How is a credit card number coded for security?

AI Thread Summary
Credit card numbers are coded for security by subtracting each digit from 9, allowing for safe transmission. The coding process for the example number 3201 2342 3458 0931 results in 6798 7657 6541 9068. Both coding and decoding utilize the same operation, making the process straightforward. The function f(x) = 9 - x defines the relationship between the original and coded numbers, with the domain consisting of natural numbers from 0 to 9. The inverse function is the same, reinforcing the simplicity of this coding method.
aisha
Messages
584
Reaction score
0
For security, a credit card number is coded in the following way, so that it can be sent as a message. "Subtract each digit from 9"

code the credit card number 3201 2342 3458 0931

I don't understand the subtract each digit from 9 is that to code or uncode? Also for the above code the credit card what do I do to each number? do I add 9 or subtract 9?

I have another credit card number that is already coded, to find the original card number do i subtract each number from 9?
 
Physics news on Phys.org
aisha said:
For security, a credit card number is coded in the following way, so that it can be sent as a message. "Subtract each digit from 9"
code the credit card number 3201 2342 3458 0931

I don't understand the subtract each digit from 9 is that to code or uncode? Also for the above code the credit card what do I do to each number? do I add 9 or subtract 9?
I have another credit card number that is already coded, to find the original card number do i subtract each number from 9?

I believe it's pretty clear.It gives a credit card number and askes for the coded version.It should be:6798 7657 6541 9068.
Simple subtraction from 9999 9999 9999 9999.
The uncoding is simple:again subtraction from that "99..."number.

Daniel.
 
aisha said:
I don't understand the subtract each digit from 9 is that to code or uncode?
Does it make a difference? Try it and see.
 
dextercioby said:
I believe it's pretty clear.It gives a credit card number and askes for the coded version.It should be:6798 7657 6541 9068.
Simple subtraction from 9999 9999 9999 9999.
The uncoding is simple:again subtraction from that "99..."number.

Daniel.


How come we subtract by 9 to uncode and code?
 
aisha said:
How come we subtract by 9 to uncode and code?

I guess you haven't read the post/problem very carefully.It mentions "Subtract each digit from 9".So the problem tells you how to code.As Doc depicted,it makes no difference between coding and uncoding.Both are made through the same opperation.Subtraction of each digit from 9.

Daniel.
 
ok my coded credit card number for 3201 2342 3458 0931 is
6798 7657 6541 9068
my original credit card number for another credit card 2341 0135 7923 0133 is
7658 9864 2076 9866

the question says find f(x) if x represents a single input digit. What is the domain of f(x)

and find^-1(x) what is the domain of f^-1(x)?

I don't know how to find f(x) and the inverse? What do I do? The inverse is probably all the numbers backwards but which set of numbers am I using?
 
aisha said:
the question says find f(x) if x represents a single input digit. What is the domain of f(x)
and find^-1(x) what is the domain of f^-1(x)?
I don't know how to find f(x) and the inverse? What do I do? The inverse is probably all the numbers backwards but which set of numbers am I using?

The function is f:\{0,1,2,3,4,5,6,7,8,9}\rightarrow \{0,1,2,3,4,5,6,7,8,9}\

f(x)=9-x.

Find the inverse and its domain.

Daniel.
What numbers backwards? :confused:
 
dextercioby said:
The function is f:\{0,1,2,3,4,5,6,7,8,9}\rightarrow \{0,1,2,3,4,5,6,7,8,9}\

f(x)=9-x.

Find the inverse and its domain.

Daniel.
What numbers backwards? :confused:

lol sorry no numbers backwards. if f(x)=9-x then is the domain {x:x<=9,XER}?
and is the inverse of this (x-9)/-1? If so then is the domain of the inverse {x:x>=9,XER}?
 
aisha said:
lol sorry no numbers backwards. if f(x)=9-x then is the domain {x:x<=9,XER}?
and is the inverse of this (x-9)/-1? If so then is the domain of the inverse {x:x>=9,XER}?

I've already told u what the function and its domain are.The inverse it's easy to find.And its domain can be seen from ISS. :-p
By "XER",do you mean:x\in R ??If so,then it's wrong,the digits are natural numbers.

Daniel.
 
  • #10
dextercioby said:
I've already told u what the function and its domain are.The inverse it's easy to find.And its domain can be seen from ISS. :-p
By "XER",do you mean:x\in R ??If so,then it's wrong,the digits are natural numbers.

Daniel.
:-p well is my inverse wrong? I don't know the notation for not real numbers :P ahhh HELP ME PLZ
 
  • #11
aisha said:
:-p well is my inverse wrong? I don't know the notation for not real numbers :P ahhh HELP ME PLZ

As both I and Doc figured decades ago,the inverse coincides with the function.They share both the domain and the range.That is all digits from 0 till 9.
Hope it's clear. :wink:

Daniel.
 
  • #12
dextercioby said:
As both I and Doc figured decades ago,the inverse coincides with the function.They share both the domain and the range.That is all digits from 0 till 9.
Hope it's clear. :wink:

Daniel.

Lol thanks a lot but u said it wasnt real numbers natural numbers, what is the notation for that? Also (x-9)/-1 can I leave the inverse like that? Or can it be simplified to -(x-9)?
 
  • #13
aisha said:
Lol thanks a lot but u said it wasnt real numbers natural numbers, what is the notation for that? Also (x-9)/-1 can I leave the inverse like that? Or can it be simplified to -(x-9)?

1.Check the posts again.I haven't used the expression "real numbers",but "natural numbers",because digits are natural numbers.
2.f(x)=9-x ;f^{-1} (x) =9-x
Wasn't it obvious from what i said?

Daniel.
 
  • #14
dextercioby said:
1.Check the posts again.I haven't used the expression "real numbers",but "natural numbers",because digits are natural numbers.
2.f(x)=9-x ;f^{-1} (x) =9-x
Wasn't it obvious from what i said?

Daniel.

LOL WHAT AM I SAYING:P IM SAYING THAT U SAID THEY WERE NATURAL NUMBERS SOOOO IF ITS NOT XER THEN WHAT iS IT? WHAT DO I WRITE IN THE BRACKETS {} lol UR SOOO FUNNY OMG :-p and is the inverse (x-9)/-1? if so is that the same as -(x-9) :cry:

N+?
 
Last edited:
  • #15
aisha said:
LOL WHAT AM I SAYING:P IM SAYING THAT U SAID THEY WERE NATURAL NUMBERS SOOOO IF ITS NOT XER THEN WHAT iS IT? WHAT DO I WRITE IN THE BRACKETS {} lol UR SOOO FUNNY OMG :-p and is the inverse (x-9)/-1? if so is that the same as -(x-9) :cry:

ROFL :smile: :smile: :smile: :smile: :smile: :smile: :smile:
You're incredible........ :-p

I already told you what to put between those brackets.Hell,i've been trying myself,but i just couldn't... :cry: :-p Only 2 '{' instead of 4 (chack post no.7,two paranthesis missing :biggrin: ).
I already told you the inverse was the same function:9-x.It is the same with -(x-9),but why the hell write it like that??

Daniel.
 
  • #16
dextercioby said:
ROFL :smile: :smile: :smile: :smile: :smile: :smile: :smile:
You're incredible........ :-p

I already told you what to put between those brackets.Hell,i've been trying myself,but i just couldn't... :cry: :-p Only 2 '{' instead of 4 (chack post no.7,two paranthesis missing :biggrin: ).
I already told you the inverse was the same function:9-x.It is the same with -(x-9),but why the hell write it like that??

Daniel.

LOL :smile: :smile: :smile: :smile: OMG I JUST REALIZED THAT THEY ARE THE SAME FUNCTION, ahhh lol and yes ur right y the hell would I write it like that -(x-9) and the domain is the same for both too , hhmmmmm so here this is what I am going to right now lol don't freak if this is still wrong {x:x<=9,N+} domain for f(x) and inverse? or or or {x:0,1,2,3,4,5,6,7,8,9} is that what u want me to write :-p Cant u just write it out properly once :!) pleasezzzzzz lol :-p DEXTERCIOBY ? WHERE ARE U :eek: Someone please say something please.
 
Last edited:
  • #17
aisha said:
LOL :smile: :smile: :smile: :smile: OMG I JUST REALIZED THAT THEY ARE THE SAME FUNCTION, ahhh lol and yes ur right y the hell would I write it like that -(x-9) and the domain is the same for both too , hhmmmmm so here this is what I am going to right now lol don't freak if this is still wrong {x:x<=9,N+} domain for f(x) and inverse? or or or {x:0,1,2,3,4,5,6,7,8,9} is that what u want me to write :-p Cant u just write it out properly once :!) pleasezzzzzz lol :-p DEXTERCIOBY ? WHERE ARE U :eek:

1.I'm in my room.
2.Though it's not in the spirit of this help forum,i'll write the answer:
f:A\rightarrow A ,A=\{x\in N,x\leq 9},
f(x)=9-x
f^{-1}:A\rightarrow A,<br /> f^{-1} (x)=9-x

Is everything clear,FINALLLLLLLLLLLLLLLLLLLLLLLLLLLYYYYYYYYYY :-p ??

Daniel.

PS.Anyway,i give up.It's no longer funny... :-p
 
  • #18
Just one little point here...since the Naturals don't include 0, it would be better to say that x belongs to the Whole Numbers (W?).
 
  • #19
lol so XEW? instead of XEN?
 
  • #20
aisha said:
lol so XEW? instead of XEN?

You're in Canada,he's in US and I'm in Belgium.We have different views about the sets of numbers.For me,natural numbers (N) include 0.If i want to say that zero is excluded,i write (N*).
I was too surprised to learn that the Americans use N (natural numbers),W (whole numbers) & i can't remember what they use for {...,-3,-2,-1,0,1,...} or the negative axis.I find his weird.
Advice:to avoid confusions and unnecessary complications simply write
{0,1,...,9} or without the dots:{0,1,2,3,4,5,6,7,8,9}. :-p

Daniel.

EDIT:I'd use BMW if i were u... :-p
 
Last edited:
  • #21
dextercioby said:
You're in Canada,he's in US and I'm in Belgium.We have different views about the sets of numbers.For me,natural numbers (N) include 0.If i want to say that zero is excluded,i write (N*).
I was too surprised to learn that the Americans use N (natural numbers),W (whole numbers) & i can't remember what they use for {...,-3,-2,-1,0,1,...} or the negative axis.I find his weird.
Advice:to avoid confusions and unnecessary complications simply write
{0,1,...,9} or without the dots:{0,1,2,3,4,5,6,7,8,9}. :-p

Daniel.

lol :smile: OK OK SMARTY PANTS I GET IT Thanks SOOO MUCH! :smile:
 
Last edited:

Similar threads

Probability of Two Consecutive Same-Value Cards in a Shuffled Deck
Replies
31
Views
5K
News Massive Target credit/debit card security breach
Replies
9
Views
4K
B How to pick some numbers out of 13 integers, by a 4 digits code
Replies
4
Views
2K
How can I receive security codes overseas without a traditional phone number?
Replies
2
Views
1K
Can this be solved without trial and error?
Replies
6
Views
1K
Studying Help How do I raise my GPA? I have a full schedule with hard classes
Replies
9
Views
3K
MCNP Modelling Detector Energy Response Vs Empirical Results
Replies
3
Views
2K
B In dire Straights: Straights of 11+ w/ 2 Poker decks
Replies
7
Views
2K
How to make a mathematica code with vectors and magnitude
Replies
1
Views
2K
Why isn't my algorithm code working?
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top