Simple CAPTCHA?
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- Subject: Simple CAPTCHA?
- From: PA <petite.abeille@...>
- Date: 2007年8月19日 21:48:12 +0200
Hello,
Anyone has a suggestion for a simple (simplistic?) CAPTCHA mechanism?
By simple, I mean not necessarily requiring heavy duty image generation
or such...
Any ideas?
Here is a rather feeble attempt which generates a simple mathematical
question (e.g. 27 + 58), compute its result (85), and generates a HMAC
of the challenge using its result as the key (e.g. HMAC( '85', '27 +
58' ) ) for later validation:
local function Challenge()
local Operator = { '+', '-' }
local aBuffer = {}
math.randomseed( os.time() )
math.random( 1, os.time() )
aBuffer[ #aBuffer + 1 ] = tostring( math.random( 1, 100 ) )
aBuffer[ #aBuffer + 1 ] = Operator[ math.random( 1, #Operator ) ]
aBuffer[ #aBuffer + 1 ] = tostring( math.random( 1, 100 ) )
return table.concat( aBuffer, ' ' )
end
local function HMAC( aKey, aValue )
local md5 = require( 'md5' )
local bit = require( 'bit' )
if aKey:len() > 64 then
aKey = md5.digest( aKey, true )
end
if aKey:len() < 64 then
aKey = aKey .. string.char( 0 ):rep( 64 - aKey:len() )
end
local anInnerKey = aKey:gsub( '.', function( aChar ) return
string.char( bit.bxor( aChar:byte(), 54 ) ) end )
local anOuterKey = aKey:gsub( '.', function( aChar ) return
string.char( bit.bxor( aChar:byte(), 92 ) ) end )
return md5.digest( anOuterKey .. md5.digest( anInnerKey .. aValue,
true ) )
end
local aChallenge = Challenge()
local aResult = loadstring( 'return ' .. aChallenge )()
print( aChallenge )
print( aResult )
print( HMAC( tostring( aResult ), aChallenge ) )
Thoughts?