Decryption of a file,whose encrypted algorithm is not known

i am working with Authentication log files.i installed certificate authentication server.when i view its log files.they are encrypted with SHA1 algorithm,but i dont know about this algorothm,nor do i have its decryption key.
is there any way to view those log files.
urgently required
tulipnoorAsked:
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jhanceCommented:
SHA1 is not an encryption algorithm but rather a HASH algorithm.  SHA1 hashed data is not decrypted since this is a ONE-WAY hashing function.  Its purpose is to "sign" or validate a block of data so that you can know it's not been altered rather than to provide security against outsiders from viewing the data.

Hashes are used with log files to permit the administrator to determine whether or not the log files have been altered.  An attacker will  not be able to generate the same hash from the altered data so the attack will be detected.

The way you use the hash is to use the (publicly available) SHA1 algorithm to re-hash the log file data and validate that the hash you calculate matches the original hash.
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jhanceCommented:
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decoleurCommented:
we need more information about your configuration.

on first glance, without knowing the application or the OS... No you will not be able to read those logs, although there are issues with the security of SHA you cannot easily reverse engineer a hash file of a log file to determine its content.
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jhanceCommented:
???
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jhanceCommented:
decoleur,

SHA-1 is a HASH, not an encryption scheme.  It's a ONE WAY HASH, that means that even knowing the key doesn't get you back to the plaintext.  SHA-1, as well as other HASHES are NOT suitable for data encryption.  They are used for signing and other sorts of verification schemes.

In this question, the log files themselves are NOT encrypted with SHA-1.  They may be hashed with SHA-1 and they may (or may not) be encrypted using some other scheme.
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decoleurCommented:
yes j you are right, SHA is a hash and it is not encryption... did I ever say that it was?

SHA is however also called a cryptographic hash function that is computationally infeasable to reverse engineer. for more info: http://unixwiz.net/techtips/iguide-crypto-hashes.html

I still think we need more information about the configuration to assist.

cheers-

-t
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jhanceCommented:
It's my opinion that this question is fully answered.
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decoleurCommented:
the question was answered, sha is a cryptographic one way hash, the poster wanted a way to reverse the process.

the answer was that it could not be done. we both said it in different ways.
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