Patent Application
20210320796
The present invention relates generally to systems and methods directed toward post-quantum cryptosystems, and, more particularly, relates to cryptosystems utilizing quadratic extension field arithmetic such as pairing-based cryptography, elliptic curve cryptography, code-based cryptography and post-quantum elliptic curve cryptography.
Cryptology is the practice and study of techniques for secure communication in the presence of third parties called adversaries. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages and includes various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation. Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications. Cryptosystems are a suite of cryptographic algorithms needed to implement a particular security service, most commonly for achieving confidentiality. Due to the typical amount and time of computations required for a cryptography session, namely one utilizing post-quantum cryptography, the hardware or processing footprint is quite expansive. As such, utilizing such methods and systems is made impossible or commercially impracticable when desired for use in smaller devices, such as IoT devices.
Therefore, those known systems and methods fail to address small implementations of post-quantum cryptosystems, particularly those which utilize quadratic extension field arithmetic. As these cryptosystems have only just been gaining popularity and acceptance in the cryptographic community, implementations of arithmetic computations for cryptosystems have also made its deployment problematic. More specifically, the primary deficiency with post-quantum cryptosystems has typically been their efficiency. As such, much of the research community has focused on making high-speed implementations. These efforts, however, have resulted in the creation of systems generating large processing footprints that are often inefficient.
In addition, the naive way to implement quadratic extension field arithmetic is to use a random-access register file with a modular addition and multiplication unit. As discussed above, however, these configurations are spatially inefficient and not commercially practicable when smaller devices are the targeted implementation environment. As such, there are no known lightweight implementations of elliptic curve or post-quantum cryptography. Some known hardware implementations target very high performance with very large register files and replicated arithmetic units. Other known implementations of finite-field arithmetic that attempt to target a small processing footprint environment are not versatile and still commercially impracticable in that they utilize binary fields and elliptic curve cryptography.
Therefore, a need exists to overcome the problems with the prior art as discussed above.
The invention provides a system and method for reducing the processing footprint in cryptosystems utilizing quadratic extension field arithmetic that overcomes the hereinbefore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that creates a cryptosystem utilizing quadratic extension field arithmetic implemented with a protocol having a much smaller processing footprint. Specifically, one embodiment of the present invention implements a circular-access register file with three registers operably configured to implement all necessary quadratic extension field arithmetic. The present invention is also directed toward a small accelerator for quadratic extension field arithmetic, or arithmetic in Fp2. The goal of this architecture is to perform these arithmetic operations with as small processing area as possible. By reducing the processing area, the system and process achieves a much smaller resource footprint as well as reduce the necessary power and energy for computing various cryptographic primitives. Additionally, the present invention includes a system and method beneficially operably configured to (1) perform quadratic extension field addition, multiplication, squaring, and inversion in a constrained environment; (2) minimize the number of registers needed to hold intermediate values; (3) minimize the register complexity; (4) minimize the number of arithmetic operations required for extension field arithmetic; and (5) select small arithmetic units to perform extension field arithmetic.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a computer processing system for reducing a processing footprint in cryptosystems utilizing quadratic extension field arithmetic having at least one computer processor with a register file including three processor registers operably configured to implement quadratic extension field arithmetic equations in a finite field of Fp2 and a multiplexer operably configured to selectively shift from each of the three processor registers in sequential order to generate modular addition results and modular multiplication results from the three processor registers.
In accordance with a further feature of the present invention, the register file is of a circular-access register file block.
In accordance with another feature, an embodiment of the present invention includes the three processor registers consisting essentially of a first work processor register, a second work processor register, and an accumulator register.
In accordance with another feature, an embodiment of the present invention includes a digit-serial adder unit operably coupled to the first work processor register and a constant prime number for which the finite field of Fp2 is defined and a modular multiplication unit operably coupled to the second work processor register and the constant prime number for which the finite field of Fp2 is defined.
In accordance with a further feature of the present invention, wherein the digit-serial adder unit and modular multiplication unit are single units.
In accordance with yet another feature of the present invention, the quadratic extension field arithmetic equations have an irreducible polynomial of i2+1. That is, the finite field of Fp2 is defined as Fp[i]/(i2+1). Or in other words, the polynomial field in i, modulo the irreducible polynomial i2+1 yields a finite field containing p2 elements, namely Fp2.
In accordance with another feature, an embodiment of the present invention includes the register file having five processor registers operably configured to implement quadratic extension field arithmetic equations in a finite field of Fp2, wherein the five processor registers consist essentially of a first work processor register, a second work processor register, a third work processor register, a first accumulator register, and a second accumulator register.
In accordance with the present invention, a method for reducing a processing footprint in cryptosystems utilizing quadratic extension field arithmetic comprising the steps of providing at least one computer processor having a register file with a first work processor register, a second work processor register, and an accumulator register and initiating, through the least one computer processor, a cryptography session. The cryptography session includes selecting a constant prime number p for which a finite field of Fp2 is defined, receiving numerical data into the first and second work processor registers sequentially and executing quadratic extension field arithmetic equations in the finite field of Fp2 using the numerical data to generate arithmetic results from each of the first and second work processor registers, receiving the arithmetic results into the accumulator register and providing the arithmetic results from the accumulator register to the first work processor register to define a circular-access register file block, and outputting the arithmetic results through the first work processor register.
In accordance with another feature, an embodiment of the present invention also includes receiving numerical data into the first and second work processor registers sequentially through a one-way data flow.
In accordance with yet another feature, an embodiment of the present invention includes the cryptography session also having the steps of sequentially shifting from first and second work processor registers and the accumulator register through a multiplexer and choosing a quadratic extension field with an irreducible polynomial of i2+1 after the constant prime number p has been defined.
Although the invention is illustrated and described herein as embodied in a system and method for reducing the processing footprint in post-quantum cryptosystems, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention.
Other features that are considered as characteristic for the invention are set forth in the appended claims. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. The figures of the drawings are not drawn to scale.
Before the present invention is disclosed and described, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms “a” or “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term “providing” is defined herein in its broadest sense, e.g., bringing/coming into physical existence, making available, and/or supplying to someone or something, in whole or in multiple parts at once or over a period of time. Also, for purposes of description herein, the terms “upper”, “lower”, “left,” “rear,” “right,” “front,” “vertical,” “horizontal,” and derivatives thereof relate to the invention as oriented in the figures and is not to be construed as limiting any feature to be a particular orientation, as said orientation may be changed based on the user's perspective of the device. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
As used herein, the terms “about” or “approximately” apply to all numeric values, whether or not explicitly indicated. These terms generally refer to a range of numbers that one of skill in the art would consider equivalent to the recited values (i.e., having the same function or result). In many instances these terms may include numbers that are rounded to the nearest significant figure. In this document, the term “longitudinal” should be understood to mean in a direction corresponding to an elongated direction of any processing chip. The terms “program,” “software application,” and the like as used herein, are defined as a sequence of instructions designed for execution on a computer system. A “program,” “computer program,” or “software application” may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and explain various principles and advantages all in accordance with the present invention.
While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. It is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms.
The present invention provides a novel and efficient system and method for reducing the processing footprint of arithmetic computations for cryptosystems. More specifically, the system and method is directed toward a cryptosystem having a lightweight accelerator for arithmetic operations in Fp2 (hereinafter “Fp2 accelerator”) containing p2 elements, wherein “p” is a prime number, preferably a constant prime number for which Fp2 field is defined. The system is lightweight in that it is structurally and operably configured to minimize the number of processor registers, namely intermediate registers, uses a circular work register block, and includes a digit-serial adder and modular multiplier. Specifically, the system is configured with hardware and instructions to target prime fields where extension field arithmetic can be defined over an irreducible polynomial i2+1, wherein this characteristic is specifically targeted to design the Fp2 accelerator.
One embodiment of the present invention is shown schematically through a block diagram in
As those of skill in the art will appreciate, a register file is an array of processor registers in a central processing unit (CPU). In one embodiment, the processor registers 104, 106, 108 are circuit-based register files and may be implemented by way of fast static random access memories (RAMs) with multiple ports. Such RAMs are distinguished by having dedicated read and write ports, whereas ordinary multi-ported RAMs will usually read and write through the same ports. In other embodiments, the processor registers 104, 106, 108 may be implemented by way of fast dynamic RAMs. The instruction set architecture of a CPU will almost always define a set of registers which are used to stage data between memory and the functional units on the chip. In simpler CPUs, these architectural registers correspond one-for-one to the entries in a physical register file (PRF) within the CPU. More complicated CPUs use register renaming, so that the mapping of which physical entry stores a particular architectural register changes dynamically during execution.
In the embodiment shown in
More specifically, the cryptography session may include step 306 defining a constant prime number, p, for which a finite field of Fp2 is defined. The prime number p may be predefined or dynamically and selectively defined by the user and/or the processor. Next, step 308 may include receiving numerical data into the first and second work processor registers 104, 106 sequentially and executing quadratic extension field arithmetic equations (represented schematically in
As those of skill in the art will appreciate, the multiplexer 110 is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send the output. A multiplexer can also be used to implement Boolean functions of multiple variables.
The system may also include a digit-serial adder unit 114 operably coupled to the first work processor register 104 and a constant prime number p (depicted in
The quadratic extension field arithmetic equations operably configured to be carried out by the Fp2 accelerator can include modular addition, subtraction, squaring, multiplication, and inversion in the finite field Fp2. More specifically, elements in Fp2 are represented in the form of A=a0+ia1, wherein i is a non-quadratic residue and a0 and a1 are elements of Fp. When the irreducible polynomial is selected as i2+1, where i=√{square root over (−1)} in Fp2, certain finite field operations can be defined in Fp2 with specific formulas involving Fp2 operations:
A+B=a
0
+b
0
+i(a1+b1)
A−B=a
0
−b
0
+i(a1−b1)
A×B=(a0+a1)(b0−b1)+a0b1−a1b0+i(a0b1+a1b0)
A
2=(a0+a1)(a0−a1)+i2a0a1
A
−1
=a
0(a02+a12)−1−ia1(a02+a12)−1
Thus, an addition and subtraction require 2 Fp additions, a multiplication requires 3 Fp multiplications and 5 Fp additions, a squaring requires 2 Fp multiplications and 3 Fp additions, and an inversion requires 1 Fp inversion, 2 Fp multiplications, 2 Fp squarings, and 2 Fp additions. Table 1, below, exemplifies the Fp2 accelerator carrying out Fp2 squaring. More specifically, assume that we are squaring the value A=a0+ia1 to get A2=(a0+a1)(a0−a1)+i2a0a1. This architecture uses an accumulate-based approach. It is also assumed the file register is of a circular register buffer in the order register R0 to R1 to R2 to R0 and that R0 and R1 are work registers. Therefore, A2 and A×B with the controls shown in Tables 1-2, respectively. Said another way, one register, e.g., register 108 is temporary to accumulate the intermediate results and perform operations sequentially in the work registers, e.g., registers 104, 106.
Table 2, below, exemplifies the Fp2 accelerator carrying out Fp2 multiplication.
Table 3, below, depicts operation complexities for Fp2 arithmetic as compared to known prior art. Specifically, the system and method of the present invention utilizes these multiplication and squaring formulas to minimize their arithmetic complexity. As those of skill in the art will appreciate, Fp multiplication is much more arithmetically intensive than Fp addition.
One benefit to the architecture depicted in
Therefore, to minimize the register footprint, the present inventions preferably utilizes two work registers 104, 106 and an accumulator register 108, which is sufficient for all necessary Fp2 operations. The number of arithmetic operations needed is then minimized by choosing a quadratic extension field with the irreducible polynomial i2+1. In the resulting architecture, digit-serial addition and modular multiplication units 114, 116 may also be utilized to perform the necessary prime field arithmetic in series, using circular register shifts and loads, implemented through the multiplexer as needed.
Beneficially, some principal applications of the present invention may include reducing the processing area overhead (i.e., the number of gates in a digital circuit) to perform Fp2 arithmetic. As such, features such as providing a circular register file, an accumulator-based flow with minimum register complexity, the choice of special form for primes in quadratic extension fields, and small digit-serial arithmetic units to create a separated Fp2 arithmetic unit generates the advantageous small processing footprint in hardware. Another goal or target of the aforementioned system and method is in post-quantum cryptography use, which also translates to uses in elliptic curve cryptography. Other applications include pairing-based cryptography, elliptic curves with isomorphisms (such as 4Q), code-based cryptography, and lattices. With reference now to
More specifically, the Fp2 accelerator architecture 200 utilizes the bit-parallel modular multiplier 202 and a digit-serial adder 204 with a 32-bit adder/subtractor. In this embodiment, two additional work registers 208, 210 (also depicted in
Table 5, below, depicts implementation results of instantiated Fp2 accelerator on Artix-7 FPGA.
The primary source of gates come from the bit-parallel multiplier and there are also many 2:1 multiplexers as a result of interfacing between the registers for various operations. As reflected in Table 5, above, the efficacy of the Fp2 architecture in an Artix-7 FPGA can be seen. This implementation, however, did not include additional control signals, which would constitute an extremely small additional area overhead. The processing area and time complexities are also shown in Table 5 and it can be seen that the Fp2 time complexity uses the operation counts in Table 3. The critical path is the digit-serial adder, which was a 32-bit adder in this case. When discussing the complexity of this instantiated Fp2 accelerator, it is important to note the naive approach. From Table 5, again, it becomes readily apparent that performing extra multiplications becomes very costly.
Thus, by using the formulas we provide for Fp2 operations, the aforementioned system and method are saving many cycles by replacing a modular multiplication with a few modular additions or subtractions. In Table 6, below, a timing comparison between the present invention's Fp2 multiplication and squaring formulas versus naive formulas are shown. It can be seen that Fp2 multiplication is approximately 20% faster and Fp2 squaring is 30% faster when compared to naive formulas. However, the choice of modular multiplier and modular adder were combined in three work registers. This adds additional multiplexers for interfacing logic, but also reduces multiplexers that would be used to initialize these registers. The logical flow of the registers in the circular buffer eliminates the need for excess 2:1 multiplexers.
Table 7, below, depicts the Fp2 accelerator performing addition operations.
By way of example utilizing the Fp2 accelerator depicted in
Table 8, above, depicts an example of modular multiplication in depth. This performs a bit-parallel modular multiplier based on the Montgomery multiplication algorithm. For this, the system will calculate m smaller modular multiplications for an m-bit prime p. For p=71, we have a 7-bit prime, so we perform 7 smaller modular multiplications for the final result. The idea of a multiplier is that it is based on the carry-save adder technique, where we perform very fast additions in parallel without worrying about carry propagations. Algorithm 1, below, shows the algorithm that the multiplier follows. Table 8 shows a cycle-by-cycle breakdown of what the 7 cycles will be in Table 8. We perform the multiplication with a=13 and b=5, which when using R=27, will produce the result c=abR−1 mod 71=41.
Algorithm 1—Bit-serial CSA Montgomery multiplication. Sc and Ss refer to the carry and sum bits of the result S, respectfully. Specifically, the input may be a Modulus M, R=2k>M, operands x, y<M. The output may be z=xyR−1 mod M. Therefore, an exemplary software-based algorithm to effectuate the same is depicted below:
Table 9, below, depicts exemplary results of the Fp2 accelerator generating computations and depicting what the registers hold when implementing exemplary quadratic extension field arithmetic equations in a finite field of Fp2. For this example, p=71 and perform an Fp2 multiplication (with irreducible polynomial i2+1) between A=5+3i and B=13+9i to produce the result C. What is not shown, for brevity, are the cycle-by-cycle contents of the modular multiplier or addition, as exemplary results of these are depicted in Tables 7 and 8, respectively. The values are converted to the Montgomery form by performing the computation ajR mod p and bjR mod p with R=27 for j=0; 1. Thus, the inputs in the Montgomery domain are A=1+29i and B=31+16i. The final value for C=36+31i, so the normal representation of this result is C=38+13i, which can be recovered in a simple way by performing the computations C=(5×13-3×9)+(5×9+3×13)=38+13i.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US18/46825 | 8/16/2018 | WO | 00 |
