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• hH)q'4'`~
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n
•:∈ Z
n
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1/[W;%N6`∀ a, b, c ∈ Z
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Z/[MFu)*=W=MF:(%R∈ Z
n
) là n-a, nghĩa
là a+(n-a) = (n-a)+a= 0 @∀ a ∈ Z
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/
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n ,
:f:
w/[WG;%N`∀ a, b, c ∈ Z
n ,
:f:

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Pl/[WG;(GH)H@W/
4
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n
, (a+b)c = •::•f:•
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b) mod n = ((a mod n) (b mod n)) mod n
(b + c)) mod n = (((ab) mod n) + ((ac) mod n)) mod n
2.1.2  !S#/U612I(6'6' !J#
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Không gian khóa là n nhỏ (bảng chữ tiếng anh n=26) nên có thể thám mã
bằng phương pháp vét cạn các khóa.
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∀ y ∈ Z
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k
là song
ánh và ánh xạ ngược là d
k
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2.1.3  !S#/U612/'0,(
- ,*CF%>:*L[7>)E!.:*B7g
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HOT
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k
(x)=7x+3

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k
(H)= (7 × 7 +3) mod 26 =0
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