After 9 1/2 years as Scottish Security Lead with Ernst & Young I've just started a new role as a Director at 7 Elements. Along with two other notable names in Information Security in Scotland we will provide technical security consultancy and penetration testing services.
As part of that we've started up a blog here to talk through some of the ideas we've got for approaching security and testing in a pragmatic way.
There may be the odd post here, but all industry focused stuff will be on the 7 Elements blog or cross posted to twitter.
Wednesday, September 22, 2010
Tuesday, May 25, 2010
Number theory never ceases to amaze me
Alex Bellos writes in New Scientist :
"I have two children. One is a boy born on a Tuesday. What is the probability I have two boys?"
The first thing to remember about probability questions is that everyone finds them mind-bending, even mathematicians. The next step is to try to answer a similar but simpler question so that we can isolate what the question is really asking.
So, consider this preliminary question: "I have two children. One of them is a boy. What is the probability I have two boys?"
This is a much easier question, you need to first look at all the equally likely combinations of two children it is possible to have: BG, GB, BB or GG. The question states that one child is a boy. So we can eliminate the GG, leaving us with just three options: BG, GB and BB. One out of these three scenarios is BB, so the probability of the two boys is 1/3.
Now we can repeat this technique for the original question. Let's list the equally likely possibilities of children, together with the days of the week they are born in. Let's call a boy born on a Tuesday a BTu. Our possible situations are:
When the first child is a BTu and the second is a girl born on any day of the week: there are seven different possibilities.When the first child is a girl born on any day of the week and the second is a BTu: again, there are seven different possibilities.When the first child is a BTu and the second is a boy born on any day of the week: again there are seven different possibilities.Finally, there is the situation in which the first child is a boy born on any day of the week and the second child is a BTu – and this is where it gets interesting. There are seven different possibilities here too, but one of them – when both boys are born on a Tuesday – has already been counted when we considered the first to be a BTu and the second on any day of the week. So, since we are counting equally likely possibilities, we can only find an extra six possibilities here.
Summing up the totals, there are 7 + 7 + 7 + 6 = 27 different equally likely combinations of children with specified gender and birth day, and 13 of these combinations are two boys. So the answer is 13/27, which is very different from 1/3.
It seems remarkable that the probability of having two boys changes from 1/3 to 13/27 when the birth day of one boy is stated – yet it does, and it's quite a generous difference at that. In fact, if you repeat the question but specify a trait rarer than 1/7 (the chance of being born on a Tuesday), the closer the probability will approach 1/2.
"I have two children. One is a boy born on a Tuesday. What is the probability I have two boys?"
The first thing to remember about probability questions is that everyone finds them mind-bending, even mathematicians. The next step is to try to answer a similar but simpler question so that we can isolate what the question is really asking.
So, consider this preliminary question: "I have two children. One of them is a boy. What is the probability I have two boys?"
This is a much easier question, you need to first look at all the equally likely combinations of two children it is possible to have: BG, GB, BB or GG. The question states that one child is a boy. So we can eliminate the GG, leaving us with just three options: BG, GB and BB. One out of these three scenarios is BB, so the probability of the two boys is 1/3.
Now we can repeat this technique for the original question. Let's list the equally likely possibilities of children, together with the days of the week they are born in. Let's call a boy born on a Tuesday a BTu. Our possible situations are:
When the first child is a BTu and the second is a girl born on any day of the week: there are seven different possibilities.When the first child is a girl born on any day of the week and the second is a BTu: again, there are seven different possibilities.When the first child is a BTu and the second is a boy born on any day of the week: again there are seven different possibilities.Finally, there is the situation in which the first child is a boy born on any day of the week and the second child is a BTu – and this is where it gets interesting. There are seven different possibilities here too, but one of them – when both boys are born on a Tuesday – has already been counted when we considered the first to be a BTu and the second on any day of the week. So, since we are counting equally likely possibilities, we can only find an extra six possibilities here.
Summing up the totals, there are 7 + 7 + 7 + 6 = 27 different equally likely combinations of children with specified gender and birth day, and 13 of these combinations are two boys. So the answer is 13/27, which is very different from 1/3.
It seems remarkable that the probability of having two boys changes from 1/3 to 13/27 when the birth day of one boy is stated – yet it does, and it's quite a generous difference at that. In fact, if you repeat the question but specify a trait rarer than 1/7 (the chance of being born on a Tuesday), the closer the probability will approach 1/2.
Friday, September 04, 2009
On Being Ecologically Responsible
Following Charles Stross' lead, I went through this Guardian link last night on how to reduce emissions. In everything but flying it looks like as a household we come out saving about 4.4 tonnes as we do most things right, but then I'm screwed on flights, doing 16 shorthaul and 4 longhaul this year. At least I have cut down since last year by over 70% so I am reducing my footprint.
Amused by the 'take up vegan' idea - can't think of anything worse. Wonder if I get points for giving up all no meat items...
And in Scotland the whole solar power thing.... well...
Amused by the 'take up vegan' idea - can't think of anything worse. Wonder if I get points for giving up all no meat items...
And in Scotland the whole solar power thing.... well...
Thursday, March 22, 2007
Scheme to improve business trust in penetration testing is launched
From next month, the Council of Registered Ethical Security Testers (CREST) is open for business. Designed to ensure that penetration testing provided meets minimum standards, and appropriate methodologies and processes are in place, it involves practical assault courses to test skill levels of penetration testers, similar to the UK CHECK scheme.I like this idea - seems more relevant and usable to non-government organisations.
read more | digg story
read more | digg story
Sunday, January 07, 2007
Ever wanted to go to Morocco for a holiday
Well, my brother went out to Essaouira for a kite-surfing holiday and loved it so much he bought an apartment which he is letting out during the summers. If you fancy it, check out Apartment Simoom
Sunday, December 03, 2006
This Post at Blorge.com pitches itself as the definitive security comparison between Vista and XP but actually tells us nothing. Seems weirdly biased towards Vista even though the points laid out do not support this at all.
Most depressing.
Most depressing.
Wednesday, November 08, 2006
Monday, October 16, 2006
Sunday, October 15, 2006
Cthulhu Invocations by Language
Sensible use of the Google Code search tool here
This is what being a geek is all about...although does this mean Google is at least measuring evil, if not actually doing it?
This is what being a geek is all about...although does this mean Google is at least measuring evil, if not actually doing it?
Tuesday, October 03, 2006
Monday, September 04, 2006
Sunday, August 13, 2006
Security Theatre - liquids on a plane
My thoughts exactly.
Why not follow El Al's lead in this - as they have been dealing with the terrorist threat fro a Very Long Time (tm)
---Use humans trained in this sort of thing to interview everyone who wishes to fly---
It appears to work pretty well!
See Schneier's take on it as well
Why not follow El Al's lead in this - as they have been dealing with the terrorist threat fro a Very Long Time (tm)
---Use humans trained in this sort of thing to interview everyone who wishes to fly---
It appears to work pretty well!
See Schneier's take on it as well
Friday, May 26, 2006
Tuesday, February 21, 2006
Thursday, February 16, 2006
Wednesday, February 15, 2006
Thursday, January 26, 2006
The Blog Worm
For those of you who linked to the blog worm (cute though it may be) please
read this to see why you should replace it with a gif you control.Ahhh - the joys
Friday, November 11, 2005
Wednesday, October 12, 2005
Moves to professionalise Infosec
Was at the ISC2 Secure London conference yesterday. Interesting day, and lots of interesting info. Check out uksaint.org which is a site supported by Intellect, the trade body for the UK hi-tech industry. It is currently hosting the working group info for the move to professionalising the information security industry.
Another interesting URL mentioned was www.staysafeonline.org which could be of use to your average user.
Interesting stats - from Gartner originally
75% of attacks are at application level
70% of vulnerabilities as at application level
and
Reducing the number of application vulnerabilities by 50% should lead to a 75% reduction in costs!
Another interesting URL mentioned was www.staysafeonline.org which could be of use to your average user.
Interesting stats - from Gartner originally
75% of attacks are at application level
70% of vulnerabilities as at application level
and
Reducing the number of application vulnerabilities by 50% should lead to a 75% reduction in costs!
Subscribe to:
Posts (Atom)