SHA1 Decryption in VB.Net

Is it possible to decrypt a SHA1 string in VB.Net, knowing the key?

I have seen "decryption" of creden开发者_StackOverflow社区tials before, however - in Java: http://pastebin.com/P0LuN00P

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The entire point of SHA1 is to make this impossible.

However, SHA1 has weaknesses which make this less impossible.
You should use SHA512 to make it more impossible.

You might be looking for Rijndael, a (good) symmetric encryption algorithm.

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I think you got SHA1 wrong. SHA1 is not an encryption algorithm, it is a hash function.

A hash function is a function taking some unconditionally long argument string and transform that string to a much smaller string, called the hash. It is very hard to get from a hash to the string used to generate the hash. Actually, since the input are arbitrarily long, there are multiple such inputs that give the same hash. Two such inputs are called collisions. Therefore you really cant "decrypt" a hash, you can find a input which gives the same hash though.

Commonly hashing functions are used to hash a user password, store it in a database on the server. When the server is supplied a password from a user, the server checks to see if the password is correct by checking that hashing the password gives the same result as stored in the database. If a malicious user grabs what is stored in the database, he is unable to know the actual password since it is very hard to go from hash to the string used to generate the hash.

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SHA1 isn't encrypted, it's hashed. So no, it's not possible to decrypt it. You might try a Rainbow Tables: http://www.freerainbowtables.com/