Today we continue reading Jigsaw : Efficient, low effort mashup isolation by James Mickens and Matthew Finifter. Mashups are web applications that contain code from different principals.
Jigsaw lets mashups be isolated with its framework and lets them selectively expose private states. Jigsaw had four goals:
Isolation by default: The integrator has access to browser resources and the guest may be provided some access. However by default a guest cannot access these resources. Most principal's JavaScript namespace is hidden from external code by default .
Efficient, synchronous sharing: Jigsaw enables synchronous, pass-by-reference sharing. If an object is to be shared outside its local domain, a proxy or 'surrogate' automatically wraps and unwraps the object.
Simplicity: Using the above two, Jigsaw can secure mashups with a few lines of policy code
Fail-safe legacy code: If legacy code has not been adapted for Jigsaw, it will work within a single domain and unmodified legacy code will fail safely when accessed by external domains.
Jigsaw lets mashups be isolated with its framework and lets them selectively expose private states. Jigsaw had four goals:
Isolation by default: The integrator has access to browser resources and the guest may be provided some access. However by default a guest cannot access these resources. Most principal's JavaScript namespace is hidden from external code by default .
Efficient, synchronous sharing: Jigsaw enables synchronous, pass-by-reference sharing. If an object is to be shared outside its local domain, a proxy or 'surrogate' automatically wraps and unwraps the object.
Simplicity: Using the above two, Jigsaw can secure mashups with a few lines of policy code
Fail-safe legacy code: If legacy code has not been adapted for Jigsaw, it will work within a single domain and unmodified legacy code will fail safely when accessed by external domains.
Jigsaw prohibits some Javascript features but these are advanced features that are typically not used and usually exploited by malicious programs. Jigsaw also makes some changes to the core JavaScript language only to make it behave more like an object oriented. Jigsaw also preserves many of the language features that make JavaScript an easy to use scripting language. For example, objects are passed by reference even when they are exposed out of the isolation domain.
Jigsaw does mashups from different domains. Domains are origins just as we use it in the term cross origin policy. A principal is an instance of web-content provided by a particular domain. An integrator is one that includes another principal by explicitly downloading content from the other principal's origin. Principals can be chained and consolidated just like in a tree hierarchy. A user visiting a top level site is visiting an integrator.
Jigsaw also has a concept of a box. Each box is associated with the following resources:
a JavaScript namespace containing application defined objects and functions
a DOM tree which represents the HTML or CSS of the principal
an event loop which captures mouse and keyboard activity intended for that box
a rectangular visual region with a width, height and location within the larger browser viewport
a network connection which allows the principal to issue HTTP fetches and data.
a local storage area which stores cookie and implements the DOM storage abstraction.
#codejam problem
A R x C matrix of positive numbers wraps around a drum. Each number represents the number of cells that share an edge with the cell of the same number. For eg the front and back of the drum can be :
3 3 3
3 3 3
2 2 2
The top and bottom of the drum can be different so the line containing 2 can appear in the first line instead of the last and this will make it a different arrangement. If an arrangement can be rotated to get another, they are the same. How many different arrangements exist for given R x C
Solution:
htamas gave a python solution as follows:
Take an inital pattern with the positive integer 1 and take initial patterns of these numbers for arrays of 1 x 5 When arranged vertically we can take the arrays corresponding to rows a1, a3, a4, a6, a12. For all rows greater than five to R + 1, we can repeat their sequences as a pattern of the previous. That is a3 can be extended based on a sequence of a3 and a1 and so on.
The initial answer will be sum of the R and R - 2 column in a.
If the column C is divisible by 3, 4, 6 and 12, the corresponding columns from the a3, a4, a6 and a12 will cumulate to the answer and when we take a modulo with a sufficiently large number we can be accurate to that extent.
Jigsaw does mashups from different domains. Domains are origins just as we use it in the term cross origin policy. A principal is an instance of web-content provided by a particular domain. An integrator is one that includes another principal by explicitly downloading content from the other principal's origin. Principals can be chained and consolidated just like in a tree hierarchy. A user visiting a top level site is visiting an integrator.
Jigsaw also has a concept of a box. Each box is associated with the following resources:
a JavaScript namespace containing application defined objects and functions
a DOM tree which represents the HTML or CSS of the principal
an event loop which captures mouse and keyboard activity intended for that box
a rectangular visual region with a width, height and location within the larger browser viewport
a network connection which allows the principal to issue HTTP fetches and data.
a local storage area which stores cookie and implements the DOM storage abstraction.
#codejam problem
A R x C matrix of positive numbers wraps around a drum. Each number represents the number of cells that share an edge with the cell of the same number. For eg the front and back of the drum can be :
3 3 3
3 3 3
2 2 2
The top and bottom of the drum can be different so the line containing 2 can appear in the first line instead of the last and this will make it a different arrangement. If an arrangement can be rotated to get another, they are the same. How many different arrangements exist for given R x C
Solution:
htamas gave a python solution as follows:
Take an inital pattern with the positive integer 1 and take initial patterns of these numbers for arrays of 1 x 5 When arranged vertically we can take the arrays corresponding to rows a1, a3, a4, a6, a12. For all rows greater than five to R + 1, we can repeat their sequences as a pattern of the previous. That is a3 can be extended based on a sequence of a3 and a1 and so on.
The initial answer will be sum of the R and R - 2 column in a.
If the column C is divisible by 3, 4, 6 and 12, the corresponding columns from the a3, a4, a6 and a12 will cumulate to the answer and when we take a modulo with a sufficiently large number we can be accurate to that extent.
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