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Polynomial over a finite field

Polynomialf(x) {\ displaystyle f (x)} f (x) over the final fieldFq {\ displaystyle \ mathbb {F} _ {q}} \ mathbb {F} _ {q} called the formal sum of the form

f(x)=f0+fonex+...+fmxm,fi∈Fq,fm≠0.{\ displaystyle f (x) = f_ {0} + f_ {1} x + \ ldots + f_ {m} x ^ {m}, \ quad f_ {i} \ in \ mathbb {F} _ {q}, \ quad f_ {m} \ neq 0.} {\ displaystyle f (x) = f_ {0} + f_ {1} x + \ ldots + f_ {m} x ^ {m}, \ quad f_ {i} \ in \ mathbb {F} _ {q}, \ quad f_ {m} \ neq 0.}

Herem {\ displaystyle m} m Is a non-negative integer called the degree of the polynomialf(x) {\ displaystyle f (x)} f (x) , butxk,k∈N0 {\ displaystyle x ^ {k}, k \ in \ mathbb {N} _ {0}} x ^ k, k \ in \ mathbb N_0 Are elements of algebra overFq, {\ displaystyle \ mathbb {F} _ {q},} \ mathbb {F} _ {q}, the multiplication of which is specified by the rules:

xk⋅xm=xk+m,{\ displaystyle x ^ {k} \ cdot x ^ {m} = x ^ {k + m},} x ^ k \ cdot x ^ m = x ^ {k + m},
x0≡one.{\ displaystyle x ^ {0} \ equiv 1.} x ^ 0 \ equiv 1.

Such a definition allows us to formally multiply polynomials without worrying about the fact that different degrees of the same element of a finite field can coincide [1] [2] .

Any function over a finite field can be defined using some polynomial (for example, the Lagrange interpolation polynomial ).

Content

  • 1 Related Definitions
  • 2 Roots of a polynomial
  • 3 Cyclotomy class
    • 3.1 Examples of cyclotomic classes
    • 3.2 Relations with the roots of polynomials
  • 4 Types of polynomials
    • 4.1 Primitive polynomials
    • 4.2 Circular polynomials
    • 4.3 Zhegalkin polynomials
  • 5 Application
  • 6 See also
  • 7 notes
  • 8 Literature

Related Definitions

  • Numberm⩾0 {\ displaystyle m \ geqslant 0} m\geqslant 0 called the degree of the polynomial and is denoted asdeg⁡(f(x)) {\ displaystyle \ deg (f (x))} \deg(f(x)) [2] .
  • Iffm=one {\ displaystyle f_ {m} = 1} f_m=1 , then the polynomial is called normalized (reduced) [2] . A polynomial can always be normalized by dividing it by a coefficientfm {\ displaystyle f_ {m}} f_m with an older degree.
  • The sum and product of polynomials are defined in the usual way, and operations with coefficients are carried out in the fieldFq {\ displaystyle \ mathbb {F} _ {q}} \mathbb {F} _{q} .
  • For two polynomialsf(x) {\ displaystyle f (x)} f(x) andh(x)≠0 {\ displaystyle h (x) \ neq 0} h(x)\ne 0 there are always polynomialst(x) {\ displaystyle t (x)} t(x) andr(x) {\ displaystyle r (x)} r(x) over the fieldFq {\ displaystyle \ mathbb {F} _ {q}} \mathbb {F} _{q} that the relation will be satisfied
    f(x)=t(x)h(x)+r(x).{\ displaystyle f (x) = t (x) h (x) + r (x).} f(x)=t(x)h(x)+r(x).
    • If the degreer(x) {\ displaystyle r (x)} r(x) strictly less degreeh(x) {\ displaystyle h (x)} h(x) , then this relation is called the polynomial representationf(x) {\ displaystyle f (x)} f(x) in the form of quotient and remainder of divisionf(x) {\ displaystyle f (x)} f(x) onh(x) {\ displaystyle h (x)} h(x) , and such a representation is unique [3] . It's clear thatf(x)-r(x) {\ displaystyle f (x) -r (x)} f(x)-r(x) divided without remainder intoh(x) {\ displaystyle h (x)} h(x) that is written asf(x)≡r(x)(modh(x)) {\ displaystyle f (x) \ equiv r (x) {\ pmod {h (x)}}} f(x)\equiv r(x)\pmod{h(x)} [4] .
    • Ifr(x)=0 {\ displaystyle r (x) = 0} r(x)=0 then the polynomialh(x) {\ displaystyle h (x)} h(x) called a polynomial divisorf(x) {\ displaystyle f (x)} f(x) [5] .
  • A polynomial is irreducible over a fieldFq {\ displaystyle \ mathbb {F} _ {q}} \mathbb {F} _{q} if it has no non-trivial divisors (degrees greater than 0 and lessdeg⁡(f(x)) {\ displaystyle \ deg (f (x))} \deg(f(x)) ) [5] [6] .
  • Field extensionGF(q) {\ displaystyle GF (q)} GF(q) called setF[x]/(p(x)) {\ displaystyle F [x] _ {/ (p (x))}} F[x]_{/(p(x))} residue classes modulo an irreducible polynomialp(x) {\ displaystyle p (x)} p(x) over the fieldGF(q) {\ displaystyle GF (q)} GF(q) [6] .
  • Minimum polynomial (minimum function) for an elementβ {\ displaystyle \ beta} \beta from the extended field such a normalized polynomial is calledm(x) {\ displaystyle m (x)} m(x) overGF(q) {\ displaystyle GF (q)} GF(q) minimum degree thatm(β)=0 {\ displaystyle m (\ beta) = 0} m(\beta)=0 [7] [8] .
  • The root of a polynomial is any element of a field whose value of this polynomial is equal to zero.
  • Conjugate elements of a field that are the roots of the same irreducible polynomial are called conjugate [9] .

Polynomial Roots

A polynomial of degree m has exactly m roots (taking into account multiplicity) belonging to some extended fieldFQ,Fq⊆FQ {\ displaystyle \ mathbb {F} _ {Q}, \ quad \ mathbb {F} _ {q} \ subseteq \ mathbb {F} _ {Q}}   . Ifq=ps {\ displaystyle q = p ^ {s}}   wherep {\ displaystyle p}   - simple thenQ=pS,S⩾s {\ displaystyle Q = p ^ {S}, \; S \ geqslant s}   . Based on the properties of the finite fields, any element of the fieldFQ {\ displaystyle \ mathbb {F} _ {Q}}   is the root of the binomialxQ-x {\ displaystyle x ^ {Q} -x}   :

xQ-x=∏α∈FQ(x-α){\ displaystyle x ^ {Q} -x = \ prod _ {\ alpha \ in \ mathbb {F} _ {Q}} {(x- \ alpha)}}  

So the roots of the polynomialf(x) {\ displaystyle f (x)}   are also the roots of the binomialxQ-x {\ displaystyle x ^ {Q} -x}   [10] .

The Bezout theorem and its corollaries are valid:

Remainder of the divisionf(x) {\ displaystyle f (x)}   on(x-a) {\ displaystyle (xa)}   is equal tof(a) {\ displaystyle f (a)}   .

Ifx0 {\ displaystyle x_ {0}}   - rootf(x) {\ displaystyle f (x)}   then(x-x0) {\ displaystyle (x-x_ {0})}   dividesf(x) {\ displaystyle f (x)}   .

Ifxone,...,xm {\ displaystyle x_ {1}, \; \ ldots, \; x_ {m}}   the essence of the rootsf(x) {\ displaystyle f (x)}   then

f(x)=a(x-xone)(x-x2)...(x-xm).{\ displaystyle f (x) = a (x-x_ {1}) (x-x_ {2}) \ ldots (x-x_ {m}).}  

The following theorems are also valid:

Theorem 1 Ifx0 {\ displaystyle x_ {0}}   - rootf(x) {\ displaystyle f (x)}   thenx0q {\ displaystyle x_ {0} ^ {q}}   - also rootf(x) {\ displaystyle f (x)}   [11] .

Theorem 2 The conjugate elements of the Galois field are of the same order [9] .

Cyclotomy class

A consequence of Theorem 1 may be the fact that ifα∈FQ {\ displaystyle \ alpha \ in \ mathbb {F} _ {Q}}   - polynomial rootf(x) {\ displaystyle f (x)}   over the fieldFq {\ displaystyle \ mathbb {F} _ {q}}   thenαq,αq2,αq3,...∈FQ {\ displaystyle \ alpha ^ {q}, \; \ alpha ^ {q ^ {2}}, \; \ alpha ^ {q ^ {3}}, \; \ ldots \ in \ mathbb {F} _ {Q }}   are its roots.

Definition: cyclotomic class over a fieldFq,q=ps {\ displaystyle \ mathbb {F} _ {q}, \; q = p ^ {s}}   generated by some elementα∈FQ,Q=pS {\ displaystyle \ alpha \ in \ mathbb {F} _ {Q}, \; Q = p ^ {S}}   called the set of all the different elementsFQ {\ displaystyle \ mathbb {F} _ {Q}}   which areq {\ displaystyle q}   degreesα {\ displaystyle \ alpha}   [12] .

Ifα {\ displaystyle \ alpha}   Is a primitive element [13] (such an element thatαQ-one=one {\ displaystyle \ alpha ^ {Q-1} = 1}   andαk≠one {\ displaystyle \ alpha ^ {k} \ neq 1}   at0<k<Q-one {\ displaystyle 0 <k <Q-1}   ) fieldsFQ,Q=qm {\ displaystyle \ mathbb {F} _ {Q}, \; Q = q ^ {m}}   then the cyclotomic classC={α,αq,αq2,...,αqm-one} {\ displaystyle C = \ {\ alpha, \; \ alpha ^ {q}, \; \ alpha ^ {q ^ {2}}, \; \ ldots, \; \ alpha ^ {q ^ {m-1} } \}}   over the fieldFq {\ displaystyle \ mathbb {F} _ {q}}   will have exactlym {\ displaystyle m}   elements.

It should be noted that any element of the cyclotomic class can generate this and only this class, and, therefore, belong only to it.

Examples of cyclotomic classes

Example 1. Letq=2 {\ displaystyle q = 2}   ,Q=23=8 {\ displaystyle Q = 2 ^ {3} = 8}   andα {\ displaystyle \ alpha}   - primitive field elementF8 {\ displaystyle \ mathbb {F} _ {8}}   , i.eα7=one {\ displaystyle \ alpha ^ {7} = 1}   andαi≠one {\ displaystyle \ alpha ^ {i} \ neq 1}   ati<7 {\ displaystyle i <7}   . Considering also thatα8=α {\ displaystyle \ alpha ^ {8} = \ alpha}   , we can obtain the expansion of all nonzero elements of the fieldF8 {\ displaystyle \ mathbb {F} _ {8}}   into three cyclotomic classes over the fieldF2 {\ displaystyle \ mathbb {F} _ {2}}   :

{one},{α,α2,αfour},{α3,α6,α5}.{\ displaystyle {\ begin {matrix} \ {1 \}, \\\ {\ alpha, \; \ alpha ^ {2}, \; \ alpha ^ {4} \}, \\\ {\ alpha ^ { 3}, \; \ alpha ^ {6}, \; \ alpha ^ {5} \}. \ End {matrix}}}  

Example 2. Similarly, we can construct classes on the fieldF16 {\ displaystyle \ mathbb {F} _ {16}}   over the fieldFfour {\ displaystyle \ mathbb {F} _ {4}}   , i.eq=four,Q=q2=16 {\ displaystyle q = 4, \; Q = q ^ {2} = 16}   . Let beα {\ displaystyle \ alpha}   - primitive field elementF16 {\ displaystyle \ mathbb {F} _ {16}}   meansαfifteen=one,α16=α {\ displaystyle \ alpha ^ {15} = 1, \; \ alpha ^ {16} = \ alpha}   .

{one},{α,αfour},{α2,α8},{α3,α12},{α5},{α10},{α6,α9},{α7,α13},{αeleven,αfourteen}.{\ displaystyle {\ begin {matrix} \ {1 \}, \\\ {\ alpha, \; \ alpha ^ {4} \}, \; \ {\ alpha ^ {2}, \; \ alpha ^ { 8} \}, \\\ {\ alpha ^ {3}, \; \ alpha ^ {12} \}, \; \ {\ alpha ^ {5} \}, \; \ {\ alpha ^ {10} \}, \\\ {\ alpha ^ {6}, \; \ alpha ^ {9} \}, \; \ {\ alpha ^ {7}, \; \ alpha ^ {13} \}, \\\ {\ alpha ^ {11}, \; \ alpha ^ {14} \}. \ end {matrix}}}  

Connection with the roots of polynomials

The following theorem establishes a connection between cyclotomic classes and the expansion of a polynomialxQ-one-one {\ displaystyle x ^ {Q-1} -1}   to irreducible polynomials over a fieldFq {\ displaystyle \ mathbb {F} _ {q}}   .

Theorem 3. Letα,αq,αq2,...,αqm-one {\ displaystyle \ alpha, \; \ alpha ^ {q}, \; \ alpha ^ {q ^ {2}}, \; \ ldots, \; \ alpha ^ {q ^ {m-1}}}   element cyclotomic classα∈Fql {\ displaystyle \ alpha \ in \ mathbb {F} _ {q ^ {l}}}   and polynomialf(x)=f0+fonex+f2x2+...+fm-onexm-one+xm {\ displaystyle f (x) = f_ {0} + f_ {1} x + f_ {2} x ^ {2} + \ ldots + f_ {m-1} x ^ {m-1} + x ^ {m }}   has as its roots the elements of this cyclotomic class, i.e.

f(x)=(x-α)(x-αq)...(x-αqm-one).{\ displaystyle f (x) = (x- \ alpha) (x- \ alpha ^ {q}) \ ldots (x- \ alpha ^ {q ^ {m-1}}).}  

Then the coefficientsf0,fone,...,fm-one {\ displaystyle f_ {0}, \; f_ {1}, \; \ ldots, \; f_ {m-1}}   polynomialf(x) {\ displaystyle f (x)}   lie in the fieldFq {\ displaystyle \ mathbb {F} _ {q}}   , and the polynomial itself is irreducible over this field.

One can establish the following corollary from Theorem 3 . From the property of finite fields, which says that all nonzero elements of the fieldFQ {\ displaystyle \ mathbb {F} _ {Q}}   are the roots of the polynomialxQ-one-one {\ displaystyle x ^ {Q-1} -1}   , we can conclude that the polynomialxQ-one-one {\ displaystyle x ^ {Q-1} -1}   can be decomposed into irreducible over the fieldFq {\ displaystyle \ mathbb {F} _ {q}}   polynomialsf0(x),fone(x),...,fd {\ displaystyle f_ {0} (x), \; f_ {1} (x), \; \ ldots, \; f_ {d}}   , each of which corresponds to its cyclotomic class [14] .

Types of Polynomials

Primitive polynomials

Definition The root order of the irreducible polynomial is called the exponent to which this polynomial belongs. An irreducible polynomial is called primitive if all its roots are generating elements of the multiplicative group of the field [15] .

All roots of a primitive polynomial have an order equal to the order of the multiplicative group of the extended fieldFQ {\ displaystyle \ mathbb {F} _ {Q}}   , i.eQ-one {\ displaystyle Q-1}   [11] .

Circular Polynomials

Let beα {\ displaystyle \ alpha}   is the generating element of the multiplicative group of the fieldGF(qm) {\ displaystyle GF (q ^ {m})}   , and its order isn=qm-one {\ displaystyle n = q ^ {m} -1}   , i.eαqm-one=one {\ displaystyle \ alpha ^ {q ^ {m} -1} = 1}   . Let all the elements of orderd {\ displaystyle d}   are the roots of the polynomialψd(x),n⋮d {\ displaystyle \ psi _ {d} (x), \; n \, \ vdots \, d}   . Then such a polynomial is called circular and equality is true [16] :

xqm-one-one=∏d∣qm-oneψd(x){\ displaystyle x ^ {q ^ {m} -1} -1 = \ prod _ {d \, \ mid \, q ^ {m} -1} \ psi _ {d} (x)}  

Zhegalkin polynomials

Among the polynomials over finite fields, Zhegalkin polynomials are especially distinguished. They are polynomials of many variables over a fieldGF(2) {\ displaystyle GF (2)}   [17] .

f(xone,x2,...,xN)=a+∑one⩽i⩽Naixi+∑one⩽i<j⩽Nai,jxixj+∑one⩽i<j<k⩽Nai,j,kxixjxk+...+aone,2,...,Nxonex2...xN{\ displaystyle f (x_ {1}, \; x_ {2}, \; \ ldots, \; x_ {N}) = a + \ sum _ {1 \ leqslant i \ leqslant N} a_ {i} x_ {i } + \ sum _ {1 \ leqslant i <j \ leqslant N} a_ {i, j} x_ {i} x_ {j} + \ sum _ {1 \ leqslant i <j <k \ leqslant N} a_ {i , \; j, \; k} x_ {i} x_ {j} x_ {k} + \ ldots + a_ {1, \; 2, \; \ ldots, \; N} x_ {1} x_ {2} \ ldots x_ {N}}  

With the help of such a polynomial, any Boolean function can be specified [18]f(xone,x2,...,xN) {\ displaystyle f (x_ {1}, \; x_ {2}, \; \ ldots, \; x_ {N})}   , and uniquely [17] [19] .

Application

There are many algorithms that use polynomials over finite fields and rings.

  • Euclidean Algorithm
  • Burlekamp Algorithm
  • Burlekamp Algorithm - Massey
  • Burlekamp Method
  • Bowes Code - Chowdhury - Hockingham
  • Reed - Solomon Code
  • CRC
  • Agrawala Test - Kayala - Saxen
  • Shamir's secret sharing scheme

Also, polynomials over finite fields are used in modern noise-resistant coding [20] (for describing cyclic codes [21] and for decoding the Reed – Solomon code using the Euclidean algorithm [22] ), pseudorandom number generators [23] (implemented using shift registers ) [24] , stream encryption [25] and data integrity verification algorithms.

See also

  • Polynomial
  • Final field
  • Polynomial ring

Notes

  1. ↑ Akritas, 1994 , p. 146.
  2. ↑ 1 2 3 Bleikhut, 1986 , p. 88.
  3. ↑ Bleichut, 1986 , p. 90.
  4. ↑ Bleichut, 1986 , p. 91.
  5. ↑ 1 2 Bleikhut, 1986 , p. 89.
  6. ↑ 1 2 Sagalovich, 2014 , p. 79.
  7. ↑ Sagalovich, 2014 , p. 93.
  8. ↑ Bleichut, 1986 , p. 104.
  9. ↑ 1 2 Sagalovich, 2014 , p. 101.
  10. ↑ Sagalovich, 2014 , p. 82.
  11. ↑ 1 2 Sagalovich, 2014 , p. 96.
  12. ↑ Sagalovich, 2014 , p. 105.
  13. ↑ Bleichut, 1986 , p. 99.
  14. ↑ Sagalovich, 2014 , p. 97.
  15. ↑ Bleichut, 1986 , p. 103.
  16. ↑ Sagalovich, 2014 , p. 102.
  17. ↑ 1 2 Yablonsky, 1986 , p. 32.
  18. ↑ Yablonsky, 1986 , p. 12.
  19. ↑ Gabidulin, Kshevetsky, Kolybelnikov, 2011 , p. 81.
  20. ↑ Sagalovich, 2014 , p. 169-172.
  21. ↑ Bleichut, 1986 , p. 116-121.
  22. ↑ Bleichut, 1986 , p. 223-228.
  23. ↑ Gabidulin, Kshevetsky, Kolybelnikov, 2011 , p. 77-83.
  24. ↑ Alferov, Teeth, Kuzmin et al., 2005 , p. 251-260.
  25. ↑ Gabidulin, Kshevetsky, Kolybelnikov, 2011 , p. 74-83.

Literature

  • Akritas A. Fundamentals of computer algebra with applications / trans. from English E.V. Pankratieva . - M .: Mir, 1994 .-- 544 p.
  • Alferov A. P. , Zubov A. Yu. , Kuzmin A. S. et al. Fundamentals of cryptography : Textbook - 3rd ed., Rev. and add. - M .: Helios ARV , 2005 .-- 480 p. - ISBN 978-5-85438-137-6
    <a href=" https://wikidata.org/wiki/Track:Q22304400 "> </a> <a href=" https://wikidata.org/wiki/Track:Q27449770 "> </a> <a href = " https://wikidata.org/wiki/Track:Q27048435 "> </a> <a href=" https://wikidata.org/wiki/Track:Q27976247 "> </a> <a href = " https://wikidata.org/wiki/Track:Q27449771 "> </a> <a href=" https://wikidata.org/wiki/Track:Q27449773 "> </a>
  • Bleikhut R. E. Theory and Practice of Error Control Codes / Ed. K. Sh. Zigangirova - M .: Mir , 1986 .-- 576 p.
    <a href=" https://wikidata.org/wiki/Track:Q2440867 "> </a> <a href=" https://wikidata.org/wiki/Track:Q27976630 "> </a> <a href = " https://wikidata.org/wiki/Track:Q27976629 "> </a> <a href=" https://wikidata.org/wiki/Track:Q7324196 "> </a>
  • Gabidulin E.M. , Kshevetsky A.S. , Kolybelnikov A.I. Information security : a training manual - M .: MIPT , 2011. - 225 p. - ISBN 978-5-7417-0377-9
    <a href=" https://wikidata.org/wiki/Track:Q4130888 "> </a> <a href=" https://wikidata.org/wiki/Track:Q26887236 "> </a> <a href = " https://wikidata.org/wiki/Track:Q26887244 "> </a> <a href=" https://wikidata.org/wiki/Track:Q26887242 "> </a>
  • Sagalovich Yu. L. Introduction to algebraic codes - 3rd ed., Rev. and add. - M .: IPPI RAS , 2014 .-- 310 p. - ISBN 978-5-901158-24-1
    <a href=" https://wikidata.org/wiki/Track:Q21789632 "> </a> <a href=" https://wikidata.org/wiki/Track:Q21789631 "> </a>
  • Yablonsky S. V. Introduction to discrete mathematics : Textbook. manual for universities - 2nd ed., revised. and add. - M .: Nauka , 1986 .-- 384 p.
    <a href=" https://wikidata.org/wiki/Track:Q248326 "> </a> <a href=" https://wikidata.org/wiki/Track:Q27976594 "> </a> <a href = " https://wikidata.org/wiki/Track:Q3710055 "> </a>
  • Peterson W., Weldon E. Error Correcting Codes. - M .: Mir, 1976 .-- S. 596.


Source - https://ru.wikipedia.org/w/index.php?title=Monitor_of_final_field&oldid=100601176


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