Class: Ciphers::Caesar

Inherits:
Object
  • Object
show all
Defined in:
lib/crypto-toolbox/ciphers/caesar.rb

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.decipher(msg, shift) ⇒ Object 



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# File 'lib/crypto-toolbox/ciphers/caesar.rb', line 10

def self.decipher(msg,shift)
  ::Ciphers::Caesar.new.decipher(msg,shift)
end

.encipher(msg, shift) ⇒ Object 



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# File 'lib/crypto-toolbox/ciphers/caesar.rb', line 6

def self.encipher(msg,shift)
  ::Ciphers::Caesar.new.encipher(msg,shift)
end

Instance Method Details

#decipher(message, shift) ⇒ Object 



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# File 'lib/crypto-toolbox/ciphers/caesar.rb', line 39

def decipher(message,shift)
  assert_valid_shift!(shift)
  real_shift = convert_shift(shift)
  
  message.split("").map do |char|
    mod    = (char =~ /[a-z]/) ? 123 : 91
    offset = (char =~ /[a-z]/) ? 97  : 65
    
    # first reduce by 65 to map A to 0 ; then mod-sub with "A"(91)-65; and re-add the 65 to convert back to real ascii A value
    (char =~ /[^a-zA-Z]/) ? char :  CryptBuffer(char).sub(offset).mod_sub(real_shift,mod: mod-offset).add(offset).str
  end.join
end

#encipher(message, shift) ⇒ Object

Within encipher and decipher we use a regexp comparision. Array lookups are must slower and byte comparision is a little faster, but much more complicated

Alphabet letter lookup algorithm comparision:

Comparison: (see benchmarks/string_comparision.rb) string.bytes.first == A : 3289762.7 i/s string =~ [A-Za-Z] : 2010285.8 i/s - 1.64x slower Letter Array include?(A): 76997.0 i/s - 42.73x slower



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# File 'lib/crypto-toolbox/ciphers/caesar.rb', line 27

def encipher(message,shift)
  assert_valid_shift!(shift)
  real_shift = convert_shift(shift)
  
  message.split("").map do|char|
    mod    = (char =~ /[a-z]/) ? 123 : 91
    offset = (char =~ /[a-z]/) ? 97  : 65
    
    (char =~ /[^a-zA-Z]/) ? char : CryptBuffer(char).add(real_shift, mod: mod, offset: offset).str
  end.join
end