flied Approved f?r pUb'iC re'ease by the 0an 20160818 United States Foreign lntoillgence Surveiliance Court of Review AF i 4 20:5 LeeAnn Hall, Clerk at Court ?atten 5mm foreign immigrate ?uma??a?m (Eourt at 332mm IN RE: CERTIFIED QUESTION OF LAW Docket No. FISCR 16-01 Upon Certi?cation for Review by the United States Foreign Intelligence Surveillance Court Decided: MARC ZWILLINGER, ZwillGen PLLC, Washington, DC, argued the case as court?appointed amicus curiae. With him on the brief was JACOB A. SOMMER. ADITYA BAMZAI, United States Department of Justice, Washington, D.C., argued the case for the United States. With him on the brief were JOHN P. CARLIN, STUART J. EVANS, J. BRADFORD WIEGMANN, AND LISA M. FARABEE. Before BRYSON, CABRANES, AND TALLMAN, Judges. PER CURIAM. The Foreign Intelligence Surveillance Court certi?ed this matter under 50 U.S.C. 18036) for review by this court. The FISC certi?ed the following question to us: Whether an order issued under 50 U.S.C. 1842 may authorize the Government to obtain all post-cut-through Approved for public release by the ODNI 20160818 2 digits, subject to a prohibition on the af?rmative investi- gative use of any contents thereby acquired, when there is no technology reasonably available to the Government that would permit: (1) a [pen register/trap-and-trace] device to ac- quire post-cubthrough digits that are non?content DRAS {dialing routing, addressing, and signaling] information, while not acquiring post-cut-through digits that are contents of a communication; or (2) the Government at the time it receives infor- mation acquired by a device, to discard post-cut-through digits that are contents of a communication, while retaining those digits that are non-content DRAS information. We have reviewed the record and considered briefs from the government and from amicus curiae appointed by the court under 50 U.S.C. 1803(i) to present argu- ment in this matter. We conclude that section 1842 authorizes, and the Fourth Amendment to the Constitu- tion of the United States does not prohibit, an order of the kind described in the certi?cation. Read fairly and as a whole, the governing statutes evince Congress?s understanding that pen registers and trap-and-trace devices Will, under some circumstances, inevitably collect content information. Congress has addressed this dif?? culty by requiring the government to minimize the inci? dental collection of content through the employment of such technological measures as are reasonably availa- ble?not by barring entirely, as a form of pr0phylaxis, the use of pen registers and trap-and~trace devices simply because they might gather content incidentally. Nor does an order authorizing such surveillance run afoul of the Fourth Amendment?s guarantee against unreasonable searches and seizures. The warrant re- quirement is generally a tolerable proxy for ?reasonable- ness? when the government is seeking to unearth Approved for public release by the ODNI 20160818 evidence of criminal wrongdoing, but it fails properly to balance the interests at stake when the government is instead seeking to preserve and protect the nation?s security from foreign threat. We therefore hold that surveillance of this type may be constitutionally reasona- ble even When it is not authorized by a probable-cause warrant. We further hold, on the facts presented here, that the order under review reasonably balances the investigative needs of the government and the privacy interests of the people. I On January 21, 2016, a judge of the FISC approved an Application for Pen Register and Trap and Trace Device(s) after ?nding that the application met the requirements for a pen register/trap-and-trace authorization order under the Foreign Intelligence Surveillance Act The authorization provided for the installation and use of pen register/trap-and-trace devices on a cellular telephone number used by the subject of an ongoing investigation to protect against clandestine intelligence activities, with the assistance of the service provider for that number.1 As requested by the government, the court?s order granted ?the authority to record and decode all post-cut- through digits,? as described in a memorandum ?led by the government with the FISC on August 17, 2009, in connection with an earlier request for similar authoriza- tion. The court?s order further provided that the govern- 1 A pen register is a device or process that records or decodes dialing signals transmitted from a telephone or other wire or electronic communication instrument or facility. A trap-and-trace device is a device or process that captures incoming signals and therefore identi?es the originating number or source of an incoming wire or electronic communication. Approved for public release by the ODNI 20160818 ment ?shall not make any af?rmative investigative use of post-cut-through digits acquired through pen register authorization that do not constitute call dialing, routing, addressing or signaling information, unless separately authorized by this Court.? In a secondary order, the court directed the service provider to ?lrnish ?all information, facilities, or technical assistance necessary to accomplish the installation and Operation of the . . . ?Post-cut-through digits? are numbers or characters that are dialed after the call is initially connected or ?cut through.? Frequently, those numbers are other telephone numbers, as when a caller places a calling card, credit card, or collect call by ?rst dialing a carrier access number and then, after the initial call is ?out through,? dialing the telephone number of the intended recipient. See US. Telecom Ass?n v. FCC, 227 F.3d 450, 456, 462 (DC. Cir. 2000); In re Application of the United States, 396 F. Supp. 2d 45, 48 (D. Mass. 2005). Both the ?rst dialed number (the carrier access number) and the second dialed number (the intended recipient?s number) constitute dialing information.2 The initial dialed number, however, is likely to be of little interest to investigators who are seeking to determine what speci?c number the caller is 2 The statute that de?nes pen registers and trap-and- trace devices for the purposes of this case refers to such information as ?dialing, routing, addressing, or signaling information? utilized in the processing and transmitting of Wire or electronic communications, 18 U.S.C. 3127(3), (4). That phrase is sometimes represented by the aero- DRAS. For simplicity, we will refer to that infor- mation simply as ?dialing information,? but with the understanding that the term is meant to include all four categories of information set forth in section 18 U.S.C. 3127, and to exclude What we shall refer to as ?content information.? Approved for public release by the ODNI 20160818 calling. In such a situation, in order to discover what number is being called, the investigators must be able to intercept the post-cut-through digits. In some instances, after a caller has dialed a tele- phone number, the caller dials additional digits that do not constitute dialing information, but instead constitute a form of content information. For example, after dialing a bank, the caller may be prompted to input a password, a personal identi?cation number, or a bank account num- ber. Or, under certain circumstances, a customer may enter a credit card number or a Social Security number by dialing additional digits. That information is considered content information. As the government acknowledges, pen register orders do not target the interception and decoding of such content information.3 The authorization granted by the FISC judge in this case was consistent with prior FISC practice. Since at least 2006, FISC judges have issued pen register/trap- and-trace orders under 50 U.S.C. 1842 that have au- thorized the acquisition of all post-cut-through digits, while generally prohibiting the use of those digits that do not constitute dialing information. 3 The term ?contents? has the same meaning in this context as in the federal wiretapping statute, Where it is de?ned to mean ?any information concerning the sub- stance, purport, or meaning of [a wire, oral, or electronic} communication.? 18 U.S.C. 2510(8); id. 3127(1). A different definition of ?contents? is set forth at 50 U.S.C. 1801(n). The de?nitions in section 1801, however, apply to terms used in this subchapter??i.e., in 50 U.S.C. 1801-1812, the FISA subchapter on electronic surveil- lance. That de?nition does not apply to ?contents? for purposes of the FISA subchapter on pen registers and trapvand-trace devices, 50 U.S.C. 1841-1846. Approved for public release by the ODNI 20160818 In the order certifying the question of law to this court, the FISC judge set forth in detail the background of the legal issue presented by the government?s application. The FISC judge also described the manner in which other courts have dealt with this issue under the pen regis- provisions of title 18 of the United States Code, which govern the use of such devices in the context of criminal investigations. The FISC judge explained that the pen register/trap- and-trace statutes provide that the information intercept- ed by pen registers and trap-and-trace devices ?shall not include the contents of any communication.? 18 U.S.C. ?3127(3), (4). A related section, however, states that the government ?shall use technology reasonably available to it? that restricts the recording or decoding of electronic or other impulses ?so as not to include the contents of any wire or electronic communications.? Id. ?3121(c). In the past, the FISC judge explained, the government has argued, and the FISC has accepted, that in the absence of such reasonably available technology, the government is permitted to obtain all post-cut- through digits, so long as the investigative use of any content information contained therein is prohibited. Because there is not now and has not previously been any known or reasonably available technology to segregate dialing information from content information in post-cut- through digits prior to the interception of those digits, the government has contended that it is entitled to obtain post-cut-through digits even when the acquisition of such digits comes with some risk of intercepting content infor- mation. The FISC judge explained that the government?s interest in acquiring such digits is concretely presented in this case. The subject of the investigation is suSpected of engaging in clandestine intelligence activities on behalf of a foreign government contrar to the interests of the United Approved for public release by the ODNI 20160818 Using currently available technology, the government cannot identify the foreign telephone number without obtaining the entire set of post-cut-through digits. Considering the competing privacy interests, the FISC judge concluded that they are not great. Even though some post-cut?through digits may constitute content information, they ?nonetheless involve a narrow category of information from a subset of calls placed from a targeted phone number.? The intrusion, the judge explained, is less than obtaining the full contents of calls to or from a targeted number, and the intrusion is also ?mitigated by the prohibition on af?rmative investigative use? of the non-dialing information. In view of the uniformity of the authorities holding that post-cut-through digits may not be intercepted in the parallel setting of criminal investigations, the F180 judge concluded that the ?disagreement between the F180 and other courts provides reason to believe that consideration of these issues by the [Foreign Intelligence Surveillance Court of Review] would serve the interests of ustice.? See 50 U.S.C. 18030). We ?nd that it is appropriate for this court to address the certi?ed question. II The problem in this case is this: Under presently available technology, there is no way for a pen register to distinguish between dialing information and content information contained in post-cut-through digits so that it can be directed to intercept only the former and not the latter.4 Therefore, in the case of a pen register order that 4 The amicus curiae argues that such technology al- ready exists: the government can limit the collection of Approved for public release by the ODNI 20160818 8 authorizes the interception of post-cut-through digits, there is some risk that content information will be inter- cepted along with dialing information. The question we have been asked to decide is whether the statute that authorizes the issuance of pen register orders for foreign intelligence purposes permits courts to authorize the interception of post-cut-through digits, even though there is some risk that such digits might sometimes include content information. A The statute that governs the use of pen registers and trap-and-trace devices for foreign intelligence purposes is title IV of FISA, 50 U.S.C. 1841-46. That statute provides that the government can obtain an order author- izing the installation and use of a pen register or trap- and-trace device upon a statutorily suf?cient showing, made either to a judge of the F180 or to a pr0perly au- thorized magistrate judge. Id. 1842. An application for a pen register or a trap-and?trace device under section 1842 requires the approval of the Attorney General or a designated attorney for the gov- ernment. Id. 1842(c). It also requires a certi?cation by the applicant that the information likely to be obtained ?is foreign intelligence information not concerning a United States person or is relevant to an ongoing investigation to protect against international terrorism or clandestine digits to the ?rst ten dialed digits. To be sure, that ap- proach would exclude all content information, but at the expense of excluding all dialing information that might be present in post-cut?through digits, even in settings where there is no reasonable likelihood of intercepting content information. That is not a technological solution that discriminates between dialing and content information, as referred to in section 3121(c). Approved for public release by the ODNI 20160818 intelligence activities.? Id. 1842(c)(2). Finally, the application must contain a ?speci?c selection term? to be used as the basis for the use of the pen register or the trap-and-trace device. Id. 1842(c)(3). A ?speci?c selec- tion term? is a term ?that speci?cally identi?es a person, account, address, or personal device, or any other speci?c identi?er.? Id. It must be used to limit, ?to the greatest extent reasonably practicable, the scope of information sought, consistent with the purpose for seeking the use of the pen register or trap and trace device.? Id. 1841(4)(A)(ii). Section 1842(h)(1) of FISA provides that the Attorney General ?shall ensure that appropriate policies and pro- cedures are in place to safeguard nonpublicly available information concerning United States persons that is collected through the use of a pen register or trap and trace device installed under this section.? Section 1842(h)(2) further provides that the F180 is not prohibit- ed from imposing ?additional privacy or minimization procedures with regard to the installation or use of a pen register or trap and trace device.? The de?nitional section of title IV of FISA, section 1841, provides that the terms pen register and trap-and- trace device have the same meanings that are given to those terms in section 3127 of the title 18. The de?nition of pen register in section 3127 provides as follows, in pertinent part: [Tlhe term ?pen register? means a device or pro- cess which records or decodes dialing, routing, ad- dressing, or signaling information transmitted by an instrument or facility from which a wire or electronic communication is transmitted, provid- ed, however, that such information shall not in- clude the contents of any communication . . . . 18 U.S.C. 3127(3). The de?nition of ?trap and trace device? in title 18 contains similar language: Approved for public release by the ODNI 20160818 10 [Tlhe term ?trap and trace device? means a device or process which captures the incoming electronic or other impulses which identify the originating number or other dialing, routing, addressing, and signaling information reasonably likely to identify the source of a wire or electronic communication, provided, however, that such information shall not include the contents of any communication; Id. 3127(4). The question whether title IV of FISA authorizes pen register orders to collect post-cut?through digits turns on the meaning of the de?nitional language in 18 U.S.C. ?3127(3), and in particular the ?proviso? clause, which reads as follows: ?provided, however, that such infor- mation shall not include the contents of any communica- tion.? It is clear that the statutory language is intended to prohibit the use of pen registers for the purpose of intercepting content communications, such as bank account numbers, social security numbers, and personal identi?cation numbers. The statute expresses that intent in an unusual way, however, by making the prohibition against intercepting content information part of the de?nition of ?pen register.?5 The most literal interpretation of section 3127(3), read in isolation, leads to a problem. If a device ceases to be a pen register whenever it intercepts post-cut-through content information, it is impossible to know in advance 5 The statutory provisions that apply to trap-and- trace devices are largely (but not entirely) parallel to the provisions that apply to pen registers. Because our anal- ysis of the legal issue presented in this case is the same for both pen registers and trap-and-trace devices, we will generally refer only to pen registers for simplicity. Approved for public release by the ODNI 20160818 11 whether the device is a pen register (and thus whether its use may be authorized under title IV of FISA). A pen register intercepts the digits that are dialed. It does not distinguish between dialing information, on the one hand, and dialed digits that constitute ?the contents of any communication,? on the other. With currently available technology, that distinction can be drawn only after the information collected by the pen register has been decoded. De?ning a device as a pen register depend- ing on the nature of the material it ultimately collects thus poses a dilemma for courts that are asked to author- ize the collection of dialing information, and in particular post-cut-through digits. A court seeking to determine whether to authorize a pen register application that includes post-cut-through digits cannot know in advance whether the device will intercept some content infor- mation and therefore be ineligible for an authorization order. One approach to resolving that problem is to conclude that if there is any chance that content information will be intercepted, a pen register order that authorizes the collection of post-cut-through digits may not be entered. Adopting that theory, several courts have held that the pen register statute does not authorize the collection of any post-cut-through digits. See In re Application of the United States, 622 F. Supp. 2d 411 (SD. Tex. 2007); In re Application of the United States, No. 6:06-mj-1130 (MD. Fla. June 20, 2006), affg In re Application of the United States, No. 6:06-mj-1130 (May 23, 2006); In re Applica- tions of the United States, 515 F. Supp. 2d 325 (E.D.N.Y. Approved for public release by the ODNI 20160818 12 2007); In re Application of the United States, 441 F. Supp. 2d 816 (SD. Tex. 2006).6 The theory adopted by those courts might lead to the conclusion that the collection of post-cut-through digits may be authorized in circumstances in which the govern- 6 One of the courts that has addressed this issue has concluded that all post-cut-through digits constitute content information. In re Application of the United States, No. 08 MC 0595, 2008 WL 5255815 (E.D.N.Y. Dec. 16, 2008). On that premise, the court declined to author- ize the interception of post-cut-through digits. That premise, however, is ?awed, as it is well understood that post-cut-through digits can include both dialing infor- mation and content information, and that they may often include only dialing information. The amicus curiae argues that all post-rcut?through digits are content with reSpect to the service provider, and that the interception of post-cut-through digits should never be authorized. That argument is unconvincing, as the de?nition of ?contents? for purposes of pen registers is ?information concerning the substance, purport, or mean- ing of [a wire, oral, or electronic] communication.? 18 U.S.C. 2510(8). That de?nition does not include dialing information, Whether viewed from the perspective of the individual or the provider. The fact that the provider is not the one who uses that information for dialing purpos- es does not alter the fact that the information is dialing information. The FCC made that point in its decision on remand from US. Telecom Ass?n v. FCC, 227 F.3d 450 (DC. Cir. 2000), cited by the amicus curiae. The FCC explained that whether particular information is call- identifying information has nothing to do with ?whether a carrier uses the dialed digits as part of its own call pro- cessing.? In re Communications Assistance for Law Enforcement Act, 17 F.C.C.R. 6896 (2002). Approved for public release by the ODNI 20160818 13 ment can assure the court that it is highly unlikely that content information will be intercepted along with dialing information. None of the above-cited decisions have drawn that distinction, however. Rather, they have ?atly barred the government from relying on the pen register statutes to intercept post-cut-through digits. See In re Application of the United States, 622 F. Supp. 2d at 422 (?If the Government has no means to exclude collecting content when collecting post-cut?through dialed digits, the Government may not obtain such information under the Pen Register Statute?); In re Applications of the United States, 515 F. Supp. 2d at 339 (?Until the Government can separate that do not contain content from those that do, pen register authorization is insuf?cient for the Government to obtain any In re Application of the United States, 441 F. Supp. 2d at 827 (?Post-cut- through dialed digit contents . . . are not available to law enforcement under the Pen/Trap Statute?); In re Applica? tion. of the United States, No. 6:06?mj?1130, at 5 (M.D. Fla. June 20, 2006) Court rejects the United States? argument that it can obtain post-cut-through digits on the lesser showing permitted by the pen register and trap- and-trace statutes?). We think the better approach is to interpret the de?nitional language of section 3127(3) to mean that a court may not authorize the use of a pen register to collect content information, and that any content information that is collected cannot be used for any investigative purposes. Under that interpretation, a court can author- ize the use of a pen register to collect post-cut-through digits, as long as the collecting agency takes all reasona- bly available steps to minimize the collection of content information and is prohibited from making use of any content information that may be collected. We conclude that the latter interpretation of section 3127(3) is more in line with the statutory text and the Approved for public release by the ODNI 20160818 14 purpose the provision was intended to serve. In particu- lar, we do not believe Congress intended to prohibit the use of pen registers Whenever there was any risk that the intercepted digits would constitute content information. To the contrary, we believe the best interpretation of the related provisions of the pen register statutes is that Congress understood that content information might sometimes be intercepted by authorized pen registers, but intended that steps should be taken to minimize that risk to the extent reasonably possible. Both the text and the legislative history of the pen register statutes support this interpretation of section 3127(3). 1 It is clear from the text of the pen register provisions in title 18, read as a whole, that Congress understood that some content information might be intercepted in the course of executing a valid pen register order. One of those provisions is 18 U.S.C. 3121(0). The statute states: Limitation. A government agency author- ized to install and use a pen register or trap and trace device under this chapter or under State law shall use technology reasonably available to it that restricts the recording or decoding of elec- tronic or other impulses to the dialing, routing, addressing, and signaling information utilized in the processing and transmitting of Wire or elec? tronic communications so as not to include the contents of any wire or electronic communications. 18 U.S.C. 3121(c). That language requires the government to use ?rea- sonably available? technology to avoid recording content information. But the prohibition is conditional, requiring the government to use such restricting technology only if it is ?reasonably available.? Thus, by requiring the use of Approved for public release by the ODNI 20160818 15 ?technology reasonably available? to restrict recording and decoding of intercepted information to dialing infor- mation, Congress recognized that such technology might not be available or might not achieve the objective with perfect accuracy. The plain import of the statutory language is that, ab- sent such ?reasonably available? technology, law?illy authorized pen registers will sometimes intercept and decode content information contained in dialed digits, in addition to information regarding dialing information. Thus, section 3121(c) strikes a compromise that allows the government to obtain the dialing information to which it is entitled, While requiring that all reasonably available measures be taken to avoid or minimize the collection of content information. As the amicus curiae points out, section 3121(0) is not incorporated by reference in title IV of FISA and therefore does not directly apply to FISA pen register applications. Nonetheless, it is important to our analysis here because it provides guidance in determining how Congress intend- ed courts to interpret the de?nitional provisions, sections 3127(3) and (4), which apply to both title 18 and title IV of FISA. The argument that section 3121(c) is irrelevant to FISA pen registers also ignores the body of law that teaches that ?where words are employed in a statute which had at the time a well-known meaning at common law or in the law of this country they are presumed to have been used in that sense unless the context compels to the contrary.? Lorillard v. Pans, 434 US. 5?75, 583 (1978) (quoting Standard Oil v. United States, 221 US. 1, 59 (1911)). Based on the legislative history of, and amendments to, the criminal pen register statute, and Congress?s understanding of the developing technology, it can safely be assumed that Congress?in incorporating the criminal pen register de?nition into PISA?understood that it was Approved for public release by the ODNI 20160818 16 incorporating more than just the de?nition of a pen register at section 3127. Indeed, the author of what became section 3121(c), Senator Patrick Leahy, was quite clear that the provision was necessary to address the incidental collection of content under a pen register order. 147 Cong. Rec. 20,680 (2001) (statement of Sen. Patrick Leahy). But at the same time Senator Leahy recognized that the government?s ability to avoid the collection of content information was subject to the limitations of ?reasonably available technology.? Id. The amicus curiae takes the position that the de?ni- tional language of section however, that such information shall not include the contents of any communication??plainly forecloses the conclusion that a pen register may lawfully intercept content under any circumstances. And some courts, likewise seizing on the ?provided? clause of section 3127(3), have dismissed section 3121(c) as a mere ?added precaution to ensure that the Government does not use an authorized pen register to collect contents.? In re Application of the United States, 622 F. Supp. 2d at 421. We cannot agree with either position. Our duty is ?to construe statutes, not isolated provisions,? and to properly discharge that duty, ?we must read the [statute?s] words in their context and with a View to their place in the overall statutory scheme.? King 0. Burwell, 135 S. Ct. 2480, 2489 (2015). Of particular salience here, we are to avoid interpreting one statutory provision in a manner that would render another provision super?uous. Carley v. United States, 556 US. 303, 314 (2009). In focusing narrowly on section 3127(3) and giving short shrift to the natural implication of section 3121(c), the amicus curiae?s plain-language argument and the ?added precaution? theory run afoul of these principles. If section 3127(3) haired courts from authorizing the collec- tion of post-cut-through digits, there would be no need for Approved for public release by the ODNI 20160818 technology to distinguish between dialing information and content information. The need for technology to distin- guish between the two types of information arises only if the courts can authorize investigators to intercept signals that can sometimes contain content. Because only post- cut-through digits can contain content information, the limitation of section 3121(c) must necessarily be directed to post-cut-through digits. And because the limitation in section 3121(c) is conditional, not absolute, the two provi- sions can be read in harmony only by construing them to permit the interception of post-cut?through digits under appropriate circumstances.7 2 The background and development of the provisions of title 18 that authorize the installation and use of pen registers confirm our understanding of the statutory text by shedding further light on the meaning of the pen '7 The amicus curiae contends that if the government?s argument were applied to Internet pen registers, the government could collect information generated by a wide variety of activities on the Internet, includin searchin uploading documents, and drafting emails. onet ess, am1cus argues at pro- spect 0 such collections indicates that the government?s statutory construction must be wrong. We disagree. Even assuming that the government?s statutory theory would apply in the same manner in that different techno- logical setting, we would have to determine whether any technology is reasonably available to excise content. Moreover, the application of the government?s theory in that setting, if it had the consequences argued by amicus curiae, might call for a different Fourth Amendment balancing of interests. Approved for public release by the ODNI 20160818 18 register statutes in general, and section 3121(c) in partic- ular. Prior to 1986, there was no federal statute that gov- erned the use of pen registers and trap-and-trace devices. Title of the Omnibus Crime Control and Safe Streets Act of 1968, Pub. L. No. 90-351, 82 Stat. 197, dealt with the interception of oral or wire communications that could ?be overheard and understood by the human ear.? S. Rep. No. 99-541, at 2 (1968). Title was silent, however, as to the use of pen registers or other devices that could intercept non-content information. In Smith v. Maryland, 442 U.S. 735 (1979), the Su- preme Court held that the Fourth Amendment does not apply to a pen register that simply monitors the digits dialed on a party?s telephone. The Court reasoned that the calling party has voluntarily turned that dialing information over to a third party and has assumed the risk that the third party would turn that information over to the government. Thus, the Court held that pen regis- ters, unlike wiretaps that intercept conversations, could be installed and operated without the need for a court order. In 1986, Congress changed that regime with the enactment of the Electronic Communications Privacy Act of 1986, Pub. L. No. 99-508, 100 Stat. 1848. That statute added a provision authorizing the government to install and use pen registers and trap-and?trace devices, but only upon obtaining a court order, The showing required to obtain such an order was less demanding than the proba- ble cause showing required for a Wiretap authorization, however. For the installation and use of a pen register or trap-and-trace device, the statute required only that the government represent that the information being sought was ?relevant to an ongoing criminal investigation being conducted? by the requester?s agency. 18 U.S.C. 3122(b) (1988). Approved for public release by the ODNI 20160818 19 Eight years later, in the Communications Assistance for Law Enforcement Act of 1994, Pub. L. No. 103?414, 108 Stat. 4279, Congress revisited the use of pen registers and trap-and-trace devices. The legislative history of that statute shows that Congress understood that pen regis- ters were capable of intercepting content information in the course of performing their authorized function of intercepting dialing information.8 Congress?s response to that problem was to direct that the interception of content incidental to the interception of dialing information was to be minimized to the extent that it was technologically feasible to do so. In particular; Congress added the ?limitation? provi- sion, section 3121(c), to the pen register statutes. The enacted version of section 3121(0) stated: A government agency authorized to install and use a pen register under this chapter or under State law shall use technology reasonably availa- ble to it that restricts the recording or decoding of electronic or other impulses to the dialing and signaling information utilized in call processing. 18 U.S.C. 3121(c) (1994). That provision recognized that pen registers were capable of intercepting content information. Congress?s solution to that problem was to direct agencies using pen - 3 The problem of pen registers intercepting ?content? or ?transactional? information was discussed throughout the Joint Hearing on the bill that became the 1994 stat- ute. See Digital Telephony Law Enforcement Access to Advanced Telecomms. Techs. and Serve: Joint Hearings Before the Subcomm. on TechComm. on the Judiciary and the Subcomm. on Civil and Constitutional Rights of the H. Comm. on the Judiciary, 103d Cong. 39-40, 50, 110-11, 114, 116, 158, 161 (1994). Approved for public release by the ODNI 20160818 20 registers to use technology that was ?reasonably availa? ble? to restrict the recording or decoding of content infor? mation and limit the information'obtained to ?the dialing and signaling information utilized in call processing.? In effect, Congress directed the agencies to do the best they reasonably could to limit the interception of content information, but it did not suggest that, in the absence of such reasonably available technology, a pen register could not be authorized if it posed the risk of intercepting content information. Both the House and Senate Reports on the 1994 Act explained that the purpose of the amendment was not to prohibit the use of pen registers, but to ?require[] law enforcement to use reasonably available technology to minimize information obtained through pen registers.? S. Rep. No. 103-402, at 18 (1994); HR. Rep. No. 103-827, pt.1, at 17 (1994).9 In particular, the reports explained that the new provision would require government agen- cies ?to use, when reasonably available, technology that restricts the information captured by such device to the dialing or signaling information necessary to direct or process a call, excluding any further communication conducted through the use of dialed digits that would otherwise be captured.? S. Rep. 0. 103-402, at 31; HR. Rep. No. 103-827, pt. 1, at 32. 9 The term ?minimization? has a familiar meaning in the context of interceptions of electronic communications. Section 2518(5) of title 18 directs that electronic surveil- lance must ?be conducted in such a way as to minimize the interception of communications not otherwise subject to interception.? The requirement of minimization thus contemplates that some unauthorized interception will inevitably occur, but that the agency must take steps to keep that interception to a minimum. Approved for public release by the ODNI 20160818 21 Senator Leahy, the principal sponsor of the legisla- tion, used the same language when explaining the text of the amendment during ?oor consideration of the legisla- tion in the Senate. See 140 Cong. Rec. 20,451 (1994) (statement of Sen. Patrick Leahy). Accordingly, as matters stood after the 1994 legisla- tion, the government could obtain authorization to use pen registers, even though those devices might in some instances intercept content information, as long as the government used all technology that was reasonably available to minimize the extent to which such content information was intercepted and decoded. Four years later, Congress amended FISA by adding the pen register and trap-and-trace provisions of title IV, 50 U.S.C. 1841 et seq. The new section 1841 provided that the terms ?pen register? and ?trap and trace device? were to ?have the meanings given such terms in section 3127 of title 18.? Pub. L. No. 105?272, 112 Stat. 2396, 601 (1998). Following the attacks against New York and Wash- ington on September 11, 2001, Congress enacted the USA PATRIOT Act of 2001, Pub. L. No. 107-56, 115 Stat. 272. Among many other provisions, Congress modi?ed portions of the pen register/trap-and-trace statute. The changes made at that time are at the heart of the issue before the court today. The principal change to the pen register/trap-and- trace provisions was to make those provisions applicable not just to telephony, but to all forms of wire and electron- ic communications. In so doing, Congress made four amendments that bear on the present issue. First, Congress omitted the words ?call processing? and added the words ?routing? and ?addressing? to section 3121(c) to cover technologies other than telephony. Id. 216(a). Approved for public release by the ODNI 20160818 22 Second, Congress modi?ed section 3121(c) to state ex? plicitly that the purpose of directing the government to use ?reasonably available? technology to limit the collec- tion of certain electronic signals was ?so as not to include the contents of any wire or electronic communications.? Id. Third, Congress amended the de?nition of ?pen regis- ter? by expanding the de?nition to include ?dialing, rout- ing, addressing, or signaling information transmitted by an instrument or facility from which a wire or electronic communication is transmitted.? Id. 216(c). Fourth, Congress added the proviso in the de?nitions of pen register and trap-and-trace device that read: ?pro- vided, however, that such information shall not include the contents of any communication.? Id. The USA PATRIOT Act was enacted seven weeks after the September 11, 2001, attacks, and in light of the Speed with which it was enacted, there is only limited legislative history for the statute. The changes to sections 3121(c) and 3127 were added in the Senate. In the ab- sence of a committee report, Senator Leahy, the chairman of the Senate Judiciary Committee, presented a detailed summary of the changes on the day before the Act was passed. He explained that the language used in the pen register and :trap-and-trace statutes was intended ?to expressly exclude the use of pen-trap devices to intercept ?content? which is broadly de?ned in 18 U.S.C. 147 Cong. Rec. 20,680 (2001) (statement of Sen. Patrick Leahy). He added that the Act ?requires the government to use reasonably available technology that limits the interceptions under the pen/trap device laws ?so as not to include the contents of any wire or electronic communica- tions.? Id. Importantly, Senator Leahy recognized that, notwith? standing the statutory directive to use reasonably availa- ble technolOgy to avoid collecting content information, the Approved for public release by the ODNI 20160818 23 ?pen/trap devices in use today collect ?content.?? Id. In particular, he recognized the risk of collecting content information from ?[tlhe impulses made after a phone call is connected.? Id. He explained that the amendment to section 3121(0) was intended to underscore the need to incentivize the development of better technology to limit the interception of content information, particularly in light of the fact that the USA PATRIOT Act made the pen register provisions applicable to a Wide array of modern communications technologies, such as the Internet, and not simply traditional telephone lines. See also HR. Rep. o. at 52-53 (2001). Senator Leahy stated that he was concerned that in broadening the types of dialing information that could be intercepted to include routing and addressing infor- mation, Congress might be misunderstood as authorizing the interception of content information. He said that to address that issue, he had favored including de?nitions of those terms in the 2001 statute, but that the administra- tion had objected. Instead, to address his concerns, the administration agreed to include the references to content information in sections 3121(c) and 3127(3) and (4). Senator Leahy also noted that, in light of the known risk of collecting content information from post-cut- through digits, he would have preferred a requirement of somewhat heightened judicial review for pen register and trap-and-trace applications. But in the absence of such a requirement, he acknowledged that the statute continued to require only that the government ?use reasonably available technology? to limit the collection of content information. Senator Leahy?s comments make clear that the new language added in the 2001 statute was intended to avoid expanding the type of information that could be intercept- ed, not to narrow it. In particular, nothing in his com- ments, or elsewhere in the legislative history, suggests Approved for public release by the ODNI 20160818 24 that, in the absence of an effective technological solution, the amendments to the pen register/trap-and-trace stat- utes were intended to prohibit the collection of dialing information simply because there was some risk that content information might incidentally be collected as well. Analysis of the sequence of pertinent statutes leads us to conclude that Congress recognized, from as early as 1994, that judicial authorization to collect post-cut- through digits posed the risk that some content infor- mation would be intercepted. But Congress chose to deal with that risk by requiring the government to use reason- ably available technology to minimize the extent to which such content information was collected. It could have dealt with that risk by preventing the collection of post- cut-through digits altogether, but it did not. We therefore conclude that a close analysis of the statutes that have authorized pen register orders starting in 1986 does not support the view that Congress sought to prohibit any authorized collection of dialing information whenever it posed some risk of additionally collecting content information. What Congress elected was a course of minimization, principally through the use of ?reasona- bly available technology.? Our analysis of the pen register statutes requires us to consider whether those statutes, if construed to author? ize the interception of post-cut-through digits, would run afoul of the Fourth Amendment. As noted above, the Supreme Court in Smith v. Mary- land held that the use of a pen register to collect the numbers dialed on a target telephone does not constitute a ?search? for Fourth Amendment purposes. The Smith case, however, involved the use of a pen register to obtain dialing information only; no content information was at Approved for public release by the ODNI 20160818 issue in that case, in the form of post-cut-through digits or otherwise. It may be that if a pen register interception were di- rected at the acquisition and use of content information, it would be unlawful in the absence of a court order issued on a showing of probable cause. In the context of criminal investigations, that would certainly be the case for the interception of conversations through electronic surveil- lance, Berger v. New York, 388 U.S. 41 (1967), and it has been held that probable cause is required to authorize the disclosure and use of content information in email com- munications, see Warshak v. United States, 490 F.3d 455 (6th Cir. 2007), vacated, 532 F.3d 521 (6th Cir. 2008) (en bane). The same rule might apply to the use of a pen register for the purpose of intercepting content infor- mation. But the F180 judge?s authorization order for post-cut- through digits does not target content information; it targets dialing information. If content information is collected at all, the collection of that information is inci- dental, and the F130 judge?s authorization order directs that no investigative use be made of that information (at least in the absence of a further order from the court). The constitutional issue, therefore, is not whether a probable cause warrant is required to use a pen register to obtain content information for investigative purposes. Rather, the question is whether the risk of incidental collection of content information renders the collection of dialing information in post-cut-through digits unreasona- ble in the absence of a probable cause warrant, even when the content information will not be used for any purpose. We think the answer to that question is no. The touchstone of the Fourth Amendment is reasona- bleness. Riley v. California, 134 S. Ct. 2473, 2482 (2014); United States v. Knights, 534 U.S. 112, 118 (2001); see also Vernonia Sch. Dist. 47J v. Acton, 515 US. 646, 652 Approved for public release by the ODNI 20160818 26 (1995); In re Sealed Case, 310 F.3d 717, 742 (F.I.S.C.R. 2002). In determining the reasonableness of particular governmental action, the court must assess, ?on the one hand, the degree to which it intrudes upon an individual?s privacy and, on the other, the degree to which it is needed for the promotion of legitimate governmental interests.? Wyoming 0. Houghton, 526 US. 295, 300 (1999); see also Tennessee 0. Garner, 471 US. 1, 8 (1985); United States v. Place, 462 US. 696, 703 (1983); In. re Directives Pursuant to Section 1053 of the Foreign Intelligence Surveillance Act, 551 F.3d 1004, 1,012 (F.I.S.C.R. 2008). When law enforcement of?cials undertake a search to uncover evidence of criminal wrongdoing, the familiar requirement of a probable-cause warrant generally achieves an acceptable balance between the investigative needs of the government and the privacy interests of the people. See Vernonia Sch. Dist. 47J, 515 U.S. at 653. But it has long been recognized that some searches occur in the service of ?special needs, beyond the normal need for law enforcement,? and that, when it comes to intrusions of this kind, the warrant requirement is sometimes a poor proxy for the textual command of reasonableness. Id. We conclude that, in the circumstances presented here, the incidental collection of content information during the collection of post-cut-through digits?assuming it constitutes a search in the first place?is constitutional- ly reasonable, even when done without a probable-cause warrant. The idea that of?cial intrusions calculated to preserve the nation?s security against foreign threat might require Special constitutional treatment is not a new one. In Katz v. United States, the ?rst page in the modern chapter of our search-and-seizure jurisprudence, the Supreme Court paused to observe that the Fourth Amendment?s usual strictures might require adjustment ?in a situation involv- ing national security.? 389 US. 347, 358 n.23 (1967). Approved for public release by the ODNI 20160818 27 Five years later, in United States v. United States District Court (Keith), the Court rejected the argument that no warrant need be obtained whenever the government engages in domestic surveillance related to ?internal security matters.? 407 US. 297, 299 (1972). But it took care to emphasize that Keith ?involve only the domestic aspects of national security,? not any ?issues which may be involved with respect to activities of foreign powers or their agents,? id. at 321-22, and it noted ?the View that warrantless surveillance, though impermissible in domes- tic security cases, may be constitutional Where foreign powers are involved,? id. at 322 n.20. Consistent with this counsel, in the decade following Keith, a number of federal appeals courts recognized a ?foreign intelligence? exception to the warrant require- ment. See United States v. Truong Dinh Hung, 629 F.2d 908, 912-16 (4th Cir. 1980); United States 0. Buck, 548 F.2d 871, 875 (9th Cir. 1977); United States v. Butenko, 494 F.2d 593, 604-06 (3d Cir. 1974) (en bane); United States v. Brown, 484 F.2d 418, 426 (5th Cir. 1973). But see Zweibon 0. Mitchell, 516 F.2d 594, 633-51 (DC. Cir. 1975) (en banc) (plurality opinion) (suggesting, in dictum, that no such exception exists).10 1? The dictum in Zweibon was not joined by a majori- ty of the court. As the DC. Circuit has recognized in subsequent cases, the Zweibon. court barred ?warrantless electronic surveillance of persons not suspected of collabo- ration with foreign interests adverse to this country,? but ?there was no opinion of the court on the question of warrantless electronic surveillance of collaborators or suspected collaborators of foreign interests.? Halperin v. Helms, 690 F.2d 977, 1000 n.82 (DC. Cir. 1982); see also Ellsberg 1). Mitchell, 7 09 F.2d 31, 66 11.63 (DC. Cir. 1983); United States v. Bel?eld, 692 F.2d 141, 145 (DC. Cir. Approved for public release by the ODNI 20160818 28 Truong is illustrative. In that case, the FBI became aware that David 'I?ruong, a Vietnamese citizen living in the United States, was obtaining classi?ed papers from a source within the federal government and endeavoring to send them to Vietnamese of?cials in Paris. 629 F.2d at 911-12. With the approval of the Attorney General, but no judicial warrant, Truong?s phone was tapped and his apartment ?bugged.? Id. at 912. He challenged the admission at trial of evidence obtained through this warrantless surveillance, but the district court admitted much of it, and the Fourth Circuit af?rmed. The appeals court observed that, in the area of foreign intelligence, the needs of the executive are particularly ?compelling,? and that a warrant requirement would cripple the govern- ment?s ability to counter threats from abroad with the needed ?stealth, speed, and secrecy.? Id. at 913. Accord- ingly, it held that a search may be constitutionally rea- sonable, notwithstanding the absence of prior judicial authorization, when ?the object of the Search or the sur- veillance is a foreign power, its agent or its collaborators,? and ?the search is conducted primarily for foreign intelli- gence reasons.? Id. at 915 (emphasis supplied) (internal quotation marks omitted).11 More recently, this court both acknowledged the ex- istence of a foreign-intelligence exception to the warrant requirement and explained its doctrinal underpinnings. See In re Directives, 551 F.3d at 1010-12. In In re Direc- tives, we noted that in so-called ?special needs? cases, the Supreme Court has ?excused compliance with the War- 1983); Chagnon 0. Bell, 642 F.2d 1248, 1259 (DC. Cir. 1980). 11 Consistent with this ?primary purpose? require- ment, the court af?rmed the exclusion of evidence gleaned after the date when the government had ?begun to as- semble a criminal prosecution.? Truong, F.2d at 916. Approved for public release by the ODNI 20160818 rant Clause when the purpose behind the government action went beyond routine law enforcement and insisting upon a warrant would materially interfere with the accomplishment of that purpose.? Id. at 1010. The gov- ernment may, for instance, engage in certain warrantless intrusions when it acts as educator; blind adherence to the Warrant Clause in the public schools ?would unduly interfere with the maintenance of the swift and informal disciplinary procedures that are needed, and . . . undercut the substantial need of teachers and administrators for freedom to maintain order.? Vemonia Sch. Dist. 47J, 515 US. at 653. So too may it maintain sobriety checkpoints at which vehicles are stopped (and drivers thereby seized) without suspicion, in the interest of curbing the harms occasioned by drunk driving. Michigan Dep?t of State Police v. Site, 496 US. 444, 450-51 (1990). We recognized in In re Directives that when the gov- ernment engages in foreign intelligence surveillance?n0 less than when it acts to maintain discipline in the schools or operates sobriety checkpoints?its needs go beyond ?any garden-variety law enforcement objective,? and its objectives would be seriously hampered by the requirement of a warrant. In re Directives, 551 F.3d at 1011. Collecting foreign intelligence with an toward safeguarding the nation?s security serves an interest?a ?particularly intense? interest?different from the gov- ernment?s interest in the workaday enforcement of the criminal law.? And if the government were constrained 12 In discussing the importance of the government?s interest in preserving and protecting national security, we criticized Truong?s primary-purpose requirement as ?unstable, unrealistic and confusing.? In re Directives, 551 F.3d at 1011 (internal quotation marks omitted). surveillance with a foreign intelligence purpose,? we observed, ?often will have some ancillary criminal-law Approved for public release by the ODNI 20160818 30 to obtain a warrant before undertaking any foreign intel- ligence gathering that constituted a search, its ?ability to collect time-sensitive information? would be ?hinder[ed]? and ?the vital national security interests at stake? imped- ed. Id. We thus held that the Fourth Amendment does not require a probable-cause warrant ?when surveillance is conducted to obtain foreign intelligence for national security purposes and is directed against foreign powers or agents of foreign powers reasonably believed to be located outside the United States.? Id. at 1012. In re Directives virtually controls this case. The rele- vant statute at issue in this case authorizes the use of a pen register ?to obtain foreign intelligence information . . . to protect against . . . clandestine intelligence activities.? 50 U.S.C. 1842(a)(1). Pursuant to that statute, the government seeks to monitor the dealings of a person, currently in the United States, who is suspected of collect- ing intelligence in the service of a foreign power. The purpose of the proposed monitoring is the preservation of national security. Few government interests are of a higher order. The interest at stake is no less?and may even be greater?for the foreign agent?s being present in this country. And were we to insist on a showing of probable cause and the issuance of a judicial warrant in this setting, we would impede the Executive?s ability to. bring to bear against the threat those faculties??stealth, speed, and secrecy,? Truong, 629 F.2d at 913?needed to secure the nation?s well-being in this most fundamental and sensitive of government endeavors. We thus conclude that when the government, acting pursuant to a program of surveillance involving a legiti- purpose.? Id. We therefore concluded that the more sensible requirement was that the ?programmatic pur- pose? of the intelligence-gathering ?involve? some legiti- mate objective beyond ordinary crime control.? Id. Approved for public release by the ODNI 20160818 31 mate objective that goes beyond everyday crime control, seeks to use a pen register directed at a person located in the United States who is reasonably believed to be en- gaged in clandestine intelligence activities on behalf of a foreign government, it may do so Without obtaining a probable-cause warrant even if its monitoring of post-cut- through digits constitutes a search under the Fourth Amendment; This is not to say, of course, that the Fourth Amend- ment has no role to play in such cases. It is only to say that, in this context, the warrant requirement is ill-suited to gauge what is reasonable. The textual command of reasonableness??the ultimate touchstone of the Fourth Amendment,? Riley, 134 S. Ct. at 2482?sti11 governs. Indeed, it retains its whole force. We now turn to the question of reasonableness, a question that requires us to balance against the degree of the government?s intrusion on individual privacy the degree to which that intrusion furthers the government?s legitimate interests. Houghton, 526 US. at 300. In the circumstances presented here, the scale tips in the gov- ernment?s favor. The search, assuming it is one, is rea- sonable. In particular, the factors that render the search reasonable are (1) the paramount interest in investigating possible threats to national security; (2) the investigative importance of having access to the dialing information provided by post-cut?through digits, (3) the incidental nature of the collection of content information from post- cut-through digits, (4) the relatively slight intrusion on privacy entailed by the acquisition of post-cut-through digits, (5) the prohibition against the use of any content information obtained from the pen register or trap-and- trace device, (6) the steps taken by the government to minimize the dissemination of post-cut-through digits; and (7) the fact that FISA pen register interceptions are conducted only with the approval and under the supervi- Approved for public release by the ODNI 20160818 32 sion of a neutral magistrate, in this case a FISC judge. We discuss each of those factors in more detail below. First, the Supreme Court has stated that ?no govern- mental interest is more compelling? than national securi- ty. Haig v. Agee, 453 US. 280, 307 (1981); see In re Directives, 551 F.3d at 1012 (the governmental interest in national security ?is of the highest order of magnitude?); In re Terrorist Bombings of US. Embassies, 552 F.3d 157, 174 (2d Cir. 2008). Thus, the government?s investigative interest in cases arising under FISA is at the highest level and weighs heavily in the constitutional balancing pro- cess. Second, as the facts of this case demonstrate, the dial- ing information in post-cut-through digits may be of critical investigative importance in certain cases in which pen register authorization is sought. If the subject of a pen register uses a calling service, a pen register that does not collect post-cut-through digits will disclose no information at all about the ultimate destination of the call. Because subjects of national security investigations seek to avoid detection of their activities, the loss of access to post-cut-through digits is likely to substantially under- cut the value of a pen register in a signi?cant number of cases. Third, a pen register authorized in a FISA investiga- tion is targeted at dialing information; the collection of any content information from post-cut-through digits is incidental to the purpose of the pen register. The inci- dental collection of constitutionally protected material does not render the authorized collection of unprotected material unlawful. See In re Directives, 551 F.3d at 1015 (citing United States v. Kahn, 415 US. 143 (1974), and United States v. Schwartz, 535 F.2d 160 (2d Cir. 1976) (?Incidental collections occurring as a result of constitu~ tionally permissible acquisitions do not render those acquisitions Approved for public release by the ODNI 20160818 33 The application of that rule to searches of documents is particularly instructive here. The Supreme Court recognized in Andresen. v. Maryland, 427 US. 463, 482 11.11 (1976), that ??lm searches for papers, it is certain that some innocuous documents will be examined, at least cursorily, in order to determine whether they are, in fact, among those papers authorized to be seized.? The inci- dental examination of such documents to determine whether they are subject to authorized seizure is analo- gous to the examination of post-cut-through digits to determine if they contain content information; once it is determined that particular post-cut-through digits con- tain content information, that information is excluded from any investigative use. Fourth, the content information found in some post- cut-through digits is likely to be of marginal privacy value. As the FISC judge explained in the certi?cation order, post-cut?through digits that constitute contents ?involve a narrow category of information from a subset of calls placed from a targeted phone number? and thus represent ?a lesser intrusion than, for example, obtaining the full contents of all calls to or from a targeted phone number.? For that reason, in balancing the seriousness of the invasion of the individual?s personal privacy against the importance of the government?s interest, the degree of the intrusion resulting from collecting post-cut-through digits will typically be modest. Fifth, as the FISC judge?s authorization order makes clear (and is uniformly re?ected in FISC pen regis- ter/trap-and-trace authorization orders), any content information that is collected as part of the interception of post-cut?through digits may not be used for any investiga- tive purpose, absent an order from the court.13 That 13 The government advises us that in the course of its pen register investigations, no such order has ever been Approved for public release by the ODNI 20160818 34 prohibition on use protects against the risk that an inves- tigative agency might seek to obtain authorization to intercept post-cut?through digits in order to obtain access to the content information contained therein. Sixth, minimization procedures are available, and are regularly employed, to limit the extent to which content information that is incidentally intercepted during the collection of post-cut?through digits is made available to, or used and disseminated by, government agents. The Department of Justice has taken several steps to minimize access to post-cut-through digits and reduce the risk that content information will be intercepted or dis- closed. The prohibition against targeting or using content information obtained from post?cut-through digits was set forth in a 2002 memorandum of the Deputy Attorney General, and the ?eld of?ces have been instructed to implement procedures to ensure compliance with the policies in that memorandum. See Memorandum from Larry D. Thompson, Deputy US. Attorney Gen., Avoiding Collection and Investigative Use of ?Content? in the Operation of Pen Registers and Trap and Trace Devices (May 24, 2002). Among those procedures is a measure that requires masking post-cut-through digits in investigative ?le materials. Only an analyst who has undergone special training may unmask the post-cut-through digits, and only after providing justi?cation for doing so. Record on Appeal, Tab 3, at 17-20. In some circumstances, depend- ing on the nature of the subscriber to the telephone that was initially contacted, even an analyst may not examine post-cut-through digits. For example, if the initial con- granted; in fact, the government has never even sought such an order. See also Record on Appeal, Certi?cation at 2 n.1. Approved for public release by the ODNI 20160818 35 nection is to a ?nancial institution, an analyst may not examine any post-cut-through digits because there is reason to believe that post-cut-through digits may contain content. Minimization measures have been recognized as important to the lawfulness of investigative procedures in various settings. Most signi?cantly, federal Wiretap law recognizes that some conversations that were not intend- ed to be intercepted will inevitably be overheard. The answer given by Congress and endorsed by the courts is to require minimization of such intrusions to the extent reasonably practicable. See Scott v. United States, 436 US. 128, 139-43 (1978); Drimal v. Tai, 786 F.3d 219, 223- 24 (2d Cir. 2015); United States v. Glover, 681 F.3d 411, 420-21 (DC. Cir. 2012). The Supreme Court has applied the same principle to document searches, emphasizing the importance of mini- mization in both settings. See Andresen, 427 US. at 482 n.11 (?In both kinds of searches [searches of conversations and searches of documents], reSponsible of?cials, includ- ing judicial of?cials, must take care to assure that they are conducted in a manner that minimizes unwarranted intrusions upon And in other Fourth Amend- ment contexts as well, the Supreme Court has empha? sized the importance of minimization steps employed to reduce the intrusiveness of the invasion in question. See, Maryland v. King, 133 S. Ct. 1958, 1979-80 (2013) (acquisition of arrestees? DNA less intrusive because authorized for use only for limited purpose of identi?ca- tion); Bd. of Educ. of Indep. Sch. Dist. No. 92 of Pottawat- omie Cly. u. Earls, 536 US. 822, 832-33 (2002) (school drug testing program less intrusive because results kept in con?dential ?les and used for only limited purposes); Vemonia School Dist. 47J, 515 US. at 658 (school drug testing program less intrusive because of limited purpose of tests and limited dissemination of results). Approved for public release by the ODNI 20160818 36 Finally, an important aspect of the use of pen regis- ters in FISA investigations is the role played by FISC judges in authorizing and supervising pen register inter- ceptions. Although the court does not require a showing of probable cause to authorize pen register interceptions, it is responsible for supervising the execution of pen register orders. As noted above, title IV of FISA contains a provision authorizing FISC judges ?to impose additional privacy or minimization procedures with regard to the installation or use of a pen register or trap and trace device.? 50 U.S.C. 1842(hX2). In appropriate circumstanCes, FISC judges can use that authority to ensure that the interception of content information through the collection of post-cut?through digits is kept to a minimum, consistent with the govern- ment?s right to intercept dialing information. Besides requiring that the government use all reasonably availa- ble technology to minimize or eliminate the collection of content information, FISC judges can insist that the government assess the risk of intercepting content infor- mation in particular cases and can deny authorization for post-cut-through digits (or impose further restrictions) when that risk is deemed to be unacceptably high as, for example, in the case of a request to renew an application for a pen register that has previously intercepted a sub- stantial amount of content information.14 The judicial scrutiny of pen register applications and the supervision of the execution of pen register orders further reduces the risk that such measures will be em- 14 In addition to the statutory authorization for the imposition of minimization procedures, FISA contains a suppression remedy that is available if information from pen registers or trap-and-trace devices was unlawfully acquired or if the devices were not operated in conformity with the authorizing order. 50 U.S.C. 1845(e)(1). Approved for public release by the ODNI 20160818 37 played under circumstances, or in a manner, that unrea? sonably intrudes on individuals? privacy interests. In sum, we hold that the request in this case for authorization to intercept post-cut-through digits satis?es the reasonableness standard of the Fourth Amendment. Put another way, the Constitution does not go so far as to impose an across-the~board prohibition on the collection of dialing information in the absence of probable cause, simply because of the risk that some content information Will be incidentally intercepted as well. IV We conclude that Congress intended to minimize the collection of content information by insisting that reason- ably available technology be used to segregate dialing information from content information. The government represents?and we have no reason to doubt-?that no such technology is currently reasonably available. In that circumstance, we conclude that the government is not barred from using pen registers and trap-and-trace devic- es to intercept post-cut-through digits because of the risk that the use of those devices might, in some instances, intercept digits that turn out to constitute content infor- mation. It is true that Congress intended to bar courts from authorizing the use of pen registers that target content information. That is not to say, however, that Congress intended to prevent the use of pen registers for the legiti- mate purpose of obtaining dialing information simply because there was some risk that the pen registers would inadvertently intercept content information in the course of an authorized and lawful interception. For the reasons set forth above, we answer the certi? ?ed question in this matter as follows: the FISC may authorize the collection and decoding of post-cut-through digits as long as the government is prohibited from mak? 38 ing investigative or evidentiary use of any content infor- mation contained in that material, and as long as the court directs that appropriate procedures be used to minimize the collection of content information, including the use of any reasonably available technology that may be developed to restrict the recording and decoding of pen register or trap-and-trace information to dialing infor- mation.