Getting a bad decrypt error in ruby - ruby-on-rails

Question

I am using this snippet to extend the String class in Rails:
require 'openssl'
class String
def encrypt(key)
cipher = OpenSSL::Cipher.new('DES-EDE3-CBC').encrypt
key = cipher.random_key
cipher.key = key
s = cipher.update(self) + cipher.final
s.unpack('H*')[0].upcase
end
def decrypt(key)
cipher = OpenSSL::Cipher.new('DES-EDE3-CBC').decrypt
key = cipher.random_key
cipher.key = key
s = [self].pack("H*").unpack("C*").pack("c*")
cipher.update(s) + cipher.final
end
end
However when de-crypting the string I get the "Bad decrypt error":
puts plain = 'confidential' # confidential
puts key = 'secret' # secret
puts cipher = plain.encrypt(key) # 5C6D4C5FAFFCF09F271E01C5A132BE89
puts cipher.decrypt(key) # BAD DECRYPT
I tried adding padding like this to the decrypt action (Similar SO question here):
cipher.padding = 0
The error goes away but I am getting gibberish instead.

Answer 1

Even if you are passing key (secret) to the encrypt & decrypt functions, you are redefining key again with the below mentioned code.
key = cipher.random_key
You should be using same key for both encrypt & decrypt.
Try the below code snippet:
require 'openssl'
class String
def encrypt(key)
cipher = OpenSSL::Cipher.new('DES-EDE3-CBC').encrypt
cipher.key = (Digest::SHA1.hexdigest key)[0..23]
s = cipher.update(self) + cipher.final
s.unpack('H*')[0].upcase
end
def decrypt(key)
cipher = OpenSSL::Cipher.new('DES-EDE3-CBC').decrypt
cipher.key = (Digest::SHA1.hexdigest key)[0..23]
s = [self].pack("H*").unpack("C*").pack("c*")
cipher.update(s) + cipher.final
end
end
puts plain = 'confidential' # confidential
puts key = 'secret' # secret
puts cipher = plain.encrypt(key) # 5C6D4C5FAFFCF09F271E01C5A132BE89
puts cipher.decrypt(key) # confidential