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require 'prime'
class Rsa
def initialize(keys = {})
@e ||= keys[:e]
@n ||= keys[:n]
end
def cipher(message)
message.bytes.map do |byte|
cbyte = ((byte.to_i ** e) % n).to_s
missing_chars = n.to_s.size - cbyte.size
'0' * missing_chars + cbyte
end.join
end
def decipher(ciphed_message)
ciphed_message.chars.each_slice(n.to_s.size).map do |arr|
(arr.join.to_i ** d) % n
end.pack('c*')
end
def public_keys
{ n: n, e: e }
end
private
def p
@p ||= random_prime_number
end
def q
@q ||= random_prime_number
end
def n
@n ||= p * q
end
def totient
@totient ||= (p - 1) * (q - 1)
end
def e
@e ||= totient.downto(2).find do |i|
Prime.prime?(i) && totient % i != 0
end
end
def d
@d ||= invmod(e, totient)
end
# Thanks for https://rosettacode.org/wiki/Modular_inverse#Ruby
def extended_gcd(a, b)
last_remainder, remainder = a.abs, b.abs
x, last_x, y, last_y = 0, 1, 1, 0
while remainder != 0
last_remainder, (quotient, remainder) = remainder, last_remainder.divmod(remainder)
x, last_x = last_x - quotient*x, x
y, last_y = last_y - quotient*y, y
end
return last_remainder, last_x * (a < 0 ? -1 : 1)
end
# Thanks for https://rosettacode.org/wiki/Modular_inverse#Ruby
def invmod(e, et)
g, x = extended_gcd(e, et)
raise 'The maths are broken!' if g != 1
x % et
end
def random_prime_number
number = Random.rand(10..100)
until Prime.prime?(number) || number == p || number == q do
number = Random.rand(10..100)
end
number
end
end