Introduction
The VBA Rnd() function is often used to generate "random" numbers. Of course, you can't generate truly random numbers using any programmatic algorithm. But some pseudo random number generator algorithms are better than others. This article discusses why the native PRNG is bad and what you can use instead if you truly need "randomness ".
How VBA generates its random numbers
Source: https://support.microsoft.com/en-us/kb/231847
While the above linked article is for VB 6.0, VBA is based on the same code base. I was able to confirm that it uses the same algorithm by manually computing the first few numbers from the VB 6.0 algorithm and comparing it to the VBA output.
Basically, it uses a recursive function to generate its random numbers.
Where x0 = 327680 for the first run, otherwise, use the previously calculated value.
The Problem
One issue with the Rnd() implementation is its short periodicity, meaning the amount of numbers it can generate until it starts repeating itself. It will start repeating numbers after 2^24 numbers have been generated.
Another issue is that it is serially correlated. Which means that knowing the first few outputs of the function reveals information that you can use to predict the future output. You can't really call something random if you can start predicting its "random" output.
While for some applications, this isn't an issue, it can pose a problem if you truly need random numbers. For example, it probably doesn't matter if you are just using it to generate a small random sample to split a population into two groups. But it is a major issue if you want to generate random numbers for a lottery game.
The Solution
While there are many many other PRNG algorithms, such as the Mersenne Twister, you can implement that will not suffer from these problems, my solution builds off a base of code that I already have: Cryptographic Algorithms.
Basically, cryptography is a fancy PRNG. The purpose of cryptography is to take a password (i.e. seed) and use it to encode data into an unpredictable (i.e. pseudo random) form.
Therefore, you can take any sufficiently strong cryptographic algorithm and turn it into a PRNG. The way you do this is by running the algorithm in counter mode. That is, when you want to start generating random numbers, you use the seed as the password and begin encrypting starting with the number 0. Then you encrypt the number 1. Then 2 and so on. Of course you can start with any number and you don't have to increment by 1 each time. It's just the simple example.
The Code
The code below is a sample implementation using zmbd's VBA implementation of my VBScript AES code in counter mode.
The AES code is slightly modified to take the plaintext input as a string rather than a file. And since it will only ever encode 1 block at a time, some of the loops have been removed.
You can drop a different cryptographic algorithm in place of the AES function as long as it produces output of a string of at least 8 bytes. AES produces a 16 byte output per block so the last 8 bytes is dropped by this implementation to avoid overflowing a double.
The VBA Rnd() function is often used to generate "random" numbers. Of course, you can't generate truly random numbers using any programmatic algorithm. But some pseudo random number generator algorithms are better than others. This article discusses why the native PRNG is bad and what you can use instead if you truly need "randomness ".
How VBA generates its random numbers
Source: https://support.microsoft.com/en-us/kb/231847
While the above linked article is for VB 6.0, VBA is based on the same code base. I was able to confirm that it uses the same algorithm by manually computing the first few numbers from the VB 6.0 algorithm and comparing it to the VBA output.
Basically, it uses a recursive function to generate its random numbers.
Code:
x1 = ( x0 * 1140671485 + 12820163 ) MOD (2^24) return x1 / (2^24)
The Problem
One issue with the Rnd() implementation is its short periodicity, meaning the amount of numbers it can generate until it starts repeating itself. It will start repeating numbers after 2^24 numbers have been generated.
Another issue is that it is serially correlated. Which means that knowing the first few outputs of the function reveals information that you can use to predict the future output. You can't really call something random if you can start predicting its "random" output.
While for some applications, this isn't an issue, it can pose a problem if you truly need random numbers. For example, it probably doesn't matter if you are just using it to generate a small random sample to split a population into two groups. But it is a major issue if you want to generate random numbers for a lottery game.
The Solution
While there are many many other PRNG algorithms, such as the Mersenne Twister, you can implement that will not suffer from these problems, my solution builds off a base of code that I already have: Cryptographic Algorithms.
Basically, cryptography is a fancy PRNG. The purpose of cryptography is to take a password (i.e. seed) and use it to encode data into an unpredictable (i.e. pseudo random) form.
Therefore, you can take any sufficiently strong cryptographic algorithm and turn it into a PRNG. The way you do this is by running the algorithm in counter mode. That is, when you want to start generating random numbers, you use the seed as the password and begin encrypting starting with the number 0. Then you encrypt the number 1. Then 2 and so on. Of course you can start with any number and you don't have to increment by 1 each time. It's just the simple example.
The Code
The code below is a sample implementation using zmbd's VBA implementation of my VBScript AES code in counter mode.
The AES code is slightly modified to take the plaintext input as a string rather than a file. And since it will only ever encode 1 block at a time, some of the loops have been removed.
You can drop a different cryptographic algorithm in place of the AES function as long as it produces output of a string of at least 8 bytes. AES produces a 16 byte output per block so the last 8 bytes is dropped by this implementation to avoid overflowing a double.
Code:
Option Compare Database
Option Explicit
Dim iSeed As Double
Dim iCounter As Double
Function RNG(seed As Double)
Dim sCounter As String, sPassin As String
Dim i As Integer, sResult As String, dResult As Double
If iSeed <> seed Then
iCounter = 0
End If
iSeed = seed
iCounter = iCounter + 1
sCounter = ""
sPassin = ""
For i = 0 To 7
sPassin = sPassin & Chr((iSeed / (256 ^ i)) And 255)
sCounter = sCounter & Chr((iCounter / (256 ^ i)) And 255)
Next
sResult = RunAES(sCounter, sPassin)
dResult = 0
For i = 1 To 8
dResult = dResult + Asc(Mid(sResult, i, 1)) * (256 ^ (i - 1))
Next
RNG = dResult / (256 ^ 8)
End Function
Function RunAES(sCounter, sPassin)
Dim sbox(), sboxinv(), rcon()
Dim g2, g3, g9, g11, g13, g14
g2 = Array( _
&H0, &H2, &H4, &H6, &H8, &HA, &HC, &HE, &H10, &H12, &H14, &H16, &H18, &H1A, &H1C, &H1E, _
&H20, &H22, &H24, &H26, &H28, &H2A, &H2C, &H2E, &H30, &H32, &H34, &H36, &H38, &H3A, &H3C, &H3E, _
&H40, &H42, &H44, &H46, &H48, &H4A, &H4C, &H4E, &H50, &H52, &H54, &H56, &H58, &H5A, &H5C, &H5E, _
&H60, &H62, &H64, &H66, &H68, &H6A, &H6C, &H6E, &H70, &H72, &H74, &H76, &H78, &H7A, &H7C, &H7E, _
&H80, &H82, &H84, &H86, &H88, &H8A, &H8C, &H8E, &H90, &H92, &H94, &H96, &H98, &H9A, &H9C, &H9E, _
&HA0, &HA2, &HA4, &HA6, &HA8, &HAA, &HAC, &HAE, &HB0, &HB2, &HB4, &HB6, &HB8, &HBA, &HBC, &HBE, _
&HC0, &HC2, &HC4, &HC6, &HC8, &HCA, &HCC, &HCE, &HD0, &HD2, &HD4, &HD6, &HD8, &HDA, &HDC, &HDE, _
&HE0, &HE2, &HE4, &HE6, &HE8, &HEA, &HEC, &HEE, &HF0, &HF2, &HF4, &HF6, &HF8, &HFA, &HFC, &HFE, _
&H1B, &H19, &H1F, &H1D, &H13, &H11, &H17, &H15, &HB, &H9, &HF, &HD, &H3, &H1, &H7, &H5, _
&H3B, &H39, &H3F, &H3D, &H33, &H31, &H37, &H35, &H2B, &H29, &H2F, &H2D, &H23, &H21, &H27, &H25, _
&H5B, &H59, &H5F, &H5D, &H53, &H51, &H57, &H55, &H4B, &H49, &H4F, &H4D, &H43, &H41, &H47, &H45, _
&H7B, &H79, &H7F, &H7D, &H73, &H71, &H77, &H75, &H6B, &H69, &H6F, &H6D, &H63, &H61, &H67, &H65, _
&H9B, &H99, &H9F, &H9D, &H93, &H91, &H97, &H95, &H8B, &H89, &H8F, &H8D, &H83, &H81, &H87, &H85, _
&HBB, &HB9, &HBF, &HBD, &HB3, &HB1, &HB7, &HB5, &HAB, &HA9, &HAF, &HAD, &HA3, &HA1, &HA7, &HA5, _
&HDB, &HD9, &HDF, &HDD, &HD3, &HD1, &HD7, &HD5, &HCB, &HC9, &HCF, &HCD, &HC3, &HC1, &HC7, &HC5, _
&HFB, &HF9, &HFF, &HFD, &HF3, &HF1, &HF7, &HF5, &HEB, &HE9, &HEF, &HED, &HE3, &HE1, &HE7, &HE5)
g3 = Array( _
&H0, &H3, &H6, &H5, &HC, &HF, &HA, &H9, &H18, &H1B, &H1E, &H1D, &H14, &H17, &H12, &H11, _
&H30, &H33, &H36, &H35, &H3C, &H3F, &H3A, &H39, &H28, &H2B, &H2E, &H2D, &H24, &H27, &H22, &H21, _
&H60, &H63, &H66, &H65, &H6C, &H6F, &H6A, &H69, &H78, &H7B, &H7E, &H7D, &H74, &H77, &H72, &H71, _
&H50, &H53, &H56, &H55, &H5C, &H5F, &H5A, &H59, &H48, &H4B, &H4E, &H4D, &H44, &H47, &H42, &H41, _
&HC0, &HC3, &HC6, &HC5, &HCC, &HCF, &HCA, &HC9, &HD8, &HDB, &HDE, &HDD, &HD4, &HD7, &HD2, &HD1, _
&HF0, &HF3, &HF6, &HF5, &HFC, &HFF, &HFA, &HF9, &HE8, &HEB, &HEE, &HED, &HE4, &HE7, &HE2, &HE1, _
&HA0, &HA3, &HA6, &HA5, &HAC, &HAF, &HAA, &HA9, &HB8, &HBB, &HBE, &HBD, &HB4, &HB7, &HB2, &HB1, _
&H90, &H93, &H96, &H95, &H9C, &H9F, &H9A, &H99, &H88, &H8B, &H8E, &H8D, &H84, &H87, &H82, &H81, _
&H9B, &H98, &H9D, &H9E, &H97, &H94, &H91, &H92, &H83, &H80, &H85, &H86, &H8F, &H8C, &H89, &H8A, _
&HAB, &HA8, &HAD, &HAE, &HA7, &HA4, &HA1, &HA2, &HB3, &HB0, &HB5, &HB6, &HBF, &HBC, &HB9, &HBA, _
&HFB, &HF8, &HFD, &HFE, &HF7, &HF4, &HF1, &HF2, &HE3, &HE0, &HE5, &HE6, &HEF, &HEC, &HE9, &HEA, _
&HCB, &HC8, &HCD, &HCE, &HC7, &HC4, &HC1, &HC2, &HD3, &HD0, &HD5, &HD6, &HDF, &HDC, &HD9, &HDA, _
&H5B, &H58, &H5D, &H5E, &H57, &H54, &H51, &H52, &H43, &H40, &H45, &H46, &H4F, &H4C, &H49, &H4A, _
&H6B, &H68, &H6D, &H6E, &H67, &H64, &H61, &H62, &H73, &H70, &H75, &H76, &H7F, &H7C, &H79, &H7A, _
&H3B, &H38, &H3D, &H3E, &H37, &H34, &H31, &H32, &H23, &H20, &H25, &H26, &H2F, &H2C, &H29, &H2A, _
&HB, &H8, &HD, &HE, &H7, &H4, &H1, &H2, &H13, &H10, &H15, &H16, &H1F, &H1C, &H19, &H1A)
g9 = Array( _
&H0, &H9, &H12, &H1B, &H24, &H2D, &H36, &H3F, &H48, &H41, &H5A, &H53, &H6C, &H65, &H7E, &H77, _
&H90, &H99, &H82, &H8B, &HB4, &HBD, &HA6, &HAF, &HD8, &HD1, &HCA, &HC3, &HFC, &HF5, &HEE, &HE7, _
&H3B, &H32, &H29, &H20, &H1F, &H16, &HD, &H4, &H73, &H7A, &H61, &H68, &H57, &H5E, &H45, &H4C, _
&HAB, &HA2, &HB9, &HB0, &H8F, &H86, &H9D, &H94, &HE3, &HEA, &HF1, &HF8, &HC7, &HCE, &HD5, &HDC, _
&H76, &H7F, &H64, &H6D, &H52, &H5B, &H40, &H49, &H3E, &H37, &H2C, &H25, &H1A, &H13, &H8, &H1, _
&HE6, &HEF, &HF4, &HFD, &HC2, &HCB, &HD0, &HD9, &HAE, &HA7, &HBC, &HB5, &H8A, &H83, &H98, &H91, _
&H4D, &H44, &H5F, &H56, &H69, &H60, &H7B, &H72, &H5, &HC, &H17, &H1E, &H21, &H28, &H33, &H3A, _
&HDD, &HD4, &HCF, &HC6, &HF9, &HF0, &HEB, &HE2, &H95, &H9C, &H87, &H8E, &HB1, &HB8, &HA3, &HAA, _
&HEC, &HE5, &HFE, &HF7, &HC8, &HC1, &HDA, &HD3, &HA4, &HAD, &HB6, &HBF, &H80, &H89, &H92, &H9B, _
&H7C, &H75, &H6E, &H67, &H58, &H51, &H4A, &H43, &H34, &H3D, &H26, &H2F, &H10, &H19, &H2, &HB, _
&HD7, &HDE, &HC5, &HCC, &HF3, &HFA, &HE1, &HE8, &H9F, &H96, &H8D, &H84, &HBB, &HB2, &HA9, &HA0, _
&H47, &H4E, &H55, &H5C, &H63, &H6A, &H71, &H78, &HF, &H6, &H1D, &H14, &H2B, &H22, &H39, &H30, _
&H9A, &H93, &H88, &H81, &HBE, &HB7, &HAC, &HA5, &HD2, &HDB, &HC0, &HC9, &HF6, &HFF, &HE4, &HED, _
&HA, &H3, &H18, &H11, &H2E, &H27, &H3C, &H35, &H42, &H4B, &H50, &H59, &H66, &H6F, &H74, &H7D, _
&HA1, &HA8, &HB3, &HBA, &H85, &H8C, &H97, &H9E, &HE9, &HE0, &HFB, &HF2, &HCD, &HC4, &HDF, &HD6, _
&H31, &H38, &H23, &H2A, &H15, &H1C, &H7, &HE, &H79, &H70, &H6B, &H62, &H5D, &H54, &H4F, &H46)
g11 = Array( _
&H0, &HB, &H16, &H1D, &H2C, &H27, &H3A, &H31, &H58, &H53, &H4E, &H45, &H74, &H7F, &H62, &H69, _
&HB0, &HBB, &HA6, &HAD, &H9C, &H97, &H8A, &H81, &HE8, &HE3, &HFE, &HF5, &HC4, &HCF, &HD2, &HD9, _
&H7B, &H70, &H6D, &H66, &H57, &H5C, &H41, &H4A, &H23, &H28, &H35, &H3E, &HF, &H4, &H19, &H12, _
&HCB, &HC0, &HDD, &HD6, &HE7, &HEC, &HF1, &HFA, &H93, &H98, &H85, &H8E, &HBF, &HB4, &HA9, &HA2, _
&HF6, &HFD, &HE0, &HEB, &HDA, &HD1, &HCC, &HC7, &HAE, &HA5, &HB8, &HB3, &H82, &H89, &H94, &H9F, _
&H46, &H4D, &H50, &H5B, &H6A, &H61, &H7C, &H77, &H1E, &H15, &H8, &H3, &H32, &H39, &H24, &H2F, _
&H8D, &H86, &H9B, &H90, &HA1, &HAA, &HB7, &HBC, &HD5, &HDE, &HC3, &HC8, &HF9, &HF2, &HEF, &HE4, _
&H3D, &H36, &H2B, &H20, &H11, &H1A, &H7, &HC, &H65, &H6E, &H73, &H78, &H49, &H42, &H5F, &H54, _
&HF7, &HFC, &HE1, &HEA, &HDB, &HD0, &HCD, &HC6, &HAF, &HA4, &HB9, &HB2, &H83, &H88, &H95, &H9E, _
&H47, &H4C, &H51, &H5A, &H6B, &H60, &H7D, &H76, &H1F, &H14, &H9, &H2, &H33, &H38, &H25, &H2E, _
&H8C, &H87, &H9A, &H91, &HA0, &HAB, &HB6, &HBD, &HD4, &HDF, &HC2, &HC9, &HF8, &HF3, &HEE, &HE5, _
&H3C, &H37, &H2A, &H21, &H10, &H1B, &H6, &HD, &H64, &H6F, &H72, &H79, &H48, &H43, &H5E, &H55, _
&H1, &HA, &H17, &H1C, &H2D, &H26, &H3B, &H30, &H59, &H52, &H4F, &H44, &H75, &H7E, &H63, &H68, _
&HB1, &HBA, &HA7, &HAC, &H9D, &H96, &H8B, &H80, &HE9, &HE2, &HFF, &HF4, &HC5, &HCE, &HD3, &HD8, _
&H7A, &H71, &H6C, &H67, &H56, &H5D, &H40, &H4B, &H22, &H29, &H34, &H3F, &HE, &H5, &H18, &H13, _
&HCA, &HC1, &HDC, &HD7, &HE6, &HED, &HF0, &HFB, &H92, &H99, &H84, &H8F, &HBE, &HB5, &HA8, &HA3)
g13 = Array( _
&H0, &HD, &H1A, &H17, &H34, &H39, &H2E, &H23, &H68, &H65, &H72, &H7F, &H5C, &H51, &H46, &H4B, _
&HD0, &HDD, &HCA, &HC7, &HE4, &HE9, &HFE, &HF3, &HB8, &HB5, &HA2, &HAF, &H8C, &H81, &H96, &H9B, _
&HBB, &HB6, &HA1, &HAC, &H8F, &H82, &H95, &H98, &HD3, &HDE, &HC9, &HC4, &HE7, &HEA, &HFD, &HF0, _
&H6B, &H66, &H71, &H7C, &H5F, &H52, &H45, &H48, &H3, &HE, &H19, &H14, &H37, &H3A, &H2D, &H20, _
&H6D, &H60, &H77, &H7A, &H59, &H54, &H43, &H4E, &H5, &H8, &H1F, &H12, &H31, &H3C, &H2B, &H26, _
&HBD, &HB0, &HA7, &HAA, &H89, &H84, &H93, &H9E, &HD5, &HD8, &HCF, &HC2, &HE1, &HEC, &HFB, &HF6, _
&HD6, &HDB, &HCC, &HC1, &HE2, &HEF, &HF8, &HF5, &HBE, &HB3, &HA4, &HA9, &H8A, &H87, &H90, &H9D, _
&H6, &HB, &H1C, &H11, &H32, &H3F, &H28, &H25, &H6E, &H63, &H74, &H79, &H5A, &H57, &H40, &H4D, _
&HDA, &HD7, &HC0, &HCD, &HEE, &HE3, &HF4, &HF9, &HB2, &HBF, &HA8, &HA5, &H86, &H8B, &H9C, &H91, _
&HA, &H7, &H10, &H1D, &H3E, &H33, &H24, &H29, &H62, &H6F, &H78, &H75, &H56, &H5B, &H4C, &H41, _
&H61, &H6C, &H7B, &H76, &H55, &H58, &H4F, &H42, &H9, &H4, &H13, &H1E, &H3D, &H30, &H27, &H2A, _
&HB1, &HBC, &HAB, &HA6, &H85, &H88, &H9F, &H92, &HD9, &HD4, &HC3, &HCE, &HED, &HE0, &HF7, &HFA, _
&HB7, &HBA, &HAD, &HA0, &H83, &H8E, &H99, &H94, &HDF, &HD2, &HC5, &HC8, &HEB, &HE6, &HF1, &HFC, _
&H67, &H6A, &H7D, &H70, &H53, &H5E, &H49, &H44, &HF, &H2, &H15, &H18, &H3B, &H36, &H21, &H2C, _
&HC, &H1, &H16, &H1B, &H38, &H35, &H22, &H2F, &H64, &H69, &H7E, &H73, &H50, &H5D, &H4A, &H47, _
&HDC, &HD1, &HC6, &HCB, &HE8, &HE5, &HF2, &HFF, &HB4, &HB9, &HAE, &HA3, &H80, &H8D, &H9A, &H97)
g14 = Array( _
&H0, &HE, &H1C, &H12, &H38, &H36, &H24, &H2A, &H70, &H7E, &H6C, &H62, &H48, &H46, &H54, &H5A, _
&HE0, &HEE, &HFC, &HF2, &HD8, &HD6, &HC4, &HCA, &H90, &H9E, &H8C, &H82, &HA8, &HA6, &HB4, &HBA, _
&HDB, &HD5, &HC7, &HC9, &HE3, &HED, &HFF, &HF1, &HAB, &HA5, &HB7, &HB9, &H93, &H9D, &H8F, &H81, _
&H3B, &H35, &H27, &H29, &H3, &HD, &H1F, &H11, &H4B, &H45, &H57, &H59, &H73, &H7D, &H6F, &H61, _
&HAD, &HA3, &HB1, &HBF, &H95, &H9B, &H89, &H87, &HDD, &HD3, &HC1, &HCF, &HE5, &HEB, &HF9, &HF7, _
&H4D, &H43, &H51, &H5F, &H75, &H7B, &H69, &H67, &H3D, &H33, &H21, &H2F, &H5, &HB, &H19, &H17, _
&H76, &H78, &H6A, &H64, &H4E, &H40, &H52, &H5C, &H6, &H8, &H1A, &H14, &H3E, &H30, &H22, &H2C, _
&H96, &H98, &H8A, &H84, &HAE, &HA0, &HB2, &HBC, &HE6, &HE8, &HFA, &HF4, &HDE, &HD0, &HC2, &HCC, _
&H41, &H4F, &H5D, &H53, &H79, &H77, &H65, &H6B, &H31, &H3F, &H2D, &H23, &H9, &H7, &H15, &H1B, _
&HA1, &HAF, &HBD, &HB3, &H99, &H97, &H85, &H8B, &HD1, &HDF, &HCD, &HC3, &HE9, &HE7, &HF5, &HFB, _
&H9A, &H94, &H86, &H88, &HA2, &HAC, &HBE, &HB0, &HEA, &HE4, &HF6, &HF8, &HD2, &HDC, &HCE, &HC0, _
&H7A, &H74, &H66, &H68, &H42, &H4C, &H5E, &H50, &HA, &H4, &H16, &H18, &H32, &H3C, &H2E, &H20, _
&HEC, &HE2, &HF0, &HFE, &HD4, &HDA, &HC8, &HC6, &H9C, &H92, &H80, &H8E, &HA4, &HAA, &HB8, &HB6, _
&HC, &H2, &H10, &H1E, &H34, &H3A, &H28, &H26, &H7C, &H72, &H60, &H6E, &H44, &H4A, &H58, &H56, _
&H37, &H39, &H2B, &H25, &HF, &H1, &H13, &H1D, &H47, &H49, &H5B, &H55, &H7F, &H71, &H63, &H6D, _
&HD7, &HD9, &HCB, &HC5, &HEF, &HE1, &HF3, &HFD, &HA7, &HA9, &HBB, &HB5, &H9F, &H91, &H83, &H8D)
sbox = Array( _
&H63, &H7C, &H77, &H7B, &HF2, &H6B, &H6F, &HC5, &H30, &H1, &H67, &H2B, &HFE, &HD7, &HAB, &H76, _
&HCA, &H82, &HC9, &H7D, &HFA, &H59, &H47, &HF0, &HAD, &HD4, &HA2, &HAF, &H9C, &HA4, &H72, &HC0, _
&HB7, &HFD, &H93, &H26, &H36, &H3F, &HF7, &HCC, &H34, &HA5, &HE5, &HF1, &H71, &HD8, &H31, &H15, _
&H4, &HC7, &H23, &HC3, &H18, &H96, &H5, &H9A, &H7, &H12, &H80, &HE2, &HEB, &H27, &HB2, &H75, _
&H9, &H83, &H2C, &H1A, &H1B, &H6E, &H5A, &HA0, &H52, &H3B, &HD6, &HB3, &H29, &HE3, &H2F, &H84, _
&H53, &HD1, &H0, &HED, &H20, &HFC, &HB1, &H5B, &H6A, &HCB, &HBE, &H39, &H4A, &H4C, &H58, &HCF, _
&HD0, &HEF, &HAA, &HFB, &H43, &H4D, &H33, &H85, &H45, &HF9, &H2, &H7F, &H50, &H3C, &H9F, &HA8, _
&H51, &HA3, &H40, &H8F, &H92, &H9D, &H38, &HF5, &HBC, &HB6, &HDA, &H21, &H10, &HFF, &HF3, &HD2, _
&HCD, &HC, &H13, &HEC, &H5F, &H97, &H44, &H17, &HC4, &HA7, &H7E, &H3D, &H64, &H5D, &H19, &H73, _
&H60, &H81, &H4F, &HDC, &H22, &H2A, &H90, &H88, &H46, &HEE, &HB8, &H14, &HDE, &H5E, &HB, &HDB, _
&HE0, &H32, &H3A, &HA, &H49, &H6, &H24, &H5C, &HC2, &HD3, &HAC, &H62, &H91, &H95, &HE4, &H79, _
&HE7, &HC8, &H37, &H6D, &H8D, &HD5, &H4E, &HA9, &H6C, &H56, &HF4, &HEA, &H65, &H7A, &HAE, &H8, _
&HBA, &H78, &H25, &H2E, &H1C, &HA6, &HB4, &HC6, &HE8, &HDD, &H74, &H1F, &H4B, &HBD, &H8B, &H8A, _
&H70, &H3E, &HB5, &H66, &H48, &H3, &HF6, &HE, &H61, &H35, &H57, &HB9, &H86, &HC1, &H1D, &H9E, _
&HE1, &HF8, &H98, &H11, &H69, &HD9, &H8E, &H94, &H9B, &H1E, &H87, &HE9, &HCE, &H55, &H28, &HDF, _
&H8C, &HA1, &H89, &HD, &HBF, &HE6, &H42, &H68, &H41, &H99, &H2D, &HF, &HB0, &H54, &HBB, &H16)
sboxinv = Array( _
&H52, &H9, &H6A, &HD5, &H30, &H36, &HA5, &H38, &HBF, &H40, &HA3, &H9E, &H81, &HF3, &HD7, &HFB, _
&H7C, &HE3, &H39, &H82, &H9B, &H2F, &HFF, &H87, &H34, &H8E, &H43, &H44, &HC4, &HDE, &HE9, &HCB, _
&H54, &H7B, &H94, &H32, &HA6, &HC2, &H23, &H3D, &HEE, &H4C, &H95, &HB, &H42, &HFA, &HC3, &H4E, _
&H8, &H2E, &HA1, &H66, &H28, &HD9, &H24, &HB2, &H76, &H5B, &HA2, &H49, &H6D, &H8B, &HD1, &H25, _
&H72, &HF8, &HF6, &H64, &H86, &H68, &H98, &H16, &HD4, &HA4, &H5C, &HCC, &H5D, &H65, &HB6, &H92, _
&H6C, &H70, &H48, &H50, &HFD, &HED, &HB9, &HDA, &H5E, &H15, &H46, &H57, &HA7, &H8D, &H9D, &H84, _
&H90, &HD8, &HAB, &H0, &H8C, &HBC, &HD3, &HA, &HF7, &HE4, &H58, &H5, &HB8, &HB3, &H45, &H6, _
&HD0, &H2C, &H1E, &H8F, &HCA, &H3F, &HF, &H2, &HC1, &HAF, &HBD, &H3, &H1, &H13, &H8A, &H6B, _
&H3A, &H91, &H11, &H41, &H4F, &H67, &HDC, &HEA, &H97, &HF2, &HCF, &HCE, &HF0, &HB4, &HE6, &H73, _
&H96, &HAC, &H74, &H22, &HE7, &HAD, &H35, &H85, &HE2, &HF9, &H37, &HE8, &H1C, &H75, &HDF, &H6E, _
&H47, &HF1, &H1A, &H71, &H1D, &H29, &HC5, &H89, &H6F, &HB7, &H62, &HE, &HAA, &H18, &HBE, &H1B, _
&HFC, &H56, &H3E, &H4B, &HC6, &HD2, &H79, &H20, &H9A, &HDB, &HC0, &HFE, &H78, &HCD, &H5A, &HF4, _
&H1F, &HDD, &HA8, &H33, &H88, &H7, &HC7, &H31, &HB1, &H12, &H10, &H59, &H27, &H80, &HEC, &H5F, _
&H60, &H51, &H7F, &HA9, &H19, &HB5, &H4A, &HD, &H2D, &HE5, &H7A, &H9F, &H93, &HC9, &H9C, &HEF, _
&HA0, &HE0, &H3B, &H4D, &HAE, &H2A, &HF5, &HB0, &HC8, &HEB, &HBB, &H3C, &H83, &H53, &H99, &H61, _
&H17, &H2B, &H4, &H7E, &HBA, &H77, &HD6, &H26, &HE1, &H69, &H14, &H63, &H55, &H21, &HC, &H7D)
rcon = Array( _
&H8D, &H1, &H2, &H4, &H8, &H10, &H20, &H40, &H80, &H1B, &H36, &H6C, &HD8, &HAB, &H4D, &H9A, _
&H2F, &H5E, &HBC, &H63, &HC6, &H97, &H35, &H6A, &HD4, &HB3, &H7D, &HFA, &HEF, &HC5, &H91, &H39, _
&H72, &HE4, &HD3, &HBD, &H61, &HC2, &H9F, &H25, &H4A, &H94, &H33, &H66, &HCC, &H83, &H1D, &H3A, _
&H74, &HE8, &HCB, &H8D, &H1, &H2, &H4, &H8, &H10, &H20, &H40, &H80, &H1B, &H36, &H6C, &HD8, _
&HAB, &H4D, &H9A, &H2F, &H5E, &HBC, &H63, &HC6, &H97, &H35, &H6A, &HD4, &HB3, &H7D, &HFA, &HEF, _
&HC5, &H91, &H39, &H72, &HE4, &HD3, &HBD, &H61, &HC2, &H9F, &H25, &H4A, &H94, &H33, &H66, &HCC, _
&H83, &H1D, &H3A, &H74, &HE8, &HCB, &H8D, &H1, &H2, &H4, &H8, &H10, &H20, &H40, &H80, &H1B, _
&H36, &H6C, &HD8, &HAB, &H4D, &H9A, &H2F, &H5E, &HBC, &H63, &HC6, &H97, &H35, &H6A, &HD4, &HB3, _
&H7D, &HFA, &HEF, &HC5, &H91, &H39, &H72, &HE4, &HD3, &HBD, &H61, &HC2, &H9F, &H25, &H4A, &H94, _
&H33, &H66, &HCC, &H83, &H1D, &H3A, &H74, &HE8, &HCB, &H8D, &H1, &H2, &H4, &H8, &H10, &H20, _
&H40, &H80, &H1B, &H36, &H6C, &HD8, &HAB, &H4D, &H9A, &H2F, &H5E, &HBC, &H63, &HC6, &H97, &H35, _
&H6A, &HD4, &HB3, &H7D, &HFA, &HEF, &HC5, &H91, &H39, &H72, &HE4, &HD3, &HBD, &H61, &HC2, &H9F, _
&H25, &H4A, &H94, &H33, &H66, &HCC, &H83, &H1D, &H3A, &H74, &HE8, &HCB, &H8D, &H1, &H2, &H4, _
&H8, &H10, &H20, &H40, &H80, &H1B, &H36, &H6C, &HD8, &HAB, &H4D, &H9A, &H2F, &H5E, &HBC, &H63, _
&HC6, &H97, &H35, &H6A, &HD4, &HB3, &H7D, &HFA, &HEF, &HC5, &H91, &H39, &H72, &HE4, &HD3, &HBD, _
&H61, &HC2, &H9F, &H25, &H4A, &H94, &H33, &H66, &HCC, &H83, &H1D, &H3A, &H74, &HE8, &HCB)
Dim expandedKey, block(16), aesKey(32), i, j, isEncode
Dim sPlain, sPass, sCipher, sTemp, nonce(16), priorCipher(16)
Dim x, r, y, temp(4), intTemp
For i = 0 To 15
nonce(i) = 0
Next
For i = 0 To (Len(sPassin) - 1)
aesKey(i) = Asc(Mid(sPassin, i + 1, 1))
Next
For i = Len(sPassin) To 31
aesKey(i) = 0
Next
expandedKey = expandKey(aesKey, sbox, rcon)
sPlain = sCounter
sCipher = ""
j = 0
sTemp = Mid(sPlain, j * 16 + 1, 16)
If Len(sTemp) < 16 Then
For i = Len(sTemp) To 15
sTemp = sTemp & Chr(0)
Next
End If
For i = 0 To 15
block(i) = Asc(Mid(sTemp, (i Mod 4) * 4 + (i \ 4) + 1, 1))
Next
j = j + 1
r = 0
For i = 0 To 15
block(i) = block(i) Xor nonce(i) Xor expandedKey((i Mod 4) * 4 + (i \ 4))
Next
For x = 1 To 13
block(0) = sbox(block(0))
block(1) = sbox(block(1))
block(2) = sbox(block(2))
block(3) = sbox(block(3))
intTemp = sbox(block(4))
block(4) = sbox(block(5))
block(5) = sbox(block(6))
block(6) = sbox(block(7))
block(7) = intTemp
intTemp = sbox(block(8))
block(8) = sbox(block(10))
block(10) = intTemp
intTemp = sbox(block(9))
block(9) = sbox(block(11))
block(11) = intTemp
intTemp = sbox(block(12))
block(12) = sbox(block(15))
block(15) = sbox(block(14))
block(14) = sbox(block(13))
block(13) = intTemp
r = x * 16
For i = 0 To 3
temp(0) = block(i)
temp(1) = block(i + 4)
temp(2) = block(i + 8)
temp(3) = block(i + 12)
block(i) = g2(temp(0)) Xor temp(3) Xor temp(2) Xor g3(temp(1)) Xor expandedKey(r + i * 4)
block(i + 4) = g2(temp(1)) Xor temp(0) Xor temp(3) Xor g3(temp(2)) Xor expandedKey(r + i * 4 + 1)
block(i + 8) = g2(temp(2)) Xor temp(1) Xor temp(0) Xor g3(temp(3)) Xor expandedKey(r + i * 4 + 2)
block(i + 12) = g2(temp(3)) Xor temp(2) Xor temp(1) Xor g3(temp(0)) Xor expandedKey(r + i * 4 + 3)
Next
Next
block(0) = sbox(block(0)) Xor expandedKey(224)
block(1) = sbox(block(1)) Xor expandedKey(228)
block(2) = sbox(block(2)) Xor expandedKey(232)
block(3) = sbox(block(3)) Xor expandedKey(236)
intTemp = sbox(block(4)) Xor expandedKey(237)
block(4) = sbox(block(5)) Xor expandedKey(225)
block(5) = sbox(block(6)) Xor expandedKey(229)
block(6) = sbox(block(7)) Xor expandedKey(233)
block(7) = intTemp
intTemp = sbox(block(8)) Xor expandedKey(234)
block(8) = sbox(block(10)) Xor expandedKey(226)
block(10) = intTemp
intTemp = sbox(block(9)) Xor expandedKey(238)
block(9) = sbox(block(11)) Xor expandedKey(230)
block(11) = intTemp
intTemp = sbox(block(12)) Xor expandedKey(231)
block(12) = sbox(block(15)) Xor expandedKey(227)
block(15) = sbox(block(14)) Xor expandedKey(239)
block(14) = sbox(block(13)) Xor expandedKey(235)
block(13) = intTemp
For i = 0 To 15
nonce(i) = block(i)
Next
For i = 0 To 15
sCipher = sCipher & Chr(block((i Mod 4) * 4 + (i \ 4)))
Next
RunAES = sCipher
End Function
Function expandKey(ByRef key(), ByRef box(), ByRef rcon())
'MOD added () to array variables
Dim rConIter, temp(), i, result(240)
ReDim temp(4)
rConIter = 1
For i = 0 To 31
result(i) = key(i)
Next
For i = 32 To 239 Step 4
temp(0) = result(i - 4)
temp(1) = result(i - 3)
temp(2) = result(i - 2)
temp(3) = result(i - 1)
If i Mod 32 = 0 Then
temp = keyScheduleCore(temp, rConIter, box, rcon)
rConIter = rConIter + 1
End If
If i Mod 32 = 16 Then
temp(0) = box(temp(0))
temp(1) = box(temp(1))
temp(2) = box(temp(2))
temp(3) = box(temp(3))
End If
result(i) = result(i - 32) Xor temp(0)
result(i + 1) = result(i - 31) Xor temp(1)
result(i + 2) = result(i - 30) Xor temp(2)
result(i + 3) = result(i - 29) Xor temp(3)
Next
expandKey = result
End Function
Function keyScheduleCore(ByRef row(), ByVal a, ByRef box(), ByRef rcon())
Dim result(4), i
For i = 0 To 3
result(i) = box(row((i + 5) Mod 4))
Next
result(0) = result(0) Xor rcon(a)
keyScheduleCore = result
End Function