Ristenpart Decl.
`
`
`
`
`
`UNITED STATES PATENT AND TRADEMARK OFFICE
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`_____________________
`
`Zoom Video Communications, Inc.,
`Petitioner,
`
`v.
`
`Cyph, Inc.,
`Patent Owner.
`______________________________________________________________
`
`Case No. IPR2023-00140
`
`U.S. Patent No. 9,948,625
`Issue Date: April 17, 2018
`
`
`
`
`DECLARATION OF DR. RISTENPART IN SUPPORT OF PETITION FOR
`INTER PARTES REVIEW OF
`U.S. PATENT NO. 9,948,625
`
`
`
`
`
`
`
`
`
`
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`
`TABLE OF CONTENTS
`
`Page
`
`INTRODUCTION ........................................................................................... 4
`I.
`QUALIFICATIONS ....................................................................................... 4
`II.
`III. MATERIALS CONSIDERED ........................................................................ 6
`IV. PERSON OF ORDINARY SKILL IN THE ART .......................................... 9
`V.
`LEGAL STANDARDS ................................................................................. 10
`A.
`Relevant Time Period for Invalidity Analysis .................................... 11
`B.
`Claim Construction ............................................................................. 11
`C.
`Anticipation ......................................................................................... 13
`D. Obviousness ........................................................................................ 13
`VI. SUMMARY OF OPINIONS ........................................................................ 16
`VII. TECHNOLOGY BACKGROUND .............................................................. 16
`A.
`Cryptography and Encryption ............................................................. 16
`B.
`Key Distribution in Symmetric Encryption ........................................ 23
`VIII. THE ’625 PATENT ...................................................................................... 24
`A.
`Specification ....................................................................................... 25
`B.
`Prosecution History ............................................................................. 26
`C.
`Challenged Claims .............................................................................. 27
`IX. OVERVIEW OF THE PRIOR ART ............................................................. 28
`A. U.S. Patent No. 6,363,154 (“Peyravian”; Ex. 1005) ........................... 28
`B.
`UK Patent Application Publication No. GB 2 422 277 (“Yeun”; Ex.
`1006) ................................................................................................... 32
`X. GROUNDS ................................................................................................... 35
`A. Ground 1: Claims 1 and 2 Are Obvious Over Peyravian .................... 35
`1.
`Claim 1 ..................................................................................... 35
`a.
`[1.0] “A method, comprising:” ....................................... 35
`
`
`
`1
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`
`
`
`B.
`
`b.
`
`c.
`
`d.
`
`e.
`
`f.
`
`g.
`
`[1.1] “generating a shared symmetric key to begin a
`communication session among a group of users by a first
`user;” .............................................................................. 35
`[1.2] “distributing, by the first user, the generated shared
`symmetric key to each user in the group of users;” ....... 40
`[1.3] “communicating within the communication session
`among a group of users, wherein” .................................. 42
`[1.4] “each user encrypts a message to the group of users
`to be distributed through the communication session
`using the generated shared symmetric key, and” ........... 43
`[1.5] “each user decrypts a message received from the
`communication session using the generated shared
`symmetric key;” ............................................................. 46
`[1.6] “wherein additional users are added to the existing
`communication session when the first user distributes to
`the additional users the generated shared symmetric key.”
` ........................................................................................ 47
`Claim 2 ..................................................................................... 49
`a.
`[2.0] “The method of claim 1, further comprising
`changing users within the group of users to reform the
`communication session among a new group of users
`comprises:” ..................................................................... 49
`[2.1] “generating a new shared symmetric key by the first
`user;” .............................................................................. 51
`[2.2] “distributing, by the first user, the generated new
`shared symmetric key to each user in the new group of
`users;” ............................................................................. 51
`[2.3] “communicating to the communication session
`among a new group of users, wherein” .......................... 52
`[2.4] “each user encrypts a message to the new group of
`users to be distributed through the communication
`session using the generated new shared symmetric key,
`and” ................................................................................ 53
`[2.5] “each user decrypts a message received from the
`communication session using the generated new shared
`symmetric key.” ............................................................. 54
`Ground 2: Claims 1 and 2 Are Obvious Over Yeun ........................... 55
`1.
`Claim 1 ..................................................................................... 55
`a.
`[1.0] “A method, comprising:” ....................................... 58
`
`2.
`
`b.
`
`c.
`
`d.
`
`e.
`
`f.
`
`2
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`b.
`
`c.
`
`d.
`
`e.
`
`f.
`
`g.
`
`[1.1] “generating a shared symmetric key to begin a
`communication session among a group of users by a first
`user;” .............................................................................. 59
`[1.2] “distributing, by the first user, the generated shared
`symmetric key to each user in the group of users;” ....... 64
`[1.3] “communicating within the communication session
`among a group of users, wherein” .................................. 69
`[1.4] “each user encrypts a message to the group of users
`to be distributed through the communication session
`using the generated shared symmetric key, and” ........... 70
`[1.5] “each user decrypts a message received from the
`communication session using the generated shared
`symmetric key;” ............................................................. 74
`[1.6] “wherein additional users are added to the existing
`communication session when the first user distributes to
`the additional users the generated shared symmetric key.”
` ........................................................................................ 76
`Claim 2 ..................................................................................... 77
`a.
`[2.0] “The method of claim 1, further comprising
`changing users within the group of users to reform the
`communication session among a new group of users
`comprises:” ..................................................................... 77
`[2.1] “generating a new shared symmetric key by the first
`user;” .............................................................................. 78
`[2.2] “distributing, by the first user, the generated new
`shared symmetric key to each user in the new group of
`users;” ............................................................................. 79
`[2.3] “communicating to the communication session
`among a new group of users, wherein” .......................... 80
`[2.4] “each user encrypts a message to the new group of
`users to be distributed through the communication
`session using the generated new shared symmetric key,
`and” ................................................................................ 80
`[2.5] “each user decrypts a message received from the
`communication session using the generated new shared
`symmetric key.” ............................................................. 82
`XI. NO SECONDARY CONSIDERATIONS .................................................... 84
`
`
`
`2.
`
`b.
`
`c.
`
`d.
`
`e.
`
`f.
`
`
`
`3
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`
`I.
`
`I, Thomas Ristenpart, Ph.D., declare as follows:
`
`INTRODUCTION
`1.
`I have been retained by counsel for Zoom Video Communications,
`
`Inc. (“Petitioner”) to provide my opinion regarding the validity of claims 1 and 2
`
`of U.S. Patent No. 9,948,625 (the “challenged claims” of the “’625 patent”)
`
`(attached as Ex. 1001 to the accompanying Petition for Inter Partes Review).
`
`2.
`
`I am being compensated at my standard rate of $400 per hour (plus
`
`expenses) for this matter. My payment is not contingent in any way on the
`
`outcome of this mater. I have no financial or other personal interest in the outcome
`
`of this matter.
`
`II. QUALIFICATIONS
`3.
`I have summarized in this section my educational background, career
`
`history, publications, and other relevant qualifications. My Curriculum Vitae,
`
`which includes my qualifications as well as my publications, is included as Ex.
`
`1004.
`
`4.
`
`I am an expert in the field of computer security, including applied and
`
`theoretical cryptography and privacy.
`
`5.
`
`I received a Bachelor of Science degree in Computer Science and
`
`Engineering from University of California, Davis in 2003. In 2005, I earned my
`
`Master of Science degree in Computer Science from University of California,
`
`
`
`4
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`Davis. And, in 2010, I earned a Ph.D. degree in Computer Science from
`
`University of California, San Diego. My doctoral studies focused on computer
`
`security and cryptography. My dissertation topic was on “New Approaches for
`
`Building Cryptographic Hash Functions”, which introduced new design methods
`
`for hash functions, a widely used cryptographic primitive.
`
`6.
`
` My work as an academic researcher has grown to touch on many
`
`areas of applied cryptography, with over one hundred peer-reviewed publications
`
`at the top academic venues in cryptography, security, and beyond. I have published
`
`in the area of encrypted messaging, for example my work on “Traceback for End-
`
`to-End Encrypted Messaging”; “Asymmetric Message Franking: Content
`
`Moderation for Metadata-Private End-to-End Encryption”; and “Orca: Blocklisting
`
`in Sender-Anonymous Messaging”. I served as co-program chair of the Advances
`
`in Cryptology—CRYPTO conference, a flagship publication venue conference of
`
`the International Association of Cryptologic Research (IACR). Being selected to
`
`be co-chair reflects the academic community’s high regard for my breadth and
`
`depth of expertise in cryptography. In addition to my academic work, I have
`
`experience working in industry to build cryptographic systems. I worked part time
`
`at Cloudflare to design and implement advanced cryptographic protocols that are
`
`now deployed for use in helping improve security in practice. Previously I served
`
`on the cryptographic advisory board for Skyhigh Networks, which built
`
`
`
`5
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`cryptographic security products. My work has also led to many industry standards
`
`of wide use.
`
`III. MATERIALS CONSIDERED
`7.
`In forming the opinions set forth in this Declaration, I have considered
`
`and relied upon my education, research, experience, knowledge, and professional
`
`judgment, all documents cited in this Declaration, and the following documents,
`
`which I understand are being submitted as exhibits along with the Petition:
`
`Exhibit No.
`
`Description
`
`1001
`
`1002
`
`1005
`
`1006
`
`1007
`
`1008
`
`1009
`
`U.S. Patent No. 9,948,625 (“’625 patent”)
`
`File History for the ’625 patent (“’625 patent FH”)
`
`U.S. Patent No. 6,363,154 (“Peyravian”)
`
`UK Patent Application Publication No. GB 2 422 277 (“Yeun”)
`
`Gustavus J. Simmons, Symmetric and Asymmetric Encryption,
`Vol. 11, No. 4 ACM Computing Surveys 305-330 (Dec. 1979),
`available at https://dl.acm.org/doi/10.1145/356789.356793
`
`Whitfield Diffie & Martin E. Hellman, New Directions in
`Cryptography, IEEE Trans. on Information Theory, vol. IT-22, no.
`6, pp. 644–654 (Nov. 1976), available at
`https://ieeexplore.ieee.org/document/1055638;
`https://ee.stanford.edu/~hellman/publications/24.pdf
`
`R.L. Rivest, A. Shamir, and L. Adleman, A Method for Obtaining
`Digital Signatures and Public-Key Cryptosystems, Commc’n of
`the ACM, vol. 21, no. 2, pp. 120–126 (Feb. 1978), available at
`https://dl.acm.org/doi/10.1145/359340.359342
`
`1010
`
`U.S. Patent No. 4,405,829
`
`
`
`6
`
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`
`
`Exhibit No.
`
`Description
`
`1011
`
`1012
`
`1013
`
`1014
`
`1015
`
`1016
`
`1017
`
`Neal Koblitz, Elliptic Curve Cryptosystems, Mathematics of
`Computation, vol. 48, no. 177, pp. 203–209 (Jan. 1987), available
`at https://www.jstor.org/stable/2007884;
`https://www.ams.org/journals/mcom/1987-48-177/S0025-5718-
`1987-0866109-5/
`
`Nat’l Inst. of Standards & Tech., U.S. Dep’t. of Com., FIPS PUB
`180-1 (Secure Hash Standard) (Apr. 17, 1995) (withdrawn on
`Aug. 1, 2002, and superseded by FIPS 180-2), available at
`https://csrc.nist.gov/publications/detail/fips/180/1/archive/1995-
`04-17
`
`Nat’l Inst. of Standards & Tech., U.S. Dep’t. of Com., FIPS PUB
`180-4 (Secure Hash Standard (SHS)) (Mar. 2012) (withdrawn on
`Aug. 5, 2015), available at
`https://csrc.nist.gov/publications/detail/fips/180/4/archive/2012-
`03-06
`
`Simon Singh, THE CODE BOOK: THE SCIENCE OF SECRECY FROM
`ANCIENT EGYPT TO QUANTUM CRYPTOGRAPHY (First Anchor
`Books Ed., Sept. 2000), available at https://books-
`library.net/files/books-library.net-04040109Rq2I5.pdf (“The Code
`Book”)
`
`Cyph, Inc. v. Zoom Video Communications, Inc., No. 4:22-cv-
`00561-JSW, Dkt. No. 58 (N.D. Cal. July 11, 2022)
`
`Raymond B. Jennings III et al., A Study of Internet Instant
`Messaging and Chat Protocols, Vol. 20, Issue 4 IEEE Network
`pp. 16–21 (July/August 2006), available at
`https://ieeexplore.ieee.org/document/1668399
`
`Bazara I.A. Barry & Fatma M. Tom, Instant Messaging:
`Standards, Protocols, Applications, and Research Directions, in
`INTERNET POLICIES AND ISSUES, VOL. 7 1-15 (Chapter 8) (B.G.
`Kutais ed., Nova Science Publishers, Inc. 2010), available at
`https://www.researchgate.net/publication/280307922_Instant_Mes
`
`7
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`
`
`Exhibit No.
`
`Description
`saging_Standards_Protocols_Applications_and_Research_Directio
`ns
`
`1018
`
`1019
`
`1020
`
`1021
`
`1022
`
`1023
`
`1024
`
`Adam Pash, Chat with AIM, MSN, Yahoo, and other contacts over
`Google Talk, LifeHacker (Aug. 14, 2007),
`https://lifehacker.com/chat-with-aim-msn-yahoo-and-other-
`contacts-over-goog-289097
`
`Cyph, Inc. v. Zoom Video Communications, Inc., No. 22-cv-
`00561-JSW, Dkt. No. 74 (N.D. Cal. Oct. 7, 2022), Dkt. No. 75
`(N.D. Cal. Oct. 11, 2022).
`
`Table N/A—U.S. District Courts–Combined Civil and Criminal
`Federal Court Management Statistics (June 30, 2022),
`https://www.uscourts.gov/statistics/table/na/federal-court-
`management-statistics/2022/06/30-2
`
`Cyph, Inc. v. Zoom Video Communications, Inc., No. 21-cv-
`03027-RM-MEH, Dkt. No. 32 (D. Co. Jan. 27, 2022)
`
`National Institute of Standards and Technology’s Cryptography
`website, https://www.nist.gov/cryptography
`
`Nat’l Inst. of Standards & Tech., U.S. Dep’t. of Com., NIST SP
`800-90A (Recommendation for Random Number Generation
`Using Deterministic Random Bit Generators) (January 23, 2012)
`(withdrawn June 2015, and superseded by SP 800-90A Revision
`1), available at
`https://www.nist.gov/publications/recommendation-random-
`number-generation-using-deterministic-random-bit-generators-
`3?pub_id=910345
`
`Nat’l Inst. of Standards & Tech., U.S. Dep’t. of Com., FIPS PUB
`197 (Advanced Encryption Standard (AES)) (Nov. 26, 2001),
`available at https://www.nist.gov/publications/advanced-
`encryption-standard-aes
`
`8
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`
`Exhibit No.
`
`Description
`
`1025
`
`Nat’l Inst. of Standards & Tech., U.S. Dep’t. of Com., FIPS PUB
`46 (Data Encryption Standard (DES)) (Jan. 15, 1977), available at
`https://csrc.nist.gov/publications/detail/fips/46/archive/1977-01-15
`
`IV. PERSON OF ORDINARY SKILL IN THE ART
`8.
`I understand that an assessment of the validity of the patent claims
`
`should be considered from the perspective of a person of ordinary skill in the art
`
`(“POSA”).
`
`9.
`
`I have been advised by counsel that a POSA is a person who
`
`possesses conventional wisdom in the art and is presumed to be aware of all
`
`relevant art at the time of the invention. To determine the appropriate level of a
`
`POSA, the following factors may be considered: (1) the type of problems
`
`encountered in the art; (2) prior art solutions to those problems; (3) the rapidity
`
`with which innovations are made; (4) the sophistication of the technology; and (5)
`
`the educational level of active workers in the field.
`
`10. As described in detail below, the ’625 patent purports to relate to
`
`cryptography and encrypted group communications, in particular, a
`
`communication session among a group of users who encrypt and decrypt data
`
`using the same key. Ex. 1001, Title; 1:58–60; Claims 1–2. The ’625 patent relies
`
`on obvious variations of elements that were well known for many years before
`
`2015, such as symmetric key encryption and distribution of symmetric keys.
`
`
`
`9
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`11.
`
`In view of the purported invention of the ’625 patent and my
`
`experience as a practicing engineer and researcher in this field since at least the
`
`early 2000s, it is my opinion that a POSA at the time of the alleged invention of
`
`the ’625 patent (approximately January of 2015) would have at least a bachelor’s
`
`degree (or equivalent) in applied mathematics, computer science, computer
`
`engineering, electrical engineering, or a related field, and at least one year of
`
`undergraduate (or higher level) coursework, industry experience, or equivalent
`
`research experience in the field of cryptography, and at least one year of
`
`undergraduate (or higher) coursework, industry experience, or equivalent research
`
`experience in the field of instant messaging or chat applications or video- or audio-
`
`conferencing applications. This description is approximate, and a higher level of
`
`education or skill might make up for less experience, and vice versa.
`
`12. My analysis and opinions stated in this Declaration would remain the
`
`same even if a POSA were determined to have somewhat more or less education
`
`and/or experience than I have described above.
`
`V. LEGAL STANDARDS
`13.
`I am not an attorney, but in expressing my opinions in this Declaration
`
`and considering the subject matter of the claims of the ’625 patent, I am relying on
`
`certain legal principles counsel has provided and explained to me.
`
`
`
`10
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`A. Relevant Time Period for Invalidity Analysis
`14.
`I have been asked to assume that the priority date for the claims of the
`
`’625 patent is January 7, 2015, the filing date of a provisional application No.
`
`62/100,684. Therefore, for the purposes of this Declaration, I have analyzed
`
`validity from the perspective of a POSA as of January 2015.
`
`B. Claim Construction
`15.
`I understand that when evaluating the validity of patent claims, claim
`
`terms are generally given their ordinary and customary meaning, which is the
`
`meaning that the term would have to a POSA as of the effective filing date of the
`
`patent. I also understand that a POSA is deemed to read the claim term not only in
`
`the context of the particular claim which a claim term appears, but in the context of
`
`the entire patent, including the specification.
`
`16. Counsel has informed me that, in the pending district court case,
`
`Patent Owner took the position that the phrase “wherein additional users are added
`
`to the existing communication session when the first user distributes to the
`
`additional users the generated shared symmetric key” (element [1.6]) “is a
`
`conditional statement that is not performed in all instances” and requires that “the
`
`referenced step [be] performed only when ‘additional users’ are desired to be
`
`added.” Ex. 1015, 7–8 (emphasis in original).
`
`
`
`11
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`17.
`
`I disagree that this phrase is a conditional statement and is therefore
`
`optional.
`
`18.
`
`I also understand that Applicant added this phrase to overcome prior
`
`art cited by the Examiner during prosecution of the application that issued as the
`
`’625 patent. Ex. 1002, 98–102 (explaining that the prior art “describes creating a
`
`new group of users either ‘by inviting users’ or ‘receiving requests to join from a
`
`user’ which is different from adding additional users to the existing
`
`communication session” (emphasis added by Applicant)); see also id., 30–32, 132–
`
`137; Section VIII.B, below. Thus, if this limitation was optional, the claim could
`
`not be distinguished from the prior art considered by the Examiner when the
`
`condition is not met. And Applicant did not argue during prosecution that the
`
`phrase is optional or that the step need not be performed to practice the claim.
`
`19. My analysis and opinions in this Declaration do not depend on any
`
`particular construction of terms in the challenged claims. I have applied what I
`
`believe a POSA would consider to be the plain and ordinary meaning of all claim
`
`terms. It is my opinion that the prior art discussed below discloses the subject
`
`matter of the challenged claims under any reasonable construction of the claim
`
`terms as discussed below.
`
`
`
`12
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`20. Even under Patent Owner’s claim construction position, however, I
`
`conclude that the prior art discussed below discloses the subject matter of the
`
`challenged claims as discussed below.
`
`C. Anticipation
`21.
`I understand that patent claims may be invalid as “anticipated” in
`
`view of a single prior art reference. Counsel has informed me that a patent claim is
`
`anticipated by the prior art if each and every element of the claim is express or
`
`inherently disclosed in a single prior art reference.
`
`D. Obviousness
`22.
`It is my understanding that a patent claim is invalid if the claimed
`
`invention, as a whole, would have been obvious to a POSA at the time of the
`
`critical date—the effective filing date in the case of the ’625 patent—in view of the
`
`prior art in the field and analogous fields.
`
`23.
`
`I understand that the following factors are considered as part of the
`
`obviousness inquiry: (1) the scope and content of the prior art; (2) the differences
`
`between the prior art and the claims at issue; (3) the level of ordinary skill in the
`
`pertinent art; and (4) secondary considerations such as commercial success, long
`
`felt but unsolved needs, failure of others, and simultaneous invention. I understand
`
`that a “nexus” must be established between the evidence of secondary
`
`
`
`13
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`considerations and what is both claimed and novel in the claim at issue for such
`
`evidence to be relevant to the obviousness analysis.
`
`24.
`
`I understand that a reference qualifies as prior art for obviousness
`
`purposes when it is analogous to the claimed invention. The reference is
`
`analogous art (thus prior art) to the claimed invention if: (1) the reference is from
`
`the same field of endeavor as the claimed invention (even if it addresses a different
`
`problem); or (2) the reference is reasonably pertinent to the problem faced by the
`
`inventor (even if it is not in the same field of endeavor as the claimed invention).
`
`25.
`
`I understand that obviousness may be shown by demonstrating that it
`
`would have been obvious to modify what is taught in a single piece of prior art, or
`
`to combine the teachings of more than one prior art reference, to create the claimed
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`invention. In determining whether a piece of prior art could have been modified,
`
`or combined with other prior art references or with other information within the
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`knowledge of a POSA, the following are examples of approaches and rationales
`
`that may be considered:
`
`a.
`
`b.
`
`c.
`
`Combining prior art elements according to known methods to
`yield predictable results;
`Simple substitution of one known element for another to obtain
`predictable results;
`Use of known technique to improve similar devices (methods,
`or products) in the same way;
`
`
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`26.
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`d.
`
`e.
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`Applying a known technique to a known device (method, or
`product) ready for improvement to yield predictable results;
`Applying a technique or approach that would have been
`“obvious to try” (that is, choosing from a finite number of
`identified, predictable solutions, with a reasonable expectation
`of success);
`Known work in one field of endeavor may prompt variations of
`it for use in either the same field or a different one based on
`design incentives or other market forces if the variations are
`predictable to a POSA; or
`Some teaching, suggestion, or motivation in the prior art that
`would have led a POSA to modify the prior art reference or to
`combine prior art reference teachings to arrive at the claimed
`invention.
`I understand that the suggestion or motivation may come from such
`
`f.
`
`g.
`
`sources as explicit statements in the prior art or from the knowledge or common
`
`sense of a POSA. I also understand that a motivation to combine may be found
`
`explicitly or implicitly in market forces; design incentives; the interrelated
`
`teachings of multiple patents; any need or problem known in the field of endeavor
`
`at the time of invention and addressed by the patent; and the background
`
`knowledge, creativity, and common sense of a POSA.
`
`27.
`
`I understand that the approaches and rationales listed above are not
`
`exhaustive. Other approaches and rationales may also support a conclusion of
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`obviousness.
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`
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`28.
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`I understand that an invention that might be considered an obvious
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`variation or modification of the prior art may be considered non-obvious if one or
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`more prior art references discourage or teach away from the line of inquiry
`
`disclosed in the reference(s). However, for purposes of assessing obviousness, a
`
`reference does not “teach away” from an invention simply because the reference
`
`expresses a general preference for an alternative invention. It is my understanding
`
`that the doctrine of teaching away requires an indication that the combination
`
`should not be attempted, because, for example, the combination would fail and/or
`
`be inoperative for its intended purpose.
`
`VI. SUMMARY OF OPINIONS
`29.
`It is my opinion that claims 1 and 2 of the ’625 patent are obvious
`
`over U.S. Patent No. 6,363,154 (“Peyravian”; Ex. 1005).
`
`30.
`
`It is my opinion that claims 1 and 2 of the ’625 patent are obvious
`
`over UK Patent Application Publication No. GB 2 422 277 (“Yeun”; Ex. 1006) in
`
`view of National Institute of Standards and Technology (“NIST”) Special
`
`Publication (SP) 800-90A “Recommendation for Random Number Generation
`
`Using Deterministic Random Bit Generators” (“Barker”; Ex. 1024).
`
`VII. TECHNOLOGY BACKGROUND
`A. Cryptography and Encryption
`31. The title of the ’625 patent is “Encrypted Group Communication
`
`Method.” Ex. 1001, Title. It states that the “embodiments herein generally relate
`
`
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`to cryptography, and, more particularly, to a method of encrypted group
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`communications.” Id., 1:58–60.
`
`32. Cryptography is the science, and art, of secret writing. One of the
`
`goals of cryptography is to prevent an unauthorized and unintended receiver from
`
`determining the content of the message being communicated. Ex. 1007, 306.
`
`33. Encryption is an application of cryptography. It produces an
`
`unintelligible, scrambled message (called “ciphertext”) by applying a key to a
`
`plain, original message (called “plaintext”). Ex. 1014, 11; Ex. 1007, 307.
`
`Decryption reverses that process—it is the process of unscrambling (or recovering)
`
`the scrambled message. Ex. 1014, 11; Ex. 1007, 307. Figure 4 of The Code Book
`
`schematically illustrates the encryption and decryption process:
`
`
`
`Ex. 1014, 11.
`
`34. One of the benefits of cryptography is that only the key needs to be
`
`kept secret from unauthorized parties. See Ex. 1014, 11; Ex. 1007, 307. The
`
`encrypted message (i.e., ciphertext) may be eavesdropped or intercepted by
`
`unauthorized parties during the transmission, but its content is protected by
`
`
`
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`safeguarding the key that should not be exposed. Thus, only the authorized
`
`receiver, who has the right key (or who is able to deduce the right key), should be
`
`able to recover (i.e., decrypt) the encrypted message. See Ex. 1014, 11. Any
`
`unauthorized receiver should not be able to deduce either the message or the
`
`unknown key.
`
`35. The use of keys for purposes of encryption is ancient. History records
`
`that Julius Caesar famously used a substitution shift (the “Caesar shift”) that
`
`replaces each letter in the message with the letter three places further on in the
`
`alphabet (i.e., key) to send a message to Cicero. Ex. 1014, 9–12; see Ex. 1007,
`
`307. For example, “veni, vidi, vici” is encrypted to “YHQL, YLGL, YLFL.”
`
`
`
`Ex. 1014, 10. According to the convention in cryptography, the plain alphabet is
`
`written in lower case letters and the cipher alphabets are written capitals. Id.
`
`36. The “key” to the Caesar shift is that each letter was replaced by the
`
`letter three places further on. The reader who knows this key can recover the
`
`original message by reversing the encryption process and replacing each letter by
`
`the letter three places ahead in the alphabet.
`
`
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`37. The Caesar shift is an example of “symmetric” or “symmetric key”
`
`encryption. The same key (or keys that can be easily computed from each other) is
`
`used for both encryption and decryption. Ex. 1007, 305, 316–318; see Ex. 1008,
`
`644–646. Anyone who knows a particular symmetric key would be able to decrypt
`
`the message encrypted with that symmetric key. It is therefore important that the
`
`symmetric key remains a secret and is known only to the authorized parties to the
`
`communication if the content of the communication is to remain private among the
`
`authorized parties and inaccessible to unauthorized parties. Seeid., 644–645.
`
`Thus, symmetric encryption is also known as “secret key” cryptography. Because
`
`any insecure distribution of the symmetric key would risk unauthorized access to
`
`confidential communications encrypted using the symmetric key, it has long been
`
`known, and would be readily apparent to a POSA, that secure distribution of the
`
`symmetric key is critical to maintaining the privacy and security of
`
`communications encrypted using the symmetric key. See id., 644–646.
`
`38. A more complex application of symmetric key encryption are the
`
`Enigma machines used during World War II. “The strength of the cipher depends
`