Chief Justice John Roberts’s 28-page paean to digital privacy was like music to the ears of critics of the NSA’s metadata program, which sweeps up details on billions of calls and searches them for possible links to terrorist plots.

“This is a remarkably strong affirmation of privacy rights in a digital age,” said Marc Rotenberg of the Electronic Privacy Information Center. “The court found that digital data is different and that has constitutional significance, particularly in the realm of [the] Fourth Amendment…I think it also signals the end of the NSA program.”

Roberts’s opinion is replete with rhetoric warning about the privacy implications of access to data in individuals’ smart phones, including call logs, Web search records and location information. Many of the arguments parallel, or are virtually identical to, the ones privacy advocates have made about the dangers inherent in the NSA’s call metadata program.

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“Modern cell phones, as a category, implicate privacy concerns far beyond those implicated by the search of a cigarette pack, a wallet, or a purse,” the chief justice wrote in an opinion that concluded police nearly always need a warrant to look through a phone or similar device. “An Internet search and browsing history, for example, can be found on an Internet-enabled phone and could reveal an individual’s private interests or concerns — perhaps a search for certain symptoms of disease, coupled with frequent visits to WebMD.”

For the NSA debate, the most significant idea in the court’s Wednesday opinion may be the notion that scale matters. Roberts and his colleagues soundly rejected arguments from the Obama administration that because police can search a few printed photographs found in someone’s wallet, officers were free to search thousands of images and the troves of other personal data contained on a typical smartphone.

Government lawyers engaged in the NSA fight have pointed to a 1979 Supreme Court ruling that approved the use of a trap-and-trace device put on a single phone line to investigate harassing phone calls. That decision, those attorneys say, means there is no constitutional problem with authorities assembling data on many — or even all — calls made in the United States.

Critics have said the two situations bear little resemblance to one another, in part because of the huge difference in scale.

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“It’s very important that the court is recognizing that quantity matters,” said Georgia Tech professor Peter Swire, a privacy expert and member of a panel President Barack Obama set up to review the NSA’s call metadata program. “The court has said that quantity matters when it comes to the content of cell phones. And I believe the court will feel the same way when it comes to massive databases of telephone calls or computer communications.”

A former cybercrime prosecutor said the justices also seemed to recognize that scale of the collection not only gives the government more data, but also the ability to be much more intrusive than in earlier eras.

“The distinction here is more than just the capacity of the device to hold pictures,” said Alex Southwell, now with law firm Gibson, Dunn & Crutcher. “A cell phone is orders of magnitude different, not just in terms of numbers of items held but also in terms of the intrusiveness if searched. The mosaic of information available from seeing the whole of the data is transformative, just like the call records at issue in the NSA program.”

The Supreme Court’s ruling Wednesday in Riley v. California doesn’t say anything explicitly about the NSA’s metadata, nor did the justices mention national security concerns or intelligence gathering.

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However, in one somewhat opaque footnote to Roberts’s majority opinion, the justices seem to be saying they are leaving the issue of bulk collection of data for another day. “These cases do not implicate the question whether [sic] the collection or inspection of aggregated digital information amounts to a search under other circumstances,” Roberts wrote.

Even if the justices were to deem the NSA program a warrantless search that goes well beyond tracing calls made on a specific phone line, that wouldn’t mean the terrorism-focused effort is unconstitutional. Instead, the court would have to consider whether the search is reasonable in light of the national security and public safety concerns involved — and justices are often extraordinary deferential to such arguments.

One prominent defender of the NSA metadata program acknowledged that the court’s cell phone decision will now become a focus in the call-tracking litigation, but he said he doesn’t think it will make a major difference in the legal rulings handed down.

“All of the advocates for privacy will cite this decision and all of the advocates on the government side will distinguish this,” said former NSA general counsel Stewart Baker, now with law firm Steptoe & Johnson. “Atmospherically, it will free up lower courts to look more broadly at the privacy impact and they may be more sympathetic to privacy claims…but judges are going to be inclined to come down on the privacy side only if they were already leaning that way.”

University of Chicago law professor Geoffrey Stone also said there’s no direct connection between the cell phone decision and the NSA cases, but the tone of the opinion has affected the guesswork about what the court will eventually do on the surveillance issue.

“From a lawyer’s standpoint, the issues are quite different, and Riley does not necessarily tell us anything about the bulk collection issue,” said Stone, who also served on Obama’s surveillance review panel. “On the other hand, it does show that the Court is growing ever more sensitive to the ways in which technology changes reasonable expectations of privacy, and the Court’s openness to that perspective suggests that it would be more sympathetic to a constitutional challenge to the bulk collection of metadata than would have been clear before the decision.”

Analysts on both sides said the cell phone ruling is not a one-off, but seems to be part of a pattern of the court’s effortsto square privacy rights with the new challenges posed by emerging technology. Two years ago, in U.S. v. Jones, the justices rejected arguments that GPS tracking should not require a warrant because police have always been free to follow suspects around without getting one.

“What’s significant…is the justices, like the rest of us, are fully alive to the fact that technology is generating large quantities of data about us and putting it in places where it didn’t used to be,” Baker said.

President Barack Obama initially dismissed the privacy impact of the metadata program as “modest,” but in recent months he has acknowledged that it is troubling to many Americans. Earlier this year, he proposed shutting down the NSA program and replacing it with one in which telephone companies store the call information and make it readily available for the government to search. The president also implemented a procedure in which a judge approves most queries in advance, but the standard is lower than that for a search warrant.

The Obama administration has made much of safeguards it has imposed on the NSA program. However, the court’s cell phone search opinion suggests the justices might not find such self-regulation sufficient to address privacy concerns.

“The Government proposes that law enforcement agencies ‘develop protocols to address’ concerns raised by cloud computing,” the chief justice wrote. “Probably a good idea, but the Founders did not fight a revolution to gain the right to government agency protocols.”

The House passed a bill last month that would end the bulk collection of the phone metadata and move generally in the direction Obama urged, but NSA critics say the House measure is inadequate. They’re urging the Senate to pass a stronger reform bill, but it’s unclear precisely what legislation will emerge from that body, if any.

Privacy advocates have urged Obama to simply shut down the current program entirely until reform legislation is passed. However, he has rebuffed those calls and recently obtained another 90-day extension of the so-called bulk collection program revealed by NSA leaker Edward Snowden.

Even if the metadata program is changed dramatically by legislation or executive action, litigation is likely to continue over whether the earlier data-gathering violated the law or the Constitution. Several lawsuits challenging the practice are pending in various parts of the country.

One member of the Supreme Court, Justice Samuel Alito, did appear to signal Wednesday that he would defer to any legislation that made an effort to set clear rules about when and how digital data can be used by the government. Alito joined the court’s holding that warrants were generally required to search cell phones, but he said the specifics of exceptions should be sorted out by Congress, not the courts.

“It would be very unfortunate if privacy protection in the 21st century were left primarily to the federal courts using the blunt instrument of the Fourth Amendment,” Alito wrote in his concurrence. “Legislatures, elected by the people, are in a better position than we are to assess and respond to the changes that have already occurred and those that almost certainly will take place in the future.”

Swire said it’s possible the main effect of the court’s cell phone ruling on the NSA issue will be to push Congress to make changes. In the 1960s and 1970s, Supreme Court rulings on wiretapping had just that effect, he said.

“There was a dialogue among the courts and Congress that led to stricter protections for wiretaps then,” Swire noted. “The Supreme Court quite possibly is on the same path for cell phones and computer communications now…

“It’s easier for the courts to be bold when Congress and public opinion is headed in the same way.”