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Back to article list Search Articles Add Comment Printer friendly Direct link Par2: String Encryption Algorithm 2001-01-08 -- Randy Goodhew Be my guest:
!===========================================================
eqCrypt PROCEDURE(*STRING pIntext,CONST *STRING
pPass,<*STRING pOutText>) !returns ULONG
!===========================================================
! Copyright 2001 Randy Goodhew. ALL RIGHTS RESERVED.
! Prototype: eqCrypt PROCEDURE(*STRING InText, |
! CONST *STRING password, |
! <*STRING OutText>),LONG
! Parameters:
! InText - the buffer of text to be encrypted/decrypted
! Password - the password (will be CLIPped of trailing spaces)
! OutText - omittable, the buffer that will receive the output.
! If omitted, the Intext buffer will be over written.
! Returns: the number of bytes processed.
!
! NOTE: On a 200 MHz Pentium computer, this procedure will
! encrypt/decrypt greater than 6,000,000 characters per second.
! This is a symmetric encryption algorithm. The same password
! must be used for both encryption and decryption. The password
! is case sensitive. If the password is blank, no text will be
! processed.
!===========================================================
OutRef &STRING ! output reference
Len LONG,AUTO ! length of password
J LONG,AUTO ! text loop counter
K LONG,AUTO ! password loop counter
Result LONG,AUTO ! number of characters
CODE
Len = LEN(CLIP(pPass)) ! get clipped length of password
IF Len
DO R_Process ! process if there is a password
ELSE
Result = 0 ! return "0" if no password
END !if
RETURN(Result) ! return bytes processed
!-----------------------------------------------------------
R_Process ROUTINE
IF OMITTED(3) ! test for third parameter
OutRef &= pInText ! write-back to first parameter
ELSE ! if NOT Omitted(2)
OutRef &= pOutText ! write-back to second parameter
END !if
! Set Result to smaller of the two:
Result = CHOOSE(SIZE(pInText) >
SIZE(OutRef),SIZE(OutRef),SIZE(pInText))
K = 1 ! initialize password counter
LOOP J = 1 TO Result BY 1 ! loop thru input text
! encrypt/decrypt each text character:
OutRef[J] = CHR(BXOR(VAL(pInText[J]),VAL(pPass[K]))) ! See asm01
K = CHOOSE(K = Len,1,K + 1) ! adjust password counter
END !loop
OutRef &= NULL ! uninitialize reference
EXIT
asm01 !----------------------------------------------------
OMIT('***asm01***')
This is a disassembly of the Clarion code that performs the
actual encryption/decryption. Note that it is pure register
based operations. There are no RTL calls or stack operations.
----------------------------
mov ebx,[edx][-14H]
mov eax,[edx][-1CH]
mov cl,[ebx][eax][-1]
mov ebx,[edx][-28H]
mov eax,[edx][-18H]
xor cl,[ebx][eax][-1]
mov [ebp][-9],cl
mov al,[ebp][-9]
mov [ebp][-0AH],al
mov ecx,[edx][-0CH]
mov ebx,[edx][-1CH]
mov al,[ebp][-0AH]
mov [ecx][ebx][-1],al
----------------------------
***asm01***
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