Aes algorithem in C#

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i managed to make a simple program that encrypt and decrypt a text in c# using the aes algorithm but i have a few questions:
1) what is the best class and way to use the aes? cause i got those classes:AesManaged , RijndaelManaged , AesCryptoServiceProvider.
2) i understand there is a key size but i cant enter any other string rather than one that have 8 chars. so what to do?
3) why to use a string as a key isnt safe?
my code: [C#] aes - Pastebin.com[^]
ty for help!!!

What I have tried:

search tons in google about keys and all of that

Posted 1-Jun-16 7:12am

Member 12181103

Updated 1-Jun-16 7:46am

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Sergey Alexandrovich Kryukov · Answer 1 · 2016-06-01T07:46:00

Solution 1

It's all wrong. The "fact" that a key is somehow related to some strings is nothing but your fantasy. If you generated a key from a string, it's your problem. All cryptographic keys are just arrays of bytes. (Please see Aes Class (System.Security.Cryptography)[^].) Also, you should understand that those keys have nothing to do with the concept of "password".

And, just in case: if you think that a password (I'm talking about real passwords now) can be encrypted and stored, think again: the idea would be totally unsafe. Passwords should never be stored anywhere or transmitted via the network for authentication. If you feel confused or disagree, read about cryptographic has functions and their use for password-based authentication.

I have no idea what is your purpose, and this is bad. This is the fist thing you had to explain. The whole idea of symmetric encryption is questionable for most applications. You need to understand some basic cryptographic ideas first. Please see:
Symmetric-key algorithm — Wikipedia, the free encyclopedia[^],
Public-key cryptography — Wikipedia, the free encyclopedia[^],
Cryptography — Wikipedia, the free encyclopedia[^].

—SA

Posted 1-Jun-16 7:46am

Sergey Alexandrovich Kryukov

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Member 12181103 1-Jun-16 14:34pm

i understand i explained my self bad.
i know understand that its not what i taught and i will re ask the questions:
1) why i cant convert a any other string rather than a 8 char long string to array of a byte and use it as my key?
2) why to do like that ^ is less safe than that: https://msdn.microsoft.com/en-us/library/system.security.cryptography.rfc2898derivebytes%28v=vs.110%29.aspx
3) what is the best class and way to use the aes? cause i got those classes:AesManaged , RijndaelManaged , AesCryptoServiceProvider.
ty for answer and for your time!!!!

Sergey Alexandrovich Kryukov 1-Jun-16 14:57pm

1) You can represent absolutely any string as an array of bytes, but the result depends on the chosen encoding.
I have no idea where did you get "8 char long". It's not "conversion". It can be System.Text.Encoding.GetBytes.

2) What is less safe than what? I don't understand. You link is related to key generation.

3) No, they are: System.Security.Cryptography.AesCng, System.Security.Cryptography.AesCryptoServiceProvider, System.Security.Cryptography.AesManaged. You can find some considerations here: http://stackoverflow.com/questions/1228451/when-would-i-choose-aescryptoserviceprovider-over-aesmanaged-or-rijndaelmanaged, http://stackoverflow.com/questions/13486109/rijndaelmanaged-vs-aescryptoserviceprovider-aes-encryption.

AES can be considered as a special case of Rijndael symmetric algorithm.

—SA

Member 12181103 1-Jun-16 15:11pm

http://stackoverflow.com/questions/34343500/why-does-any-length-key-work-for-rijndaelmanaged/34354643#34354643
in the second comment to the question he said its less safer. why?

and in the code that i have: http://pastebin.com/NWj3pi2Y
this is the only length of string that i can do: ggwpgiy2
why?
thank you for you answers!!!!!!

Sergey Alexandrovich Kryukov 1-Jun-16 16:05pm

On that page, I could not even find the word "safer".

I don't understand what "the only length of string that I can do" means. "ggwpgiy2" is not a length, this is a string. I have no idea why do you do it all.

—SA

Member 12181103 1-Jun-16 16:34pm

Ok so what i want to do is to make a program the will encrypt and decrypt text with aes algorithem.
The key a "password" they will choose too help them decrypt it later.
So i searched online and i found what i found but i can do bigger string like: passwords.
Its too long.
There is a certain length i can enter right?

Sergey Alexandrovich Kryukov 1-Jun-16 18:47pm

The real problem is key distribution. You need to figure out your scenario. Say, if you encrypt text, anyone can decrypt it if the password becomes known. With public-key encryption, there is no such problem (many fail to understand that or think it would be impossible).
The length should be a length of the array of bytes, not string. Forget "passwords", forget strings, this is all irrelevant. The length of data should be one of allowed length; you can query the algorithm which lengths are valid. The bigger the safer, but there is no need to get crazy about it.
—SA

Member 12181103 2-Jun-16 6:16am

yes i know but my problem is that i can convert only a string that have a length of 8, to array of bytes so what i can do to make it longer?