Some other clarifications here: You can only encrypt a chunk of data (after all pre-processing including padding) that is up to the numerical value of the modulus - 1 . If you have a 64 bit key and you guarantee the highest order bit is 1, then your modulus is only guaranteed to be greater than 2^63 . Since you don't know how much greater, you can only use this modulus on 63 bits of data (again post processing, padding, etc).
If you don't need security you may not want to use RSA - especially through a wrapper API. It will be slower, and as mentioned you actually have no security anyway. Plus you'll have to deal with all the quirks of a padded block public key cipher :)
If you do want to use the encryption and have it work, you'll want to understand:
The RSA algorithm
Key generation
Key management
Padding methods
A mistake in any of these could easily leave you in the situation of spending a lot of effort and time to "secure" your data only to find out that bits of the private key leaked out with the public , or that your random number source used for key generation is basing its' values on the clock - the same clock that was used to timestamp your file, or some other such subtlety that immediately and completely invalidates your security. It's not really plug-and-play :)
Andrew
Jesse Hammons wrote:
Jesse Hammons wrote:
So to clarify: If I generate a 65-bit key, will I be able to use that 65-bit key to sign any 64-bit value?
Yes, but
Actually, I have found the answer to be "no" :-)
a 65 bit key won't be very secure AT ALL, it will be very easy to factor a modulus that small.
Security is not my goal. This is more of a theoretical exercise that happens to have a practical application for me.
Bottom line: asymmetrical (public-key) encryption has a fairly large "minimum block size" that actually increases as key size increases.
Indeed. I have found experimentally that: * The minimum signable data quantity in OpenSSL is 1 byte * The minimum size RSA key that can be used to sign 1 byte is 89 bits * A signature created using a 64-bit RSA key would create a number 64 bits long, BUT: - This is not possible to do in OpenSSL because the maximum signable quantity for a 64 bit RSA key is only a few bits, and OpenSSL input/output is done on byte boundaries
Do those number sound right?
Thanks, -Jesse
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