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Thread: VB6 - SillyStream Encrypted Text I/O

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    VB6 - SillyStream Encrypted Text I/O

    While hand-rolled encryption is never a good idea, sometimes you don't need a high-security solution. SillyStream is a text I/O class that you can set a few parameters on and then do low-volme encrypted text file I/O. It would need optimization if you really need to work on large files, but it was really intended for smaller items such as settings files.


    Usage

    Pretty simple, just add SillyStream.cls to your Project. Then create instances as you need them (each only handles one file at a a time). Call Init() to set the parameters, then one of the open methods (input, output, append), and use the read and write methods, and finally the close method. Then you can open a new file either with or without setting new parameters first.


    Parameters

    There are two mask values (one a Byte, another a Long) and two dimensional parameters. These have funny names in the class and in the demo Project. See the comments for an explanation.


    Cipher Used Here

    This is a combination cipher, based on two very very simple ciphers.

    The main feature here is a transposition cipher using the two dimensions provided to create a buffer block as a matrix. When writing or reading the file, the data is an inversion of this matrix.

    On top of that we have a simple (really simple) substitution cipher. Each of the data characters is XORed with a one-Byte mask. With some effort you could use a longer "password" mask but it complicates things (especially "open append" operations).

    The final block is padded with pseudorandom values.

    Finally, to make this work even with a padded final block, the actual data length is stored in the first 4 bytes of the file as a Long value. This is XORed with the Long mask you provide for the purpose to help obscure it a bit. Adding these 4 bytes has another advantage: It makes it all little tougher to crack because simply trying to factor the file size will be a bit of a red herring even if someone guesses it uses a rectangular transposition cipher.

    Dumb but cheap, and perhaps good enough.


    Demo

    The demo Project lets you open a new file, type some stuff, write it as characters or as a line (adding newline), etc, and then close. Then you can read it back and see it displayed, using either reading by byte count or the slower reading by line.

    Even though slower, I expect most people to just read by line most of the time. Writing by line is probably going to be more useful than by text length as well.

    Sample inputs:
    Code:
    This is a test.
    This is only a test.
    How now, brown cow?
    Mellow yellow, such a silly fellow!
    Test test test test test test test test test test testing!
    Hex dump:
    Code:
    0000	e5 54 12 f0 0f 2f 35 13  35 2c 33 37 28 2f 2f 3e   .T.../5.5,37(//>
    0010	51 7c 07 8c 15 33 75 37  34 7b 7b 7b 34 2f 3e 7b   Q|...3u74{{{4/>{
    0020	28 04 83 14 93 22 32 56  22 2c 38 22 3a 2c 7b 28   (...."2V",8":,{(
    0030	2f 2f 0b 90 1b a0 29 28  51 7b 7b 34 3e 7b 7a 2f   //....)(Q{{4>{z/
    0040	2f 3e 7b 18 97 28 a7 36  7b 0f 3a 35 2c 37 28 56   />{..(.6{.:5,7(V
    0050	3e 7b 28 2f 1f a4 2f b4  3d 32 33 7b 34 64 37 32   >{(/../.=23{4d72
    0060	51 28 2f 2f 3e 2c ab 3c  bb 4a 28 32 2f 2c 56 34   Q(//>,.<.J(2/,V4
    0070	37 0f 2f 3e 7b 28 33 b8  43 c8 51 7b 28 3e 77 51   7./>{(3.C.Q{(>wQ
    0080	2c 37 3e 7b 28 2f 2f 40  bf 50 cf 5e 3a 7b 28 7b   ,7>{(//@.P.^:{({
    0090	16 77 22 28 2f 2f 3e 32  47 cc 57 dc 65 7b 32 2f   .w"(//>2G.W.e{2/
    00a0	39 3e 7b 7b 2f 3e 7b 28  35 54 d3 64 e3 72 2f 28   9>{{/>{(5T.d.r/(
    00b0	75 29 37 28 3d 7b 28 2f  2f 3c 5b e0 6b f0 79 3e   u)7(={(//<[.k.y>
    00c0	7b 56 34 37 2e 3e 2f 2f  3e 7b 7a 68 e7 78 f7 86   {V47.>//>{zh.x..
    00d0	28 34 51 2c 34 38 37 3e  7b 28 2f 56 6f f4 7f 0e   (4Q,487>{(/Vo...
    00e0	8d                                                 .
    Hex dump of a test with the data XORing omitted. Normally you wouldn't do this but it shows that the transposition and padding can be effective all alone:
    Code:
    0000	e5 54 12 f0 54 74 6e 48  6e 77 68 6c 73 74 74 65   .T..TtnHnwhlstte
    0010	0a af 30 b5 3c 68 2e 6c  6f 20 20 20 6f 74 65 20   ..0.<h.lo   ote 
    0020	73 37 b6 3d bc 49 69 0d  79 77 63 79 61 77 20 73   s7.=.Ii.ywcyaw s
    0030	74 74 3e c3 44 c9 50 73  0a 20 20 6f 65 20 21 74   tt>.D.Ps.  oe !t
    0040	74 65 20 4b ca 51 d0 5d  20 54 61 6e 77 6c 73 0d   te K.Q.] Tanwls.
    0050	65 20 73 74 52 d7 58 dd  64 69 68 20 6f 3f 6c 69   e stR.X.dih o?li
    0060	0a 73 74 74 65 5f de 65  e4 71 73 69 74 77 0d 6f   .stte_.e.qsitw.o
    0070	6c 54 74 65 20 73 66 eb  6c f1 78 20 73 65 2c 0a   lTte sf.l.x se,.
    0080	77 6c 65 20 73 74 74 73  f2 79 f8 85 61 20 73 20   wle stts.y..a s 
    0090	4d 2c 79 73 74 74 65 69  7a ff 80 0d 8c 20 69 74   M,ystteiz.... it
    00a0	62 65 20 20 74 65 20 73  6e 87 08 8d 14 99 74 73   be  te sn.....ts
    00b0	2e 72 6c 73 66 20 73 74  74 67 8e 15 94 21 a0 65   .rlsf sttg...!.e
    00c0	20 0d 6f 6c 75 65 74 74  65 20 21 9b 1c a1 28 ad    .oluette !...(.
    00d0	73 6f 0a 77 6f 63 6c 65  20 73 74 0d a2 29 a8 35   so.wocle st..).5
    00e0	b4                                                 .

    Bugs

    I havent found any, but if you do be sure to mention them.
    Attached Files Attached Files
    Last edited by dilettante; Dec 27th, 2012 at 05:51 AM. Reason: fixed numerous typos in this description

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