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+# Le cryptosystème Kyber
+## STA Flashback
+$$
+\begin{align}
+&a = 4X^2 + 7X + 1 \\
+&b = 3X^2 + 2
+\end{align}
+$$
+### a)
+- $a+b = 7X^2 + 7X + 3$
+- $a \cdot b = 12X^4 + 8X^2 + 21X^3 + 14X + 3X^2 + 2 = 12X^4 + 21X^3 + 11X^2 + 14X + 2$
+### b)
+$X^3 = -1, \, X^4 = -X$
+- $a+b = 7X^2 + 7X + 3$
+- $a\cdot b = -12X -21 + 11X^2 + 14X + 2 = 11X^2 + 2X -19$
+### c)
+$X^3 = -1, \, X^4 = -X$
+- $a+b = 7X^2 + 7X + 3$
+- $a\cdot b = 2X^2 + 2X + 8$
+
+## Kyber
+### a)