A simple RSA

ruby-talk
1

Hi All,

I tried to implement a simple RSA crypto for my work. It seems all works fine, except that I am not satisfied with the code I wrote below:

def str_to_num(s)
  h = '0x'
  (0...s.length).each do |i|
    h += "%02x" % s[i]
  end
  eval(h)
end

def num_to_str(n)
  s = ''
  while n > 0 do
    s = "%c" % (n & 0xFF) + s
    n = n >> 8
  end
  s
end

These 2 functions convert string to bignum and vise-versa. It works, but I feel there should be better (faster) way to do this.

Could anyone point the way out?

Thanks!
Shannon

2

Please see attached:
- samples with unpack/inject and each_byte use in str_to_num;
  each_byte is faster;
- num_to_str without use of formatting;
- unit test stuff and
- benchmark code

hope these help
regards
Sergey

tStrToNum.rb (3.45 KB)

···

----- Original Message ----- On Monday, April 17, 2006 2:03 PM, Shannon Fang wrote:

Hi All,

I tried to implement a simple RSA crypto for my work. It seems all works fine, except that I am not satisfied with the code I wrote below:

def str_to_num(s)
h = '0x'
(0...s.length).each do |i|
   h += "%02x" % s[i]
end
eval(h)
end

def num_to_str(n)
s = ''
while n > 0 do
   s = "%c" % (n & 0xFF) + s
   n = n >> 8
end
s
end

These 2 functions convert string to bignum and vise-versa. It works, but I feel there should be better (faster) way to do this.

Could anyone point the way out?

Thanks!
Shannon

3

Thanks a lot, this works fine.

BTW, another related question: while I ruby code, I can write a long string like: (without using heredoc)

str = "this is very long line 1" +
        "this is line 2"

but if I write a number:

num = 0x1234132410987094750245.....

And the number is very long (an RSA key), how can I wrap the line? it seems that I cannot use a "\" by the end of line...

Thanks!
Shannon

···

From: "Sergey" <gm.vlkv@gmail.com>
Reply-To: ruby-talk@ruby-lang.org
To: ruby-talk@ruby-lang.org (ruby-talk ML)
Subject: Re: a simple RSA
Date: Tue, 18 Apr 2006 06:19:07 +0900

Please see attached:
- samples with unpack/inject and each_byte use in str_to_num;
each_byte is faster;
- num_to_str without use of formatting;
- unit test stuff and
- benchmark code

hope these help
regards
Sergey

----- Original Message ----- On Monday, April 17, 2006 2:03 PM, Shannon Fang wrote:

Hi All,

I tried to implement a simple RSA crypto for my work. It seems all works fine, except that I am not satisfied with the code I wrote below:

def str_to_num(s)
h = '0x'
(0...s.length).each do |i|
   h += "%02x" % s[i]
end
eval(h)
end

def num_to_str(n)
s = ''
while n > 0 do
   s = "%c" % (n & 0xFF) + s
   n = n >> 8
end
s
end

These 2 functions convert string to bignum and vise-versa. It works, but I feel there should be better (faster) way to do this.

Could anyone point the way out?

Thanks!
Shannon

<< tStrToNum.rb >>

4

harp:~ > cat a.rb
   num = %w(
     1234132410987094750245
   ).join.to_i

   p num

   harp:~ > ruby a.rb
   123413241098709475024512341324109870947502451234132410987094750245

-a

···

On Tue, 18 Apr 2006, Shannon Fang wrote:

Thanks a lot, this works fine.

BTW, another related question: while I ruby code, I can write a long string like: (without using heredoc)

str = "this is very long line 1" +
      "this is line 2"

but if I write a number:

num = 0x1234132410987094750245.....

And the number is very long (an RSA key), how can I wrap the line? it seems that I cannot use a "\" by the end of line...

Thanks!
Shannon

--
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama