How can I convert Matlab Integer into java.math.BigInteger

i want to use RSA algorithm to demonstrate the simple key generation in matlab (step by step); and i use GUI to pass the data.

the problem is when i using java.math.BigInteger;

i found that java.math.BigInteger needs char to calculate the modPow, modInvers, etc.

so when my input is an integer, i convert to string use "num2str", it works.

mycode:
a=23423423423454
b=num2str(a)
c=java.math.BigInteger(b)

but when i use larger number, it goes to error.

mycode:

a=999999999999999999
b=num2str(a)
c=java.math.BigInteger(b)

so i have to write manuual

mycode:
a='999999999999999999'
b=java.math.BigInteger(a)

is there a function to do it automatic without errorr??? i am newbie to Matlab

[Friedrich]

Why do you want to use BigInteger in the first place? Why don't you do the calculation completly in MATLAB?

[kkc]

rsa function to enrypt is:

(a^b)mod c

when a^b is larger than 2^31 (i think 31, maybe im wrong) then matlab give Inf answer (infinit i think).

So use BigInteger because it can calculate that.

And i execute all the code in matlab, because matlab can run some java code.

Answer 1

[Friedrich]

When using that big numbers use uint64 instead of doubles. This will also help in calling java.math.BigInteger, e.g.

>>a=uint64(999999999999999999)
>>c=java.math.BigInteger(num2str(a))

When using double values you have loss of precission, e.g.

>> a=999999999999999999;
>> sprintf('%16.0f',a)

ans =

1000000000000000000

>>

[kkc]

thanks,, it can cover my math up to 64 bit,,

any idea if i want to do more than 64 bit???

[Friedrich]

If it gets higher I would suggest using Symbolic Math Toolbox:

>> bigint = sym('999999999999999999')^10000;
>> mod(bigint,32)

ans =

1

So you can do you complete calculation using symbolic math.