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<%
OPTION EXPLICIT
const BASE_64_MAP_INIT =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
dim nl
zero based arrays
dim Base64EncMap(63)
dim Base64DecMap(127)
must be called before using anything else
PUBLIC SUB initCodecs()
init vars
nl = "<P>" & chr(13) & chr(10)
setup base 64
dim max, idx
max = len(BASE_64_MAP_INIT)
for idx = 0 to max – 1
one based string
Base64EncMap(idx) = mid(BASE_64_MAP_INIT, idx + 1, 1)
next
for idx = 0 to max – 1
Base64DecMap(ASC(Base64EncMap(idx))) = idx
next
END SUB
encode base 64 encoded string
PUBLIC FUNCTION base64Encode(plain)
if len(plain) = 0 then
base64Encode = ""
exit function
end if
dim ret, ndx, by3, first, second, third
by3 = (len(plain) \ 3) * 3
ndx = 1
do while ndx <= by3
first = asc(mid(plain, ndx+0, 1))
second = asc(mid(plain, ndx+1, 1))
third = asc(mid(plain, ndx+2, 1))
ret = ret & Base64EncMap( (first \ 4) AND 63 )
ret = ret & Base64EncMap( ((first * 16) AND 48) + ((second \ 16)
AND 15 ) )
ret = ret & Base64EncMap( ((second * 4) AND 60) + ((third \ 64)
AND 3 ) )
ret = ret & Base64EncMap( third AND 63)
ndx = ndx + 3
loop
check for stragglers
if by3 < len(plain) then
first = asc(mid(plain, ndx+0, 1))
ret = ret & Base64EncMap( (first \ 4) AND 63 )
if (len(plain) MOD 3 ) = 2 then
second = asc(mid(plain, ndx+1, 1))
ret = ret & Base64EncMap( ((first * 16) AND 48) +
((second \
16) AND 15 ) )
ret = ret & Base64EncMap( ((second * 4) AND 60) )
else
ret = ret & Base64EncMap( (first * 16) AND 48)
ret = ret & "="
end if
ret = ret & "="
end if
base64Encode = ret
END FUNCTION
decode base 64 encoded string
PUBLIC FUNCTION base64Decode(scrambled)
if len(scrambled) = 0 then
base64Decode = ""
exit function
end if
ignore padding
dim realLen
realLen = len(scrambled)
do while mid(scrambled, realLen, 1) = "="
realLen = realLen – 1
loop
dim ret, ndx, by4, first, second, third, fourth
ret = ""
by4 = (realLen \ 4) * 4
ndx = 1
do while ndx <= by4
first = Base64DecMap(asc(mid(scrambled, ndx+0, 1)))
second = Base64DecMap(asc(mid(scrambled, ndx+1, 1)))
third = Base64DecMap(asc(mid(scrambled, ndx+2, 1)))
fourth = Base64DecMap(asc(mid(scrambled, ndx+3, 1)))
ret = ret & chr( ((first * 4) AND 255) + ((second \ 16) AND 3)
)
ret = ret & chr( ((second * 16) AND 255) + ((third \ 4) AND
15) )
ret = ret & chr( ((third * 64) AND 255) + (fourth AND 63) )
ndx = ndx + 4
loop
check for stragglers, will be 2 or 3 characters
if ndx < realLen then
first = Base64DecMap(asc(mid(scrambled, ndx+0, 1)))
second = Base64DecMap(asc(mid(scrambled, ndx+1, 1)))
ret = ret & chr( ((first * 4) AND 255) + ((second \ 16) AND 3)
)
if realLen MOD 4 = 3 then
third = Base64DecMap(asc(mid(scrambled,ndx+2,1)))
ret = ret & chr( ((second * 16) AND 255) + ((third \ 4) AND
15) )
end if
end if
base64Decode = ret
END FUNCTION
initialize
call initCodecs
Testing code
dim inp, encode
inp = request.QueryString("input")
encode = base64Encode(inp)
response.write "Encoded value = " & encode & nl
response.write "Decoded value = " & base64Decode(encode) & nl
%>
