symmetric versus asymmetric security

What essential differences between asymmetric key and symmetric
key crypto-protocols, including tamper evident hardware, when is
it neccessary to support revocation of stolen keys?



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dappleAsked:
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jhanceCommented:
Is this some kind of homework problem or something?  It's an odd connection between symmetric/asymmetric crypto protocols and tamper evident hardware.

What gives?  You know that the Experts Exchange policies prohibit asking for experts to do your homework or experts from doing homework for you.
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joe_hCommented:
Basically, symmetric cryptography uses a single key for both encryption and decryption, while assymetric cryptography uses one key for encryption and a different one for decryption - therefore, it's not necessary to hide the encryption key.

This is the basics; if it is your homework, you'll have to make a more elaborate description anyway. To get you started, I'd suggest reading some info about the RSA algorithm.

What was it about tamper-evident hardware you had in mind?
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dappleAuthor Commented:
I know the basics, one uses one key the other two keys
What are the advantages and disadvantages of the using the two protocols
By tamper evident hardware i mean using these protocols with hardware rather than software

David
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joe_hCommented:
For me, tamper-evident hardware would mean something that is able to detect if someone has been fiddling around with it with a screwdriver, trying to get some unauthorized info out of it. I don't see the connection to symmetric/asymmetric cryptography.

For details about symmetric/asymmetric cryptography, check for example www.rsa.com.
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jjmcdCommented:
Often, cryptographic algorithms are embodied in hardware devices such as dongles.  Typically, these are stored on ASICs which can be microscopically decoded.  To prevent this, these ASICs are usually encapsulated in something that requires destroying the ASIC in order to access it.
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GnissmanCommented:
The great disadvantage of symmetric cryptography is that the key-management is fairly complex. That's because you need a dedicated pair of keys for everybody you wish to correspond to. Whereas in asymmetric algorithms you need just two keys for your yourself and the public key of your partner which can be easily obtained and has not to be kept secretly by you.

Gniss
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joe_hCommented:
On the other side, symmetric cryptography is usually much less time-consuming (in terms of the time it takes to encrypt/decrypt a message). Often in communication of two subjects, assymetric cryptography is used to authenticate each other and to "agree upon" a secret key for that session, and then the communication further proceeds using symmetric cryptography.
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dappleAuthor Commented:
thanks all for help
RSA has good FAQ
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