Bit rusty here, but it means that the best compression program in the
world could reduce the length of a piece of English text stored as
ASCII to about an eighth of its original length (1.1 bits for every 8
in the original encoding).
If you're talking about secret keys as before, high entropy is good.
There have been lots of attacks against software where the original
coders thought they were using a large key space, but because of
errors the keys were only distributed over a fraction of the keyspace.
We recently had the Debian SSL problem where the PRNG was not
correctly seeded:
"A weakness exists in the random number generator used by the OpenSSL
package included with the Debian GNU/Linux operating system and
derivative systems that causes the generated numbers to be
predictable. As a result of this weakness, certain encryption keys are
much more common than they should be. This vulnerability affects
cryptographic applications that use keys generated by the flawed
versions of the OpenSSL package. Affected keys include SSH keys,
OpenVPN keys, DNSSEC keys, and key material for use in X.509
certificates and session keys used in SSL/TLS connections. Any of
these keys generated using the affected systems on or after 2006-09-17
may be vulnerable."
-- http://www.kb.cert.org/vuls/id/925211
The set of generated keys had a lower entropy (was more predictable)
because it was not smeared out evenly over the keyspace, but very
bunched up.
You might also want to read the article on Kolmogorov complexity here:
http://en.wikipedia.org/wiki/Kolmogorov_complexity
cheers,
Jamie
2009/8/19 M.D.Mufambisi <mufambisi (at) gmail (dot) com [email concealed]>:
> I understand now. The digest i sent earlier is in HEX and it contains
> 40 characters. So this is 16^40 which is equal to 2^160. So yeah, i
> understand that bit now. Going back to the ealier question on
> bits.....it was linked to the information theory and shannons entropy.
> When they say english has an entropy of 1.1bits....what does that
> mean? Is high or low entropy desirable? An example would be good.
> Thanks people.
>
> On 8/19/09, M.D.Mufambisi <mufambisi (at) gmail (dot) com [email concealed]> wrote:
>> Ok. Thanks. I have an SHA-1 hash of a file and the digest is
>> DA39A3EE5E6B4B0D3255BFEF95601890AFD80709. Is this160 bit? How does the
>> output map to 160 bits?
>>
>> On 8/18/09, Shailesh Rangari <shailesh.sf (at) gmail (dot) com [email concealed]> wrote:
>>> Hi Munyaradzi,
--
Jamie Riden / jamesr (at) europe (dot) com [email concealed] / jamie (at) honeynet.org (dot) uk [email concealed]
http://www.ukhoneynet.org/members/jamie/
world could reduce the length of a piece of English text stored as
ASCII to about an eighth of its original length (1.1 bits for every 8
in the original encoding).
If you're talking about secret keys as before, high entropy is good.
There have been lots of attacks against software where the original
coders thought they were using a large key space, but because of
errors the keys were only distributed over a fraction of the keyspace.
We recently had the Debian SSL problem where the PRNG was not
correctly seeded:
"A weakness exists in the random number generator used by the OpenSSL
package included with the Debian GNU/Linux operating system and
derivative systems that causes the generated numbers to be
predictable. As a result of this weakness, certain encryption keys are
much more common than they should be. This vulnerability affects
cryptographic applications that use keys generated by the flawed
versions of the OpenSSL package. Affected keys include SSH keys,
OpenVPN keys, DNSSEC keys, and key material for use in X.509
certificates and session keys used in SSL/TLS connections. Any of
these keys generated using the affected systems on or after 2006-09-17
may be vulnerable."
-- http://www.kb.cert.org/vuls/id/925211
The set of generated keys had a lower entropy (was more predictable)
because it was not smeared out evenly over the keyspace, but very
bunched up.
You might also want to read the article on Kolmogorov complexity here:
http://en.wikipedia.org/wiki/Kolmogorov_complexity
cheers,
Jamie
2009/8/19 M.D.Mufambisi <mufambisi (at) gmail (dot) com [email concealed]>:
> I understand now. The digest i sent earlier is in HEX and it contains
> 40 characters. So this is 16^40 which is equal to 2^160. So yeah, i
> understand that bit now. Going back to the ealier question on
> bits.....it was linked to the information theory and shannons entropy.
> When they say english has an entropy of 1.1bits....what does that
> mean? Is high or low entropy desirable? An example would be good.
> Thanks people.
>
> On 8/19/09, M.D.Mufambisi <mufambisi (at) gmail (dot) com [email concealed]> wrote:
>> Ok. Thanks. I have an SHA-1 hash of a file and the digest is
>> DA39A3EE5E6B4B0D3255BFEF95601890AFD80709. Is this160 bit? How does the
>> output map to 160 bits?
>>
>> On 8/18/09, Shailesh Rangari <shailesh.sf (at) gmail (dot) com [email concealed]> wrote:
>>> Hi Munyaradzi,
--
Jamie Riden / jamesr (at) europe (dot) com [email concealed] / jamie (at) honeynet.org (dot) uk [email concealed]
http://www.ukhoneynet.org/members/jamie/
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