Base64? How do i encode and get these results?

ok i have this password encrypt and decrypt function in a dll that i can run from an exe. And i want to duplicate the encrypt and decrypt function but in vb.net only. I cannot use the dll in the project. Im not sure eactly how they encrypt it, but i believe it might be some sort of Base64. Peaking in the the dll i see this:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

im guessing its the "salt" or character set or something...

when encoding a string, it seems to always put a equal sign (=) on the end. And if i decode it without the equal sign it will still still return the origonal string.

when i enter a single character and then encode, it always gives me a 12 charater string(includeing the =)

when i enter more than 8 characters, it will encode to a 24 character string.

I have unlimited examples so here is a few.

|string| = |encrypted|

a = A0PKsdIHWus=
b = SzBQ1lTolcw=
c = jhVX2s+CGL4=
d = ZLPyxPRQjJo=
e = hmX+vknZb1o=
f = dLueWpJ4Y+E=
g = YwFVJKs9+LE=
h = Owj8Yzd2Sv8=
i = jTK1YtZlyZk=
j = SsAtvAMz/sg=
k = uO8C0TjdQcM=
l = 8eRmoycd6Kg=
m = yAmxs9+ONPY=
n = ZkQbKBrwX6c=
o = 5nK2p8NUqvA=
p = mKWH16j6ZYo=
q = deMYAGglEBQ=
r = zH/qmpA8EUg=
s = qyvKzL/OFYE=
t = 4a48yaAQP30=
u = cRsDWNf4q4E=
v = h1E0QkG7kuw=
w = kYqyUdomGEw=
x = iDDGy73UDw4=
y = oSYIy0RYMmQ=
z = 7NVyMWfk/9Q=
aa = uEhHV3z/bxI=
ab = oWS79abB+yA=
1 = Fz3WpVLNGPQ=
2 = Xg8F395V2gw=
3 = Kp+SsOupzj0=
4 = mW8PAOopbd4=
5 = bcRj9/UEblU=
6 = lbZfedgQXNQ=
7 = GvcAoszQoUQ=
8 = TsAyCq3oBz8=
9 = 0b6pNuerjcg=
0 = IqFalA+xc/E=
11 = XG+JO1e79qo=
12 = mRB3z+eN7b4=
13 = mubNQyYGA1Q=
14 = lnA9x4tjKX0=
15 = HO9r2CHAYKc=
testpassword = q82LMCmpMlY7qjYZRZnFmg==
password = ASAewVoV8Tw=
TESTPASSWORD = kfConS+nA7p2hrDatl6pBQ==



once again what i want to do is have a textbox1, an encode and a decode button(s), and another textbox2 for result. I want to beable to input a string, for example:
testpassword

press encode button and have this show in textbox2:
q82LMCmpMlY7qjYZRZnFmg==


or type this:
a
press encode button and have this show in textbox2:
A0PKsdIHWus=


but the part im stuck on is the encoding and would like to know if anyone can figure out how to get the results shown above.

ty so much in advance.

 

i always thought 1 character converts to 4 chars not 8 that you say. dont quite understand. code ive used and this website do the same:-
http://www.gulftech.org/tools/base64.pl