“It’s a wake-up call for Amer­ica and for our glob­al part­ners that we need to be­gin the de­bate on what we do on en­cryp­ted net­works be­cause it makes us blind to the com­mu­nic­a­tions and to the ac­tions of po­ten­tial ad­versar­ies,” Burr told re­port­ers after leav­ing a clas­si­fied brief­ing from U.S. in­tel­li­gence of­fi­cials.

But Burr ac­know­ledged that he doesn’t know if the at­tack­ers re­lied on any par­tic­u­lar ap­plic­a­tion or ser­vice to en­crypt their com­mu­nic­a­tions. “We think that [en­cryp­tion is] a likely com­mu­nic­a­tions tool be­cause we didn’t pick up any dir­ect com­mu­nic­a­tion,” he ex­plained.

Burr also em­phas­ized that the com­mit­tee is on an “ex­plor­at­ory route,” and it is too early to dis­cuss any spe­cif­ics about pos­sible le­gis­la­tion. “We need to fig­ure what can and should be done about [en­cryp­tion]— if any­thing,” Fein­stein agreed.

The lead­ers of the FBI and CIA have also com­plained in re­cent months about the prob­lem of ter­ror­ists “go­ing dark” from sur­veil­lance by us­ing en­cryp­ted plat­forms. But pri­vacy ad­voc­ates and tech­no­logy com­pan­ies have fiercely pushed back against any pro­pos­als to un­der­mine en­cryp­tion.

They ar­gue that any gov­ern­ment-man­dated back­door in en­cryp­tion could also be ex­ploited by hack­ers to do harm.

“The real­ity is that en­cryp­tion pro­tects se­cur­ity,” Chris Ca­labrese, the vice pres­id­ent for policy at the Cen­ter for Demo­cracy and Tech­no­logy, said in an in­ter­view. “It un­der­lines the se­cur­ity of our bank­ing, our trans­ac­tions, our vot­ing. Everything we do on­line is se­cure be­cause we have en­cryp­tion.”

The White House said last month that it won’t ask for Con­gress to pass le­gis­la­tion to thwart en­cryp­tion. Mark Stroh, a White House spokes­man, de­clined Tues­day to provide any ad­di­tion­al in­form­a­tion on the ad­min­is­tra­tion’s po­s­i­tion on the is­sue in the wake of the Par­is at­tacks.

Burr dis­missed the tech­no­logy in­dustry’s ar­gu­ment that en­cryp­tion is es­sen­tial for pub­lic trust in their products.

“We don’t have a re­spons­ib­il­ity to sell their products. We have a re­spons­ib­il­ity to keep Amer­ica safe,” Burr said. “If it means that people are go­ing to have to change their busi­ness mod­els, then so be it.”