Option Explicit
Option Private Module
Private Type udtPublicKey
n As Currency
e As Currency
End Type
Private Type udtPrivateKey
n As Currency
d As Currency
End Type
'***************************************************
' .__
' _____ _____ |__| ____
' / \\__ \ | |/ \
'| Y Y \/ __ \| | | \
'|__|_| (____ /__|___| /
' \/ \/ \/
'***************************************************
Private Sub Main()
Dim p As Currency
Dim q As Currency
Dim n As Currency
Dim lambda_n As Currency
Dim e As Currency
Dim d As Currency
p = 61
q = 53
n = p * q
lambda_n = Application.Lcm(p - 1, q - 1)
e = 17
Debug.Assert IsCoPrime(e, lambda_n)
d = ModularMultiplicativeInverse(e, lambda_n)
Debug.Assert e <> d
Dim uPrivate As udtPrivateKey
uPrivate.d = d
uPrivate.n = n
Dim uPublic As udtPublicKey
uPublic.e = e
uPublic.n = n
'* m is the message to encrypt, it needs to be a number
'* 65 is ASCII for "A"
Dim m As Currency
m = 65
'* c is the encrypted message
Dim c As Currency
c = Encrypt(m, uPublic)
'* m2 is the decrypted message
Dim m2 As Currency
m2 = Decrypt(c, uPrivate)
'* and the decrypted message should match the original
Debug.Assert m2 = m
End Sub
Private Function Encrypt(ByVal m As Currency, _
ByRef uPublic As udtPublicKey) As Currency
If m > uPublic.n Then Err.Raise vbObjectError, , _
"#text is bigger than modulus, no way to decipher!"
Dim lLoop As Long
Dim lResult As Currency
lResult = 1
For lLoop = 1 To uPublic.e
lResult = ((lResult Mod uPublic.n) * (m Mod uPublic.n)) Mod uPublic.n
Next lLoop
Encrypt = lResult
End Function
Private Function Decrypt(ByVal c As Currency, _
ByRef uPrivate As udtPrivateKey) As Currency
If c > uPrivate.n Then Err.Raise vbObjectError, , _
"#text is bigger than modulus, no way to decipher!"
Dim lLoop As Long
Dim lResult As Currency
lResult = 1
For lLoop = 1 To uPrivate.d
lResult = ((lResult Mod uPrivate.n) * (c Mod uPrivate.n)) Mod uPrivate.n
Next lLoop
Decrypt = lResult
End Function
Private Function IsCoPrime(ByVal a As Currency, ByVal b As Currency) As Boolean
IsCoPrime = (Application.Gcd(a, b) = 1)
End Function
Private Function ModularMultiplicativeInverse(ByVal e As Currency, _
ByVal lambda_n As Currency)
Dim lLoop As Currency
For lLoop = 1 To lambda_n
If lLoop <> e Then
Dim lComp As Currency
lComp = lLoop * e Mod lambda_n
If lComp = 1 Then
ModularMultiplicativeInverse = lLoop
Exit Function
End If
End If
Next
SingleExit:
End Function
