[C#] Trying to implement EC Multiplication in pure code

[BlackHatCoiner]

Thank you!

Your code works fine, there's just one thing which slips (?) the process. It adds an additional zero sometimes in front of the x & y and I don't know what's responsible for that.  For example, if I run it with k=1, it returns it properly:

Code:

x: 79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798
y: 483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8

Trying it with k=2, you'll get:

Code:

x: 0C6047F9441ED7D6D3045406E95C07CD85C778E4B8CEF3CA7ABAC09B95C709EE5
y: 1AE168FEA63DC339A3C58419466CEAEEF7F632653266D0E1236431A950CFE52A

That extra zero (0C60...) shouldn't exist, because obviously, once is hashed with SHA256 it'll give a different result.


Seriously now, I'll say this again; thank you. You wasted your time to write me code? The least I can do is merit you.

[j2002ba2]

Thank you!

Your code works fine, there's just one thing which slips (?) the process. It adds an additional zero sometimes in front of the x & y and I don't know what's responsible for that.  For example, if I run it with k=1, it returns it properly:

Code:

x: 79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798
y: 483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8

Trying it with k=2, you'll get:

Code:

x: 0C6047F9441ED7D6D3045406E95C07CD85C778E4B8CEF3CA7ABAC09B95C709EE5
y: 1AE168FEA63DC339A3C58419466CEAEEF7F632653266D0E1236431A950CFE52A

That extra zero (0C60...) shouldn't exist, because obviously, once is hashed with SHA256 it'll give a different result.

This is a C# thing, it adds a leading zero when MSB of the top byte is one, something to do with distinguishing between positive and negative numbers. You have to be careful when parsing hex numbers as well: BigInteger.Parse("ff") = -1.

Overall C# is a language with many such intricacies (or I would say stupid choices).

[pooya87]

This is a C# thing, it adds a leading zero when MSB of the top byte is one, something to do with distinguishing between positive and negative numbers. You have to be careful when parsing hex numbers as well: BigInteger.Parse("ff") = -1.

Overall C# is a language with many such intricacies (or I would say stupid choices).

This is not a C# thing at all. This is a popular way in computers to indicate positive/negative numbers which the BigInteger class also uses. In fact we are using a similar logic in bitcoin signatures that are encoded using DER encoding (use most significant bit of the most significant byte to indicate sign).

[j2002ba2]

This is a C# thing, it adds a leading zero when MSB of the top byte is one, something to do with distinguishing between positive and negative numbers. You have to be careful when parsing hex numbers as well: BigInteger.Parse("ff") = -1.

Overall C# is a language with many such intricacies (or I would say stupid choices).

This is not a C# thing at all. This is a popular way in computers to indicate positive/negative numbers which the BigInteger class also uses. In fact we are using a similar logic in bitcoin signatures that are encoded using DER encoding (use most significant bit of the most significant byte to indicate sign).

The most popular way to indicate a negative number is with "-". They are doing a memory dump. Is there a way to print and parse the number properly? In DER encoding it is justified, we get a single long hex digit sequence, but when printing a single number it just looks wrong, and consequently increases the cognitive load. One could write in the source code -0xff, and all is good, but AFAIK there's no (easy) way to parse "-0xff" as a BigInteger.

[pooya87]

The most popular way to indicate a negative number is with "-". They are doing a memory dump. Is there a way to print and parse the number properly? In DER encoding it is justified, we get a single long hex digit sequence, but when printing a single number it just looks wrong, and consequently increases the cognitive load. One could write in the source code -0xff, and all is good, but AFAIK there's no (easy) way to parse "-0xff" as a BigInteger.

You are thinking as a "human" not a "computer". In computer there is no "-" there are only bits and when we are representing an arbitrary length octet string there has to be a certain way we represent the sign and that is the most significant bit.
0xff is 0b11111111 and since the most significant bit is set this number is negative.