2.3. Let g be a primitive root for Fp. (a) Suppose that x = a and x = b are both integer solutions to the congruence g = h (mod p). Prove that a = b (mod p - 1). Explain why this implies that the map (2.1) on page 65 is well-defined.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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2.3. Let g be a primitive root for Fp.
(a) Suppose that x = a and x = b are both integer solutions to the congruence
g¹ = h (mod p). Prove that a = b (mod p − 1). Explain why this implies that
the map (2.1) on page 65 is well-defined.
-
Transcribed Image Text:2.3. Let g be a primitive root for Fp. (a) Suppose that x = a and x = b are both integer solutions to the congruence g¹ = h (mod p). Prove that a = b (mod p − 1). Explain why this implies that the map (2.1) on page 65 is well-defined. -
Remark 2.2. The discrete logarithm problem is a well-posed problem, namely
to find an integer exponent à such that g = h. However, if there is one so-
lution, then there are infinitely many, because Fermat's little theorem (The-
orem 1.24) tells us that gº−¹ = 1 (mod p). Hence if x is a solution to gª = h,
then x + k(p − 1) is also a solution for every value of k, because
gæ+k(p-1) = g. −1)k = h. 1² = h (mod p).
Thus logg (h) is defined only up to adding or subtracting multiples of p - 1.
In other words, logg (h) is really defined modulo p – 1. It is not hard to verify
(Exercise 2.3(a)) that log, gives a well-defined function
logg
: F*
P
Z
(p − 1)Z
(2.1)
Transcribed Image Text:Remark 2.2. The discrete logarithm problem is a well-posed problem, namely to find an integer exponent à such that g = h. However, if there is one so- lution, then there are infinitely many, because Fermat's little theorem (The- orem 1.24) tells us that gº−¹ = 1 (mod p). Hence if x is a solution to gª = h, then x + k(p − 1) is also a solution for every value of k, because gæ+k(p-1) = g. −1)k = h. 1² = h (mod p). Thus logg (h) is defined only up to adding or subtracting multiples of p - 1. In other words, logg (h) is really defined modulo p – 1. It is not hard to verify (Exercise 2.3(a)) that log, gives a well-defined function logg : F* P Z (p − 1)Z (2.1)
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