EppDiscMath5 8.4.040.
Use the RSA cipher with public key $(pq, e) = (23 \cdot 31, 43) = (713, 43)$ and private key $(pq, d)$, where
$d = 307$, to decrypt the given ciphertext and find the original message. (Assume the letters of the alphabet
are encoded as follows: $A = 01, B = 02, C = 03, \dots, Z = 26$.)
137 089 046
Since $d = 307 = 256 + 32 + 16 + 2 + 1$, find the first letter of the decrypted message by computing
$137^d \pmod{713}$. Now
$137^1 \equiv a \pmod{713}$
$137^8 \equiv d \pmod{713}$
$137^{64} \equiv g \pmod{713}$
$137^2 \equiv b \pmod{713}$
$137^{16} \equiv e \pmod{713}$
$137^{128} \equiv h \pmod{713}$
$137^4 \equiv c \pmod{713}$
$137^{32} \equiv f \pmod{713}$
$137^{256} \equiv i \pmod{713}$.
The result is that $a = 137$
$e = 576$
$i = 576$
, $b = 231$
, $f = 231$
, $c = 599$
, $g = 599$
, $d = 162$
, $h = 162$
, and
Thus, $137^{307} \pmod{713} = (a \cdot b \cdot e \cdot f \cdot i) \pmod{713} = \boxed{\phantom{123}} \times \boxed{\phantom{123}}$, and so the first letter in the
encrypted message is $\boxed{\phantom{123}}$.
Repeat these computations for each encrypted letter and find the completed decrypted message.
$\boxed{\phantom{123}}$