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VB.NET Private Function GCD(ByRef nPHI As Double) As Double Dim x As Double Dim nE, y As Double Const N_UP As Integer = 99999999 'set upper limit for E Const N_LW As Integer = 10000000 'set lower limit for E On Error Resume Next Randomize() nE = Int((N_UP - N_LW + 1) * Rnd() + N_LW) Do x = nPHI Mod nE y = x Mod nE If y <> 0 And IsPrime(nE) Then GCD = nE Exit Function Else nE = nE + 1 End If Loop End Function C# private double GCD(double nPHI) { double x; double nE,y; const int N_UP = 99999999; //set upper limit for E const int N_LW = 10000000; //set lower limit for E nE = Convert.ToInt64((N_UP - N_LW + 1) * _ (new Random()).NextDouble() + N_LW); while(true) { x = nPHI % nE; y = x % nE; if (y != 0 && IsPrime(nE)) { return nE; } else { nE++; } } } GCD generates a number that is relatively prime to (p-1) * (q – 1). This number must be in the order of 10’s of millions, and be prime. The last function required to generate the public and private keys is the Euler function VB.NET Private Function Euler(ByRef E3 As Double, ByRef PHI3 As Double) As Double On Error Resume Next Dim v3, v1, u2, u1, u3, v2, q As Double Dim vv, z, t2, t1, t3, uu, inverse As Double u1 = 1 u2 = 0 u3 = PHI3 v1 = 0 v2 = 1 v3 = E3 Do Until (v3 = 0) q = Int(u3 / v3) t1 = u1 - q * v1 t2 = u2 - q * v2 t3 = u3 - q * v3 u1 = v1 u2 = v2 u3 = v3 v1 = t1 v2 = t2 v3 = t3 z = 1 Loop uu = u1 vv = u2 If (vv < 0) Then inverse = vv + PHI3 Else inverse = vv End If Euler = inverse End Function 
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