Got Plaintext and Ciphertext ... Want Algorithm

Hey,

If I have a list of plaintext and its associated ciphertext, what is the best way to go about discovering the algorithm that is used to convert from one to the other?

Are there any programs out there? Should it be a simple case of writing a program that discovers the algorithm itself? Any pointers or advice would be much appreciated.

'a' => '8E'
'aa' => 'D0A8'
'aaa' => 'D97842'
'ab' => 'D2D1'
'abc' => 'A2F5D9'
'acb' => 'A93564'
'0' => 'A6'
'01' => 'C54C'
'10' => 'CB0C'
'pass' => 'E9FA5662'
'ssap' => 'E3A50C8B'
'password' => 'FC8EED0B2CE35AFC'
'passwords' => 'DF4C0F545552FC8D34'
'pastword' => '677B8869AC946845'
'pastwords' => 'ABB781CD569724696B'

Also, I'm not quite up to this stage yet, but if I have a tcp stream segment, and I know for a fact much of its content, whats the best method to decrypt it?

..f/9....a.yV...............*{...dd....k...3.....N..p..{.N6"...~.r........*D0.w.N<..........yE....
......x.T|0B..Q)^&
...,..E.}.Ft;.p..`M.6.d.....E.c|._..zv.4?......%X.ND.Yu2..:\.....a..a..S.V.`;......uud.r..?...>.....|9...z.`D..\...f.+..z..3^.....B0H......O....;|.U.....`N.az.......+s.B..'.f...|/..p.......{fi...q.......M1.(....l.......
....pH&!..%`.i..c,.k!..v....n..e...^`C.....#.A...o..u._
=...S..."m..a,p..)c.sj../.......>.R.._0....t0.s.C..Y...Nd^...u...r. ...^.O.ykz...Mpw.t&.l).3eUC......(T...k..)VXH...(97.. 9z....v...~N......1;...L.....IXW..$.....G<..?>.R.vZS.]G.C.jo..4.II...,.j.0U.p...:.S1..A.G|R.MOF.)....vr.]..C.O'[Q......U...`.E...8![]..y......c..F..h(.....9.i9~
~...u..3.Y.l.)P.".......0..
....0oV...Mh...x.(..-..O..J.........._y..Y..a.....j..y.rv.bA.."B..o..&....so.......
..E....|.C..X.go4g:....S.Q.?
..5..
..j}.)....IP...O.L....!......]+
....l.b.'...T.t.......\..?..D..k0...F...{.E.!...(}c.~7.\.....N..h...D4.....J.q...... ...4...+........+..}..X..r..k..x...|.Q.:..3f.pY...:[...b.....z....4.-.#..c.T......7......<...7.. ..h....
...X..N..lm...S{c.$........*roq.r...\^.n1...y...b=zV
k..5..p..xT..-.'./y.
...6 ..Y..a._%c.^2..3....o....d)^<..TS...c...K$L:..l...
.....wt,.\..OJ..F.}.37..l.g_.EZH.C..v..2..w.t....).V|.pt_..h9C1.`.e.j...q.&......AzQ35u.{j.f...5..Gh..Pb..>]!9.o.l..k.]...b..Cl...Vh.N........jr.X.$.*.8~J..).
6..dy.u..F.]...E...6z.....I..;e p.8`E..w...f:V3.W.44`...aN;...........r=.*A.uA.S.........b....G,.L...U.#..+.*K}...

contains words including:

buMzy
Corrosive
dolly
elluznist
Elphi
emeh!
garrick
Google
Gus
hadokenstyle

(Obviously a lot more words in there). Am I in over my head with that second task?

Thanks heaps.

Steve
.

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