RC4 encryption

This code has been declared by its author to be Public Domain code.

RC4 encryption by RepeatUntil

2006

This encryption/decryption uses the RC4 algorithm. The same function encrypt and decrypt a string, with the use of a key. See the code to see a simple example.
Function adapted to BlitzMax by Wave and RepeatUntil.

Noel rewrote this function, and now it's 20 times faster than mine!! Use his! See the first comment...

Local pass$ = "mySecretKey"
Local msg$ = "Blitz Research Ltd is a software development company dedicated to bringing you the ultimate in game creation tools and utilities.Our flagship product is Blitz3D, the hit 3D games programming language used by thousands of programmers around the world.Our latest product is BlitzMax, a cross platform programming language based on BASIC, but with many weird And wonderful additions."

Print ""
Print "Message before encryption: " + msg

Print ""

Local crypt$ = RC4(msg$, pass$)

Print "Message after encryption: " + crypt

Print ""
Local decrypt$ = RC4(crypt$,pass$)
Print "Message after decryption: " + decrypt




' This function encrypts and decrypts a string with the use of a key
Function RC4$(inp$, key$)
	Local S[256] ' 255 byte Arrays
	Local K[256]

	Local i,j,t,temp,y
	Local Output$

	For i = 0 To 255
		S[i] = i
	Next

	j = 1
	For i = 0 To 255
		If j > key.length
 			j = 1
		EndIf
		K[i] = Asc(Mid(key,j,1))
		j:+ 1
	Next

	j = 0
	For i = 0 To 255 '
		j = ( j + S[i] + K[i] ) & 255
		temp = S[i]
		S[i] = S[j]
		S[j] = temp
	Next

	i = 0
	j = 0
	For Local x = 1 To Len(inp)
		i = (i + 1) & 255
		j = (j + S[i]) & 255
		temp = S[i]
		S[i] = S[j]
		S[j] = temp
		t = (  S[i] + ( S[j] & 255 )  ) & 255
		y = S[t]
		Output:+ Chr(Asc(Mid(inp,x,1)) ~ Y)
	Next
	
	Return Output$
EndFunction

Comments

2006

Very nice work, one of the few code archive entries I've actually considered using (and I will be using this).

It's a tad slow though, so here's an optimized version that runs much faster (based on your code, of course) and produces the same results:

Strict

Local pass$ = "h089HSCx;chjS(PC hsP:s8(Y{s(YACXh{PAP(SCY)X_)cyP_S(CyXZ(_CYu" ' Weeeeee mashing the keyboard
Local msg$ = "DebugLog( ~q clampucube: ~q+c.clampucube[0] + ~q ~q + c.clampucube[1] + ~q ~q + c.clampucube[2] + ~q ~q + c.clampucube[3] + ~q ~q + c.clampucube[4] + ~q ~q + c.clampucube[5] + ~q ~q + c.clampucube[6] + ~q ~q + c.clampucube[7] )"
Local t%

Print "Old results:"
Print RC4o(msg$, pass$)
Print ""
Print RC4o(RC4o(msg$, pass$),pass$)
Print ""

For Local x% = 0 To 5
    t = Millisecs( )
    For Local i% = 0 To 1000-1
        RC4o(RC4o(msg$, pass$),pass$)
    Next
    t = Millisecs( ) - t
    Print t
Next

Print ""
Print "-------------------------------------------------"
Print ""

Print "New results:"
Print RC4(msg$, pass$)
Print ""
Print RC4(RC4(msg$, pass$),pass$)
Print ""

For Local x% = 0 To 5
    t = Millisecs( )
    For Local i% = 0 To 1000-1
        RC4(RC4(msg$, pass$),pass$)
    Next
    t = Millisecs( ) - t
    Print t
Next

Input



' New version
Function RC4$(inp$, key$)
    Local S%[512+Ceil(inp.Length*.55)]
    Local i%, j%, t%, x%
    Local outbuf@@ Ptr = Short Ptr(Varptr s[512])
    
    j = 0
    For i = 0 To 255
        S[i] = i
        If j > (Key.length-1) Then
            j = 0
        EndIf
        S[256+i] = key[j]&$ff
        j:+ 1
    Next
    
    j = 0
    For i = 0 To 255
        j = (j + S[i] + S[256+i]) & $ff
        t = S[i]
        S[i] = S[j]
        S[j] = t
    Next
    
    i = 0
    j = 0
    For Local x% = 0 To inp.Length-1
        i = (i + 1) & $ff
        j = (j + S[i]) & $ff
        t = S[i]
        S[i] = S[j]
        S[j] = t
        t = (S[i] + S[j]) & $ff
        outbuf[x] = (inp[x] ~ S[t])
    Next
    
    Return String.FromShorts(outbuf, inp.Length)
End Function


' Old version
Function RC4o$(inp$, key$)
    Local S[256] ' 255 byte Arrays
    Local K[256]
    
    Local i,j,t,temp,y
    Local Output$
    
    For i = 0 To 255
        S[i] = i
    Next
    
    j = 1
    For i = 0 To 255
        If j > key.length
            j = 1
        EndIf
        K[i] = Asc(Mid(key,j,1))
        j:+ 1
    Next
    
    j = 0
    For i = 0 To 255 '
        j = ( j + S[i] + K[i] ) & 255
        temp = S[i]
        S[i] = S[j]
        S[j] = temp
    Next
    
    i = 0
    j = 0
    For Local x = 1 To Len(inp)
        i = (i + 1) & 255
        j = (j + S[i]) & 255
        temp = S[i]
        S[i] = S[j]
        S[j] = temp
        t = (  S[i] + ( S[j] & 255 )  ) & 255
        y = S[t]
        Output:+ Chr(Asc(Mid(inp,x,1)) ~ Y)
    Next
    
    Return Output$
EndFunction

I imagine this optimization will benefit more than just myself.

RepeatUntil

2006

Wahou, Noel, I am very impressed, this is more than 20 times faster!! So, people, please use the Noel's version.

There is something strange with your long key, though, and I am not able to have the result printed (with both functions). Works as soon as the key has a more reasonable length...

Filax

2006

There is a bug when the key is made from numbers :

Try "123456" with key

Strict

Local pass$ = "AEZREZRE" ' Weeeeee mashing the keyboard
Local msg$ = " Wahou, Noel, I am very impressed, this is more than 20 times faster!! So, people, please use the Noel's version."
Local chaine$

Print "New results:"
chaine$=RC4(msg$, pass$)

Print chaine$
Print "----------------------------------------------------------------------------------"
Print RC4(chaine$,pass$)
Print ""

' New version
Function RC4$(inp$, key$)
    Local S%[512+Ceil(inp.Length*.55)]
    Local i%, j%, t%, x%
    Local outbuf@@ Ptr = Short Ptr(Varptr s[512])
    
    j = 0
    For i = 0 To 255
        S[i] = i
        If j > (Key.length-1) Then
            j = 0
        EndIf

        S[256+i] = key[j]&$ff
        j:+ 1
    Next
    
    j = 0
    For i = 0 To 255
        j = (j + S[i] + S[256+i]) & $ff
        t = S[i]
        S[i] = S[j]
        S[j] = t
    Next
    
    i = 0
    j = 0

    For Local x% = 0 To inp.Length-1
        i = (i + 1) & $ff
        j = (j + S[i]) & $ff
        t = S[i]
        S[i] = S[j]
        S[j] = t
        t = (S[i] + S[j]) & $ff
        outbuf[x] = (inp[x] ~ S[t])
    Next
    
    Return String.FromShorts(outbuf, inp.Length)
End Function

RepeatUntil

2006

Strange, I don't see this bug when using the key 123456 ?? Maybe other can try and report here ??

plash

2008

Encrypt a block of memory (directly, no copy(s) made):

Function RC4_Bytes(inp:Byte Ptr, count:Int, key:String) 
  Local S:Int[512 + Ceil(count *.55)] 
  Local i:Int, j:Int, t:Int, X:Int
    
    j = 0
    For i = 0 To 255
        S[i] = i
        If j > (key.Length - 1) Then
            j = 0
        EndIf
        S[256 + i] = key[j] & $ff
       j:+1
    Next
    
    j = 0
    For i = 0 To 255
        j = (j + S[i] + S[256 + i] ) & $ff
        t = S[i] 
        S[i] = S[j] 
        S[j] = t
    Next
    
    i = 0
    j = 0
    For Local X:Int = 0 To count - 1
        i = (i + 1) & $ff
        j = (j + S[i] ) & $ff
        t = S[i] 
        S[i] = S[j] 
        S[j] = t
        t = (S[i] + S[j] ) & $ff
        inp[X] = (inp[X] ~ S[t] ) 
    Next
 
End Function

Ked

2008

Why is there a URL in the new RC4 Function? What was that Local previously?

Edit: Nevermind, I got it. :)

Ked

2008

I get an error when I decrypt using Noel's new code. I get a "Unhandled Memory Exception Error":

    Local S%[512+Ceil(inp.Length*.55)]
    Local i%, j%, t%, x%
    Local outbuf:Short Ptr = Short Ptr(Varptr s[512]) !!!! ON THIS LINE

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