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comp.lang.ruby

Cipher

Max Zhou

3/17/2008 12:50:00 AM

[Note: parts of this message were removed to make it a legal post.]

I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.
abcdefghijklm
nopqrstuvwxyz


---------------------------------
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7 Answers

Thomas Wieczorek

3/17/2008 1:17:00 AM

0

On Mon, Mar 17, 2008 at 1:50 AM, Max Zhou <ball908765@yahoo.com> wrote:
> I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.
> abcdefghijklm
> nopqrstuvwxyz
>

You can split a string with the String#split method:
irb
> "Foobar".split(//)
=> ["F", "o", "o", "b", "a", "r"]

You can get the ASCII value of a character either with ?character:
> ?F
=> 70

If you want to loop the splitted string, try eval(has anyone a better
solution?):
> "Foobar".split(//).each { |c| puts eval("?#{c}") }

You can use Fixnum#chr to turn an ASCII value in a character:
> 65.chr #=> "A"

You're trying to implement the ROT13 or ROTx algorithm. A naive
approach, still buggy might look like that:
plaintext = "Hello"
encrypted = ""
plaintext.split(//).each { |c| i=eval("?#{c}"); encrypted << (i+13).chr }
puts encrypted #=> Uryy|

As you see, the encrypted string contains a |(vertical line) and it
also chokes on spaces. I leave the rest to you. Ask again if you're
stuck.

Regards, Thomas

Christian

3/17/2008 1:33:00 AM

0

[Note: parts of this message were removed to make it a legal post.]

input = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
!@#$%^&*()_+-={}|[]\;\':",./<>?`~'
input.tr! "A-Za-z", "N-ZA-Mn-za-m"
=> "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM
!@\#$%^&*()_+-={}|[]\\;':\",./<>?`~"

On Mon, Mar 17, 2008 at 11:16 AM, Thomas Wieczorek <wieczo.yo@googlemail.com>
wrote:

> On Mon, Mar 17, 2008 at 1:50 AM, Max Zhou <ball908765@yahoo.com> wrote:
> > I am trying to make a program that takes what you input, and encrypts it
> by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the
> left (a to c) and moves it down (c to p). (See below.) Even though you can
> just say that a will be n, how do you seperate each letter and turn it into
> a string? Please put it in terms that a Ruby beginner would understand.
> > abcdefghijklm
> > nopqrstuvwxyz
> >
>
> You can split a string with the String#split method:
> irb
> > "Foobar".split(//)
> => ["F", "o", "o", "b", "a", "r"]
>
> You can get the ASCII value of a character either with ?character:
> > ?F
> => 70
>
> If you want to loop the splitted string, try eval(has anyone a better
> solution?):
> > "Foobar".split(//).each { |c| puts eval("?#{c}") }
>
> You can use Fixnum#chr to turn an ASCII value in a character:
> > 65.chr #=> "A"
>
> You're trying to implement the ROT13 or ROTx algorithm. A naive
> approach, still buggy might look like that:
> plaintext = "Hello"
> encrypted = ""
> plaintext.split(//).each { |c| i=eval("?#{c}"); encrypted << (i+13).chr }
> puts encrypted #=> Uryy|
>
> As you see, the encrypted string contains a |(vertical line) and it
> also chokes on spaces. I leave the rest to you. Ask again if you're
> stuck.
>
> Regards, Thomas
>
>


--

"Every child has many wishes. Some include a wallet, two chicks and a cigar,
but that's another story."

Todd Benson

3/17/2008 2:00:00 AM

0

On Sun, Mar 16, 2008 at 7:50 PM, Max Zhou <ball908765@yahoo.com> wrote:
> I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.
> abcdefghijklm
> nopqrstuvwxyz
>
>
>
> ---------------------------------
> Never miss a thing. Make Yahoo your homepage.

There are many ways to do it, but if it was all lower case, I would probably...

a = "abcdefghijklmnopqrstuvwxyz"
ascii_offset = 15 - 97
str = "antidisestablishmentarianism"
str.each_byte {|b| new_str << a[(b + ascii_offset) % a.size]}
puts new_str

The 15 is to turn a into a p (?p - ?a == 15). The minus 97 part is to
make sure we work in the ascii byte code range. each_byte runs
through each byte of the string, where, in the block, the offset is
added and the mod by the size of a (26) to keep the index of a within
the correct bounds. a[] selects a byte to be appended (<<) to
new_str.

You could wrap this in a method or make it part of String class.
Ideally, I think a person would really want to include the full 256
character set to deal with punctuation and spaces.

Todd

Todd Benson

3/17/2008 2:03:00 AM

0

On Sun, Mar 16, 2008 at 9:00 PM, Todd Benson <caduceass@gmail.com> wrote:
>
> On Sun, Mar 16, 2008 at 7:50 PM, Max Zhou <ball908765@yahoo.com> wrote:
> > I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.

Also, I forgot to mention that you should realize that a String object
should be thought of as really just an ordering of bytes with some
special methods to make it human readable.

Todd

Todd Benson

3/17/2008 10:21:00 AM

0

On Sun, Mar 16, 2008 at 9:00 PM, Todd Benson <caduceass@gmail.com> wrote:
>
> On Sun, Mar 16, 2008 at 7:50 PM, Max Zhou <ball908765@yahoo.com> wrote:
> > I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.
> > abcdefghijklm
> > nopqrstuvwxyz
> >
> >
> >
> > ---------------------------------

Just for fun, I revisited this. To include the printable characters
on an english-based system (ASCII codes 32 through 126), not including
tab, return, line-feed, etc...


puts str = "Hello, world! Yabba dabba doo!"
puts

char_set = (32..126).map.pack('c*')
start, finish, offset = ?a, ?p, ?p - ?a
puts "char_set:\n" + char_set = (?\s..?~).map.pack('c*')
puts

size = char_set.size
new_str = ""
str.each_byte do |byte|
new_str << char_set[(byte + offset - char_set[0]) % size]
end
puts "enciphered: \n" + new_str


Todd

Todd Benson

3/17/2008 10:33:00 AM

0

On Mon, Mar 17, 2008 at 5:21 AM, Todd Benson <caduceass@gmail.com> wrote:
> On Sun, Mar 16, 2008 at 9:00 PM, Todd Benson <caduceass@gmail.com> wrote:
> >
>
> > On Sun, Mar 16, 2008 at 7:50 PM, Max Zhou <ball908765@yahoo.com> wrote:
> > > I am trying to make a program that takes what you input, and encrypts it by turning a to p, b to q, z to b, etc. It moves the letter 2 spaces to the left (a to c) and moves it down (c to p). (See below.) Even though you can just say that a will be n, how do you seperate each letter and turn it into a string? Please put it in terms that a Ruby beginner would understand.
> > > abcdefghijklm
> > > nopqrstuvwxyz
> > >
> > >
> > >
> > > ---------------------------------
>
> Just for fun, I revisited this. To include the printable characters
> on an english-based system (ASCII codes 32 through 126), not including
> tab, return, line-feed, etc...
>
>
> puts str = "Hello, world! Yabba dabba doo!"
> puts
>
> char_set = (32..126).map.pack('c*')
> start, finish, offset = ?a, ?p, ?p - ?a
> puts "char_set:\n" + char_set = (?\s..?~).map.pack('c*')
> puts
>
> size = char_set.size
> new_str = ""
> str.each_byte do |byte|
> new_str << char_set[(byte + offset - char_set[0]) % size]
> end
> puts "enciphered: \n" + new_str

Dang it! Another thing that unit tests won't catch: code that is
redundant! Removing the first "char_set =" line will have the same
result...

puts str = "Hello, world! Yabba dabba doo!"
puts

start, finish, offset = ?a, ?p, ?p - ?a
puts "char_set:\n" + char_set = (?\s..?~).map.pack('c*')
puts

size = char_set.size
new_str = ""
str.each_byte do |byte|
new_str << char_set[(byte + offset - char_set[0]) % size]
end
puts "enciphered: \n" + new_str


Todd

Todd Benson

3/17/2008 9:21:00 PM

0

On Sun, Mar 16, 2008 at 9:00 PM, Todd Benson <caduceass@gmail.com> wrote:

> a = "abcdefghijklmnopqrstuvwxyz"
> ascii_offset = 15 - 97
new_str = ""
> str = "antidisestablishmentarianism"
> str.each_byte {|b| new_str << a[(b + ascii_offset) % a.size]}
> puts new_str

I think I'm going to drop google mail; that, or come up with a more
clear way to cut and paste :/

Todd