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Re: [CPROG] Encryption/decryption



On Fri, 24 Mar 2000 22:47:48 +0100 (CET), Mads Bondo Dydensborg wrote:

>> Er der nogen der kender til noget ala encrypt(string), decrypt(string) eller
>> tilsvarende simpelt ?
>
>man crypt?

crypt() er jo en een-vejs kryptering -- det lyder som om han vil ogsaa hente
den krypterede vaerdi i klartekst igen senere.

Hvad er det du vil opnaa med krypteringen? Hvis du bare vil undgaa
at kodeordene ligger i klar tekst paa disken kan du maaske klare
dig med noget saa trivielt som "memfrob". Den XOR'er data med 42,
og saadan en XOR er symmetrisk, saa du kan memfrob'e det kodede
igen for at faa de data tilbage. Se man memfrob.

Hvis du vil have noget lidt mere kompliceret, fx at beskytte data
med en kryptering baseret paa et kodeord kunne du lave en lignende
XOR men som noegle bruge ikke bare et enkelt tal, men et password
som du beder brugeren om.

Det er dog forholdsvis let at bryde med et brute-force attack.

For noget endnu mere kompliceret kan du jo lede efter fx.
"encryption library" paa www.freshmeat.net -- der er en bunke.


PS: Jeg er tilbage efter et jobskift :)


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